Stumped!
10-31-2007, 05:18 PM
#1
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Stumped!
I have finally(!) got my 1987 S4 auto project running after the PO had an engine fire and TBF, but it is rough.
It appears to me to be running rich from the lumpy feel, the smell of the exhaust and also the smokey plugs.
The symptoms are:
Starts fine hot or cold.
Drives ok from cold.
Once warm (about 1 mile drive) it wants to stall when approaching a stop. Also, pulling away from rest is best described as "chug, chug" until rpm > 1000.
Slipping into neutral and blipping throttle clears the situation and it then idles correctly ~700 rpm. Returning to drive it will try to stall again.
Holding the gas open to maintain 1000 rpm against the brake keeps the show running but I hope this is not normal!
My testing has included the following:
Temp II - hot and cold resistance readings good at both LH and EZK connectors.
Fuel pressure appears close to spec and does rise on open throttle - note to self, must get a liquid damped gauge!
TPS works fine at idle end - clicks nicely and shows correct resistances at LH and EZK.
Ignition timing is ~10 degrees at idle, rises to ~20 degrees on opening throttle.
O2 sensor is new and shows varying voltage within specified range.
MAF reads 4.2 ohms static. Voltage reading varies from ~2.0 to 3.8 volts but my blowing technique may be below par.
Torque converter stall test was ok.
No obvious vacuum leaks.
The areas of doubt are:
TPS high end switch shows no change at WOT, measured at LH and EZK connectors.
MAF may not be original to the S4 - it has the adjustment pot. There is no Porsche part number - only Bosch 280 214 01.
I soaked the ISV in carb cleaner when I had the engine apart but did not have the info to test it before installation.
Is there any hope for me?
It is my first 928 and I really wanted to feel the BWAAAAH that you guys all talk about.
Any constructive thoughts would be appreciated.
Brian.
It appears to me to be running rich from the lumpy feel, the smell of the exhaust and also the smokey plugs.
The symptoms are:
Starts fine hot or cold.
Drives ok from cold.
Once warm (about 1 mile drive) it wants to stall when approaching a stop. Also, pulling away from rest is best described as "chug, chug" until rpm > 1000.
Slipping into neutral and blipping throttle clears the situation and it then idles correctly ~700 rpm. Returning to drive it will try to stall again.
Holding the gas open to maintain 1000 rpm against the brake keeps the show running but I hope this is not normal!
My testing has included the following:
Temp II - hot and cold resistance readings good at both LH and EZK connectors.
Fuel pressure appears close to spec and does rise on open throttle - note to self, must get a liquid damped gauge!
TPS works fine at idle end - clicks nicely and shows correct resistances at LH and EZK.
Ignition timing is ~10 degrees at idle, rises to ~20 degrees on opening throttle.
O2 sensor is new and shows varying voltage within specified range.
MAF reads 4.2 ohms static. Voltage reading varies from ~2.0 to 3.8 volts but my blowing technique may be below par.
Torque converter stall test was ok.
No obvious vacuum leaks.
The areas of doubt are:
TPS high end switch shows no change at WOT, measured at LH and EZK connectors.
MAF may not be original to the S4 - it has the adjustment pot. There is no Porsche part number - only Bosch 280 214 01.
I soaked the ISV in carb cleaner when I had the engine apart but did not have the info to test it before installation.
Is there any hope for me?
It is my first 928 and I really wanted to feel the BWAAAAH that you guys all talk about.
Any constructive thoughts would be appreciated.
Brian.
10-31-2007, 05:59 PM
#2
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Rennlist Member
Rennlist Member
Not sure if this would be a possible cause but this is what my MAF connector looked like behind the boot.(And wires were close together when removing the boot)
Might be worth checking yours as well.
/Peter
Might be worth checking yours as well.
/Peter
10-31-2007, 06:31 PM
#3
Rennlist Member
Bosch 280 214 01 is the only type of MAF fitted to all 928s from 85-95.
MAF calibration can only be accurately measured on a flow jig, and the tolerance between good running and problems is only +/-4% or so.
Try disconnecting the MAF when engine is warm, and see if it idles better, with the O2 sensor volts fluctuating in the range 03-0.9v.
MAF calibration can only be accurately measured on a flow jig, and the tolerance between good running and problems is only +/-4% or so.
Try disconnecting the MAF when engine is warm, and see if it idles better, with the O2 sensor volts fluctuating in the range 03-0.9v.
