LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

No start when warm

Old 10-20-2008, 07:02 PM
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Question No start when warm

Hi Guys,

Long time lurker, first time poster since the search feature hasn't helped.
I have a 1994 iron head LT1 in my Fiero that I built a couple years ago.
It is 65 over, with forged pistons, new accel injectors, MSD Optispark, mild Nitrous friendly cam for the NX LT1-Pro Direct Pro 100-300 Nitrous kit. The rest of the recently rebuilt engine is stock except hugger headers. The ECM has been replaced (92/93 ODBI) and is using a Street and Performance custom chip and wiring harness.

This summer after no changes to the motor in a year, I developed a hard/no start condition when the engine is up to operating temp.
I replaced the ICM and changed the NGK TR6 plugs to fresh TR55's. I thought it was grounds or charging system but none of those fixes have helped. I later discovered it is fuel related as a small spray of Quik Start on the K&N filter will cause the engine to start. Also the MSD digital - 6 box light shows spark during cranking and it starts fine when cold (using a powermaster 9004 start and a OPTIMAX red top).

Could I possiby be getting vapour lock? The fuel pressure is good with key on and during cranking. I have tried both a stock LT1 PROM chip and the custom one and no change (the main difference is the custom chip helps the idle as I only have 12Hg/in at idle with the new cam).

The engine ran great for a couple years, so I don't know what has failed. The fuel pump is a Holley Walbro 255LPH. I have a GM Tech I scanner and no codes or unusual stuff seem to show up.

Help, as I'm running out of ideas and money and am considering parting out the powertrain. I can start it cold and drive around fine, but if I shut it off after it's warm it won't start on its own again until its cold.

Thanks,
Ryan
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Old 10-21-2008, 05:33 AM
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Next time you have a chance to start it when it's hot. Try cycling power on at the ignition with out starting for 4 or 5 seconds and then back off. Do this about 5 or 6 times before finally trying to start it and see if it lights up quicker.

If so it could be a lot of things. Start by monitoring fuel pressure after shut down. Start with the fuel filter first.
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Old 10-21-2008, 11:29 PM
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I've had ign coils do this before, when it does this try and put a damp rag on the coil to cool it down or something of that effect and see if it will restart.
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Old 10-22-2008, 04:34 PM
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Unhappy Update

Ok - here's the update...

Haynes manual says to check this when hard to start warm:
1. Air filter dirty - tried removing (no change)
2. Bad engine ground connection - added a second (no change)
3. Fuel not reaching the injectors - confirmed (no change)
4. Loose connection in the ignition system - tried omiting MSD box (no change)

New stuff I installed:
1. Fuel filter (no change)
2. Ignition Coil - (did run smoother on cold startup but didn't help when hot)
3. O2 sensors (no change)
4. New Battery (old one dies within 30 secs of cranking)
5. New full tank of fuel (no change)

Tests I ran:
1. Fuel Pressure (47psi when pump turned on then drops to 42 and holds)
2. Disconnected Nitrous line to ensure no fuel leakage into manifold (none)
3. Removed vacuum line from FPR to ensure no fuel leakage into manifold (none)
4. Tried retarding the timing 20 degrees during cranking under 500 rpm (no change)
5. Tried the suggestion with the key on 5 times for 5 secs each (no change)
6. Tried to start when hot with the pedal to the floor - flood clearing mode (no start)

I know that the problem is heat related but not sure it's heat internal to the engine or engine compartment heat - I did relocate the ICM and coil to a cooler spot away from the engine.

So after all that I've got nothing to show for it - same problem.
Once its up to temp, I can shut it off and immediately restart usually with success.
If it doesn't catch immediately or if I let it sit off a couple minutes, it's toast until the engine in left alone a 1/2 hour.
Spraying a little Quik Start in the intake manifold is the only chance I have to start unless you wait the 1/2 hour.
When I'm lucky and it does start, it idles and revs fine so it is only a starting issue.

I guess I'll just wait until someone posts for me to change my Optispark (for the 3rd time) or install a new CTS...

Cheers,
Ryan
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Old 10-23-2008, 04:53 PM
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Well it turns out I had a new Coolant Temp Sensor that I never installed before so I exchanged it last night. It didn't restart while warm.
I'm going to refill and burp the cooling system and try it again but it doesn't sound promising.
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Old 10-23-2008, 09:48 PM
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Is your starter just getting too hot? Ever since my header install thats been my problem. I don'y know what it's like when you turn the key, but it's just something to check if you haven't
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Old 10-23-2008, 10:11 PM
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I know you said you replaced it, but this sounds exactly like my ICM problem. What brand did you replace it with? Was it AC Delco or a cheap Autozone part? I've had problems with my Autozone ICM right out of the box. Went back to AC Delco and have no problems. You also HAVE to put grease on the back, or it will get heat soaked and destroyed (shouldn't matter much since you relocated it).
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Old 10-24-2008, 07:59 AM
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Originally Posted by LT1 POWAH View Post
Is your starter just getting too hot? Ever since my header install thats been my problem. I don'y know what it's like when you turn the key, but it's just something to check if you haven't
Actually, I've ruled out a "heat soaked" starter.
It cranks fine and fairly quickly for about 3 ten second bursts before the battery starts to drain a little slowing the crank.

Maybe this might help - it's a video/audio clip of the sound it makes when trying to start warm:http://www.youtube.com/watch?v=ZC5GYozAmv8

Last edited by Fiero2m8; 10-28-2008 at 05:40 PM. Reason: correct link
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Old 10-24-2008, 08:26 AM
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Originally Posted by Green96Z View Post
I know you said you replaced it, but this sounds exactly like my ICM problem. What brand did you replace it with? Was it AC Delco or a cheap Autozone part? I've had problems with my Autozone ICM right out of the box. Went back to AC Delco and have no problems. You also HAVE to put grease on the back, or it will get heat soaked and destroyed (shouldn't matter much since you relocated it).
Yes I siliconed the back.
You are correct that this time I used a cheaper ICM from Parts Source.
I used an AC Delco one 2 years ago and guess I could try that again.

I also got this posted suggestion on my build thread:
when it starts with quik start after being hot you have vapor lock no ifs ands or buts when the heat gets up there in the engine bay it evaporates the fuel in the injecter lines it holds pressure but there is no liquid fuel to burn and no start as the engine cools the fuel re liquifies and it starts

I agree with that theory, I just don't understand how for 2 years it was fine and then just failed one day a couple months ago and has done it ever since.
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Old 10-24-2008, 11:55 AM
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Going to pick up some noid lights tonight to test whether fuel injectors are pulsing when cranking hot.
I suspect either the distributor harness or the Optispark may be faulty and confuse the ECM on where #1 cylinder is during cranking.
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Old 10-28-2008, 05:53 PM
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Update

Well with the noid light installed, I was able to prove that the injectors are getting a signal to fire while the engine is warm. However the light is quite faint, like 1/3 the brightness when compared to the brightness flashes while the engine is running - is this normal? I was expecting it to be dimmer while cranking but not that faint. It still starts on quik start, so I'll back to suspecting the Optispark, Optispark harness or the charging system.
Next I'm going to try a new battery with a much higher CCA rating or maybe even a deep cycle type. The reason I am thinking this is because if I shut it off warm it is now restarting if I try it immediately. I can do this about 3-4 times in a row before it goes back to a no start condition. After the next 3-4 tries with no success, the cranking speed drops dramatically. Keep in mind that I still don't believe it's a heat soaked starter as mine isn't in the stock location and I'm using hugger shorty headers that don't pass near the starter.

Any further suggestion or questions would be appreciated.

Ryan
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Old 10-29-2008, 05:44 AM
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Hope to be rich like you some day!!!!!

Originally Posted by Fiero2m8 View Post
New stuff I installed:
1. Fuel filter (no change)
2. Ignition Coil - (did run smoother on cold startup but didn't help when hot)
3. O2 sensors (no change)
4. New Battery (old one dies within 30 secs of cranking)
5. New full tank of fuel (no change)

I guess I'll just wait until someone posts for me to change my Optispark (for the 3rd time) or install a new CTS...

Cheers,
Ryan
Originally Posted by Fiero2m8 View Post
so I'll back to suspecting the Optispark, Optispark harness or the charging system.
Next I'm going to try a new battery with a much higher CCA rating or maybe even a deep cycle type. The reason I am thinking this is because if I shut it off warm it is now restarting if I try it immediately. I can do this about 3-4 times in a row before it goes back to a no start condition. After the next 3-4 tries with no success, the cranking speed drops dramatically.
Either it cranks too slow or it doesn't. An another new battery????? What about the fact that the first 3 or 4 times it cranks ok THEN it slows down? Stop throwing money at the problem and look at some facts first. Then theorize and test the theory. Like the battery being the problem. Instead of going and buying ANOTHER battery, use jumper cables and another battery you already have. Then take the f ing starter out and have it hot load tested. Not at a cheap auto parts store by the guy that empties trash cans.

And why you keep dropping back to the distributor is beyond me. You proved the ignition system works when you sprayed it with ether. What do you think changes when it gets hot????? You said that you have changed it 3 times in the past. Isn't that enough to convince you it's ok?

Stop over analyzing and move to the items that make more sense.

It starts on ether so now try squirting fuel in the intake and see if that gets it going consistently. If you can get it to start consistently on fuel squirted in then start focusing on the fuel system. I've heard a lot of problems from Walbro pumps. Maybe there's more to this then you think.
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Old 10-29-2008, 04:41 PM
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Thanks Speedy

I'm not sure if I've found the root cause yet, but after installing a 875 CCA battery today and removing the 650 CCA unit, I haven't been able to get it to not start when hot. So for now the problem seems to bandaided as I was able to restart the engine a dozen times with no issues from normal temp all the way up to hot on the guage. The new battery definately cranks the Powermaster 9004 starter quicker than the Optimax Red Top did.
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Old 11-06-2008, 12:35 PM
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Originally Posted by speedygonzales View Post
It starts on ether so now try squirting fuel in the intake and see if that gets it going consistently. If you can get it to start consistently on fuel squirted in then start focusing on the fuel system. I've heard a lot of problems from Walbro pumps. Maybe there's more to this then you think.
Thanks Speedy, I will try these tips as it is definately is still an engine compartment temp issue and I'll focus on the fuel system.
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Old 02-09-2009, 09:57 PM
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Post Update

Just an update for the benefit of the search feature.
The test drive went well, as no tire clearance issue, engine ran smooth with no stalling - I think it likes the cold weather!
Then I worked on the no start when warm condition.
I was able to get the no start condition to happen idling the car for 10-15 minutes then letting it sit in its own heat for 5 minutes with the decklid closed.
With the theory of vaporizing fuel being the cause, I pulled the intake off and gave one shot of fuel in each side of the throttle body using a spray bottle.
Turning the key after that and it fired to life instantly and kept idling fine.
A repeatedly the test a few more times to make sure it wasn't a fluke and it solved the problem each time.

Next I'm going to reroute the fuel lines so they don't pass above the wrapped header (maybe through the insulated trunk instead).
Then I'm going to install this electric blower to suck the heat out of the engine compartment and exhaust out the back of the lower trunk.
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