RSAErick

Hi everyone,

I could use some troubleshooting guidance....

Problem:
When the car is cold or warm, the engine runs perfectly. But when the engine temperature gets to full 'hot' (above the "8-o'clock' line on the temp gauage), the engine begins to run poorly. The engine misfires; is low on power; and the idle is unstable (nearly stalls when clutch is engaged). And it sounds like a VW microbus!

Initial troubleshooting findings:
1. Checked CEL for fault codes - none.
2. From researching the archives, I thought that it may a failing engine temperature sensor. However, I tested the temp sensor resistance at the DME control unit, and it was right within specifications at both cold and hot engine temps. So it appears to be functioning correctly.
3. No visible arcing from ignition wires or coil when misted with water.

Any other troubleshooting ideas would be greatly appreciated!

Thanks as always.

Shamus964

Check the codes first - there's a procedure to do this and (from memory) I think it's - press the accelerator pedal all the way down to WOT, put key in ignition, turn to the 'on' position (not fully on, you don't want the engine to fire), when the CEL light flashes let off the accelerator pedal and then read the code denoted by the flashing lights.

I had a serious misfire that was related to an intermittent injector valve fault on the cylinder one that behaved similarly. Up here in the NW it could just be that the injector electrical clip has developed some corrosion.

Good luck - let us know what you find!

Laker

here is a link to the procedure for checking codes

RSAErick

Thanks Shamu! Sorry, I forgot to mention that I did check the fault codes - there were none. I'll add that important point to the original post.

Laker

long shot here, but how about the distributor belt?

RSAErick

Thanks Laker... you guys are quick! Added results to original post.

RSAErick

I suspect that a broken distributor would cause poor running symptoms at all temperatures. Everything runs perfect and strong when cold or warm. I will unplug each coil to verify, though. Thanks.

RSAErick

Did this generate a CEL fault code?

Laker

how old are the spark plug wires? Any arcing when misted?

RSAErick

Probably old... maybe even original. Does it matter that I don't want this to be the problem? They are expensive and time consuming to replace!

Anyway, in all seriousness... do you think that engine temp might really trigger a problem with the wires?

Thanks.

Laker

dunno, suppose as the wires expand due to heat, some cracks could also expand allowing an arc.
Mist it and find out. Easy enough to do. Would also swap the DME relay with your spare, just to rule that out.

TR6

Check for acrcing plug wires in the dark. Thats how I found mine. Easy to spot (at least on top side of the engine). Misting probably helps but I didn't do that.

Shamus964

yeah, it was the 1251 code if memory serves - intermittent injector valve fault on cylinder 1.

You know, this could be a flaky ISV too - you might try unplugging the ISV after warmup when the idle stumble begins - if the issue is the ISV having a problem post-warmup, then the problem will go away when you unplug it. Just an FYI though, unplugging the ISV with the car running will cause the CEL to light until it's reconnected so be aware of that. I've done this procedure and it was a great way to diagnose a dirty ISV.

FeralComprehension

That's never worked for me (though I still try it from time to time....)

ThomasC2

Or maybe the igniton coils? But before you buy new ones, try to borrow coils from another car and test.

Thomas