Intermittent Starting Issue with Excessive Cranking During Cold Weather Topic is solved

[jonesg]

Went out this afternoon to look at it some more and low and behold it started fine as if nothing happened. Temperature rose to about 43 today and its supposed to be warmer then average all week with 70 possible for a high Wednesday, so I'm pretty sure I'll get no reaction the rest of the week.

If the problem returns you might try a hairdryer on suspect components.

[hu5ker555]

Very interesting thread. Having similar issues with my 2008 S60 2.5T 177k. If it sits in cold weather < 25F, sometimes it doesn't want to start. It cranks, the tach jumps, and it eventually has started but makes me wonder...someday it might not. Have to release the ignition at just the right time. Sometimes I've given it a little gas to help it out. Would really like to see more on this.

[hu5ker555]

So as the weather begins to warm up, I'm concerned this thread will fade away. Anyone with suggestions?

[abscate]

OK - I had a mild erratic miss over a week period in my P2 last summer, which then ended. This winter, in a cold spell, I got a no-start - but the engine would fire a bit, but not catch.

It turned out my Pump electronics module (PEM) was dirty and causing poor fuel pump operation, when I caught it in the no-start I had no fuel pressure at the rail, With the help of my Olympic team partner I was able to kick the pump on in VIDA and got it going.

So - I would find your PEM and open it up and clean it out as a precaution and see if that helps. I dumped out about a palmful of aluminum oxide corrosion from the heatsink

I have a spare PEM I can send you if you want to try troubleshoot with known good one. the other way is the monitor the fuel pressure at the rail or the duty cycle signal to the fuel pump from the PEM with some decent electronics tools

[RickHaleParker]

So as the weather begins to warm up, I'm concerned this thread will fade away. Anyone with suggestions?

In warmer weather one could chill suspected components with a refrigerant.

[mrbrian200]

I'm still chewing on this. I think that 'interesting case' I came across while googling with regard to an electrical arc between the closely spaced pins at the TCM that interferes with CAN communication might be on to something.

I plugged some numbers into a Paschen's law calculator.
https://www.fxsolver.com/solve/

The Voltage potential is too large to be induced by the CAN signal. The voltages required to jump that distance would either be a static discharge -or- ignition spark that normally should discharge through the head back to the coil secondary at the small bolt that secures the coil pack to the engine. If for whatever reason if this high voltage can't find it's way back to the secondary through design path it might be arcing back through the wire harness to get back where it wants to go (complete the circuit back to the secondary).
Keep in mind, Paschen's law defines that the voltage potential for an arc to occur will lower as a function of gas pressure increases. As atmospheric temperature drops, pressure/density increases, so it would be more likely to occur at lower temperatures. As the arcing continues (assuming it's regular pulses with the ignition system), the air around the terminals would heat and arcing would likely stop.

So, this could either be due to a partially failed coil pack, or, excessive resistance/insulator (such as engine oil or salt corrosion) between coil pack(s) and the cylinder head.

[abscate]

I would evaluate the fuel pressure before going so esoteric.

There is an interesting dip in thePaschen effect at about 3000 meters height in RF electronics, you have to turn off high power RF when you cross this regime or blow all your circuit boards. Useful for people who fly lasers around

[RickHaleParker]

If you want to test your theory, disconnect coil packs one at a time and try starting it on four cylinders.

[abscate]

Nice, Rick.

[mrbrian200]

If you want to test your theory, disconnect coil packs one at a time and try starting it on four cylinders.

I'd rather not use my own perfectly good car as a guinea pig. If this is indeed what might be happening the arc could conceivably manifest at any multitude of different places (not solely at the TCM connector where it appeared to not cause any permanent damage). We're talking 30-60,000 volts here. In the wrong place that could dispatch a computerized module about as effectively as a sledge hammer.

This is something to test on a vehicle that's currently experiencing the issue or on older running T6 with a crapped out tranny that nobody wants that's headed to the boneyard.

Keep in mind, the voltage potential I was coming up with is roughly 1/2 what the coil pack secondary produces. So there might still be a weak spark in the cylinder(s). We're talking about resistance in the return path, not an open/blocked path.

The russian mechanic I suspect when he repaired the terminals at the TCM and packed the connector with dielectric, I suspect the arc is still occuring. It just 'moved' somewhere else basically in a game of wack a mole. Where ever it moved to isn't interfering with engine management/CAN communication so the car appears to start/run normally again.