1999 FRC pulls throttle
Drifting
Joined: Jan 2015
Posts: 1,256
Likes: 157
From: Pennsylvania
Well in my experience interpreting fuel trims and O2 sensors are the MOST valuable diagnostic tool we have. Now at idle you said if you are "throwing a lean code" ….well let's say it's a P0171/P0174 the PCM will NOT throw this code at an 8% positive LTFT if that's what you were referring too...the LTFT have to be above 23% !!!...if below 23% the short terms will usually read "stoic" (450 mV)...LTFT #1 job is to keep the STFT at 0 !!!... now if you increase RPM to around 3,000 RPM and the LTFT decrease it's a vacuum leak. at higher RPM you can diagnose dirty MAF's, fuel delivery issues etc at the higher RPM's...yes, fuel trims will vary with all those thigs you mentioned but for me idle and 2500-3000 RPM gets the job done !!...now I had an experience with my '01 a while back...it was running just a little rough so I hooked up my scan tool...my LTFT's were around 16%...MMM !!...bought the RPM's up to 3000 and LTFT dropped to 0...ok, vacuum leak...I tried propane and brakekleen….nothing !!...hooked up my smoke machine and there was a pretty good leak out of the PCV connector where the "metal condensation band" comes out of the connector...what a crappy design !!...I bet a LOT of C5 owners have leaks there and don't know it...well anyway ripped out the metal band and used some high temp RTV...problem solved. Smooth as a babys' A$$.
Drifting
Joined: Jan 2015
Posts: 1,256
Likes: 157
From: Pennsylvania
it is on the pcv valve with a wire attached to it that goes to the engine. I believe the theory was that it helps heat the valve to clear condensation out of it but it is not necessary and can be removed like already mentioned.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,512
Likes: 4,003
From: Cape Coral, Florida
Go ahead and clean the MAF...just make sure the ducting is secured when you’re putting it back together. Now you’re saying it feels like there is just a “dead spot” between 2900-3200 RPM ??. Like I had previously said if your scan tool shows LTFT’s and the they are above 10% at idle and if you bring up the RPM to 3000 and they decrease after a little bit you have a vacuum leak...if the LTFT increase you have a fuel delivery issue or a dirty MAF. This is how 99.9% of diag’s would approach this...It can also be a TPS sensor going bad...if your scan tool shows TPS voltage and you can graph it with KOEO push the accelerator down and see if the voltage signal spikes or drops out. That’s about it.... if it’s fuel delivery now we have to look at fuel pump/ injectors...you can pick up a cheap fuel pressure gauge at Harbor Freight...I’ll include a video I did with my scope doing a “TPS Sweep”...there are 2 separate signal wires in that system for redundancy (safety) !!...I’m looking at the voltage signals. with a bad TPS basically there are dead spots or hesitation while accelerating.
Rob
One Test Is Worth 1,000 “Expert” Opinions
Rob
One Test Is Worth 1,000 “Expert” Opinions
Last edited by C5 Diag; Sep 21, 2018 at 10:47 PM.
Drifting
Joined: Jan 2015
Posts: 1,256
Likes: 157
From: Pennsylvania
Short term fuel trims are more accurate for diagnosing a vac leak long term fuel trims are a calculated average over a period of time. When doing here and now diagnostic it is better to use short term fuel trim as they are representing real time.
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 18
Likes: 0
OK so i got into the DIC today. I was doing something else and had the battery out, now I'm getting the warning "Shocks inactive, 80mph limit, etc", but my car did not come with the F55 option from the factory! So i thought it was worth more effort to get into the DIC. Here's the codes:
PCM - 1652 H C
RTD - No Comm
SDM - B1001 H
RFA - U 1096 H
RFA - U 1064 H
RFA - U 1016 H
None of these appear to be related to the fuel issue i originally asked about, but i could be wrong?
PCM - 1652 H C
RTD - No Comm
SDM - B1001 H
RFA - U 1096 H
RFA - U 1064 H
RFA - U 1016 H
None of these appear to be related to the fuel issue i originally asked about, but i could be wrong?
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Drifting
Joined: Jan 2015
Posts: 1,256
Likes: 157
From: Pennsylvania
The 1652 is the only current code all the others are history. You would want to start with it and go from there although it is a cooling fan code it should be fixed. What would be nice is if you could get your hands on a scan tool that has live data and post your findings on here so we could have a better direction to point you in.
Thread Starter
Heel & Toe
Joined: Sep 2018
Posts: 18
Likes: 0
Cleaned the MAF yesterday, seems to have fixed the throttle issue. Thanks for the help y'all !!!
Going to get the PCM / whatever else re-flashed to try and fix the shocks.
Going to get the PCM / whatever else re-flashed to try and fix the shocks.
Last edited by david43r; Sep 30, 2018 at 08:01 PM.