please i need help with my S4
06-28-2010, 10:48 AM
#16
Rennlist Member
Search Andrew Olson's LH diagnostic
First thing that came to error-riddled mind was carbon build-up, but you say it has returned, next is search on above: a quick look here:
https://rennlist.com/forums/928-foru...nt-thread.html
does mention temp II + lumpy idle: but I thought that sensor was more about cold start issues. Anyway, my second guess is fuel delivery and WOT issues. Have fun.
First thing that came to error-riddled mind was carbon build-up, but you say it has returned, next is search on above: a quick look here:
https://rennlist.com/forums/928-foru...nt-thread.html
does mention temp II + lumpy idle: but I thought that sensor was more about cold start issues. Anyway, my second guess is fuel delivery and WOT issues. Have fun.
06-28-2010, 01:02 PM
#17
Drifting
i cleaned the connector when i did the hall sensor, havnt washed engine at all.scotsman, thats may thought, iif it where leads they would be gone all the time. was out in her agian today and the heitation still still there but not as bad as on some days. it pull with no hesitation all the way to 5000 then when it stifted up to the next gear it started the hesitation at about 4300 and did it a couple of time before hitting 5 again. it had no cats from the factory, non cat model euro spec. it comes up with a fault on the duramatics system, saying there is a faults with the knock sensor control unit. does anyne know where that is? or is it built into the brain. after reading a few post on here, im thinking it mite be the MAF, but im not sure. it runs fine, no cutting out,or lumpy idle.it runs so much better though when its cold. could that mean its running lean when hot?
06-28-2010, 06:12 PM
#20
Rennlist Member
If it's running without an O2 sensor in the exhaust, then you can check that the idlke mixture can be adjusted with the pot above the fuse/relay panel to be 1.5% at idle.
If you can't get up to that value (turn pot several turns clockwise) then the MAF is running weak and that could cause a hesitation at WOT.
If you can't get up to that value (turn pot several turns clockwise) then the MAF is running weak and that could cause a hesitation at WOT.
06-28-2010, 06:19 PM
#22
Rennlist Member
Look just above the fuse relay panel, half way along. Look for a 1/2" dia "snout" with a slotted adjuster in it. It's a 20 turn pot, but no end stops. Stop tunring when CO no longer rises as pot is turned.
06-28-2010, 08:08 PM
#26
Rennlist Member
Ren,
Listen to Dean, when he tells you to listen to Malcom: If it misses only under load then it definitely could be bad ignition wires. They are not cheap, but they also do not last forever.
You've replaced everything else, why not the wires?
The reason that wires often cause problems only under load is because of the spark voltage. An ignition coil, with the wire disconnected, generates a very high voltage and will throw a spark a centimeter or more. If you connect it to a spark plug then the small gap will arc with a much lower voltage, maybe a thousand volts (a good rule of thumb is 33KV per cm, in free air). So the wire insulation only needs to stand up to maybe 1KV, even a lousy cracked wire can do that.
With the engine idling, or running with light load, the throttle is mostly closed, not much air, not much pressure in the cylinder, so the spark voltage is still pretty low. Now open the throttle, and much higher pressures means much higher voltages are needed to make a spark, and our lousy cracked wire suddenly starts breaking down and arcing to the engine block somewhere-- path of least resistance. So no spark, engine momentarily loses power, fuel gets very rich (no spark) which causes black smoke.
Just replace the wires, and carefully check everything else on the high-voltage side of the ignition circuit.
Cheers, Jim
Listen to Dean, when he tells you to listen to Malcom: If it misses only under load then it definitely could be bad ignition wires. They are not cheap, but they also do not last forever.
You've replaced everything else, why not the wires?
The reason that wires often cause problems only under load is because of the spark voltage. An ignition coil, with the wire disconnected, generates a very high voltage and will throw a spark a centimeter or more. If you connect it to a spark plug then the small gap will arc with a much lower voltage, maybe a thousand volts (a good rule of thumb is 33KV per cm, in free air). So the wire insulation only needs to stand up to maybe 1KV, even a lousy cracked wire can do that.
With the engine idling, or running with light load, the throttle is mostly closed, not much air, not much pressure in the cylinder, so the spark voltage is still pretty low. Now open the throttle, and much higher pressures means much higher voltages are needed to make a spark, and our lousy cracked wire suddenly starts breaking down and arcing to the engine block somewhere-- path of least resistance. So no spark, engine momentarily loses power, fuel gets very rich (no spark) which causes black smoke.
Just replace the wires, and carefully check everything else on the high-voltage side of the ignition circuit.
Cheers, Jim
07-14-2010, 04:36 PM
#28
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had her on the co meter today and couldnt get it to go above 0.23 CO? should it be at 1.5 CO at idle? still have the miss but i can get it to nearly go away when playing with the pot.
07-14-2010, 07:23 PM
#29
Nordschleife Master
Its possible someone has broken the pot - there are not stops at either end of the range, so it'll just keep turning (the adjustment range is about 20 turns end to end).
I'd pull the pot out (wiggle the three-pin connector off, then just one bolt - careful you don't drop the washer behind the CE panel) and measure it before trying to adjust it on the bench. From memory clockwise should raise the resistance of the pot.
Start by adjusting it to around 300 ohms - if you can, its not broken. If the value isn't changing, keep turning another bunch of turns to make sure its broken. If it does adjust to 300 ohms, then put it back in the car (300 ohms is reasonably close to a new MAF's spec), and try adjusting the pot with the gas analyser on the car.
If your pot works, and was already at 900+ohms when you pulled it out the car, then either you have a large manifold vacuum leak, or your MAF is likely out of spec.
Check for vacuum leaks by spraying brake cleaner around the intake while the car is idling to see if revs change. If no leaks, then the MAF is suspect.
As MAF's age, they tend towards lean, and eventually the voltage range is so low you can't compensate with the potentiometer. If this is the case, adjust it back to 300 and send your MAF off for rebuild
Practical experience with my non-cat 89 suggests to me that adjustment above 650 or so ohms on the potentiometer means your MAF needs replacement.
