Hesitation when pulling away
10-08-2007, 07:09 PM
#1
3rd Gear
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Hesitation when pulling away
I purchased my first 928 in February 2006 (65k miles) after years of wanting one. It is a 1989 S4 Auto (UK) with digital dash in guards red (hopefully a picture of it is attached!)
The car is in good condition and a joy to drive hence I plan to keep the car long term. However, I have noticed that the running has deteriorated over the last 18 months. I have read a few posts in the forum and quickly realised the number of components that could be at fault is vast! Unfortunately I am not sure where to start investigating.
Here is a summary of the symptoms:
Early summer 2006 (68k miles): Car easily starts from cold on first crank every time. Occasional stalling in traffic when the outside temperature (and the car) is very hot; however it easily starts up again after.
Late summer 2006 (70k miles): Tension on flex plate released (undone before I had time to measure the deflection!). I serviced the car with new oil, filters and spark plugs. Stalling problem diminishes.
November 2006 (70k miles): Car smelling richer at idle.
February 2007 (71k miles): Recon MAF installed as old MAF is right on the limit of tolerance. I measured the CO at 4% - 5 % with pot in passenger foot well at 300 ohms. By turning the pot right down to 0 ohms 1% CO was achieved but added to the running problems. The car does not start as “positively” as before. Noticeable hesitation when pulling away from stationary (when pressing the gas pedal there is approximately 1 second delay in power delivery – gives the impression the car might stall whilst pulling out of a junction!). The car now stalling more frequently, typically 30 seconds after start up from cold (usually when slow speed manoeuvring / changing from “Reverse” into “Drive” or vice versa). Subsequently, it takes 2 to 3 attempts to restart the car, once fired the engine has misfire but eventually smoothes out as car warms up. The car can also be hard to start if left for an hour or two when hot (starting takes 2 – 3 attempts).
Summer 2007 (72k miles):
Temp II sensor resistance checked at ECU – ok.
Ignition leads changed.
Bosch Hammer was connected and reported a knock sensor fault (at front of engine).
I Borrowed a MAF from a 928 GT. Without adjusting the pot the car stalled even more frequently than with my reconditioned MAF. However, the car started up after each stall. Unfortunately I did not have a chance to adjust the pot whilst hooked up to an exhaust gas analyser. Turning up the pot helped however I was only able to test the MAF for a few minutes since it was needed for the other car. The problems from February 2007 still persist on returning to my reconditioned MAF with the pot turned up.
Any suggestions would be very gratefully received!
The car is in good condition and a joy to drive hence I plan to keep the car long term. However, I have noticed that the running has deteriorated over the last 18 months. I have read a few posts in the forum and quickly realised the number of components that could be at fault is vast! Unfortunately I am not sure where to start investigating.
Here is a summary of the symptoms:
Early summer 2006 (68k miles): Car easily starts from cold on first crank every time. Occasional stalling in traffic when the outside temperature (and the car) is very hot; however it easily starts up again after.
Late summer 2006 (70k miles): Tension on flex plate released (undone before I had time to measure the deflection!). I serviced the car with new oil, filters and spark plugs. Stalling problem diminishes.
November 2006 (70k miles): Car smelling richer at idle.
February 2007 (71k miles): Recon MAF installed as old MAF is right on the limit of tolerance. I measured the CO at 4% - 5 % with pot in passenger foot well at 300 ohms. By turning the pot right down to 0 ohms 1% CO was achieved but added to the running problems. The car does not start as “positively” as before. Noticeable hesitation when pulling away from stationary (when pressing the gas pedal there is approximately 1 second delay in power delivery – gives the impression the car might stall whilst pulling out of a junction!). The car now stalling more frequently, typically 30 seconds after start up from cold (usually when slow speed manoeuvring / changing from “Reverse” into “Drive” or vice versa). Subsequently, it takes 2 to 3 attempts to restart the car, once fired the engine has misfire but eventually smoothes out as car warms up. The car can also be hard to start if left for an hour or two when hot (starting takes 2 – 3 attempts).
Summer 2007 (72k miles):
Temp II sensor resistance checked at ECU – ok.
Ignition leads changed.
Bosch Hammer was connected and reported a knock sensor fault (at front of engine).
I Borrowed a MAF from a 928 GT. Without adjusting the pot the car stalled even more frequently than with my reconditioned MAF. However, the car started up after each stall. Unfortunately I did not have a chance to adjust the pot whilst hooked up to an exhaust gas analyser. Turning up the pot helped however I was only able to test the MAF for a few minutes since it was needed for the other car. The problems from February 2007 still persist on returning to my reconditioned MAF with the pot turned up.
Any suggestions would be very gratefully received!
10-09-2007, 05:53 AM
#2
Rennlist Member
Did you do an idle adaptation with the Hammer ? Is the idle speed correct ? 675rpm ?
Are there any signs of any misfire ?
I would suggest you consider that a fuel injector may not be flowing correctly. When you set the CO, you are setting the average of exhaust CO. An injector not flowing properly would corrupt that figure.
Are there any signs of any misfire ?
I would suggest you consider that a fuel injector may not be flowing correctly. When you set the CO, you are setting the average of exhaust CO. An injector not flowing properly would corrupt that figure.
10-09-2007, 04:49 PM
#3
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Thanks John - I will investigate your suggestions. Unfortunately I don't have my own hammer - a local garage was kind enough to let me use theirs! Please forgive my naivety, but what is an idle adaptation with the hammer?
Incidentally I have noticed that occasionally the car starts with a very high idle (1000+ rpm).
Shall keep you posted on what I find…
Incidentally I have noticed that occasionally the car starts with a very high idle (1000+ rpm).
Shall keep you posted on what I find…
10-09-2007, 05:06 PM
#4
Racer
Nice car ! please allow me to chime in: 1000 rpm or above is normal, but in a few seconds the engine speed should decrease to 800 and gradually down to 675 or so. That is the normal value for a auto-gearbox.
Idle adaptation is a feature of the Bosch KTS300 "hammer" tool which instructs the LH ecu to adapt itself to operating conditions of the car. It more or less learns the car's behavior and sets parameters for smooth and optimal behavior.
Now to the hesitation issue: it could be quite a few things. Have the ecu's (LH and EZK) checked for any errors first, using the hammer. Take it from there.
regards,
Idle adaptation is a feature of the Bosch KTS300 "hammer" tool which instructs the LH ecu to adapt itself to operating conditions of the car. It more or less learns the car's behavior and sets parameters for smooth and optimal behavior.
Now to the hesitation issue: it could be quite a few things. Have the ecu's (LH and EZK) checked for any errors first, using the hammer. Take it from there.
regards,
10-09-2007, 05:09 PM
#5
Rennlist Member
The idle speed will be higher at a cold start ca 1000rpm IIRC.
The idle adaptation is a standard menu on any of the diagnostic testers.
Is there any hint of a slight misfire, car in neutral, slowly increase rpm to about 300rpm, does it sound uneven (except for the V8 sound) at any point ?
I had a slight (internmittant misfire on my S2, it turned out to be injectors not flowing properly.
I
The idle adaptation is a standard menu on any of the diagnostic testers.
Is there any hint of a slight misfire, car in neutral, slowly increase rpm to about 300rpm, does it sound uneven (except for the V8 sound) at any point ?
I had a slight (internmittant misfire on my S2, it turned out to be injectors not flowing properly.
I
