Hard starts when hot

[mp470]

After it warms up, even on shorter trips, it's hard to start. Cranks just fine, and wants to turn over but doesn't. It's not a slow crank but cranking just doesn't seem to result in anything. Cold starts perfectly with one crank. Something that heats up and is worn internally, but what? Starter, ICM, coil, efi components. Best way to test these? Would rather not fire the parts cannon at it since these are all expensive parts.

[ctubutis]

I am guessing you're talking about a 1985/86 EFI 302, correct?

Sounds like the engine cranks just fine ("crank" and "turn over" are the same thing in my mind) but the engine doesn't want to start... does it EVER start when warm/hot? What do you do to get it to start?

My first thought is vapor lock in the fuel system.

Check for spark & fuel when the problem occurs.

This can also be a bad electrical connection in the ignition system (at the coil in particular) that doesn't pass enough energy when heated up.

It can be a lot of other things, too, easiest to diagnose it when the problem is actually occurring.

[Gary Lewis]

Let's make sure we understand - "turn over" doesn't mean the engine rotating with the starter. It means "run" or "fire". Right?

Have you checked to see if the computer is trying to tell you something?

And there are steps for testing the EEC-IV systems in the Resources.

[mp470]

I am guessing you're talking about a 1985/86 EFI 302, correct?

Sounds like the engine cranks just fine ("crank" and "turn over" are the same thing in my mind) but the engine doesn't want to start... does it EVER start when warm/hot? What do you do to get it to start?

My first thought is vapor lock in the fuel system.

Check for spark & fuel when the problem occurs.

This can also be a bad electrical connection in the ignition system (at the coil in particular) that doesn't pass enough energy when heated up.

It can be a lot of other things, too, easiest to diagnose it when the problem is actually occurring.

Yes it's a 1985 EFI. Usually I floor the gas pedal and it starts with a bad struggle after which I have to hold the gas partially down for a minute or two to keep it going otherwise it will stall out.

[mp470]

Let's make sure we understand - "turn over" doesn't mean the engine rotating with the starter. It means "run" or "fire". Right?

Have you checked to see if the computer is trying to tell you something?

And there are steps for testing the EEC-IV systems in the Resources.

Yes, I mean running / firing. I've checked for codes - only KOEO though - and there are none.

[Gary Lewis]

Yes, I mean running / firing. I've checked for codes - only KOEO though - and there are none.

Maybe you have a vacuum leak. David/1986F150Six used the smoke test to find a leak on his. And while his was carb'd I don't think that mattered.

I haven't seen it done, but my understanding is that he found a large hose going into the intake manifold or the base of the carb, blocked the top of the carb, and blew smoke from a cigar into the hose. On the second puff smoke came out from somewhere it shouldn't, and he discovered a bad vacuum cap.

[mp470]

Maybe you have a vacuum leak. David/1986F150Six used the smoke test to find a leak on his. And while his was carb'd I don't think that mattered.

I haven't seen it done, but my understanding is that he found a large hose going into the intake manifold or the base of the carb, blocked the top of the carb, and blew smoke from a cigar into the hose. On the second puff smoke came out from somewhere it shouldn't, and he discovered a bad vacuum cap.

A vacuum leak only when hot though? I suppose it's possible.

[Gary Lewis]

A vacuum leak only when hot though? I suppose it's possible.

I'm thinking that the running engine can handle it, but it can't when trying to start.

[ctubutis]

Yes it's a 1985 EFI. Usually I floor the gas pedal and it starts with a bad struggle after which I have to hold the gas partially down for a minute or two to keep it going otherwise it will stall out.

You shouldn't need to touch the gas pedal when starting an EFI engine, something is wrong if you need to do that. And I'm guessing whatever is wrong/failing is now bad enough to cause this kind of behavior.

This could be a lot of things, or a combination of two or more things.

My approach has always been to first make the computer happy (KOEO/CM/KOER) and the real problems make themselves evident as you get the computer to give you 11's across the board.

[PetesPonies]

First, your engine is turning over. turning over has nothing to do with starting . .other than if it is not turning over it won't start :) This is a common misuse of the tern "turning over'. You engine is spinning, it is turning over . .it's just not starting. You should not be using the gas pedal when starting a fuel injected engine. Typically heat related starting or even running issues, are electronic in nature.Heat causes extra resistance, can make small breaks in wiring grow to larger gaps, etc. When you turn your engine off, it heat soaks, meaning more heat is present to this components than were present when it was running. I would not suggest just buying parts to try, but if you can find a loaner coil, that is where I would start first, it's easy. Next would be the module inside the distributor.