Air or Fuel delivery issues, I think!
06-11-2014, 12:44 PM
#16
Nordschleife Master
Have you checked your vacuum lines?
06-11-2014, 12:47 PM
#17
Drifting
Thread Starter
Yes, a couple of times. I've noticed that my car also smells very bad, I have a cat and it seems to run very rich. Could my o2 sensor be defective, I'll check it tonight with an ohm meter.
06-11-2014, 03:38 PM
#18
Just as a data point, when I swapped an S2 manifold onto my S, I had to extend the TPS wires. When I did this, I got to excited and forgot insulate some stuff. Long story short, I had some wires crossing for the TPS and a similar situation with the ISV wiring. The car produced a similar issue as far as not wanting rev unless WOT was reached. For me though, it could barely even idle (ISV wiring and later found a bad ISV as well). Bottom line is check wiring for issues especially if it was messed with at all for the rebuild. Chances are all your sensors are fine. Good luck figuring this out! I hate chasing this stuff.
06-11-2014, 10:35 PM
#19
Are you saying that the whole text is wrong, or No to the last sentence only? Your No seems to imply that it's all wrong.
I agree the last sentence is to be taken with a grain of salt.
So the DME controls your mixture at idle and WOT, the AFM controls everything else in between.
The AFM does not control anything, it sends a signal (barn door position and temperature) to the DME which controls the fuel delivery, timing, etc.
I agree the last sentence is to be taken with a grain of salt.
So the DME controls your mixture at idle and WOT, the AFM controls everything else in between.
The AFM does not control anything, it sends a signal (barn door position and temperature) to the DME which controls the fuel delivery, timing, etc.
06-11-2014, 11:17 PM
#20
Drifting
Thread Starter
Funny, haven't heard that word in a while, just repeating it in my head makes me chuckle. I would have spelled it gobbledigook, but whatever, like you say, life's too short.
How would you describe this process? I thought it made a lot of sense.
How would you describe this process? I thought it made a lot of sense.
06-12-2014, 10:14 PM
#21
Yeah, ipad wanted to replace 'goppledigook' with 'toppled igloo' by the way.
HondaDustR wrote it up pretty well over on Pelican:
Wilks' site might also be worth a look.
HondaDustR wrote it up pretty well over on Pelican:
Open loop mode is where it reads straight off its fuel delivery maps as a function of rpm, air flow meter position, coolant temp, and air temp. There is no feedback loop as the O2 sensor circuitry trims the injection duty cycle depending on whether it is too rich or too lean. The problem is, it is a rudimentary system tacked on after the fact. the DME was not originally designed for it, and it was added on to allow import to the US. It does not constantly monitor the O2 sensor signal, it only triggers an interrupt when the sensor signals too rich or too lean, meaning the mixture constantly oscillates about ideal. As the sensor response speed slows with age and the range reduces, the mixture can vary more wildly and end up offsetting too rich as the sensor sensitivity declines. Unplugging the sensor puts the DME back on track.
Unplugging the O2 sensor is also a useful troubleshooting trick, as a properly functioning sensor can mask other problems such as dirty injectors and vacuum leaks. If the engine doesn't run well without the sensor plugged in, something is definitely wrong.
Another interesting tidbit...the DME also goes into open loop mode at wide open throttle (assuming your throttle switch is working and adjusted correctly), but WOT open loop mode also disregards the airflow sensor as well. If you have any vacuum leak problems that will cause the AFM to read low, you'll notice the car runs poorly at part throttle, but wakes up and runs fine if the throttle is floored. This reaction will also diagnose a defective O2 sensor. If the car still runs badly at WOT and you've confirmed the WOT switch is properly activating, then the problem can be narrowed down to fuel pressure, crank sensors, fuel injectors, or ignition (or wiring to those systems...
), as o2 sensor problems, vacuum leaks, and air metering issues are irrelevant in WOT mode.
Unplugging the O2 sensor is also a useful troubleshooting trick, as a properly functioning sensor can mask other problems such as dirty injectors and vacuum leaks. If the engine doesn't run well without the sensor plugged in, something is definitely wrong.
Another interesting tidbit...the DME also goes into open loop mode at wide open throttle (assuming your throttle switch is working and adjusted correctly), but WOT open loop mode also disregards the airflow sensor as well. If you have any vacuum leak problems that will cause the AFM to read low, you'll notice the car runs poorly at part throttle, but wakes up and runs fine if the throttle is floored. This reaction will also diagnose a defective O2 sensor. If the car still runs badly at WOT and you've confirmed the WOT switch is properly activating, then the problem can be narrowed down to fuel pressure, crank sensors, fuel injectors, or ignition (or wiring to those systems...
), as o2 sensor problems, vacuum leaks, and air metering issues are irrelevant in WOT mode.
06-12-2014, 11:00 PM
#22
Drifting
Thread Starter
OK, i agree, this is much more detailed !
One sentence got me wondering, i know these cars do not have LTFT (Long term fuel trim) but the sentence about unplugging the o2 sensor to put back the DME on track sounds a lot like reseting the LTFT, right? How does the DME react if it no longer detects the o2 sensor, it will try to readjust the fuel trim to compensate, for either too rich or too lean, I guess it will adjust for too rich since this is less armful.
One sentence got me wondering, i know these cars do not have LTFT (Long term fuel trim) but the sentence about unplugging the o2 sensor to put back the DME on track sounds a lot like reseting the LTFT, right? How does the DME react if it no longer detects the o2 sensor, it will try to readjust the fuel trim to compensate, for either too rich or too lean, I guess it will adjust for too rich since this is less armful.
07-06-2014, 03:18 PM
#23
Drifting
Thread Starter
Status Update:
Problem solved, for future unfortunate 944 S2 owners that would be stuck with this problem, ie. running extremely rich and random loss of power, read the first post for a good description of the symptoms.
Drum roll.......Oxygen sensor ! I tested it early on in my troubleshooting and it measured the correct ~8ohms. But I later did the test on Clarks-Garage http://www.clarks-garage.com/shop-manual/fuel-18.htm and I got off the scale results, ordered a generic 3 wires O2 sensor and voila, both problems are gone , hooray !!!
My guess is that the heater in the sensor failed sending wrong mixture signals to the ecu, it would randomly also send a too rich signal cutting off the injectors, explaining my random issue where it wanted to die when I pressed the accelerator.
Thanks to everyone that helped and now the car no longer stinks
The wife is happy.
Problem solved, for future unfortunate 944 S2 owners that would be stuck with this problem, ie. running extremely rich and random loss of power, read the first post for a good description of the symptoms.
Drum roll.......Oxygen sensor ! I tested it early on in my troubleshooting and it measured the correct ~8ohms. But I later did the test on Clarks-Garage http://www.clarks-garage.com/shop-manual/fuel-18.htm and I got off the scale results, ordered a generic 3 wires O2 sensor and voila, both problems are gone , hooray !!!
My guess is that the heater in the sensor failed sending wrong mixture signals to the ecu, it would randomly also send a too rich signal cutting off the injectors, explaining my random issue where it wanted to die when I pressed the accelerator.
Thanks to everyone that helped and now the car no longer stinks
The wife is happy.