Help with my dyno - really rich + low power at high RPM.
03-17-2008, 10:57 PM
#1
Rennlist Member
Thread Starter
Help with my dyno - really rich + low power at high RPM.
A gold star for anyone who can figure this out.
So I dyno'd my 993, which is stock except for GIAC chip and 100-cell sport cats. The power and torque look good until around 5500 rpm, then they drop off a lot. I say that based on comparing them to the factory dyno plot (see Paul Frere's book) and assuming 15% drivetrain losses. (see graphs). I also see that my car is running *really* rich, especially at high rpms. A/F goes down to 10.1.
First thought was "not enough air" but I checked the resonance flap actuator and it seems to be working fine. When the engine is keyed on, it cycles through completely (not hung up).
So I'm out of ideas.
So I dyno'd my 993, which is stock except for GIAC chip and 100-cell sport cats. The power and torque look good until around 5500 rpm, then they drop off a lot. I say that based on comparing them to the factory dyno plot (see Paul Frere's book) and assuming 15% drivetrain losses. (see graphs). I also see that my car is running *really* rich, especially at high rpms. A/F goes down to 10.1.
First thought was "not enough air" but I checked the resonance flap actuator and it seems to be working fine. When the engine is keyed on, it cycles through completely (not hung up).
So I'm out of ideas.
03-18-2008, 12:55 AM
#3
Rennlist Member
Thread Starter
Just had a thought: could I possibly have MAF issues, causing it to think it's getting more air than it is? I ran a K&N air filter for a while.
Last edited by TheOtherEric; 03-18-2008 at 01:12 AM.
03-18-2008, 01:16 AM
#4
RL Technical Advisor
Check to make sure that your resonance flap (vacuum actuated) is working. Been seeing more of these issues lately due to deterioration of the rubber vacuum hoses and fittings.
You might check MAFS voltages in case it became contaminated from the K&N.
You might check MAFS voltages in case it became contaminated from the K&N.
03-18-2008, 11:22 AM
#5
Rennlist Member
Thread Starter
I was able to confirm with my hand that it travels the entire distance when the car is keyed on. That was about 15 min after running the car, so that seems to confirm it's holding vacuum sufficient enough.
03-18-2008, 11:34 AM
#6
Burning Brakes
I've seen more than one 993 that ran a K&N filter that toasted the MAF sensor. Apparently the oils in the filter get discharged overtime and stick to the MAF sensor causing it to fail.
All that said, if the MAF was screwed up badly, it would idle in such a way that you'd notice.
All that said, if the MAF was screwed up badly, it would idle in such a way that you'd notice.
03-18-2008, 05:41 PM
#7
Nordschleife Master
Do you have the dyno graph of the HP & torque curve?
Maybe a faulty FPR, or a leak on the FPR line?
If you are running WOT, you are running open loop, so the 02's are not being read, so why not just check for leaks, & clean the MAF.
Maybe a faulty FPR, or a leak on the FPR line?
If you are running WOT, you are running open loop, so the 02's are not being read, so why not just check for leaks, & clean the MAF.
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03-18-2008, 07:27 PM
#8
Rennlist Member
Thread Starter
Interesting thought on the FPR. They don't typically go bad AFAIK, but it's certainly possible. I'm not sure what you mean by a leak on the FPR line (I'm not leaking fuel anywhere). I would think a bad FPR would cause problems *across* the rev band, but I only have problems at higher RPMs.
03-18-2008, 07:45 PM
#9
Drifting
Does the MAF have a 'hot wire' in it? I could have sworn that I saw in the Streather book that the hot wire is auto-heated to 1000 degrees or so when the engine is swicthed off to prevent fouling.
03-18-2008, 07:57 PM
#10
Nordschleife Master
Here's the dyno plot, which is what I graphed out above.
Interesting thought on the FPR. They don't typically go bad AFAIK, but it's certainly possible. I'm not sure what you mean by a leak on the FPR line (I'm not leaking fuel anywhere). I would think a bad FPR would cause problems *across* the rev band, but I only have problems at higher RPMs.
Interesting thought on the FPR. They don't typically go bad AFAIK, but it's certainly possible. I'm not sure what you mean by a leak on the FPR line (I'm not leaking fuel anywhere). I would think a bad FPR would cause problems *across* the rev band, but I only have problems at higher RPMs.
Humm, you are dropping off torque & HP early. Maybe the resonance chamber isn't working, even if it's getting vacuum. It's also weird, that it really seams to be only in the top end where the problem is.
I know "other" Bosh ECU cars, a problem like this is usually related to the CTS (coolant temp sensor) but we don't have'em. Maybe the oil temp sensor for the ECU?
05-27-2008, 06:02 PM
#11
Rennlist Member
Thread Starter
Just to follow up on this thread. I believe my problem was caused by leaks in the air intake system. I found that I had only one of four screws holding the throttle body to the intake. So the throttle body was a bit loose, and intake leaks can cause rich running (see shop manual under DME Diagnosis). Because of the high air flow at high RPMs, that's probably where leaks would be most problematic.
Unfortunately, I wasn't able to dyno it again after fixing the problem so I won't know for sure.
Unfortunately, I wasn't able to dyno it again after fixing the problem so I won't know for sure.
05-27-2008, 08:10 PM
#12
Three Wheelin'
Hey, you could do a full throttle run with a wideband stand alone 02 sensor if one is available to verify whether you've solved your problem. Don't know if it's worth the trouble but interesting to see if it solved the problem.
FWIW, my vote was going to be the chip itself...
Dave
FWIW, my vote was going to be the chip itself...
Dave
05-28-2008, 10:44 AM
#14
Rennlist Member
Thread Starter
