Starts missing when warm . . .

[Dave]

Ok, 1990 325i, bone stock, no mods.

Here is my issue - last weekend, car started running rough once it warmed up. I had found that my CPS wire was no longer in the loom and was perislously close to the ater pump pulley (though i could not see any wear on it). I fixed that, and the rest of the day at an auto-x, the car ran fine.

Today, starts exhibiting the same symptom. Car starts and runs fine for a while, but once it starts to get warm - it starts cutting/running really rough.

No intake leaks - we just had that smoke tested recently when chasing another issue.

I threw some parts at it - things I had here. New plug wires, new cap and rotor. I have another CPS, but have not swapped it on yet. Unplugged the ICV when it was doing this and it had no effect.

My thinking is try the CPS, (though I am not sure why temp would matter there), then plugs and temp sensor. Plugs are a little old and need changed anyway.

Any ideas?

Jim Levie - your wisdom?

[jlevie]

This sort of problem could have any of a number of causes. I'd check the rail fuel pressure when the engine is running rough, swap in a different CPS, check the resistance of the ECT, try a different AFM, and probably try a different DME (changing one thing at a time).

You can try a different CPS w/o removing the one that is currently in place. The cable is long enough to run over the thermostat housing.

[Dave]

Thanks Jim.

ECT - I'm having a brain fart - what is that?

A couple of things I'd add - if it has any value - is that the change from runnning properly to this sputtering is very abrupt. No slight miss turning into a rougher one - it is a snap change.

I also have a supsect alternator - my battery does not seem to be charging properly lately.

I'll try a thing at a time today - save for the fuel pressure, as I dont have a guage handy - that is something I need to pick up.

[Dave]

tried a different CPS - same result.
Different AFM -same result.

Than Captain Obvious here did a stomp test. Note - I probably had not done it as I had recently had a bad TPS which, as you know, will make the stomp test not work. So, in haste, I skipped that step in the early diagnosis. Shame on me.

It throws the code for bad coolant temp sensor. I am going to track one down today and hope that fixes it.

Jim, if I ever make it to a NASA SE event, I'll track you down and buy you dinner. Your help here in responding to posts that I have either made or found in searches, is invaluable.

[Eric Giles]

I agree-Jim is a great asset to this board. We appreciate all of your helpful and informative posts.

[Sirotto]

tried a different CPS - same result.
Different AFM -same result.

Than Captain Obvious here did a stomp test. Note - I probably had not done it as I had recently had a bad TPS which, as you know, will make the stomp test not work. So, in haste, I skipped that step in the early diagnosis. Shame on me.

It throws the code for bad coolant temp sensor. I am going to track one down today and hope that fixes it.

Jim, if I ever make it to a NASA SE event, I'll track you down and buy you dinner. Your help here in responding to posts that I have either made or found in searches, is invaluable.

If your coolant temp sensor fix doesnt work, go drive the car until it cuts out again. Take a fluke meter with you and check the coil resitance when it is hot. Mine had the exact same sytom and ended up being a bad coil. When it was hot the reistance was way way to high.

[Dave]

After I took care of my rear wheel bearing issue today, I tried to finish this one off as the new coolant temp sensor came in the same shipment as the wheel bearing.

swapped the coolant temp sensor - same results

swapped the coil - same results

banged my head against the wall some more - went back and went over every part of the intake to check for visible leaks. Found the breather tube that goes into the valve cover was loose- not sure why. So as I was trying to snug it up, found it had some damage. So I cut off the end, snugged it into place, clamped it on and BAM - runs like a champ again.

Now to solve my charging/battery drain issue.