euro s4 running better when cold, please help

[renopor]

hi all, my 1989 s4 928 was running really bad a while ago so i done the two knock sensors and refresh on the intake. car is running alot better but not perfect. i have a new hall sensor to fit and hope to fit it this week. but i have noticed that the car pulls alot better and sounds alot better when cold. any ideas? also is the a knock sensor control unit?

[Maleficio]

You're saying the car runs better cold than warm?

[renopor]

yep, in the morning or when its cold it runs and pulls much better when cold. the minate it warms up it seems to lose a bit of power.

[Maleficio]

Originally Posted by renopor

yep, in the morning or when its cold it runs and pulls much better when cold. the minate it warms up it seems to lose a bit of power.

Sounds like you should check out the Warm-Up Regulator thread going on right now.

Your car runs rich when cold, so when it warms up, the richness is scheduled back to lean/rich (stoich). You may have a condition telling your ECU to lean out the mix too much causing loss of power.

Perhaps your O2 sensor is going bad?

Have you been screwing with your mixture control screw? have you been screwing with your timing?

What have you done to it lately?

[renopor]

hi, mine has no O2 sensors, and havent gone never any of the timing or mixture. i took the inlet manifold off to do the knock sensors because it was running really bad. i check everything on the manifold and it all seems good. the faults that showed up on the computer were the two knock sensors and a knock sensor control uint, but i dont know where this unit is or if it is part of the ecu. i thought the hall sensor mit be bad so i have a new one, would this cause this problem?

[MPDano]

Originally Posted by Maleficio

Sounds like you should check out the Warm-Up Regulator thread going on right now.

Your car runs rich when cold, so when it warms up, the richness is scheduled back to lean/rich (stoich). You may have a condition telling your ECU to lean out the mix too much causing loss of power.

Perhaps your O2 sensor is going bad?

Have you been screwing with your mixture control screw? have you been screwing with your timing?

What have you done to it lately?

WUR is only on CIS.

[Danglerb]

A lot more S4 expertise is on 928 Forum - Rennlist Discussion Forums we tend to focus more on the older models here.

General rule, look for new faults in the area most recently worked on, perhaps a wire or hose damaged or disconnected?

[dr bob]

With no O2 sensors and no catalysts, mixture needs to be set with a CO gauge at the exhaust. The adjustment is a small potentiometer on a cable in the passenger-side footwell, inside the electrics panel door. As the MAF ages, it is less sensitive to changes in air flow, and without the exhaust sensors there's no way for the injection controller to know that the MAF is getting tired. Be sure to actually use the analyser for exhaust CO, and don't just try to turn the pot and see what happens. You might get it kind of close, but it would be dumb luck if it's exactly right.

The LH controller reads the engine temperature and adjusts mixture richer when the engine is cold. Your "runs better when cold" symptom identifies the problem for you. If the car has more than 75K or so o it, you might decide to replace or rebuild the MAF before doing the mixture calibration.

[John Speake]

Dr Bob is 100% correct. However on your 89 car the CO adjuster is above the middle of the fuse/relay board. It is a slotted adjuster in a plastic "snout".

Use the adjuster to set the idle CO at the tailpipe to 1%. Turn the adjuster several turns clcokwaise to richen.

Stop turning once the CO stops increasing as the pot has no end stops and can be damaged by winding it repeatedly at the end of travel.

If you can't get to 1% then the MAF needs replacing.

You can obtain exchange rebuilt MAFs from me at Porsche Electronics Specialist - JDSPorsche