[f512tr]

I could really use some help here guys if anyone knows the answer.

Car is a 1991 S4 totally stock, no AC.

Two problems (related?). One she idles smoothly at 550rpm and not 900 as the book says. Secondly, has a real loss of power at midrange almost like the timing is off.

First I thought it was the VVT. On my S4, and I have checked the function of the TPS and it works like the book says, the VVT only throws for about 1 second when you press the accelerator. Checking all the wiring it is clear that the signal from the ECU that makes a ground and throws the relay for the VVT is only making a ground for 1 second so the problem is why is the ECU doing this?

Can anybody out there with an S4 verify for me that there VVT throws when they rev the engine and stays engaged? (I cannot believe it is suppose to go in for 1 second and then out). You can do this by blipping the throttle while looking thru the inspection hole on the VVT case; does yours stay "in" at higher revs?

The TPS makes no difference to the VVT even if I unplug it.

I was wondering aout the RPM/timing sensor that reads off the front ofthe crank under the water pump. Does anyone know if these things can go faulty and maybe cause my poor midrange acceleration?

Does anyone know what the ECU uses as a guide to throw the VVT. I assumed it would be the TPS (as it seems to be for the pre-1990 Spiders) but it doesnt seem to be on the 1991+ cars.

HELP!? Cannot find anyone here in the UK that understands these cars properly.
Many thanks
Britt

 

[ghnl]

I don't have an S4. But that won't stop me from replying...

1) It is possible your tach is reading incorrectly. Have you checked the idle RPM's with another method - many timing lights also give a RPM reading.

2) You should be able to apply 12V to the VVT's solenoid (harness dis-connected) and verify both the solenoid & VVT advance are functioning. If done at idle, the engine should either then run poorly or even stall.

On the S3's with solenoid activated VVT, the solenoid is activated when the TPS is open a specified amount (degrees of rotation). Thus 'blipping' the throttle would activate the VVT for only a moment - when the throttle is released the VVT will return to its resting (non-advanced) position.

If the S4's are ECU controlled then I don't know what I'm talking about...

 

[ddouglas77]

Start your engine with the VVT diconnected, hook the VVT to an outside 12V source to engage. As soon as it engages, your engine should either stall or run like crap. If not, you've got cam timing issues (if the solenoid engages), if the solenoid does not engage with 12V hooked up, then you have solenoid issues. Our Motronics do not use the TPS to tell the solenoid to engage, but rather the TPS and MAF, engine must be running to test the solenoid. Been there-Done that!

 

[f512tr]

I have checked that the rpms are correct using a digital tacho. So it is idleing happy at 550 rpm.

If I apply 12v the VVT will throw. My problem is if I step on the gas to get the revs upto, say 3000 rpm, the relay throws only for 1 second so the vvt goes on and then off. The relay is controlled by pin 31 off the ecu....I need to know what parameters make this throw.

On a S4 is it possible to check the timing with a timing light even if it is not adjustable on the distributor? (seperate question actually)

Britt

I don't have an S4. But that won't stop me from replying...

1) It is possible your tach is reading incorrectly. Have you checked the idle RPM's with another method - many timing lights also give a RPM reading.

2) You should be able to apply 12V to the VVT's solenoid (harness dis-connected) and verify both the solenoid & VVT advance are functioning. If done at idle, the engine should either then run poorly or even stall.

On the S3's with solenoid activated VVT, the solenoid is activated when the TPS is open a specified amount (degrees of rotation). Thus 'blipping' the throttle would activate the VVT for only a moment - when the throttle is released the VVT will return to its resting (non-advanced) position.

If the S4's are ECU controlled then I don't know what I'm talking about...

 

[f512tr]

I found out the engine has to be running to test the VVT. Would you expect it to operate and stay on with the car stationary and just holding the revs to a certain level or are there other factors that the ecu uses to decide whether to activate the VVT. My car has a running issue, its like a flat spot at 2-3k rpm and with the idle so low and with every sensor checking out I am wondering if it is timing related.

Does anybody know if the RPM/Timing sensor could be affecting the VVT operation?

Many thanks
Britt

Start your engine with the VVT diconnected, hook the VVT to an outside 12V source to engage. As soon as it engages, your engine should either stall or run like crap. If not, you've got cam timing issues (if the solenoid engages), if the solenoid does not engage with 12V hooked up, then you have solenoid issues. Our Motronics do not use the TPS to tell the solenoid to engage, but rather the TPS and MAF, engine must be running to test the solenoid. Been there-Done that!

 

[ddouglas77]

I found out the engine has to be running to test the VVT. Would you expect it to operate and stay on with the car stationary and just holding the revs to a certain level or are there other factors that the ecu uses to decide whether to activate the VVT. My car has a running issue, its like a flat spot at 2-3k rpm and with the idle so low and with every sensor checking out I am wondering if it is timing related.

Does anybody know if the RPM/Timing sensor could be affecting the VVT operation?

Many thanks
Britt

I'm asking you, to engage the VVT while at idle, in nuetral, to see how the car runs, not at any specific RPM or what not, but at idle, where it seems to be running good.