Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Mazda CX-3, 2.0 AWD gasoline. It has high LTFT 18.5-20% and normal STFT(-5 to 5 variations but settles near 0 when it s stable) at idle or under normal driving conditions when the load is under 50%. LTFT seems to drop to 13%-14% if I push it harder and load exceeds 50% at over 2000 RPM. Do I have a vacuum leak or is the MAF under reporting ?I attached a pic with some data at WOT in 1st reaching 4000RPM. Also someone performed a smoke test and everything seemed ok except smoke was coming out at the end of some hose that he had disconnected from the beginning of the test and he said that it shouldn't come out through there. Then he said the only explanation he can think of is the PCV valve stuck open and needs changing. That would explain the vacuum leak but is it really that much of a leak if the PCV is open ?
99% Calculated load at WOT suggests that the maf is not under-reporting. Run the vehicle at idle and 3000 RPM to see if LTFT improve. Next time you do the WOT run, choose the Calculated load value, the RPM, the front O2 voltages and/or TPS voltage PIDs and share with us the results.
With Absolute Load at 87% on that engine, I wouldn't immediately suspect a misreporting MAF. It'd be even better if you could repeat your WOT run but take it all the way to the 1-2 shift point.
If you suspect the PCV system, you can always temporarily disconnect and cap the PCV lines/hoses where they connect to the intake. Recheck your trims. If they've significantly improved, you're onto something. If not, keep looking. Take care not to cap off the crankcase side of the PCV, only the intake. Capping the crankcase side can either lead to excessive vacuum, or excessive pressure, neither of which is good if you leave it that way too long.
99% Calculated load at WOT suggests that the maf is not under-reporting. Run the vehicle at idle and 3000 RPM to see if LTFT improve. Next time you do the WOT run, choose the Calculated load value, the RPM, the front O2 voltages and/or TPS voltage PIDs and share with us the results.Assuming is never a good thing.
The first O2(A/F ratio) reports in mA only, I don't have voltages for it. The second O2(which is before the cat) is in V. Also, I don't have TPS in voltages, only %.
Which should I use for the WOT run ?
With Absolute Load at 87% on that engine, I wouldn't immediately suspect a misreporting MAF. It'd be even better if you could repeat your WOT run but take it all the way to the 1-2 shift point.
If you suspect the PCV system, you can always temporarily disconnect and cap the PCV lines/hoses where they connect to the intake. Recheck your trims. If they've significantly improved, you're onto something. If not, keep looking. Take care not to cap off the crankcase side of the PCV, only the intake. Capping the crankcase side can either lead to excessive vacuum, or excessive pressure, neither of which is good if you leave it that way too long.
Sadly I can't cap the PCV hose as it's located under the intake manifold...This is the reason I haven't already changed the PCV valve.
Why do you say I should push it over 4k RPM to the shift point ?
It's such a headache...I'm losing faith I will ever be able to fix the car. Every mechanic or shop I found is clueless and they just want to throw parts at it costing me alot of money...I barely found the guy who did the smoke test. I don't know what I could personally do to test more thoroughly for vacuum leaks as I am not even able to identify a vacuum hose looking at the engine.
Based on the negative o2 mA and the calculated load value at WOT, I would say that you are not dealing with neither a Maf nor a fuel issue. A vacuum leak is most likely what you are dealing with.
Topic Author
