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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I have been attempting to tune out an issue that has prevailed since I rebuilt the engine about a year ago. I installed a new short block from GM Performance, rebuilt Brodix heads, same 91 Camaro TPI from before, new MSD 8366 Distributor, new plug wires. Engine is 502 Gen VI. Trans is 4L60. Rear end Lincoln Versailles 3:70 gears. Rugged idle all along. Some surging at cruise in the 45 mph. range.
Since the rebuild, I have pulled the plugs three times. Every time I have pulled the plugs, all the plugs look great except Number Six. It has always been fouled. The first time it appeared to be fuel fouled. No oil smell and a dry black appearance. I did a cylinder leak down and compression and readings were excellent. The leak down held into the next day. I installed new Bosch injectors and put on a new plug wire for number six.
A few days ago, I pulled number six plug again. Black and wet. No smoke on start up, so suspected oil from lifter galley being sucked up past a bad gasket. I pulled the intake manifold.
To my surprise, the intake runner for number six was pristine clean. Absolutely no evidence of that cylinder ever being fired. The other seven have black on the upper surfaces of their intake runners. Never firing led me to the distributor. The number six contact post on the cap of the MSD was black. All the others were bright brass. Removing the boot on the number six wire (both new and the replaced one) resulted in the contact clamp under the boot was corroded. Removing boots from Adjacent plug wires resulted in new looking clamps, no corrosion.
I have been around engines a long time. This almost appears like something wrong with the MSD that would cause it not to fire on one cylinder. But I cannot imagine how that could be with the magnetic trigger in the distributor. I also notice that the MSD appears to be out of phase. The rotor is well past the location of the cap contact when the trigger is aligned.
See pix. Photo of Intake runner for 2 & 4. Photo of intake runner for 6 & 8. Photo of MSD (Red) phasing. Photo of OEM (Black) phasing. Photo of cap and photo of plug wire end.
Not so much a tuning question, but there is a lot of knowledge and experience on this forum. My current thought it to put it back together and put the OEM distributor back in and see what happens.
Replace the distributor/cap/rotor with a GM small cap along with a GM coil. Replace the #6 spark plug wire. Check/replace the valve stem seal on the #6 intake valve. And of course a new plug on #6.
If that doesn't fix it, then need to do things such as compression and leak-down tests.
Cylinder leakdown was in the good range at 9% and held until the next morning. Compression dry was 175. I have changed the plug three times, the number six ignition wire once and changed fuel injectors once. What I haven't changed since the rebuild is the distributor, the distributor cap, the rotor or the coil. The OEM distributor is about $600 new. I have my original one that was working when I did the rebuild. I replaced it with the MSD 8366. I am going to put the old OEM distributor back in with new cap, wire and rotor.
What is baffling is the absolutely pristine clean number six intake runner and the apparently burnt post on the distributor cap (number six only).
Put back together with new Edelbrock intake manifold, new rotor, new plug wire, new plug, new distributor cap, and the OEM GM distributor. After startup, all cylinders running close at 400 * F at the exhaust port on the headers. Prior to this, replaced original injectors with Bosch units.
About 200 miles later, pulled the plugs.
Number six is the dark sooty looking plug. From left to right 2-4-6-8 7-5-3-1
7730 ECU batch firing
Looks like number six is really fuel fouled, but not sure how that can be happening.
A little more history. I had an exhaust header leak in July. The plugs are almost impossible to change on the BB due to the shorty header. Took advantage of removed headers to change plugs from the rebuild done six months before. Number six was black. See photo dated 220714. I suspected a leaking fuel injector. The injector in it were the Bosch 028150945. I had had those cleaned and flow tested before the rebuild. Regardless, I forked out the cash for eight new Bosch 115 V injectors.
Ran for month and pulled number six again. This time it was terrible. Looked oil soaked. I have no smoke at start up so suspected a leaking intake manifold gasket sucking oil from the lifter galley. But, when I pulled it down, found all sorts of issue with ignition, including a burnt post on the distributor cap and corroded wire on number six (heat). Those photos are at the beginning of this thread. Number six plug photo from 20220821.
After all those corrections, you have the September photos of all six plugs.
Prior to this, I only changed the number six plug, the other seven are original from the rebuild. The look to be cold to me
I think it unlikely to be a bad injector since I have swapped them and the problem followed the new injector in number six. The wiring harness is the same. Batch firing, even side all firing at the same time. Physically, the harness to the injectors looks in good shape.
No Cross over pipe in the exhaust. You can see the discoloration in the exhaust tip
I have rotated the crank and observed the intake and exhaust valve opening and closing on Nr 6. The block is a new short block from GM Performance ZZ502. I have seen no evidence of metal in the oil through three oil changes. Suspect the cam / lifter to be ok. Full roller rockers for Compcams. I have new Brodix oil seals coming and will remove the spring(s) on the valve and change the seal. These are Brodix BB1 heads
There is something definitely weird here, beyond my experience, so really appreciate others insight.
Have you cut apart the oil filter? Metal debris could get trapped in the filter giving the appearance of cleanliness in the oil that gets drained out of the pan.
It'd be a bit messy, but if you ran the engine with the passenger side rocker cover off, you could observe the valve openings with the engine actually running. See if anything look anomalous compared to #4 and #8 cylinders.
Earlier in the thread, RBob mentioned the valve seal. Did you address that? Possible oil getting sucked in through a bad seal?
Remove the #6 injector plug while running and see how the engine reacts? Swap the #6 and #8 injector plugs and see if the problem moves to #8? These two steps would go toward verifying the harness. Or put a noid light on #6 injector plug to see if it's actually firing the injector?
Run the car at night in the darkness and see if the #6 wire is arcing out of the wire to the engine? If so, could be caused by an inadequate engine ground. Maybe something unique about that #6 plug wire route making it more susceptible than the others. I don't skimp on grounds... I actually have one head ground-strapped to the other head (since only one head gets grounded to chassis).
Put an O2 sensor on the passenger side, hook the ECM up to it and and see how the fuel trims look vs the driver side.
none of those plugs look particularly good for 200 miles. The orange rust color is indicative of water, not sure how else you may form that color in such short a time. Oil fouling and rich/misfires #6 creating those deposits. #3 and #1 have excessive deposit accumulation around the ring which should be only a dark unbroken smooth carbon appearance.
For your issue on #6 I recommend start moving things around, move #6 injector swap with #1 for example. Move a plug wire. Wrap the wires with insulation for that cylinder to eliminate arcs. Swap parts, cap, rotors, etc...
I hate to say it but there is enough compelling evidence that something is wrong with the entire engine , not just #6. Poor tuning couldn't account for so many deposits unless your fuel was contaminated. And even that wouldn't specifically foul #6. There is a chance you have multiple issues caused by particular specifics... for example, oil ring is installed incorrectly or missing oil control ring on #6 (seen this in rebuilt GM engines). Along with wrong headgasket passages or head machine work causing the orange plugs, is your coolant orange rust colored? Are you running 100% water? Did you replace the radiator with a brand new rad when replacing the engine? And perhaps a pushrod or lifter issue thrown in for good measure, idk just thinking outloud. Oil getting into 6 I mean, its either ring related or valve seal related, or somehow sucking into #6 intake port from a PCV related. How is your PCV system setup? There should be a PCV valve somewhere between intake manifold and crankcase to keep the engine clean inside. There should be a breather tube attached just after your air filter for the same reason. Inspect these tubes if you have them for oil.
Where did you get your 'new' injectors? There are so many counterfeit bosch there could be part of your problem right there. It causes these random fueling issues you are having for starters.
Oil though, thats a catch. Fuel is alot like oil though, just shorter carbon chains. I would consider installing some used injectors from a previously running engine to fully rule out the injectors.
OR somehow track down known high quality injectors from a reputable source.
The orange, I don't know besides water how to make that color, but maybe your engine sits for prolonged periods. Fire makes water. Cylinders seal tightly. Did you drive very short distances... with insufficient warming time... perhaps this contributed with long duration sitting periods to the coloration.
Batch fire huh? I don't remember what plugs are s'pose look like on those its been too long. But maybe not as clean as a SEQEFI. Those deposits make me say tuning related to some extent but maybe you never got a chance to really tune it yet because of the issues. Try to keep track of run time, miles, distance per run, and make sure your PCV system is up to par it is critical to cleanliness and oil quality. Perform a pressure test on the intake manifold to ensure it isn't leaking anywhere. Same with the crankcase. Intake pressure test to 15psi ish. Crankcase only 1 or 2psi is plenty to find leaks. These tests are critical for new installations.
I would start by questioning the quality of the injectors, honestly. Get that sorted 100%. SBC always have a bunch of sorting out to do... ignition is tough to keep up with. I still have header fingers from 1998.
1. The intake is basically a 91 Camaro TPI set up for a big Block. It was acquired from Street and Performance back about 1995 before Mark Campbell died and the company followed suit.
2. The injectors were acquired in July from Five O Motor Sports. Theoretically, bonafide Bosch units. Certainly cost as much.
3. The GMP ZZ502 short block was installed in May, 2021. The cylinder headed were "checked over" by a local machine shop, but not re-worked. I moved from SW Colorado to Williamsburg, VA in the fall of 2021. Not much time to drive the coupe. Once in VA, had to retune everything to account from moving from 7,500 feet to 60 feet. All the plugs were changed about Feb 2022. Number six was changed again a couple of times between July and August. Total mileage on the other seven plugs maybe in the range of 1,500 miles.
4. Although number six plug appears oil soaked, I cannot smell oil on it. If the plug is allowed to sit, the "wet" look goes away.
5. I had a single spring compressor from my small block days. These Brodix BB1 head have multiple valve springs. I ordered a stud mounted spring compressor and Brodix seals. Thing that I HAVE NOT changed regarding number six are the injector wiring harness, valve seals, valve train and rings. Compression and Leak down are great. I will know more after I look at the valve seal.
Hmm being batch fire the something I would do is swap an injector WIRE from a good cylinder in the same batch to that #6. SInce they fire simultaneously it should not make any difference. This will rule out ECU and Wiring related.
I recommend you consider upgrade to Sequential EFI computer if possible.
If you dont think its oil on the plug it pretty much leaves fuel. So there is a lack of fuel control somehow- usually injector. But if you trust the injector that leaves wiring and ECU.
I Know its a pain but you should carefully monitor all plug conditions until sorted out. You need to find out whether there is water, oil, fuel, whatever getting in there.
Did you please mention whether you are using 100% water, or coolant, or how old the radiator is? Consider making a pressure test in the radiator and checking for water in the cylinders after the coolant is pressurized for a few minutes.
I am running orange antifreeze. Fluid is new. Radiator is a monster custom made Griffin aluminum that is probably six years old.
In looking at the wiring diagram and the physical wiring harness (25 year old harness), even side fires at one time. Without taking off the sleeving, it feels like, two wires split to two wires (6-8 and 2-4) then splits again for 6 vs 8 etc. The diagram would indicate that the injectors are powered at 12v and the ground side is fired from the computer. I thought about a bad insulation causing a ground short and firing the injector out of time, but all four would fire, not just six.
Fed ex is supposed to deliver the spring compressor today. I am hoping to pull the valve spring and check the seal and will report.
I find the photo at the top of this thread the most disturbing. The one I am referring to is the pristine clean fuel runner in the cylinder head for number six. I have racked my brain trying to diagnose what would have caused that single fuel runner to be clean when the other seven were not. That particular situation is when I felt the plug was shorted out (the photo of the really nasty wet looking plug) and caused the distributor cap to arc at the top post and heat up.
I am not against changing to a different ECU fueling system, but it sounds like a big project when I have yet to get this problem solved.
I will also install one range hotter plug as these appear to be too cold.
I am running orange antifreeze. Fluid is new. Radiator is a monster custom made Griffin aluminum that is probably six years old.
In looking at the wiring diagram and the physical wiring harness (25 year old harness), even side fires at one time. Without taking off the sleeving, it feels like, two wires split to two wires (6-8 and 2-4) then splits again for 6 vs 8 etc. The diagram would indicate that the injectors are powered at 12v and the ground side is fired from the computer. I thought about a bad insulation causing a ground short and firing the injector out of time, but all four would fire, not just six.
Fed ex is supposed to deliver the spring compressor today. I am hoping to pull the valve spring and check the seal and will report.
I find the photo at the top of this thread the most disturbing. The one I am referring to is the pristine clean fuel runner in the cylinder head for number six. I have racked my brain trying to diagnose what would have caused that single fuel runner to be clean when the other seven were not. That particular situation is when I felt the plug was shorted out (the photo of the really nasty wet looking plug) and caused the distributor cap to arc at the top post and heat up.
I am not against changing to a different ECU fueling system, but it sounds like a big project when I have yet to get this problem solved.
I will also install one range hotter plug as these appear to be too cold.
Don
Yeah changing to sequential injection would be a band aid. You shouldn't need that to solve the issue.
I am running orange antifreeze. Fluid is new. Radiator is a monster custom made Griffin aluminum that is probably six years old.
In looking at the wiring diagram and the physical wiring harness (25 year old harness), even side fires at one time. Without taking off the sleeving, it feels like, two wires split to two wires (6-8 and 2-4) then splits again for 6 vs 8 etc. The diagram would indicate that the injectors are powered at 12v and the ground side is fired from the computer. I thought about a bad insulation causing a ground short and firing the injector out of time, but all four would fire, not just six.
Fed ex is supposed to deliver the spring compressor today. I am hoping to pull the valve spring and check the seal and will report.
I find the photo at the top of this thread the most disturbing. The one I am referring to is the pristine clean fuel runner in the cylinder head for number six. I have racked my brain trying to diagnose what would have caused that single fuel runner to be clean when the other seven were not. That particular situation is when I felt the plug was shorted out (the photo of the really nasty wet looking plug) and caused the distributor cap to arc at the top post and heat up.
I am not against changing to a different ECU fueling system, but it sounds like a big project when I have yet to get this problem solved.
I will also install one range hotter plug as these appear to be too cold.
Don
SO you say number 6 has a super clean runner? How do we suppose the other runners get 'dirty'. Likely during combustion some carbon blows past the valve into the intake ports?
If the runner is clear perhaps the cylinder is misfiring. This would allow fuel to soak the plug and create deposits.
Otherwise how can carbon coat the runner?
Any PCV hoses attached nearby or to #6? The PCV is integral to engine cleanliness. It will have dramatic influence on oil quality.
next, orange coolant, and orange crud on plugs, that is a coincidence too much for me. I think you may have heads with leaking valves and leaking coolant? Wrong head gasket could explain the coolant but not the valves.
Maybe valves are being held open? Wrong lifter or pushrod lash or some adjustment there? I would recommend a degree wheel, perform the camshaft rotation with no lifter (remove the pushrod) to determine base circle first, then perform the degree with comparing KNOWN base circle to the proper adjustment you are using. You may find the valves are open when they should be closed. This would explain why the valves check out fine at the machine shop but blow dark carbon into the runners.
The photo of the two plugs attached hereto resulted in changing the Injectors. The plug looked fuel fouled to me
A month later, I pulled number six plug again and found the plug in the single plug attached hereto. I did not have smoke at startup, so concluded the oil could be coming from a bad intake gasket sucking oil form the lifter galley. In pulling the intake, I found the clean number six intake runner. The plug looked really fouled, perhaps completely shorted. I think that is the reason the post on the top of the distributor cap shows evidence of heat. You can also see the MSD seems to be screwed up on phase compared to the GM OEM distributor.
I am going to check / replace the valve seals on six. I will double check valve function and lash before installing hotter plugs.
The photo below this was the same cylinder after replacing the intake manifold gasket and ignition. This one look dry carbon
A '7730 only has one injector driver. So all eight injectors fire together at the same time.
The clean runner is due to the plug not firing (fouled and shorted). So no combustion gases/carbon to blow back past the opening intake valve. And the injector spraying fuel keeps the runner clean from when the plug did fire.
To me it appears that there is a lot of oil on the spark plug threads and indexing washer. Last time I had an issue with a single cylinder the valve stem seal was riding the valve stem. No longer attached to the valve guide.
A '7730 only has one injector driver. So all eight injectors fire together at the same time.
The clean runner is due to the plug not firing (fouled and shorted). So no combustion gases/carbon to blow back past the opening intake valve. And the injector spraying fuel keeps the runner clean from when the plug did fire.
To me it appears that there is a lot of oil on the spark plug threads and indexing washer. Last time I had an issue with a single cylinder the valve stem seal was riding the valve stem. No longer attached to the valve guide.
RBob.
My last single-cylinder issue was during that idle misfire years ago that I eventually traced to stuck piston rings on the #7 cylinder (some oil additive eventually freed the rings up after ~100 miles or so and the misfire went away. Detected it with a leak down test. Though I think the OP may have already said he ran the leak down...
My last single-cylinder issue was during that idle misfire years ago that I eventually traced to stuck piston rings on the #7 cylinder (some oil additive eventually freed the rings up after ~100 miles or so and the misfire went away. Detected it with a leak down test. Though I think the OP may have already said he ran the leak down...
With a leakdown it can be difficult to tell where the air is going. The sound is "coming from everywhere" we often assume 100% is passing the rings but it could be that some say 25% is really going up through the valve stem past the valve seal possibly. Usually when we do the leakdown we are not having the valve cover off and submerging the valve seal to look for bubbles but I suppose that could be done in the future? On the other hand, leaking up is not the same as leaking down, i.e. the valve may seal air from leaving but not oil from dripping down. So its one of those things where our diagnostic tools are either unappreciated fully, limited use, or tell us only one sided information.
I think the right thing is on the track of replacing the valve seals on that cylinder to rule them out.
That would leave rings for the case of oil induction, if the intake port is clear from oil. It has to come from an intake port, rings, or valve seal amirite?
Fuel wise I Think Rob pretty much came to the similar conclusion I did earlier, the injector is firing and the plug is not. So these seem to be separate issues, fix the ignition, fix the oil leak, profit?
I still wonder about the orange coloration on the other plugs and the fact some are forming deposits as well. Perhaps more than one cylinder is leaking down oil. Or has some oil related issue.
They should never form those kind of deposits. However maybe I am spoiled with modern engines which leave perfectly clean plugs, I just dont know about those old engines anymore for comparison.
Not that it guarantees a thing, but the block is a new short block from GMP about 16 months ago
I am using the brown looking anti-seize on the plugs which may contribute to the "oily' look on the threads of the plugs, etc
I personally trust used 150k miles engines more than rebuilt engines. More track record, historical evidence, it ran fine 150k you keep going.
Rebuilt you just don't know whats been done or not done. $.02
Okay, the anti seize is a huge problem if done excessively. We need to talk about that real quick.
FIrst, it makes diagnostics very difficult. We are not sure now whether you have oil inclusion or simply anti seize over-use. See what I am saying?
When you apply anti seize, first, use the gray stuff so you can see some gray colors in the future, possibly identify it.
Next, Never apply it to all the threads or near the plugs tip. Antiseize over time will OOZE and work it's way to the plug tips.
ONLY apply a very tiny dab of anti seize near the upper part of the plug, say about 7 to 10 threads up the plug away from the tip.
Over time it will ooze towards the tip. The goal is: You NEVER want the anti seize to reach the plug tip. If antiseize reaches the plug tips, it will form deposits , hot spots, hard conglomerates like what we are seeing. It will look similar to burning oil. It will ruin the plug, make combustion inefficient, it will ruin the way the engine runs. It will cause misfires.
You must keep the plugs clear from anti seize on their tips where the business end is conduction and combustion.
Over time some oil from the cylinder will develop naturally on the threads anyways, acting like anti seize, so you don't really need much if any at all for that engine.
I think we've identified quite a few issues here and gave you some thinking and work to do.
I got the spring compressor, Brodix seals and a new set of 8.5 mm wires from MSD at 6pm. So, tomorrow will be seal day. I will clean out the plug sockets with a Q tip and follow the guidance on anti-seize. I have always stressed out about screwing up the threads in these expensive aluminum heads.
Since we topic spark plugs I should also mention these
1. Never touch new spark plugs with human hands. Use fresh clean disposable gloves.
2. Never allow anti seize near the plug business ends keep it at least 6 to 8 threads away from the tip.
3. Gap using a soft tool, never hammer or slam the plug strap with metal or concrete. Use something with a rubber coating to avoid creating dimples or microscopic crevices in the strap. Avoid "piler teeth marks"
4. Tune the engine idle and cruise for 14.8 to 15.4:1 air fuel ratio to keep plugs clear from carbon buildup and prevent major carbon deposits from forming in the cylinder.
5. Tune the engine on cheap copper plugs, then discard and install new plugs on the correctly tuned engine. Then drive 2000 to 5000miles and check plugs, they should all be same quality and clean.
Once satisfied with mileage plug condition I switch to iridium plugs for longevity in turbo applications, get 60k to 80k miles from Iridium NGK style plugs for example. But NEVER tune on iridium plugs, never foul them. Engine must be fully tuned first before using iridium plugs.
Remember not to touch them with your skin. Treat plugs as surgically clean instruments. Any contact with skin, oil, contamination, dirt, etc... will have far reaching consequences with diagnostics and possible misfires in the future.
Yeah keep it away from 14.7:1 just leaner than that. 14.8 to 15.5 is fine. Gasoline scale. For cruise and idle situations.
The oxygen sensor average across all cylinders so if you see 14.7 that means some are 14.6 and some are 14.8 for example. No cylinder is perfect no injector is perfect and variations due to exhaust scavenging and compression, even firing order and VE due to overlap at low rpm and intake features play a role in distribution of fluids (air is a fluid).
Make wideband read around 15.2:1 IMO for idle cruise. This is excellent cruise and idle ratio for keeping the cylinder clean and it ensures all will run lean enough to prevent carbon buildup from being significant.
It may also improve economy slightly but negligible.
If you use 14.7 or closed loop narrowband operation the plugs will brown up, tan color and brown. The cylinder will have some carbon deposits over time. It isn't necessarily bad or wrong but it is unnecessary and easy to avoid, the point of tuning vs letting the computer automatically adjust for you "tune itself". Modern Stand-alone computers utilize full time closed loop wideband operation and we define these targets for closed loop using wideband instead of narrowband. Once you do that using SEQEFI computer you will realize that 14.7:1 is not desirable for any situation, we never use it.
Here are some of my targets for a rowdy 427cid engine I tuned a year ago or so, but it uses racing fuel, huge injectors, and very high compression so not quite apples to apples. There are times when closed loop is disabled and it runs strict from basemap near idle regions to prevent wideband deviation error for example. But you can see many times we choose 15:1 a/f ratio for keeping clean plugs in cruise situations. It also helps keep the engine cooler, oddly enough.
Next for comparison here is my daily driver, 5.3L Stock engine 600rwhp with 200,000 miles, from 2002 Tahoe in junkyard
See on gasoline with a stock engine, its fine 15.5:1 in most lower rpm cruise situations, saves fuel, makes plugs very clean. Long lasting and clean is ideal.
As the rpms rise a bit, the engine can load more easily, so I don't leave such a lean ratio, but still low 15's is fine.
Of course once driver demand torque, need to drop the ratio 13's or even 12's quickly approaching 80KPA from say 65KPA. Even by 60 KPA I run closer to 14.2 to 14.5:1 to allow some tip in fuel. Do not depend on enrichment acceleration pump shot in that situation because driver demand may be slow sometimes, fast others, better just let the base map provide some slightly enrichment there.
The higher the engine RPM rises, the more vacuum for a given load, so there is a sort of diagonal line from bottom left to top right imaginary you can follow with the enrichment values focusing on load vs demand for torque and rpm.
At present, I am running full time open loop. Trying to remove variables in tuning until..... The WBO2 and the NBO2 are on the passenger side (same as dear old number six). Consequently, being cautious on setting the final tune until I get this issue under control. I will lean idle and cruise out a bit as they have both been running slightly rich. (.98-.99). I am using Virginia 93 with 10 percent water but Lamba shouldn't care.
Once you get familiar with wideband gauge reading, make sure you have a gauge available all the time, you can learn to spot a misfire in the engine easily because of wideband behavior.
I recommend use open loop all the time unless you have access to closed loop wideband operation. No sense using narrowband closed loop, narrowband is obsolete. A wideband has a narrowband inside it, it replaced the obsolete version of itself.
One more comment before we become as bad as the "tuning with EBL" thread.
Open loop tuning is like the old days to me. Springs and weights in the distributor for the curve. Needles and jets in the carb to get the fuel table. Much more old school for someone that is "old school"
Heh. I run all my vehicles open loop. If you fully, truly tuned an engine, it doesn't need the closed loop to drag it back to some ideal ratio because you already tuned the ratio you wanted.
Of course if you drive somewhere new, like up a mountain or something, it may need re-tuning. Closed loop can compensate for that. Also as components age closed loop helps with that.
But truly, that just means the engine needs re-tuning, or maintenance, or some other tuning related issue- see what I am saying? In other words, are we the tuner, are we the mechanic? , or are we the sheep just driving the vehicle and oblivious to the computer and neglect the engine.
For customer cars, of course I let them use closed loop because I am not there to keep an eye on the wideband for years. But in my own vehicle I always watch the wideband anyways- you really have to be aware at all times if you have a performance engine because one wrong WOT blast at the wrong a/f ratio could be engine death, destruction, failure. And A/F is key to cleanliness and economy. So while I assume my engine is well tuned i still watch the gauge on and off to make sure it stays good, everything still working properly, its a habit forming hobby. You develop expectations and satisfied to see that from day to day operation, nothing changed. If you are in closed loop you will not notice any drift, any difference, until it is far past too late.
Did you measure the distance from distributor pole piece to the pickup when the distributor is pointed @ #6? Vs the rest of them?
If there's to much gap, it won't fire.
I've see that happen b4, machining issues on the pole piece not triggering the pickup on one or 2 cyls.
There's a photo in the beginning of this thread showing a red Distibutor (MSD) and a black distributor (GM OE). The black mark is aligned with number one the cap. The rotor in each photo is aligned with the magnetic pickup on the distributor shaft for firing the coil. The MSD appears way late in phase for firing relative to the cap. The MSD was installed with I had the wet number six plug, corroded wiring and heat discoloration on the cap connector post. I have not looked for a difference between the rotor contact and the cap contact.
I was thinking more along the lines of the distance between the pickup coil and the trigger wheel on the dist shaft.
Think of a 8 point star with one leg to short. If it spins and all the legs are close to a pickup but one, you'll have 7 sparks.
your cap reminds me of 80s-90s coil pack cars when they stop firing, the terminals looks nasty like that.
Old valve stem seal removed and replaced. I could see no obvious issues with the old seal other than what looked like oil inside the seal. I guess oil could be sucked up from the spring seat.
The old seal was a Brodix seal, identical to what I had acquired for the replacement. Heads were new in 2002. I sent them to Brodix in 2021 for a rebuild. They disassembled them and gave me an outrageous quote. I had them reassemble and send back to me. I doubt the changed the seals. I then sent the heads to a local machine shop (in Colorado). He said he replaced the seals. Unless he used Brodix, I don't think so.
Anyway, waiting for new plug harness to test it out. The flash gives the oil a reddish orange look, but clean oil.
I put in the new valve seal on intake number six. Installed eight new plugs one range hotter. Installed new MSD 8.5 mm plug wires.
Took a long drive logging data. Things running fine from Idle up to 75 mph. A little rich in some areas, but Lambda in the 96-99 in those areas.
Pulled off the freeway and thought the engine was going to die. Lambda now at 110 or more. SUPER lean and bouncing all over the place.
Parked and checked the fuel pressure gauge on the fuel rail. Crazy stuff, Key on, fuel pressure goes to about 50 and settles back at 43 PSI. When I start the car, it drops to 20 instanteously, then back up to 43. (See Video) (It won't let me upload a video) Regulator diaphragm is pretty old. Replaced it this morning. No change, drive a while, things look great, Lambda tracking near 1.0, then all of the sudden it goes ballistic on the lean side. Limp home and park it. .
Testing now, key on, fuel pressure goes to 50, settles back to 43. Go to "Start" engine starts, fuel pressure goes to zero and engine dies. Repeat and second time engine starts and fuel pressure remains at 43.
Three test drives. Lamba ok for about five minutes, then goes lean. Rapid changes from 1.0 to 1.2. Pulled brand new injectors and replaced with old injectors, removed and re-installed fuel regulator diaphragm. Test drive, AFR better, but after five minutes some leaning. Pulled number six plug and number five plug for comparison.
After about 25 miles on new plugs, new MSD 8.5 mm harness, new intake valve seal. Number six still fouled.
1. compression test that cylinder , verify
2. Test for spark, hold the plug on a header, disable injectors, does it spark?
3. Fuel signal, Perform a continuity test from the ECU plug through the injector to the power source, look for shorting, wiggle the connector
-Swap the injector plug with another injector
-Swap the injector
Can't be bad ECU if they all fire in batch
Can't be the injector if you swap plugs & injectors
This was a new short block from GM purchased May 2021. This is the fifth time I have changed plugs and number six is always fouled, the other seven are fine. I have changed plug wires twice, changed distributors twice, changed injectors twice, installed a new intake seal. Compression and leak down photos attached.
Not sure what it is, but I am pulling the heads off. Can't drive it if I can't trust it.
AT least visualize spark against the header or some metal materials. Takes a second and may save you twenty hours of bs
Follow the simple steps, please dont get frustrated. Engines are very simple. I know you already did a compression test I only listed it so you can see how the diagnostic procedure is outlined, as a reference. If you follow these easy 1 2 3 you can find the issue quickly without taking it apart. Just because all the ignition stuff is new doesn't mean that the issue isnt related to ignition. New stuff is bad all the time. Didnt somebody mention something about the space between the rotor and cap contact? The rotation of the engine rotor with respect to the cap for that cylinder, I think its a good idea to investigate these things.
I will know shortly. Manifold is off. Pull the headers next. Pull the plugs. Rotate the engine and watch valve train. Pull valve train. Pull heads and cross fingers.
If it has good compression, engine is good. Its probably a bad distributor related item. Or a short in the plugwire. Hold the plug to a ground and crank for spark, no spark, no ignition.
1. After pulling all eight plugs and aligning them with the prior set, number six in both sets is fouled. The other seven are in various states of being OK
2. When I pulled the head, the cylinder number six has a little pool of oil at the bottom. In the corner on top of the piston. Above the piston ring. No signs of scouring on the cylinder walls.
3. The intake valve for number six is very wet and oily looking. The exhaust on six and the other valves look ok.
My thoughts are that the oil on top of the compression ring, along with the good compression and cylinder leak down, gives me some comfort that the problem is in the head. After running and shutting off the engine, now sure how oil could come from the cylinder and get on top of the compression ring. Has to come from above. The black and wet intake valve looks to be the issue. I put a new seal on it, but may be a different problem or the clearing is too much even with a new seal.
I am going to take the heads to an automotive machine shop and have them evaluate number six. If they can find the issue, I won't pull the piston. I will have them completely re-do the heads.
Makes you wonder about all the tuning on this engine when both NB and WB are on the same side as number six.....
most likely going to have to retune. That's happened to me before.... tuned around a malfunction.
I've helped people with their cars before and I won't even start on a tune unless I'm pretty convinced the car is in good working order. Its too much of a tail-chasing exercise otherwise.
08-25-2022, 06:17 AM
