Rough cold start L98
Thread Starter
Instructor
Joined: Mar 2017
Posts: 221
Likes: 15
From: Ijamsville Maryland
Rough cold start L98
Thanks in advance: I have a 1989 L98 with 30,000 miles. The previous owner installed new injectors, but I am not sure which he used. I am hoping the forum can help me with a checklist to diagnose the following issue: On first start/cold start, the engine “stumbles” to life. All other fuel injected cars I’ve ever owned catch right away and then settle into a smooth idle. Since I’ve owned this C4, on cold start it acts like a carburetor and kind of stumbles as though not all the cylinders are firing at once, then it slowly catches and sounds very good while working itself to a smooth idle. It only happens on the first start of the day when the engine is cold. I can drive it all day and except for the cold start, it will roar to life, climb to a 1500 rpm and then settles to about 750 at idle. I’m hoping to get a list of things to check in order.
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
Timing, run 87 octane, fuel pressure should hold over 43psi with key on. Fuel pressure should respond immediately when key is turned to run, coolant full...that is a start
Melting Slicks
Joined: May 2014
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From: New Port Richey FL
Last edited by s carter; Dec 4, 2017 at 09:20 PM.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,213
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From: Southlake, TX
The Kevova is correct... If you have a hard (lots of spinning and stumbling) and then it runs after warm you most likely have a fuel pressure issue.
Team Owner
Joined: Jul 2004
Posts: 28,353
Likes: 3,253
From: Hartford WI
I get pretty nervous when you say "installed new injectors but don't.....". Did he dump bigger injectors AND DID NOT adjust the ECM? Was it from some junkyard? Hard to say.
I would scan the car and see what the ECM thinks the coolant temp is. Check that against ambient temp or better yet, against an infrared thermometer. As mentioned, fuel pressure, spark quality and if the plug wires are leaking.
I would scan the car and see what the ECM thinks the coolant temp is. Check that against ambient temp or better yet, against an infrared thermometer. As mentioned, fuel pressure, spark quality and if the plug wires are leaking.
Thread Starter
Instructor
Joined: Mar 2017
Posts: 221
Likes: 15
From: Ijamsville Maryland
Thanks all for the tips. I’ll check the distributor and coolant level. The PO has a receipt for new injectors, but it does not specify the brand or type. I installed a new water pump just after purchase as it was weeping a bit. Car runs nice and cool and will run up to 228 before fans kick on to bring it back down to 220 in heavy traffic on the hottest days. I will have to investigate the fuel pressure. It does almost seem like a fuel pressure issue as it could leak down after the car cools down and cause a cold start issue. No obvious signs of a fuel leak or fuel smells either. Will also break out my handy dandy paperclip to check for codes. Just wanted to male sure there was nothing really obvious I was not thinking of...
Thread Starter
Instructor
Joined: Mar 2017
Posts: 221
Likes: 15
From: Ijamsville Maryland
Any particular reason for 87? I have been using 92 thinking the injectors may have been a bit fouled in addition to some off the shelf fuel system cleaners, but the problem persists.
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Team Owner
Joined: Jul 2004
Posts: 28,353
Likes: 3,253
From: Hartford WI
The PO has a receipt for new injectors, but it does not specify the brand or type.
I will have to investigate the fuel pressure. It does almost seem like a fuel pressure issue as it could leak down after the car cools down and cause a cold start issue.
No obvious signs of a fuel leak or fuel smells either.
Will also break out my handy dandy paperclip to check for codes. Just wanted to male sure there was nothing really obvious I was not thinking of...
I will have to investigate the fuel pressure. It does almost seem like a fuel pressure issue as it could leak down after the car cools down and cause a cold start issue.
No obvious signs of a fuel leak or fuel smells either.
Will also break out my handy dandy paperclip to check for codes. Just wanted to male sure there was nothing really obvious I was not thinking of...
That won't happen unless something is broke. If I shut down right now and pull the key out then insert it back and turn the key to "run", the fuel pump will not prime. IDK after how long it takes but after a "wait time", it will prime again so even if there is no fuel pressure, if it primes, it will be at spec.
Kinda why I suggested a gauge. It tells if the regulator is bad or not also.
The ECM isn't that sophisticated. Codes mean something is FUBAR and really out of whack.
Team Owner
Joined: Jul 2004
Posts: 28,353
Likes: 3,253
From: Hartford WI
Problem persists after adding fuel system cleaners? Well, add more. Keep adding till you go broke or the problem goes away. The cleaners are working as planned. To separate people from their money.