P0172 - Running Rich Help

Hi,

I have a 2zzge which is currently running rich, there’s a pending fault of p0172 and no doubt once trims exceed the limit the EML will illuminate. Upon staring the engine the rev will drop and raise for a few seconds and then generally settle, if I raise the rpm to 2k and after lift off, the revs will bounce and then settle.

I’ve checked or replaced the following items;
MAF sensor cleaned; was replaced in 2019 8k miles ago with Denso sensor.
New precat Denso o2 sensor
Exhaust gasket flange replaced due to leak, no leaks pre cat…(I will need to remove the exhaust manifold heat shield to further examine the gasket or manifold cracks but no typical noises to suggest a leak here)
New spark plugs,
Injectors removed, tested and cleaned = two poor spray pattern one rectified with ultrasonic cleaning and the other replaced with new genuine Denso injector
Throttle body cleaned
IACV cleaned and tested ok
Throttle sensor replaced
Timing and compression good
Smoke tested for vacuum leaks and no leak found
ECU coolant sensor within spec
EVAP system seems to be working normal

I’ll need to get the special tool to test the fuel pressure; the engine has a returnless system with the filter, pump and FPR within the fuel tank.

I’ve attached the fuel trims, but can’t quite work out why they are working in opposites.

Thanks

If you are, in fact, having RICH moments, I don't believe the condition is present in your Fuel Trim screenshots. In the first image, at idle, fuel trims look beautiful. In the second image, at 2400 RPM, your Long Term fuel trim is -8.5 but, your Short term is +15 - +22, giving you a Total Trim of +6.5 - +13.5. My thoughts on a "sometimes" RICH condition would be a purge valve not sealing properly, when closed.

Something is not quite correct because there’s a pending P0172 code, and when I first switch on the engine, the revs hunt for a couple of seconds before settling or after blipping the throttle; the revs will drop and then settle again.

I wonder; a saturated charcoal canister causing a rich movement when the evap opens and closes?

Could be a bad ECU?

A saturated Charcoal Canister is a possibility. Try eliminating the purge line from the manifold, entirely. Either by disconnecting the line and capping the vacuum port. Or, pinching the line, if you have a rubber hose.

I wouldn't be thinking about replacing the ECU, just yet. Not until you have isolated, and eliminated all possible sources of foreign/extraneous fuel. Such as, a saturated canister, stuck-closed vent valve, pinched/clogged canister vent hose, contaminated oil,...

I caped the evap canister line into the throttle body which made no difference; the idle was hunting after starting for a few seconds and then the idle smoothed out, with the p0172 code pending. I switched the engine off and reinstated the evap and it idled ok..with minor idle hunting like it has been.

I’ve ordered the fuel pressure gauge to measure the fuel pressures; it seems to be worse when the engine has been sat for a while. I know normally IACV typically causes cold start or idle issues, but they don't normally cause rich conditions.

I plugged my laptop into the car today because it's better than my phone when looking at obd2 values. When I raised the rpm to 2500, the CEL illuminated; P0172; I have attached a screenshot displaying the parameters which caused the CEL to illuminate. I held the rpm at 2500 to observe fuel trims and It seems the fuel trims go negative briefly, so something is causing a spike in the fueling.

Parameters when the DTC Appeared



Fuel trims at 2500 rpm

Fuel pressure is 44psi when switching on the ignition, and rises to 50psi at idle. Pressure bleed off passes as per manual.

I replaced the coil packs with Denso coils and reset the ECU to clear fuel trims. Idle is fine, however when accerlating to 2k rpm LTFT goes -9 and STFT goes -10 to -15 triggering a p0172 code.

I’m not quite sure what else to test or check.

I’m having some similar issues. I’m not ASE certified, so it’s worth what you paid for it…..

I’m working on a 3rz now. I found 2 vacuum lines with the VSV and EVAP system were incorrect in location according to diagram under the hood. Also found that O2 B1S1 ohm was high at 13.6. Data I found said it should be 5-7 ohm on B1S1. I believe the AF/O2 (whichever you prefer) was giving a false rich signal causing my negative fuel trims. I’ve ordered new O2 sensor and will update.

Just the vacuum line correction has improved but not completely corrected the trims in my case.