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A few months back i purchased an 89 IROC Vert with the LB9. Felt comfortable since i have an LB9 in my 92. The 89 started and ran great, just needed some TLC. One month later, all of a sudden the car is really hard starting when cold. Been chasing down what i did and trying to see if its something simple... Here is what i got.
1. Car cranks and cranks when its cold (overnight). Eventually you can tell its trying to start but won't go. Once it catches, it runs pretty smoothly.
2. First idle is at about 900 rpm but then step climbs to 1100 rpm before dropping down to 900 as the car warms.
3. When it first fires, if you try to open the throttle, car wants to die. This gets less and less as the car warms. After a while, its a stumble with throttle plates opening. Eventually you can work the throttle normally and revs normally.
4. Never gets below 850 rpm when previously it would idle around 650-700 rpm.
5. If you shut it down and then re-fire in the next few hours, it fires right up.
Operating conditions
Base timing - 2 deg BTDC
Vacuum - 18 inches at idle
Fuel pressure - within spec, holds without dropping for more than 5 min after shutdown
TPS voltage - 0.35V to 4 V (need to adjust)
What i have done:
1. disconnected and capped off all vacuum ports and cold started car to see if i had a vacuum leak. No change.
2. Changed injectors with Bosch 3 units (was already doing this), No change. Car runs much smoother though.
3. Changed fuel pressure regulator
4. Replaced failed EGR valve.
5. Tested EGR solenoid. Good.
6. Changed ignition coil. no change.
7. Cleaned IAC. Did reset procedure. Got car to idle smoothly in D at 500 rpm. Reconnected IAC. Car started at 700 rpm, climbed to 900 rpm over the next 30 sec and stayed there.
8. Closed IAC in diagnostic mode and cold started the car; car did not start any easier.
Two odd things:
1. The CHECK ENGINE light never comes on.... ever....not even with initial key in run position... while check the bulb but this would seem odd.
2. After everything reset, backed off min throttle position, IAC kept responding to keep the car at 900 rpm.
Running out of ideas... car was fine one minute, hard cold starts the next day.... what am i missing? Once it starts and warms, it runs very nicely... does not seem to be vacuum or similar issue. What might i be missing in the cold start sequence? Cant be gas or other items that degrade over time... Went from good to bad overnight.... (I think this was the day i changed the auto tranny fluid)
Car does not have plates so i can't take it for a drive.....
If the ses never comes on check the bulb. The ecm grounds the bulb koeo.
you might have a faulty ecm.
timing spec is 6dbtdc and tps should be raised to .54vdc
I did a lot of the same things you did. Symptoms came on quickly. Turns out the original timing chain had finally stretched waaay out. Changed it and all better. Much better.
OK... so i started addressing what i could last night....
Reset the TPS so it is 0.53V closed... opens to 3.88V... might need to change out but that does not look like the source of the problem. Same starting problem.
Pulled the dash bezel to look at the SES bulb... once i got a finger on it, it lit up. Turns out the socket was loose. Tightened it up so the SES stays on when it should.
Then i decided to run a diagnostic check to see if i had any codes...and one pop'd up. A Code 42, Ignition Control Module.
As it appears to be the factory original and now 30 years old, a new one will be on order today. Probably will run the other checks in the factory manual also but it does make some sense if that is failing.
Funny how a loose bulb made me think i had no codes until i left the key in the ignition when running other checks and only then realized the SES light was not coming on.
On the CTS, actually, when i put everything back together after changing the injectors i did forget to connect the CTS... i eventually caught that but it didnt change the symptoms.
I am sure the timing chain is near the end of its life too...same car too... 89 IROC Vert with an LB9 using Bosch D3s and a TH700R4. Now that winter is coming fast, may put that in the list of winter work.
The procedure for checking the slack in the timing chain:
Remove distributor cap and spark plugs
Place extension and socket on the lower pulley center crank shaft bolt. ( I use a 1/2 inch breaker bar with pull/push on the serpentine belt at the same time )
Have another person look at the distributor cap as you turn the crank shaft back and forth
If the crank turns more than 1/2 - 1 inch before the distributor turns, the timing chain needs replacing. If they turn at or near the same time, all is good
Well I replaced the ICM....no change...convinced it has to be ignition related....rpms kept jumping up and down every few seconds...the tach was also jumping even though the engine was not changing rpms....
Was surprised by the rust on the distributor under the cap....
Talked to my brother-in-law who has had a number of third gen firebirds... His experience is all his Code 42's were caused by issues with the pickup coils. Since i found a whole lotta rust under the distributor cap, I plan on yanking it and getting a new setup. I tried cleaning it and the problem got worse.
Ok....so I replaced the whole distributor based on all the rust I found on the pick up coil....car exhibited the same starting problems. I got the engine timed right on at 0 deg base and about 22 deg at idle. Once it warms up and goes closed loop, it idles perfect at 750 RPM. Still has a bit of an off idle stumble though when you work the throttle by hand.
Tried a cold start tonight, same starting issue...once it fires, rpms run all over the place in open loop...700 up to 1200....but runs real nice in closed loop.... No codes active....not sure where to go next.... It's something in the starting sequence...it cranks and cranks...then tries to fire, tries to fire....then it might catch and off it goes.
I did notice battery voltage dropping below 10 volts when cranking....no sure if that plays in at all....may try swapping batteries tomorrow.
What sensors does the car use at cold start up? And why does the idle keep jumping around in open loop?
Decided to throw a fresher battery in the car since the one in there is 11 years old.
It seems to start faster although still went through the sequence of cranking, then cranking but trying to fire, then firing... once it did it almost died....then caught and ran fine. Still have the rpms moving around while in open loop mode. Once it goes closed loop, it runs perfectly fine.
When it tries to fire and then kinda struggles.... i am wondering if something is quenching the flame...aka coolant leak or oil leak down the valves...and it needs to burn it off to get going... I don't see any blue smoke under high vac conditions...my guess is that i need to investigate this more....
@erik69&85, Try testing your CTS with an Ohmmeter when cold here is the cross ref chart. It may think your engine is hot when actually cold. Just unplug at front of intake and measure the two pins. For a 70* day, coolant cold, you should read 3400.
I changed mine out years ago when it thought the car was in a overtemp condition
Testing the CTS was actually next on my list..... so it was go last night. Car was cold, garage was 50F exactly.
First... its a LOT harder than it sounds. That sensor is behind all the front end pulleys. And those prongs are back inside the sensor housing. I had a bear of a time getting my leads on them and not touching each other. I kept getting no reading or no ohms. After about 20 minutes and using several different sets of leads, i finally got a reading of 555 OHMs. Then i took the leads out and worked to replicate that reading. I was able to get it 2 more times.
I see that 555 corresponds to almost 150F. This would make sense. If the ECM thinks the car is warm, its giving a leaner mixture rather than the rich mixture a cold car would need. The car fires right up when its warm. but struggles to fire when cold.
As a side note, I noticed that as soon as i turn the key, one of the cooling fans turns on. I believe its the ECM controlled fan, not the the temp switch one. Would make sense if the ECM thinks the car is warm. That fan not turning on is how i noticed the CTS was disconnected after replacing the injectors. The car still struggled to start without the CTS plugged in but that might have been for other reasons with the ignition.
Will replace the CTS tonight and see what happens....
Well, that wasn't it....no change in the starting problem. I think I missed a x10 on the ohms readout....that would make sense.
Got the car started. Ran at 10 deg btdc timing in open loop mode. Rev'd decent. Once it went closed loop, it went to 22 deg btdc. But had a stumble when I tried to rev it. Had to rev it slowly. Then after a couple revs manually at the throttle plates, I got a backfire pip thru the intake.... I believe that's a lean condition... I keep coming back now to not enough fuel....the fuel pressure is steady when running....engine just does not seem to richen up when it needs to.
When it first fires, a get some type of smoke from the exhaust....but can't place the smell...it just comes out when the car first fires....then once the car goes, clears up.
It's not a blue smoke....and it does show up any other high vac time....I think it's excess fuel from the long crank burning off....
When it first fires, it stumbles for few seconds...then , click, it runs smoothly....I am going to check to see if the fuel pump is running correctly....when cranking....
Try shooting some carb and choke cleaner in the intake when cold,if it busts off right out of the gate you'll know it's a fuel related lean condition,also the stumble you described is a hole in the fuel curve (lean condition) when you talk about opening the throttle and it stumbles that's a lack of fuel,hope this helps
Those Bosch' 3 injectors are notorious for running lean and as most on this board have found out they need a matching tune for them to run right. Tootie Pang, who posted up top earlier went through about 7 tries to get his Bosh 3's right. My buddy has a 92 LB9 and is so frustrated with his he may just ditch them for the Delphi replacements. He does not want to go through the tuning process. This could be your issue here. The other thing you may want to check is your cold start injector system. It runs off it's own CTS and maybe this is not working which would definitely effect the cold starting.
I had a similar issue awhile back and it was a couple things done together that cured the problem. I 1st replaced my TPS. I have a self zeroing? in my 91 and even though it tested on the voltmeter it still would bounce at idle. 2nd I removed the TB and cleaned out the IAC passage really good. It was all carboned up. I also noticed that the vacuum passage on the back side was also clogged. this passage is a hard plastic line that ran to the ECM vacuum connector that ultimately runs the EGR....IIRC. I have a 91 and not educated enough on the different years so this vacuum line may run elsewhere on yours. I did the IAC reset after these 2. 3rd, is witchcraft, I switched to non-ethanol fuel. The idle got under control for the most part after the 1st 2 steps, after the ethanol fuel was fully out the cold starts where spot on. My cold start problem was so bad that after better than a dozen turn overs it would "diesel" for about 5 seconds or so before it would "catch" itself.
Hope this helps!
Last edited by vinny R; 11-23-2019 at 08:01 AM.
Reason: add info
You can take the intake boot off at the throttle body,open it up and shoot the carb cleaner down its throat ,if it busts right off and runs good for a bit then you'll know it's fuel related,you have to be careful though about what carb cleaner you use though as a lot of now days isn't volital, I use the Chem tool b12
I have the Bosch 3s on my 92 LB9 and I love them....no issues....the 89 doesn't have the cold start injector...first year without....
The idle is good...spot on when it goes closed loop...it's that cold start that the engine struggles with....doesn't seem to get the rich mixture it needs.
I have to believe it's a fuel thing....will try carb cleaner today....
I have never added gas...bought it with a full tank ..while working on it, it started this cold start problem....same tank of gas as when it was good...
Yeah try the carb cleaner and if it fires right up and runs good that will at least guarantee its a lean condition and a fuel problem,does the car have any mods,maybe someone installed an aftermarket chip that was set up for the cold start injector
Results.....used some highly flammable brake cleaner.....sprayed a bunch in, closed it up....car fired right up...ran rough for few seconds....then ran about 1000 rpms ....did as I described above...
Once it settled down at 750 rpms in closed loop mode, did a little drive around the neighborhood...can ran as expected....
So it's a lean condition on startup...and it's not the CTS....where to go from here...car is bone stock, no mods....I can check the ecm....didn't seem to have this issue when I bought it.
Ok...it looks like that is a part number the original Ecm could have had....was common on 305 tpi engines.....could this remanufactured part be my issue...
Try a tap test on the ecm and also the maf sensor,see if this changes anything,just use a screwdriver handle and lightly tap,also might try unplugging maf to see if anything changes
Ok...results...tapped the ecm case a few times....had changed the fuel filter, put back the old one....started car....no change....cranked a while eventually caught, but ran just hanging on for 5 sec or so, then caught and ran as normal....with a decent idle, but a little movement in rpms.
After it went closed loop, i shut it off and disconnected the MAF sensor. Car started up and idled fine but had no throttle response, just stumbled and did not rev the engine when u worked the throttle....thru a code, which I cleared. Reconnected and car went back to normal
the weird thing is that when it starts, it barely runs for a few seconds...maybe 5, the it's like -click-, and the car speeds up to 1100 RPM or so and starts running like it should....what changes at that moment?
Since I can only really test this once a day.... Tomorrow I will jumper the fuel pump to be it's always running as I crank the car ...
Jumpered the fuel pump to be sure it was running....same operation....car started after maybe 5 secs...ran rough....died. turned the key to restart and it started right up and ran fine ...what the heck....!
Each time you turn the key, it gets better with a col start....not sure where to go next...iac?
If you have a fuel pressure gauge, try doing a dump test on the cold start injector or check the ohms on the injector and voltage check on injector wires. I prefer a dump test and noid light test on injectors including the cold start injector. Connect a noid light to the plug and crank the car when cold. The light should stay light for the same amount of time that the starter is spinning. You might want to invest in an ALDL1 ( 'ALDU1 and CABL1 ) or APU1 AutoProm ( 'APU1' AutoProm Package: USB Version - backordered 'til 1/15/20) to diagnose your problem. You will be able to read the timing, IAC position, MAF, TPS ,O2 MAP, Temp ect. Good luck!
Sorry, thought it was an 85. May I suggest a noid light check on each fuel injector bank. If the light is not energized while you crank, you'r not getting fuel for cold start.
What is the fuel pressure when the car is running. My 89 firebird I bought last year had very similar symptoms and it turned out to be the fuel pump on its way out. This was after I too put Bosch 3s in. I think the fuel pressure should be around 47 psi when priming and in the 40s while running. Just thought I'd give my 2 cents.
Fuel pressure while priming - 45 psig
Fuel pressure while running - 37 psig
fuel pressure with vacuum to reg disconnected - 45 psig
Tested all injectors with a noid light....all good and normal.
Cold started after I cranked it 8 times to test the injectors....fired quickly...since the cylinders were rich with fuel (tested with ign coil disconnected). Fired pretty quickly....burned off the extra fuel and ran as before....once it goes closed loop...it idles really nice.
- replaced timing chain and front seals since it was leaking
- replaced oil pressure sending unit since there was a lot of oil in the area.
Still the same struggle to start... acts lean... stays that way until it gets nice and warm.
Observations:
- once it goes closed loop, idles dead perfect (does not look like a vac leak)
- even it closed loop, has an off idle stumble. None if you throttle slowly, more pronounced if you work it fast. I can see the engine shutter as i work the pedal.
- As soon as the car goes closed loop, one of cooling fans comes on... WTF?
- Double checked the ohms on the coolant temp sensor and air intake temp sensor. Both with the car cold, and the car hot. tested them at the ECM connector. Everything made perfect sense. Not a sensor issue.
- Once the car is warm, it fires right up... after 2 hours of siting, it fired pretty quickly...24 hours later.. back to a tough start.
My reading (TPI swappers guide) says that for a cold start, the only thing the ECM uses is the coolant temp sensor. And that checks out... its clearly a fuel issue.. i have set the TPS voltage, replaced and reset the IAC, replaced the ICM and distributor and set the timing... its fires quickly with some carb cleaner in the intake...it happened on the old injectors as well as the new, replaced the EGR valve as it had failed. i am down to the ECM...
I have 86 TPI using TunerPro RT. Wondering what is your IAC Startup Position. I set IAC Startup @ 25 steps and when cold its hard to start. I increased IAC steps to 45 and now it starts right up. In Florida I don't need 125 steps @ startup like factory because of warm temps. Good Luck!
Fixed!!!!!...what a week I am having...first I fixed the rear main leak.. (see thread in tech/general engine), then I fixed the seat issue so I can drive comfortably..(see convertible forum)... Now I fixed the starting issue ... New ECM.
Car seemed to think the engine was always hot... Lean start, high temp fan came on as soon as it went closed loop....lean when cold... All sensors checked out...at the plug on the ECM harness... Put the new ECM in... Fired up on first key turn!
Now if I could just get plates so I can drive it... Damn nys DMV is closed... Gotta mail everything in...
Great, Glad its finally running like it should! When we keep plugging away at a problem, it's always great to hear that there is a solution. My 86 TA was getting 6-8 mpg. I had changed the XDF bin definition from $32 to 6E and it took me a while to find and adjust the tune, but now my engine is running great and getting 15+ mpg.
11-05-2019, 12:11 PM
