Little background on my 94' LT1 M6.

Car has 116,000 miles on it. Back in May I was using it for a daily driver, car started having a sputtering problem and the tach would drop to zero and car would stall. Replaced Opti with a NEW cardone unit from Advanced Auto with a lifetime warranty. All seemed well, fixed the problem, car ran great. 2 months later, in traffic I go to start out from a light and the car stalls. Not from me stalling out the clutch but the car just quit. And would not refire for 10 minutes or so. When it finally did fire up I drove it straight to Advanced auto, determined battery was dead, replaced battery, all seemed well for a month. Pulled into a gas station to get a coke, come back out car won't start. It cranks and cranks, but won't start. Wait 10 minutes, finally fires up. This time I figure it has to be the alternator. So I replace the alternator with a new Delco. Again, all seems well.

Last night, I take my girlfriend out to dinner at Carrabbas, pull into a parking spot and shut off the car. I opened the door and realized I was too close too the parking space line and wanted to move the car over a bit, it wouldn't start back up. Cranks, no start. I go in and eat, come back out car fires up like nothing is wrong.

Today I replaced the ICM and coil with brand new delco units I had sitting on the shelf. I figured this has to be the problem since it seems whatever issue I am having is heat related. I then tried to duplicate the problem. I let the car run for 30 minutes in the garage and then drove it around the block. When I pulled back in the garage I shut the car off and then tried to re start it. No good, just cranks and cranks. I wait 10 minutes, fires up perfectly fine and normal. Doesn't skip a beat either when you are driving it. I do notice when its trying to crank the voltage on the display reads between 10.5 to 11. As soon as I stop trying to crank it, the voltage returns to 12.4. When the car is first started (cold start) It idles around 14.7 and slowly drops down to the 14.5-14.2 range and stays there while I am driving.


Any help guys? Possibly the PCM? Can't be the starter right? Its turning the engine over. I don't have a volt meter but I suppose I should invest in one and learn how to use it to test the opti but figured I would ask here first.

Really starting to get frustrated as this thing is getting pretty expensive to park lol. It no longer is a daily driver as I have a company car, but I sure would like it to be reliable when I want to use it. God knows I take care of it. I don't pamper and baby it, but i am sure to maintain it properly. The 89'-91' C4's are starting to look pretty appealing given they don't have the cancerous optispark.

 

I'm Leaning Towards The Idea That You Should Use Your Warranty On The Optispark.

What You're Experiencing Is Coil Like Malfunctions.

Not Sure If Optispark Has A Coil Inside It Because I Have An L98, But If It Does, That's Where I Would Start.

 

Thanks Daniel, I wonder if they would refund me for the bad opti instead of swapping it out. Might just go ahead and try a Delphi or MSD vented version this time...

 

Make sure your part #'s are correct for the ICM & coil. Did you use the "thermal paste" with the ICM? How about with the old ICM, was the "thermal paste" present?

 

Yes sir part numbers are correct. Problem is same as before. There was "thermal paste" present on the old ICM but it was a little dried which was expected for it being 19 years old. I did use new heat sink grease/compound from radio shack part # 2760255. I also used a puddy knife to spread it on even.

 

before I would do that I would check to see if you have fire when it will not start. These things are known for fuel pumps doing crazy things. It seems consistance enough that you should be able to check fuel and spark when it wont start

 

May have missed it, but have you tried down-loading trouble codes?

 

I can try that, pretty sure it has spark, but will double check. I do hear the fuel pump prime when I turn the key to ON.

Seabright- No trouble codes but will double check that also tomorrow. However, the SES light has never showed its' ugly face.

 

I should also add that I have checked all grounds, and the fusible links behind the battery.

 

Like Seabright said check for codes. Throwing parts at it is usually a lost cause. There was no reason to change your battery & alternator if the car is cranking. It sure does sound like a heat or fuel related problem which should not be too hard to find if you take your time.

 

Does the SES light appear during the initial key-on cycle?

 

Just for fun what does your gauges read KOEO Immediately after a warm shut down?
And do they appear pretty accurate while running?

 

Kimmer- according to their machine at Advanced the battery was close to being toast. I already had purchased a Gold from them 2 years ago so I got the battery for free. Alternator I did purchase on a wim figuring it might be it after 115k miles.

Seabright- I will let you know shortly, I live in an Apartment complex and my garage is 3 stories down.

Giamanut- I will let you know tomorrow what the gauges read KOEO immediately after a warm shut down tomorrow. They do appear accurate while running. Coolant is at 192 fully warm, volts 14.3-14.5. Sometimes 14.2. Oil is around 206-212. Everything seems gravy when she is running.

 

Just wondering if any temp is spiking on shut down. If you have fuel and spark but no start after a warm shut down I think I might be looking at an air temp sensor It could cause an improper mixture when hot but provide decent signal while running due to air keeping it cool. I also have a 94 and the intermittent nature and
heat relation suggest sensor to me. You did say you checked all your grounds?

 

Yes sir but will double check again. Need to get a better look at the 3 that attach to the bell housing.

 

Seabright- Just checked it. No codes aside from the normal C12. The SES light is present with the KOEO. I have a gut feeling its the opti again...

Giamanut- Checked the gauges while I was down there. 3 hours after that car has been shut off the oil reads 136 and the coolant is around that temperature too. Doesn't seem like there is a dramatic drop off in readings.

Interesting you bring up the IAT sensor, wonder if the coolant temp sensor could also have a play in this. I remember once I left the coolant temp sensor un hooked by accident and all it did was crank, no start.

 

Yes and coolant temp does go up when you shut down also a sensor can act normal while in it's normal state "Running" but if it is expose to a little extra heat could be a problem if it is not good. It could hide it's flaw so to speak. I had a knock sensor go bad I hooked a meter to it and tapped it and it did produce an ac current, some say that makes it good, but when I checked the resistance it was way out of sorts. So things can hide but if your opti won't take the heat then the car should stall or run rough when warm. Like I said if you have spark and fuel and no start then there is a possibility a sensor is telling your ecm that it's -40 out or that it's 190 out. Just my opinion there could be other problems but these are cheaper than most. And I could see where you might not get a code.
Try to put some ice near the Iat after a run so just the IAT gets cold then try to start. same with coolant sensor. Good luck

 

a lot of things could cause your issues. But honestly before I went crazy be sure you have fuel pressure and volume along with spark when it will not start. If you have these then it is time to look elsewhere in my opinion.

 

I'm betting a new fuel pump and strainer will correct the situation.
Easy fix on an LT1.

 

I appreciate it guys.

Would a fuel pump and strainer only show up under warm conditions? Seems like the start issue would be present all the time?