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I’ve been tracking down some random misfires for awhile now on my 1999 C2 and am hoping to finally have some resolution. My mechanic informed me that my long term fuel trims appear to be “stuck.” As in, they don’t move whatsoever. They are apparently both at about +7 if I am remembering correctly. His comment to me was that “It’s not enough to throw a CEL but they are definitely adding fuel.” He inquired if I had ever flashed a tune to the DME, which I have not. But a previous owner did install what I believe is a RoW DME flash so I guess anything is possible.
Is there a way to tell if a DME has an aftermarket tune installed? Will it show something on a Durametric?
I should note that I’m still acquiring data from my shop and my Durametric and will update data as needed.
Last edited by islaTurbine; Nov 16, 2021 at 09:56 AM.
The Data Version shown on the Durametric DME page is 0041550737010508. Can this be deciphered into whether my DME is USA, ROW, or some sort of aftermarket tune?
A simple test to see if the fuel trim is "stuck"::
while monitoring fuel trim RKAT or TRA with engine running::
1.Remove oil cap, fuel trim should move to RICH limit and set a code after a few minutes;;
2.Use a propane torch, turn on fully ( do not light), hold into air cleaner snorkel , fuel trim should move to LEAN limit and set a code within a few minutes.
This will verify the fuel trim is working and is capable of triming the fuel in response to 02 Sensor values.
A simple test to see if the fuel trim is "stuck"::
while monitoring fuel trim RKAT or TRA with engine running::
1.Remove oil cap, fuel trim should move to RICH limit and set a code after a few minutes;;
2.Use a propane torch, turn on fully ( do not light), hold into air cleaner snorkel , fuel trim should move to LEAN limit and set a code within a few minutes.
This will verify the fuel trim is working and is capable of triming the fuel in response to 02 Sensor values.
Thanks Skip. This made for an interesting experiment. The car was nice and hot after a jaunt around town and one run to 7000rpm about 2 minutes before pulling into the driveway. I let the car then continue to idle with the AC compressor off for quite some time as I got my laptop and Durametric set up.
In this configuration, the TRAs were initially reading -0.32 for bank 1 and -0.26 for bank 2. (FRA1 and 2 were +0.97 and +0.93 respectively.)
I then turned on the AC compressor in order to keep the cooling fans running. I then removed the oil cap and she began sound like she was running rougher. After 2 or so minutes, TRA1 went to +0.02 and TRA2 went to -0.18.
When I put the oil cap back on, TRA1 and TRA2 then went to +0.14 and -0.16 respectively.
When I introduced the propane to the intake snorkel for 2-3 minutes, nothing changed and neither TRAs changed again from that point forward.
No CELs we’re ever produced and no Fault Codes were ever detected by the Durametric.
Out of curiosity, I turned off the AC compressor and removed the oil cap again. The car began to sound even rougher than before, probably because the idle was lower due to the AC being off this time. But neither TRA budged this time. Durametric reported them as the same +0.14 and -0.16 as before. No CEL and no Fault Code.
The car is a 1999 C2 with DME 5.2.2.
Last edited by islaTurbine; Nov 19, 2021 at 03:36 PM.
Thanks Skip. This made for an interesting experiment.
I then removed the oil cap and she began sound like she was running rougher. After 2 or so minutes, TRA1 went to +0.02 and TRA2 went to -0.18.
The car is a 1999 C2 with DME 5.2.2.
According to this statement, the 02Sensors read LEAN ( 0.00volts) and the DME adjusted to a RICHER setting as expected.
Watch the actual O2 sensor voltage at the same time, it should read 0.00V when oil cap is off or you induce a vacuum leak. After seeing the 02Sensor at 0.00V for a while the DME should start moving the TRA to RICHER SETTING.. ( the limit is +- 0.36)
It should read near 1.0 volts when Propane is introduced . ( may need a bigger Propane nozzle)..After seeing 02 Sensor reading near 1.0V for a while, the DME will move TRA to a LEANER setting.
You can also induce a leaner condition by removing/creating a vacuum leak. and Richer condition by inducing more Propane..
I have done this 1000's of times to test 02 Sensors and fuel trims, it comes so simple and easy to me, but may not to everyone..
I’ll try again to see if I can get any movement and to observe the O2 sensor reading while doing so.
Btw, my bank 1 cam deviation was 3.0 and also didn’t move any, even while rev’ing the engine up to 4000rpm. Is this normal? (Bank 2 doesn’t provide any readings because the car has a RoW DME flash).
Last edited by islaTurbine; Nov 20, 2021 at 12:35 PM.
Here are my readings with a hot motor that had been running for almost an hour. It’s at idle, AC compressor off, and the oil cap removed for about 4 minutes.
The O2 voltages both hunt up and down from .09 up to .71.
The TRAs both finally reached greater than .32 after about 7 minutes of idling with the oil cap removed. The codes produced were P0506, P1124, and P1126.
Is my ICV going bad?
With the oil cap put back on, the TRAs both went to -.10 and stayed there.
Last edited by islaTurbine; Nov 21, 2021 at 06:20 PM.
The TRAs both finally reached greater than .32 after about 7 minutes of idling with the oil cap removed. The codes produced were P0506, P1124, and P1126.
Is my ICV going bad?
With the oil cap put back on, the TRAs both went to -.10 and stayed there.
No, the system is working just as expected when "Commanded Lean", and proves 02 sensor are functioning and fuel trim is functioning.
When "Commanded LEan" by removing oil cap to introduce air that by-passes MAF and TB, the 02sensors react by going to 0.00v then the DME reacts by going -0.36 (rich set point) , and sets codes P1124 and P1126. Code P0506 (IVC) is set due to idle speed has increased due to extra air that is by-passing TB/IVC and MAF, and IVC can no longer lower/control idle speed by reducing by-passed air.
No, the system is working just as expected when "Commanded Lean", and proves 02 sensor are functioning and fuel trim is functioning.
When "Commanded LEan" by removing oil cap to introduce air that by-passes MAF and TB, the 02sensors react by going to 0.00v then the DME reacts by going -0.36 (rich set point) , and sets codes P1124 and P1126. Code P0506 (IVC) is set due to idle speed has increased due to extra air that is by-passing TB/IVC and MAF, and IVC can no longer lower/control idle speed by reducing by-passed air.
Shows all is working as designed.
My O2 voltages never went all the way to 0.00, though. I think the lowest they ever got was around +0.09. Not a problem?
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Long Term Fuel Trims Stuck?
