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Discussion Starter #1
Hey guys,

So I'm having this situation with my 91 cougar. The engine starts fine from cold, and fine from full op. temp. The problem is, if you start the engine from cold and then drive it for a few minutes (ie: to the corner store, or from home to work) without letting it get to full operating temp before you shut it off, when you go to start the car again it won't start. I've checked, and have, spark and fuel to the rail when it gets into this situation. If you sit and wait about 10 or 15 mins, you can turn the key and the engine starts and runs fine.

I've recently replaced my ECM, temp sensor, distributor, dist. cap and rotor, plugs and wires, and Ignition control module, and fuel pressure regulator as part of my restoration. The problem existed before these replacements, but I figure it'd be good to know what new parts have been added to help eliminate some possible issues. Also, I tested the Ignition control module on our tester at work before I installed it, and it checked out as a good module.

Any insite/ideas would be appreciated. I'm at a loss on this one.

Stephen
 

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I see "temp sensor", but which one was swapped? The ECM uses a different one than the gauge uses.

So - cold it starts fine, hot it starts fine, warm it doesn't?

RwP
 

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Sounds like heat soak is making a fuel vapor bubble in the fuel lines. (Vapor locked)

Try turning the key on, let the fuel pump run for a sec, then off, then on again a few times to let fresh fuel get to the rails.

That's the nice feature of our circulating fuel system...

If it's vapor lock, this should let it start.

You may have a fuel line routed under/touching a heater hose; that can cause this. :)
 

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I havent seen a vapor locked engine since I worked on a carburated motor. :tongue:

If there is fuel and spark like you said, it should start.

Could be an intermittent sensor / wiring .. might try to pull some codes when it doesnt start, the EEC might throw something out since it wont start. Or try wiggling connectors / wires and see if that helps.
 

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Sounds like heat soak is making a fuel vapor bubble in the fuel lines. (Vapor locked)

Try turning the key on, let the fuel pump run for a sec, then off, then on again a few times to let fresh fuel get to the rails.

That's the nice feature of our circulating fuel system...

If it's vapor lock, this should let it start.

You may have a fuel line routed under/touching a heater hose; that can cause this. :)
I havent seen a vapor locked engine since I worked on a carburated motor. :tongue:

If there is fuel and spark like you said, it should start.
.
heh!
Vapor lock wasnt really all that common back even in the day but it does still happen
You probably didnt recognize it.. FI spider on GM 4.3L. It's why Fuel Pressure Leakdown rate is very important on those cars because they dont really have a fuel rail. From the CPFI poppet or injector in spider's point of view, it's a returnless system.

So check that FP leakdown, just to be sure.

Doesnt explain why it doesnt happen full hot, though. If cycling the pump a couple times doesnt do it, try starting it with pedal to the floor.
- I'm thinking possible leaky injector there.
 

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Discussion Starter #6
Sorry guys. The temp sensor I changed was for the computer. The one for the gauge still works fine.

Grog, that sounds like the issue! I've noticed that cycling the key and letting the pump push some fuel helps the situation. Didn't keep track as to when it did and didn't fix the problem, but I'll keep an eye on it now. I'll check the fuel lines this evening and make sure they are away from heat sources.

Leaky injector was on my list of things to check, as i've also got a slight miss on cylinder one. Compression was within spec, so I swapped the plug for a new one at proper gap, and tried a new wire but the miss was still there. Replaced the injector with a known good one and the problem didn't go away. The other cylinders all seem to be performing normally.
 

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...as i've also got a slight miss on cylinder one. Compression was within spec, so I swapped the plug for a new one at proper gap, and tried a new wire but the miss was still there. Replaced the injector with a known good one and the problem didn't go away. The other cylinders all seem to be performing normally.
Dist cap often does that. But may I ask what brand/model plugs?
 

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Discussion Starter #8
Sorry for the late reply. Had a look at the fuel lines. Doesn't seem to be anywhere that they could be getting enough heat to cause vaporization. On the same note, cycling the fuel pump 4-6 times seems to fix the no start situation.

As for dist cap, it was changed with the dist and has less then a year use on it. Might be a bad cap, but the terminals seem to be in good shape inside. The type of plug I use are Autolite. I don't remember if it was copper, double platinum, or iridium. I'll check when I get off work. i've got a spare matching plug at home.
 

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Sorry for the late reply. Had a look at the fuel lines. Doesn't seem to be anywhere that they could be getting enough heat to cause vaporization. On the same note, cycling the fuel pump 4-6 times seems to fix the no start situation.
There must be something touching the rails or a line somewhere, or all cars would do it, IMHO.

:zdunno:

A fuel pump that is barely working can cause this too, but it usually causes problems cold.
 

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Discussion Starter #10
I'm going to try to put it up in the air this weekend to get a better look. There's only so much you can see on your hands and knees in the driveway. Might have missed a line that dropped or something between the shock tower and a manifold or something.

What other kind of symptoms would a weak fuel pump exhibit at a cold start? I've noticed lately as well that the first start in the morning, or after having been parked for a few hours, doesn't go all that well. It starts, but stumbles (almost like it's being starved of fuel) and shuts off almost immediatly. Turn the key right away and it starts almost too eagerly and continues to run. I just attributed it to whatever was causing the miss on #1.

To finish my response from earlier, the engine has AutoLite copper plugs.

Don't know if this is a significant fact, but this engine is a bit of a franken-engine. It's a 95 motor with 95 internals and 95 heads, but the intake, TB, clutch fan, and all sensors were swapped from my 91 (to facilitate the change from OBD2 to EEC-IV). The no start problem occured before the engine was swapped, and the engine ran fine without the miss for the first 6 months after the engine was swapped. The car was put into storage for the winter. When it came out, it was missing on #1. Harshness of the miss varys but I haven't taken notice of what conditions it's good and bad under.
 
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