Question: cold start issue

[Bentas1ent]

This past winter I installed 8 new injectors which I purchased from Fuel Injector Connection. My 89 runs like a BEAR once it is warmed up, however it has a hard cold start condition. When I try to start it from cold in the morning , it seems to crank forever before it fires up. When it finally catches, the RPM is around 500 or less and slowly rises up to about 700. When it is warm it fires right up with no problem and runs great. Could anyone suggest where I might start to try to correct the cold start thing?

 

[aklim]

Usual culprits checked? Fuel pressure and FPR, spark plugs and wires, cap and rotor, quality of spark?

 

[Bentas1ent]

still trying

Usual culprits checked? Fuel pressure and FPR, spark plugs and wires, cap and rotor, quality of spark?

fuel pressure is at 38 to 41 psi regulator performs well under load plugs, wires, cap and rotor are by MSD and are all new and the spark is excellent.

 

[aklim]

fuel pressure is at 38 to 41 psi regulator performs well under load plugs, wires, cap and rotor are by MSD and are all new and the spark is excellent.

38-41 at idle with or without the hose off? Does the fuel pressure drop quickly after shutoff?

I forget. Do you have a cold start injector or just 8. IIRC, some years have a cold start injector spraying fuel in the manifold.

Also, just a wild thought, did you clean the MAF? I doubt that but just a thought. Also, how is your TB? All the IAC passages cleaned? Min idle set properly?

 

[Bentas1ent]

38-41 at idle with or without the hose off? Does the fuel pressure drop quickly after shutoff?

I forget. Do you have a cold start injector or just 8. IIRC, some years have a cold start injector spraying fuel in the manifold.

Also, just a wild thought, did you clean the MAF? I doubt that but just a thought. Also, how is your TB? All the IAC passages cleaned? Min idle set properly?

Yes, the MAF is clean. Fuel pressure was checked at idle and while under light load. Pressure stays up for at least 20 minutes after shutoff. No cold start injector on this one. Is there any info available on proper cleaning of the throttle body including all passages??? The idle may be set a little to low at 600 currently. Should it be bumped up a little?? Any help will be a great help. Thank You!!

 

[aklim]

Yes, the MAF is clean. Fuel pressure was checked at idle and while under light load. Pressure stays up for at least 20 minutes after shutoff. No cold start injector on this one. Is there any info available on proper cleaning of the throttle body including all passages??? The idle may be set a little to low at 600 currently. Should it be bumped up a little?? Any help will be a great help. Thank You!!

You take the TB off and clean everything you can. Also have the IAC housing removed with the IAC removed and clean it all.

You cannot set the idle since it is commanded by the ECM and it will try to achieve it as best as it can. What you need to do is hook up a scanner and see what the IAC counts are to see if it is too high or not.

 

[Bentas1ent]

You take the TB off and clean everything you can. Also have the IAC housing removed with the IAC removed and clean it all.

You cannot set the idle since it is commanded by the ECM and it will try to achieve it as best as it can. What you need to do is hook up a scanner and see what the IAC counts are to see if it is too high or not.

I think that somewhere along the past ownership trail of my car someone modified the idle control. All I need to do to set the idle anywhere I want it is to turn a small screw mounted on the side of the air plenum. It looks like a factory installed part, but who knows. The only thing you lost me on is what is the IAC??? My scanner won't read this car, only newer ones. The car does not send out any trouble codes.

 

[aklim]

I think that somewhere along the past ownership trail of my car someone modified the idle control. All I need to do to set the idle anywhere I want it is to turn a small screw mounted on the side of the air plenum. It looks like a factory installed part, but who knows. The only thing you lost me on is what is the IAC??? My scanner won't read this car, only newer ones. The car does not send out any trouble codes.

If you have the Idle Air Control solenoid or IAC, the screw should not do anything unless you push it too far out of control. The IAC is a controlled air "leak", if you will. If the engine is idling at say 500 rpm and the ECM commands 600, it will open up the IAC by withdrawing the pintle of the IAC and thus letting more air "leak" in and that will increase the idle. If the engine needs to lower the idle speed, it will close off the IAC by extending the pintle to close off the "leak". So, unless you push it so far out of adjustment that the ECM cannot compensate, it will try to achieve the idle speed commanded by the ECM.

 

[WRECKER88]

My 1989 coupe that has 5,200 miles has the same problem with cold start but i get a code 14. I have a new coolant temp sensor that is mounted in intake manifold under the TB on order and will replace it next week when i get back from vacation.

 

[aklim]

My 1989 coupe that has 5,200 miles has the same problem with cold start but i get a code 14. I have a new coolant temp sensor that is mounted in intake manifold under the TB on order and will replace it next week when i get back from vacation.

Which brings up another issue. If you didn't get the code, the sensor might still be reading wrong so you need a scanner to see what the ECM is seeing.

 

[vetteoz]

All I need to do to set the idle anywhere I want it is to turn a small screw mounted on the side of the air plenum.

Only one correct way to set idle speed and that speed has to be to whatever is set in the ECM program as outlined above.

http://www.corvetteactioncenter.com...ottle-body-adjustments-1989-l98-corvette.html

If throttle blade setting does not correspond with ECM idle setting; then ECM will be constantly fighting to achieve the impossible.

 

[aklim]

Only one correct way to set idle speed and that speed has to be to whatever is set in the ECM program as outlined above.

http://www.corvetteactioncenter.com...ottle-body-adjustments-1989-l98-corvette.html

If throttle blade setting does not correspond with ECM idle setting; then ECM will be constantly fighting to achieve the impossible.

That is NOT the only way. The problem with that way is that it works only if your system is 100% stock. Otherwise, the idle is going to be difficult to determine. If you set my idle that way, it will never work. That is why I set it with the IAC counts in mind.

 

[TedC]

That is NOT the only way. The problem with that way is that it works only if your system is 100% stock. Otherwise, the idle is going to be difficult to determine. If you set my idle that way, it will never work. That is why I set it with the IAC counts in mind.

Totally correct. The procedure I documented was for a stock 1989 L98. The key point here is making sure that the ECM can leverage the IAC to manage air flow. No IAC counts, then the IAC is fully closed which limits the control the ECM has over air flow which directly impacts idle speed.

 

[boomdriver]

This past winter I installed 8 new injectors which I purchased from Fuel Injector Connection. My 89 runs like a BEAR once it is warmed up, however it has a hard cold start condition. When I try to start it from cold in the morning , it seems to crank forever before it fires up. When it finally catches, the RPM is around 500 or less and slowly rises up to about 700. When it is warm it fires right up with no problem and runs great. Could anyone suggest where I might start to try to correct the cold start thing?

Not uncommon with the Bosch-III injector upgrade.
They do not bleed off like the multic did to help prime the cylinder so you have to wait for a couple cycles on each injector bank to get fuel back to spraying. The pressure is there, its just much more controlled than it was with the mule-tic injectors.

Try this....

turn key, crank briefly...1 second,. release, crank again and it will fire right away. Its looking for fuel that will come either way,. difference is wasting starter crank time or not. Crank it for 1 sec, stop then hit it again and it will lite up faster than if you just hold the key and wait for it to fire.

 

[aklim]

Not uncommon with the Bosch-III injector upgrade.
They do not bleed off like the multic did to help prime the cylinder so you have to wait for a couple cycles on each injector bank to get fuel back to spraying. The pressure is there, its just much more controlled than it was with the mule-tic injectors.

Try this....

turn key, crank briefly...1 second,. release, crank again and it will fire right away. Its looking for fuel that will come either way,. difference is wasting starter crank time or not. Crank it for 1 sec, stop then hit it again and it will lite up faster than if you just hold the key and wait for it to fire.

My pump will not cycle again if you do it that quickly. You have to wait for a few seconds to get it to prime the pump

 

[TedC]

Starting in 1989, GM reprogrammed the EPROM for longer crank times, especially when cold. They did this to increase oil pressure levels before actual engine start. In my 1988, the engine would fire up hot or cold with a just twist of the key (1988 uses a cold start injector). My 1989 (does not have a cold start injector) has what I call a longer crank time when cold. It is working as designed. If you don't like it, then you need to get a customized EPROM. Boomdriver's suggestion actual works because the first cold crank starts the timer process in the ECM. Try his suggestion and report back. Worked on mine and two other 1989s owners on this forum.

Now, the low idle when cold is an issue. You need to monitor the IAC counts using an OBD I scanner. The min air speed screw (not an idle speed screw) controls the minimum amount of air required to produce a base idle speed. Base idle speed is lower than desired by the ECM. This is where the IAC takes over and adds more air to reach desired idle speed. The L98 is very very very (did I say very?) sensitive to this being adjusted right.

 

[TedC]

My 1989 coupe that has 5,200 miles has the same problem with cold start but i get a code 14. I have a new coolant temp sensor that is mounted in intake manifold under the TB on order and will replace it next week when i get back from vacation.

Did you measure the resistance of the coolant sensor when cold? You should see 3400 to 7500 ohms when temp is between 70 and 40 degrees F. If you disconnect the coolant sensor wire, you force resistance way up (super high resistance), and the ECM thinks it is darn cold out (below -30 F). The ECM should not post a code 14. Otherwise, you have a short (low resistance) which fools the ECM into thinking it is darn hot (over 266 F) out does indeed post a code 14. Slim odds but you could have a defective ECM. It doesn't hurt to replace this sensor with a new one. They are more responsive to temp changes in my bench testing. Just a few suggestions to make sure you indeed find the real source of the code 14.


Additional comment added. If this sensor is bad, it can really cause starting issues hot or cold.

 

[boomdriver]

My pump will not cycle again if you do it that quickly. You have to wait for a few seconds to get it to prime the pump

Mines the same way...takes about 10 secs to cycle the pump relay again but thats does not seem to be what or how this works...The pressure is present the 1st or 2nd key turn, its more to do with the time or the finer spray of the B-III injector.I've looked into this with the pressure gauge connected and observed that its not really a pressure issue.
Mine lites off immediately if its the slightest bit warm. But 1st time in the morning I've got to where I do the 2 key-crank everytime because its just going to run the starter hard for 3-4 seconds if I don;t. I've heard of other C4s with the B-III upgrade having similar issues.

 

[Bentas1ent]

Thank all of you

The info you have all given me will get me going on the way to solve this problem. I will be away for a couple of days but I will let it be known how these suggestions worked when I get back!!