Lean mixture when engine cold?
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 64
From: The Netherlands
Lean mixture when engine cold?
I fixed a number of problems om my 'new' 86.5, but there is one issue where I need some advice:
When I start the car cold (outside temp +/- 10C / 50F) the car starts and idles perfect.
However when driving it's way down on power and sometimes backfires. After about 1 mile and the coolant is getting warmer the problems disappear and the car will pull just fine.
I am guessing a temperature sensor, but I am not sure which one I should check first. I found the inlet air temp sensor inside the airbox, the coolant temp sensor on the front of the engine (with blue bosch connector) and two other sensors with (somewhat corroded) fork-plugs (dont know if that is the correct English technical term, but you will know what I mean).
Any ideas where I should start looking?
Thanks
Michel
When I start the car cold (outside temp +/- 10C / 50F) the car starts and idles perfect.
However when driving it's way down on power and sometimes backfires. After about 1 mile and the coolant is getting warmer the problems disappear and the car will pull just fine.
I am guessing a temperature sensor, but I am not sure which one I should check first. I found the inlet air temp sensor inside the airbox, the coolant temp sensor on the front of the engine (with blue bosch connector) and two other sensors with (somewhat corroded) fork-plugs (dont know if that is the correct English technical term, but you will know what I mean).
Any ideas where I should start looking?
Thanks
Michel
Race Car
Joined: Dec 2003
Posts: 4,477
Likes: 5
From: Atlanta, GA
After that mile what is probably happening is the O2 sensor comes online and compensates for the lean condition. That does not mean it's not still there though. An easy way to verify this would be to run the car with O2 sensor disconnected to see if it still runs lean even when warm. I would check for vacuum leaks. Also, your MAF may be going, the older they get, the further they get from proper calibration towards the lean spectrum. It could also be a failing tempII sensor (the blue one).
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 64
From: The Netherlands
Vacuum has been checked thoroughly when trying to solve te harsh shifting, so I am confident the vacuum is OK.
Will check what happens if I disconnect the O2 sensor and will check them TEMP II sensor.
Dont hope the MAF is going ($$$$)
The problem only occurs when starting from cold. When driving and parking the car 2-3 hours, then there is still no problem, it will start perfectly and run great.
Problem is only there when really cold.
Will check what happens if I disconnect the O2 sensor and will check them TEMP II sensor.
Dont hope the MAF is going ($$$$)
The problem only occurs when starting from cold. When driving and parking the car 2-3 hours, then there is still no problem, it will start perfectly and run great.
Problem is only there when really cold.
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 64
From: The Netherlands
This morning I checked some thinks such as Temp II sensor and MAF sensor.
Temp II sensor looked fine, 3k Ohm reading when cold, so within spec.
MAF connector also seemed fine, but looking closer I noticed some really dumb mechanic put the thing in backwards ?!@!
There is a huge arrow on it with air direction. Apparently he thought air should be coming out of the intake
So I put it in correctly and the car immediately drove better. I did not start it before repairing it and it did not hesitate at all.
Will check again tomorrow, but have good hopes it is sorted.
cheers
Temp II sensor looked fine, 3k Ohm reading when cold, so within spec.
MAF connector also seemed fine, but looking closer I noticed some really dumb mechanic put the thing in backwards ?!@!
There is a huge arrow on it with air direction. Apparently he thought air should be coming out of the intake
So I put it in correctly and the car immediately drove better. I did not start it before repairing it and it did not hesitate at all.
Will check again tomorrow, but have good hopes it is sorted.
cheers
Three Wheelin'
Joined: Mar 2010
Posts: 1,307
Likes: 3
From: Colorado Springs, CO USA
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Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 64
From: The Netherlands
Hi Ken,
I checked resistance as described with cold engine, then I found the MAF mounted backwards.
Before measuring with hot engine and risking to burn my fingers in the process
I will check if the correctly mounted MAF will fix the problem.
Until now all problems with the car were easy fixed (and there have been quite a lot):
- Gearbox clunking (Vac modulator)
- Electric windows L + R
- Electric seat adjustment
- Central locking
- Interior lights
- Anti Lock Brake
- Brakpad warning
- Cruisecontrol
All of the above issues I managed to fix without any significant costs (OK, gearbox oil and filter, some wire and some soldering), but nothing shocking.
So I hope the MAF turnaround will also do the trick.
Hopefully next week I receive a nice package from Roger with a nice Porkensioner and a set of new cam gear, belt, etc.
This will be the next big project.
So far I am really enjoying the 928 both working on it as well as driving it.
cheers
I checked resistance as described with cold engine, then I found the MAF mounted backwards.
Before measuring with hot engine and risking to burn my fingers in the process
I will check if the correctly mounted MAF will fix the problem.Until now all problems with the car were easy fixed (and there have been quite a lot):
- Gearbox clunking (Vac modulator)
- Electric windows L + R
- Electric seat adjustment
- Central locking
- Interior lights
- Anti Lock Brake
- Brakpad warning
- Cruisecontrol
All of the above issues I managed to fix without any significant costs (OK, gearbox oil and filter, some wire and some soldering), but nothing shocking.
So I hope the MAF turnaround will also do the trick.
Hopefully next week I receive a nice package from Roger with a nice Porkensioner and a set of new cam gear, belt, etc.
This will be the next big project.
So far I am really enjoying the 928 both working on it as well as driving it.
cheers
Thread Starter
Burning Brakes
Joined: Apr 2010
Posts: 863
Likes: 64
From: The Netherlands
Quick update:
Could not resist trying the car one more time this evening:
Result - 100% solved! Car picks up great even with cold engine.
The car also runs significantly better with engine warm, feels as if I have 75 Horses extra!
Car drives like a dream now!
Could not resist trying the car one more time this evening:
Result - 100% solved! Car picks up great even with cold engine.
The car also runs significantly better with engine warm, feels as if I have 75 Horses extra!
Car drives like a dream now!
