loss of power 5.5Krpm
08-29-2020, 07:03 PM
#1
Burning Brakes
Thread Starter
loss of power 5.5Krpm
Hi all
944 S2 race car, no O2 sensor. I have just developed a hesitantancy/loss of power at 5.5K rpm, which then goes back to normal as rpm continues to rise. My first thought was AFM or spark, so on the test day I checked all the plugs (which are fairly new), they were OK. Next used the FQS to make the car slightly richer. Sure enough the loss was much reduced but still there ( so it's going lean for some reason).
The next thing was a bench test of the AFM with 5v input. the resultant graph is perfectly linear, which it should be, and a careful check of rotation with output voltage shows no odd areas of voltage rise or fall against the direction of movement. So I'm stumped.
Anything else that could cause this? injectors checked last season. if it was pump or filter it wouldn't go away with increasing rpm.
944 S2 race car, no O2 sensor. I have just developed a hesitantancy/loss of power at 5.5K rpm, which then goes back to normal as rpm continues to rise. My first thought was AFM or spark, so on the test day I checked all the plugs (which are fairly new), they were OK. Next used the FQS to make the car slightly richer. Sure enough the loss was much reduced but still there ( so it's going lean for some reason).
The next thing was a bench test of the AFM with 5v input. the resultant graph is perfectly linear, which it should be, and a careful check of rotation with output voltage shows no odd areas of voltage rise or fall against the direction of movement. So I'm stumped.
Anything else that could cause this? injectors checked last season. if it was pump or filter it wouldn't go away with increasing rpm.
08-31-2020, 09:19 AM
#5
Rennlist Member
So you say it runs OK at higher rpm, like between 6K and up to redline? Is it consistent or intermitant? Does it do it static (sitting still, just reving the engine)? Is your rev limiter working? Is there any chance that the rev limiter is getting confused? I would swap in a known good ECU. Are the spark plug wires in good shape? Rotor and cap? Coil? As an experiment, I would defeat the throttle switch so it is operating in Wide Open Throttle mode exclusively.
08-31-2020, 06:41 PM
#6
Burning Brakes
Thread Starter
Yes it's a small flat spot at 5.5 then resumes normal operation. every time. Sitting still not sure, it's only under load. rotor, cap, coil all new. TPS does all the right things all the way back at the ecu. Temp sensors reporting correctly as well. it's not rev limit related. Really, this would normally be easily an AFM problem but the bench test seems to say it's OK.
09-01-2020, 09:15 AM
#7
Rennlist Member
Yes, I would agree that it sounds like AFM. I suggested changing out the ECU on the off chance that the fuel map got corrupted somehow.
