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I replaced a leaky intake manifold gasket for the third time. Drove around with the APU 1 emulator. Open loop idle, Closed loop above 1,000 rpm. Drove fine. Stopped and changed to full time open loop. Drove fine. Stopped to get some fuel. Started back up and barely ran. Full lean. Didn't change anything other than stopping and starting logging and the dashboard. Barely made it home. I assumed something wrong with the APU. So, pulled the APU and installed a PROM with the same BIN. Still full lean. No change in Fuel Pressure about 35 lbs at idle. 45 lbs without vacuum. Changed from Open loop to Closed loop, including idle. BLM all the way to one end and full lean.
I didn't do anything but get gas. Busy EXXON station in town. Even if the gas was bad, it would barely start. Fuel rails still had original fuel.
I had an EPROM failure once (not ECM) and it acted like that. Data from logger did not make any sense so I thought ECM had gone crazy. I swapped ECM (had a back-up) and it did the same. Got an new EPROM and solved the problem. Of course, while handling the ECM in a rush one day, checking something, I shorted the EPROM with static. I was installing a Moats emulator.
Too many variables. I just changed a leaking intake manifold gasket. I have an APU1 that I am not sure is working right (since I just got it). I re-set the Fuel Pressure as it was a bit high. I set it at 45 psi with vacuum off. Idle in the 30s psi range. I left the house in Open Loop idle and Closed loop over 1000 rpm. On the drive, I tweaked the idle AF up a bit (probably the slightly lower fuel pressure). Was running ok, so stopped and changed to full time open loop. Seemed to drive ok. Decided to stop and fill up.
After fill up, it would barely run. Check Engine Light on. Turned off and restarted. Lean, lean, lean. Wasn't sure if the APU was acting up or what. Had to work at it to get back to the house. Idling in neutral at red lights, etc. The CSV attached is the drive back from the gas station. About half way in, the WB02 pegs at lean. You can see the change in the Monitor pasted in below. About 2.5 minutes from the gas station.
Back at the house, I pulled out the APU. Loaded the BIN to a chip and put a Prom back in with the current BIN. No change. I pulled the Prom and went to full time CL. No real change.
I pulled some gas out of the tank this AM from the Fuel pump into a glass wine bottle. (After yesterday, I drank the wine). After an hour, there is no evidence of water in the gas (my first suspicion).
Looking at your log, you are in open loop the majority of the time. Your MAP values are high at idle. Other than that, it's hard to say. Why run in open loop? At certain point, when in closed loop, the BLM are high in cell #5 (140). So definitely lean. Was that before gassing-up?
By the end of your log (172), your are in cell#4 at idle, lean, but stuck at BLM 128 because open loop. Your commanded AFR is 14.03 instead of 12.55 at beginning of your ride.
That is due to a higher commended idle rpm which leads to lower MAP = leaner OL AFR
It seems like the lower your engine idles, the higher the MAP value is (less vacuum). Probably your cam profile.
Higher MAP value translate into lower AFR in OL (due to tune)
Also, the lower the engine temp (CT) the higher the OL AFR is (due to tune)
For example:
Beginning of ride in OL at idle = 1125RPM / CT149 / MAP54 = 12.55AFR
Middle of ride in OL at idle = 900RPM / CT192 / MAP67 = 13.65AFR (I noticed IAC is at 231steps!!!! Unless my XDF is wrong)
End of ride in OL at idle = 1000RPM / CT185 / MAP54 = 14.06AFR (I noticed IAC is at 9 steps!!! Unless my XDF is wrong)
So this OL business yields unstable commended AFR. OL AFR is calculated using the following parameters:
Commanded AFR
Start-up AFR change
Start-up AFR change decay delay
Start-up AFR change decay
Idle AFR change
CT AFR change
MAP AFR change
MAT AFR change
When you were riding in Closed loop, the BLM were correcting lean condition (up to 142 in cell#5). Later in your ride, the BLM was locked at 138 in cell#5 in OL. Maybe it needed to add fuel but could not.
Again, why do you run OL? If you want to do so, you'll need to tune OL to take into account, engine temperature, MAT heat soaking, MAP value and idle mode.
When exactly in that log did you start having trouble I don't see any SES error. Except stored code. See picture.
Sometimes, when using emulator and changing tune on the go with engine ruining, the ecm gets a check sum error and goes into limp mode. It happened to me many time with Moates Ostrich 2.0. That's why I don't use the real time feature anymore.
1. Log 172 was before gassing up. I changed from OL idle to FT OL at about 14 minutes. I IAC went to the max just before that. Emulating on the APU. No noticeable issues in this log.
2. Log 172a is after gassing up. Nothing but trouble after start up.
3. Where did you see the error log. What is the 51 ECU error.
4. The issue was both with the APU and the Prom/Chip (replacing the APU). I have a spare ECU to test / eliminate an ECU issue
Well. Swapped the ECU. Used the BIN that was at the beginning of the "good" run yesterday before I went to full time OL. So, it was OL idle and CL over 1000 rpm.
I ran it for a while on the stand just idling until it came up to temp. The log seemed to be decent. Attached as CSV 173a.
Being encouraged, I drop the stand and took the car around the block. Terrible still. Pinned at full lean both in OL and CL. Funny as well, the thing had a hard time shifting. This is a 4L60 that is cable driven (not 4L60E). Then, it shifted hard. This is attached as CSV 173b.
This is interesting. Tune 173A was done on the on the lift. Just idle. Ranging from cold to operating temperature. BIN is OL Idle and CL over 1000 rpm. This is the last half minute of the log. The bold Red line in the lower monitor is the WBO2. Looks a little lean but pretty decent. Considering that I had dropped the Fuel Pressure at idle a bit, lead would be expected with the same VE table as with the higher idle pressure.
Now, look at this. I turned off the engine, lowered the lift. Started the car in preparation for a test drive. This is log 173b. Same BIN. Only difference is I turned off the engine and restarted it a few minutes later. Look at the WBO2 in the lower Monitor panel. Locked at LEAN. Look at SA in the middle monitor. locks in at 26*.
My gut instinct tells me you're fighting a mechanical issue, not a tuning/ECM one. Something intermittently wrong with fuel pressure regulation (regulator? pump? vac hoses?) or a vacuum leak (why have you had to replace the intake manifold gaskets 3x? Is there a mismatch in the machining/angles of the intake?) or somesuch. A failing power brake booster can be a non-obvious but substantial vacuum leak.
That car is beautiful sir! I am biased though, I have great love for 1933-1939 Chevys as well as a few select years of Buick, Cadillacs, Oldsmobiles and Pontiacs in that same era.
The intake manifold on this beast is too heavy for me to carefully align when installing. The multiple times of installing is the result of several issues unrelated to the intake gasket (like no sealer on the rocker arm studs that run into the intake runner). This last time, I built a pulley system to lower the manifold and used Gasket cinch and some fuel proof gasket dressing. I have in dash gauge for Fuel Pressure and the FP is good when the car is lean. Something odd about the fact that it can run great until you shut it off. A hot restart is pure lean. It does sound mechanical, but I am at a loss as to what it could be related to the restart. The difference between a decent log and a bad log can be two minutes and an Off-On of the engine.
Here's something interesting with 173b. Follow the logic.
During your long idle period (second half of 173b)
ECM is trying to bring down idle to commanded 900rpm. IAC is decreasing from 134 to 64 (all normal)
RPM is at 1200rpm going down to 900 rpm
MAP goes from around 50 to 63
Commanded AFR is 14.19 down to 13.77 (because MAP increases)
Since its over 1000 rpm, BLM learn is activated. Its in cell#5 at BLM 160 maxed out with INT working its way up to 140s (means ECM is adding up to 40% injectors calculated PW)
However, as rpm reaches commended 900rpm and crosses the 1000rpm threshold, ECM is in and out of closed loop. Means the BLM locks at 160 but INT resets to 128 leaning out
THEN... ECM enters cell#4 because rpm is around 900rpm. BLM is 128 in cell#4 and in open loop.
That triggers a major drop in fuel supply, rpm drops to 750rpm, ecm enters cell#8 with BLM 128, MAP increases to 75 (very high for idle), IAC starts correcting, AE-MAP is triggered due to fluctuation in MAP
RPM won't go up
IAC maxes out at 231 steps incapable of bringing idle rpm up to 900 rpm. IAC is adding air to an engine that has already too much air, lean in open loop unable to correct with BLM/INT. It's stuck in limbo, chasing its tale
And then, out of nowhere, ecm pulls timing from 26* to 19*, rpm goes up, and its out of limbo, back to cell#5 with BLM at 160 and INT at 140, IAC goes all the way down.
So you have a warm engine very lean.... and it gets bug down in limbo again with low rpm, high IAC, and 26* of timing.
Conclusion: Your VE tables are too lean and your engine does not generate enough vacuum under 900 rpm.
Conclusion: Your VE tables are too lean and your engine does not generate enough vacuum under 900 rpm.
Probably why it won't even approach a smooth idle below 900 RPM.
1. This car was never unreliable. Being unreliable means driving the car is impossible. I am struggling to determine if this is a ECM programming issue or something mechanical. Mechanical to include a harness / injector issue.
2. It seems oddly consistent that start up from cold seems to drive/run fine. Stop and hot re-start and all goes into the toilet. Same SA and Same VE tables. My VE table have been close to their current numbers from well before this issue appeared.
3. I took 15 samples from 173a and 15 samples from 173b for a side by side comparison. The WB is solid lean in 173b. Some of the distinct differences are for parameters that I do not understand. Both samplings are in OL. Attached short CSV 173a-b
What's next?
Let it sit overnight
Reactivate closed loop and get off this open loop foolishness
Start your datalog before starting engine, not 17 seconds after (so I can see data a few seconds before starting)
Go for a long drive (45-60min) without turning engine off (that's going to record, crank, start-up OL, OL, CL, WOT)
Make sure you get some cold idle, warm idle, mid throttle up hill, feather throttle down hill, highway cruise and WOT if you feel confident
Send me your log (.xdl), your definition (.xdf), your acquisition (.adx) and your tune (.bin). Don't need your .csv and graphs
Give me some time (I have lots lol) and I'll get back to you
In the mean time, don't change anything to your ride and relax, do something else.
I feel you are lost a bit with this tuning stuff. It is way harder than people will tell you, believe me.
"I replaced a leaky intake manifold gasket for the third time."
That's seems to be what started the problem, right? How did you known it was leaky? What data or testing made you conclude it was leaky? How can the car be reliable if it had a leaky gasket? You changed the gasket and it became unreliable?
OK, here's Paul Harvey's version of the rest of the story
I built this car between 1995 and 2000. Installed the HO502 with the Street and Performance intake and 91 Camaro TPI set up. Drove it 75k miles. Lost a roller lifter and sucked metal though the engine. Purchased a ZZ502 short block from GM about two years ago. Sent the Brodix heads to a machine shop in CO before reassembly. Never could get it to idle decently. Began the tuning process. Number six plug kept fouling. Hard to tell if oil or gas. Installed new injectors. Kept fouling. Figured oil. Put new seals on using compressed air. Kept fouling. Pulled the intake and installed new gasket. Kept fouling. Pulled off the heads and sent to a machine shop here in VA. They said the issue was no sealant on the intake rocker arm studs. The threaded hole goes directly into the intake runner. Exhaust studs are blind holes. Brodix recommends Red Locktite for the threads. The shop here put teflon sealant. Started fouling after a while. Pulled all the intake studs, cleaned off the teflon and used Red locktite. Fowled again on both six and eight. That made me think of the intake gasket sucking oil from the galley. Pulled the manifold and used gasket cinch and solvent based gasket dressing impervious to gasoline (had used black RTV before). Before installing, I checked the flatness of the heads and manifold with a straight edge and did a dry fit. What I could see was good.
Cylinder lead down and compression on six is good. Both NB and WB are on the even side.
That is where I am at today.
The old HO 502 had a milder cam that was ground by Compcam to the Street and Performance specs from Mark Campbell (dead now). Mark told me at the time that was to get enough vacuum for the FI set up.
I suspect the ZZ502 has a bit more cam in it from GM.
In the end, you are using antiquated technology that was NOT designed for your application and that was NOT designed to be tuned. GM engineers used complicated calculations and were limited to the technology they had. They could only dream of having all the technology we have now a days and probably would laugh at us using this '80s stuff. Maybe a carb would be better or simply a modern EFI system that can match your engine set-up. Personally, I won't bother anymore with old GM EFI systems on any of my future projects unless it's just a simple tune for an oem engine. I worked with Holley Mega Squirt on a Miata Race Car and soooooooooo much easier and accurate. Plus the local performance shop can tune it with their dyno (he would not touch older GM EFI). Holley also provide support and user manual.
I could kick myself. I changed the BIN to full time close loop. Took it out for a drive using the APU. I guess I forgot to hit the record button because when I got back there was nothing to post.
But, the drive was not long. I got up to temperature and it went full lean. It would change back and forth some. For example, I got caught by a red light trying to get to me house. In Gear, it was full lean in Closed loop and rattlng, threatening to die. Finally, trying to keep it running, I went to P/N. Picked up a bit of RPM and WB dropped down near 1.0. I did observe the Fuel Pressure and it was pretty steady at idle at 34-36 psi.
I will try to get a log, maybe tomorrow if not raining. But, for sure, it isn't right.
GM sells the deluxe ZZ502 with a Dual Plane manifold and a Holley 870 CFM.
Yep same problem of lower rpm high MAP (no vaccum).
I'm wondering if you don't have a minor intake air leak! At lower rpm that would show more and would explain the high MAP value exacerbated by IAC full opening. That would also explain why your VE tables are out of whack all of a sudden.
In Googling ZZ502 vacuum readings, this appears to be what others are seeing. There was little movement at idle. I keep thinking about what Mark Campbell told me when we put the cam in the the HO502 back in 1996. Need more vacuum for the FI.
This does seem worse since I did the last Manifold Gasket. The intake is so heavy, I have to mickey mouse a lift to lower it squarely on the heads.
Yep!!! It seems to be consistent with what the ecm is seeing. Low vacuum. Just clued in!!! You don't even have a TPI. What the heck are you doing messing around with the '7730 ? Get yourself a modern EFI or go carb. There must be a modern EFI system that can accommodate your set-up.
The more I review your log the more I believe the '7730 EFI doesn't like your set-up. It seems the ecm (and your AFR gauge) sees lean condition at idle, however, the injectors are opening more at lower rpm idle (700) because of high MAP, than 1000 rpm idle. Makes no sense. What's the smell from the exhaust? Do you see sooth? Are your spark plugs carbon fouled? You could have a false lean condition.
Drivers side has always been clean. Passenger side has always had the issue with fouling on six and eight. Mostly six. These plugs photos before I changed the intake gasket. Six/eight reason I figured was bad seal on intake. This car has never idled smoothly with the new short block. It has had some decent tunes though. This going full lean is something new. Fuel pressure is good, so don't think it's a filter issue. I can hear the injectors, but could be some debris in an injector. The plugs I have in now are one range hotter than the ones in the photo
Something worth mentioning. Your tune as it sits, reaches over 80% injector duty cycle (%DC) around 5500rpm. For a 502cid, it seems 30# injectors are too small. By the VE/Inj PW profile, it seems your 502cid is under 400hp. Makes no sense.
NBO2 just below the collector on the passenger side. Block huggers. The WBO2 is about 20 inches away from the exhaust port, also on the Passenger side. The six and eight cylinder fouling issue is on the same side. I haven't pulled the sensors to see if they are crudded up.
The 30 lb injectors were on the original engine. These are new ones, same size
NBO2 just below the collector on the passenger side. Block huggers. The WBO2 is about 20 inches away from the exhaust port, also on the Passenger side. The six and eight cylinder fouling issue is on the same side. I haven't pulled the sensors to see if they are crudded up.
The 30 lb injectors were on the original engine. These are new ones, same size
Yep something is not right to say the least! Looks like misfire. If the O2 is fouled, it's definitely a false lean condition, but you would see some sooth out of the exhaust.
Also, has your vacuum decreases at lower idle rpm, fuel pressure goes up along ecm opening the injectors more. All that points to false lean condition.
Again 30# on a ZZ502 seems out of place. I have 32# on my 400hp 383 TPI and they are right at the limit of 80%DC. I run 43.5 psi. vacuum disconnected.
Take a look at 169. Closed loop BIN that was before I changed the Intake gasket. My harness is 28 years old. Maybe a harness issue. I also had to extend the Coolant temp, the IAC and the TPS sensor wiring when I changed the gasket to reroute the harness.
Take a look at 169. Closed loop BIN that was before I changed the Intake gasket. My harness is 28 years old. Maybe a harness issue. I also had to extend the Coolant temp, the IAC and the TPS sensor wiring when I changed the gasket to reroute the harness.
Same issues with the tune. Exact same profile, all numbers are similar with same IAC behavior and high BLM number. Again, you run open loop. Too lean, VE tables are too lean and I bet ya you run lean at WOT. Probably need to bump up VE at WOT and your injectors are going to max-out. They are too small.
ONLY difference is the MAP does not go as high....So you definitely did something when you changed your gasket... vacuum leak guaranteed.
My SWAG? The ECM is going into and out of malfunction 33, MAP high. It will do this prior to setting the SES/CEL (you do have one, right?), and before setting a code.
Once the ECM detects a 33 malfunction it creates a MAP value from some calibration tables, and uses it. You don't know this as the ALDL stream only has the ADC MAP value.
With the ratty cam, these calibration tables are no longer calibrated. In N-Alpha mode the ECM is going to create and use a MAP value that is lower then the real value. Boom, lean along with SA changes.
Get the MAP/BARO ratio value into the data stream. With that can see how much to change the malf 33 threshold to prevent this issue.
Or, disable the test. There appears to be several ways to do this.
I’m tapped out explaining and i’m confusing myself now lol
In fact the MAP values appear to be in the same range. So yes maybe not vacuum leak. However the rest is true, tune behaves the same.
Here’s my last comment for today.
Your tune is not optimal for your setup, before and after gasket change. When you change the gasket, something changed and the tune is now even less optimal.
Even if you would go to the before gasket change, your tune was borderline optimal with lean BLM, IAC going to extremes and high MAP value.
My SWAG? The ECM is going into and out of malfunction 33, MAP high. It will do this prior to setting the SES/CEL (you do have one, right?), and before setting a code.
Once the ECM detects a 33 malfunction it creates a MAP value from some calibration tables, and uses it. You don't know this as the ALDL stream only has the ADC MAP value.
With the ratty cam, these calibration tables are no longer calibrated. In N-Alpha mode the ECM is going to create and use a MAP value that is lower then the real value. Boom, lean along with SA changes.
Get the MAP/BARO ratio value into the data stream. With that can see how much to change the malf 33 threshold to prevent this issue.
Or, disable the test. There appears to be several ways to do this.
Yep!!! It seems to be consistent with what the ecm is seeing. Low vacuum. Just clued in!!! You don't even have a TPI. What the heck are you doing messing around with the '7730 ? Get yourself a modern EFI or go carb. There must be a modern EFI system that can accommodate your set-up.
The 7730 will EASILY run this setup. Just have to start with the basics and tune it. No such thing as too little idle vacuum. Just have to tune the fuel and spark accordingly. I have done 7730s with about 7 in/hg @ 1,000 rpm idle vacuum. 7730 can easily handle this engine.
02-13-2023, 05:06 PM
? Get yourself a modern EFI or go carb. There must be a modern EFI system that can accommodate your set-up. 
