Poor Running, Worse Cold - Never 100%

[MauiM3Mania]

I have a rough run situation which is pretty intense when cold and gets better when the engine is warmed up, but still not 100%. When accelerating when the engine is cold, it is very sluggish and occasionally can feel a cylinder 'come online'.

What we have done and condition of the engine within the past thousand miles;

• New plugs, wires, cap and rotor.
• Smoked the system, no leaks although this was done when engine was warmed up.
• Checked compression 190 +/- 5 lbs across the board.
• Leakdown. 95% on all four.
• Fuel pressure was checked to be at 3 bar. Did not check pressure on the road.

Suggested areas that deserve a look?

[UNHCLL]

Looks like you're missing the most important part of the equation - Coolant Temp Sensor!

It sends the signal to the ECU, and if it's not functioning, your engine will run poorly.

[MauiM3Mania]

Coolant temp sensor?

I never would have imagined. Is there any tests we should run or is this one of those 'just do it' things that works?

My tech friend suggests "throwing an O2 sensor at it", an approach which rubs me the wrong way.

Thanks, Chris.

[blyguy]

Fuel pressure seems good, maybe add a clogged/stuck fuel injector to the list of culprits?

[MauiM3Mania]

Fuel pressure seems good, maybe add a clogged/stuck fuel injector to the list of culprits?

Ooops.. I should have mentioned. Injectors were sent out to be cleaned, etc. about 900 miles ago. Fuel tank was etched, cleaned, sealed and fuel filter replaced 400 miles ago.

[UNHCLL]

This may help:
http://s14.net/forums/showthread.php...nt+Temp+Sensor

[MauiM3Mania]

#7?

http://www.realoem.com/bmw/showparts...84&hg=11&fg=35

[808M]

#7?

http://www.realoem.com/bmw/showparts...84&hg=11&fg=35

Hello from a fellow Hawaiian Islander.

Correct. You don't have to replace it outright though. Put the ohm meter on it first and see what it reads. The leads can also be fragile, so that is a potential point of failure as well.

O2 sensor is easy to check, just disconnect it and see how the car runs! Same with barometric sensor, although doesn't sound like the cause.

Good luck with the troubleshooting!

[MattH]

This part is cheap and takes 5 minutes to change. I would advise just replacing it.

[kiko]

This part is cheap and takes 5 minutes to change. I would advise just replacing it.

Exactly specially as it's +20 years old and it messes it all up if it goes wrong. I replace it on all cars.

[allmotorking]

check for frayed wiring to the connectors on the injector. mine was frayed on one of the connectors.

[MauiM3Mania]

Aloha 808 and all... thanks for the input. I'm getting .540 K ohms at ~75F, which does not sound correct per the thread Chris L pointed out.

Time for a new sensor.

[MauiM3Mania]

Aloha and an update:

Coolant temp sensor gave bad resistance numbers, so was replaced. Not a noticeable change for the better.

Barometric sensor. Bad numbers. Swapped for a used but within range unit. No drastic change

TPS changed to new Bosch sensor.

AFM arm was 'tweaked' to travel a different arc. We checked the resistance of the AFM, regretfully, the numbers were not documented... although I recall that it started at a higher level than the 8 ohms we see mentioned, was a bit erratic as the door was opened and at WOT dropped from a previous high.

The TPS and AFM adjustment made a noticeable change for the better in warm running conditions. A slight surge or variance in power level is noticed at WOT around 3500 to 5000 rpm.

Cold, the car runs terribly. It idles very rough, when accelerating it seems to be operating on 2 1/2 - 3 cylinders and will randomly 'lurch' as all four come on board. This behavior lasts for about 90 seconds, and it comes around to a reasonable smooth running state, decent idle, etc.

As I understand it, neither problematic crank position sensor or O2 sensor would exhibit this behavior.

In short, car runs poorly when first started and much better after a minute or two. Ideas and suggestions are welcomed.

[Mmark]

What kind of action does the car see?
On a small island, I would imagine that the car has quite a bit of carbon build up in the combustion chambers and on the back of the exhaust valves. Carbon deposits mess up cold fuelling, and typically lean out the A/F ratio.

It may not hurt to check the static timing.

Even though the spark plugs are recent, it may not hurt to change them with new NGKs as opposed to the Bosch.

Have you ruled out a break in the coolant temp sensor sub harness yet?

Re: fiddling with the AFM....That is simply chasing your own tail. Adding an altered parameter to the trouble shooting makes things worse.

lastly, a thorough check for a good sized air leak might be prudent. Running rough when stone cold , then running better with heat in the engine hints at the improved sealing of the engine due to the softening of flexible components and/or the expansion of metallic gubbins that are in contact with the soft pieces.

m

[MauiM3Mania]

Hi Mark,

It's clear that this car was not babied by the previous owners. Although we don't have any interstate, we have one of the most rapid/highest vertical rise on a paved road. Almost a two mile rise over 30 or so miles.... the first time I drove it years ago in a rental, I managed to get the catalytic convertor to smoke. Point being, there are plenty of opportunities to spend the $4.89/gal 91 octane.

Static timing. Is that likely to change as the car warms up? I'll look into the setting, but my issue is very drastic and repeatable. As mentioned, when cold, a smooth power delivery is in the next galaxy. It's like a plug wire or two are randomly being pulled/connected... until the engine warms up. Warm/hot, it runs OK.

I'm game in regards to try different plugs, although I will say that these were supplied by VAC for use in this engine... I understand that everyone has a preferred spark plug and I am ignorant to the 'hot set up'.

Issues with the coolant temp harness makes a lot of sense to my mind. I'll look at the harness at the plug and wherever it is visble. Is there more I can do besides that and flex the accessible areas of the harness while the car is running?

Thanks for the ideas to follow!