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[DJ]

I've got an '89 Opel Vectra, 1.6l gasoline engine.

The problem is that it just won't start when it's hot. When it's been parked for a long time (more than a couple of hours), it starts right away, no problems whatsoever, and the engine works without a flaw. But when I turn it off and then try to turn it back on, it just doesn't start. The electric starter thingy (English isn't my first language, sue me) works, but there's no ignition. If it has sat for half an hour to one hour, it will sometime start, but only after a lot of trying, and then the engine doesn't work right for a while (jumps between 1-3k RPM, 2 being normal).

The strange thing is that it starts just fine if I only turn it off for a really short time, like stopping at a gas station to refuel the car.

The car is at the mechanic shop next door, but the mechanic there seems to be having a hard time coming up with the diagnosis. So, if anyone here knows cars or has had this problem, I'd like to hear what the hell is going on here.

[Heron TSG]

If it's something in the electric department, many components become less resistive based on temperature, which would cause the increase in RPM.

Other components (Diodes, transistors, etc) increase in resistance when warm.

That's all I got.

[Aqizzar]

The problem is that it just won't start when it's hot. When it's been parked for a long time (more than a couple of hours), it starts right away, no problems whatsoever, and the engine works without a flaw. But when I turn it off and then try to turn it back on, it just doesn't start. The electric starter thingy (English isn't my first language, sue me) works, but there's no ignition. If it has sat for half an hour to one hour, it will sometime start, but only after a lot of trying, and then the engine doesn't work right for a while (jumps between 1-3k RPM, 2 being normal).

Lemme guess, it has a carburetor?  And it's a prime example of Eastern European engineering?  Yeah, it's probably going to work like that no matter what, or at least without such an extensive overhaul that you'd basically have a new engine.

My father used to have a car like that, that wouldn't start when it was already hot.  It would only start running if it was already rolling, so he'd have to push start it, or at least park on top of hills.  Have you tried getting it rolling and then starting it?

[DJ]

Opel is a German manufacturer, so you can't pull the inferior engineering card

Yeah, it's got a carburettor, but I don't think that's the problem.

Giving it a running start doesn't help. I can feel the pistons move, but there's no ignition, and I get a bit of unburned gasoline out the exhaust. My guess is that sparks aren't getting any electricity, but I don't know why.

[Aqizzar]

The way you describe it sounds like a confounding problem I had a little while ago.  The car just died mid-stroke while driving, and only when it was cold would it even try to start.  I never really found out what was wrong though; after me and my dad spent several afternoons and a couple hundred dollars, we finally took it to a professional.  His best guess was that it was hit with a bolt of lightning (which of course it wasn't), and I wound up having to replace the entire ignition system.  But that's not your problem obviously.

Anyway, by the sound of it, I'm thinking one of two problems.  Your manifolds may have just shaken loose over time, so when the engine expands as it heats, it opens up airflows that it shouldn't and can't turn over properly.  I had that happen once with an exhaust system, and it even jumped around when idling like you said, but it never got bad enough to not start.  So the first thing I'd do is tighten all the bolts down, just to be sure.

The other possibility is that some part of the ignition system, probably the wiring itself or the ignition coil, has just gotten so old/corroded/worn down that it can't handle the 12 volts needed to start when it's warmed up because of an expanding relay or something.  And if it's running like crap when hot and it is an electrical problem, I'd bet on the wiring or the distributor.  So give those a once over too.

That being said, while I'm drawing experience from my own similarly aged and decrepit car, I'm not a mechanic and less an electrician.  But those are two good places to start.

[Lukas]

although i am by no standards an automobile expert, and this is probably not the issue in your case, maybe you should have a look at the battery. I have had issues with batteries in different temperature extremes, although mainly cold extremes. For example in some cases when the battery gets too cold it can loose all its charge, and you either have to recharge it for a few hours or (in my case) get a brand new battery. Maybe there's a similar effect if you have an old battery and it gets hot.

[Dasleah]

Wait, if this is a car analogy, then you're having the weirdest sex I've ever heard of.

I'm confused.

[Skorpion]

Opel is a German manufacturer, so you can't pull the inferior engineering card

Yeah, it's got a carburettor, but I don't think that's the problem.

Giving it a running start doesn't help. I can feel the pistons move, but there's no ignition, and I get a bit of unburned gasoline out the exhaust. My guess is that sparks aren't getting any electricity, but I don't know why.

Opel is vauxhall over here, and they're not overly known for their reliability.

Otherwise, has the mechanic reproduced the issue?

[DJ]

Oh yeah, it was the distribution cap, some contact there got messed up when metal expanded due to heat. It's fixed now.

[Sean Mirrsen]

This thread made me remember the old story about a car allergic to vanilla icecream.