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Have a 2001 tacoma in my shop with a lean code p0171. Long term fuel trim is 29% Short term is at around zero. Scoped maf sensor and got 4.35 volts at a snap test. Not sure where else to look. Any help would be appreciated
Classic start with a check on freeze frame data to identify what conditions the code was set in (idle? / under load?) Or just pull up live data and check fuel trims at idle and at 3k rpm.
If trims improve at higher rpm most likely the classic vacuum leak etc, if trims don't improve or get worse then possidly a fuel delivery problem.
Have a play on live data and let me know the results
Calling upon my years of experience, I froze at the controls. – Stirling Moss
The following user(s) said Thank You: ScannerDanner
johnathon.balderas wrote: Fuel trims increase with acceleration. 30% at idle and 39 when accelerating. But normal at wot.
Acceleration and WOT is not when you want to be looking at trim numbers.
Give us an idle (I think you did already) and a steady 2500-3000 rpm reading in park. Hold it there for a minute to let it stabilize.
Fuel trim climbs when I hold the throttle steady. Added propane to the intake to see if the ft would decrease it did. How high can the fuel trim numbers go?
A new guy amateur question...isn't O2 feedback ignored at WOT? Kind of like being in open loop. Is that correct, or no? Would that explain why at WOT fuel trims are normal?
Fuel pressure is within spec. But according to mitchell while idling it's slightly too high. At idle it's supposed to be between 31 and 37 psi. I got 44 at idle. So I'm kind of stumped.
Did you disconnect the vacuum line from the fuel pressure regulator & do a snap throttle test with the fuel pressure gauge? You want to make sure that the pressure doesn't drop out on this test.
So with increased fuel pressure the fuel trims got better, I wonder if your dealing with restricted injector(s) I think I'd be going up the route of injector balance test next for the moment
Calling upon my years of experience, I froze at the controls. – Stirling Moss
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