nabtastic

Hey, I've got a thread going about P0171 but I want a little more detail answer here.

I have a positive FT of 32.8%, which I presume is maxed out. My upstream O2 reads 0.1, and my downstream reads a constant 1.0 ... The computer is obviously reading lean, however it's actually running rich (as indicated by heavy carbon deposits on spark plugs.

I haven't found an exhaust leak or vacuum leak despite trying several times. My fuel pressure starts at 42 and stays 48 while running. The fuel pressure immediately begins to drop after reaching 42 in the "on" position. Should I be checking the injectors? (I'm searching how to test injectors now)

Thanks all.

nabtastic

Fixed. New MAP and TPS, reset PCM. All injectors pegged exactly at 14v so I'm assuming they all need a little cleaning but otherwise fine..

I do have a P0122 code now (low TPS voltage) that I can't figure out..

nabtastic

turns out i didn't fix it..

TheDude337

I know this thread is over 2 years old. Im havingbthe same condition wiyh my 2001. I have california emission. I get the exact same readings as you but only on bank 1. My fuel trim is the same and my o2 voltage readings are the same, but as stated before only on bank 1. My bank 2 are reading as they should going between .1 and .8 or so. Have you or anyone narrowed down this issue yet.

jordan96xj

An obd2 scanner with real-time or near real-time data is almost a prerequisite for diagnosing o2/fueltrim issues.

You can also google "diagnosing oxygen sensors". Because there are literally hundreds of youtube and web page articles about it. You'll find that this almost always this includes the use of at least an obd2 scanner.

When a sensor is locked in the full lean voltage at idle, it is usually because it is either 1. Sensing a lot of spare oxygen remaining in the exhaust stream or 2. It is faulty. If there is a lot of spare oxygen in the exhaust due to a vacuum leak, this can usually be observed by increasing the idle by hand to about 2000+ rpm while watching the data (o2 voltages and fuel trims). Vacuum will be far less at 2000+ rpm and less unmeasured air will be sucked into the system, and the o2 will start to come down from full lean. If when running at higher rpm the sensor does not react at all, that is an indication that the sensor itself is perhaps taking faulty measurements. It gets a bit deeper than this, but this is kind of how the troubleshooting starts.

Given your symptoms, it sounds like you have a failed oxygen sensor. But it would suck to swap the sensor only to find that it wasn't the root cause. But it is the most likely cause.

97grand4.0

A high POSITIVE fuel trim number means the pcm is subtracting fuel. A high NEGATIVE number means the pcm is adding fuel.
a +30 is indeed off the chart. I suspect you have a stuck injector or 2. The O2 is seeing a very rich mixture and is trying to compensate. Can you hear them all clicking?

You can also look at the pressure gauge. Key on engine off, the pressure should hold and not fall off. (there is a spec, without looking something like stay above 25 lbs after 5 mins) If it does, you have a leaky injector, OR a bad pressure regulator. The regulator will not cause your problem but the injectors will.

Cummins93

http://www.easterncatalytic.com/educ...agnostic-tool/

I was under the impression that positive fuel trims are adding fuel because of a perceived lean condition. Inverse for negative fuel trims. Stuck open injector being the latter. I also say perceived because o2 sensors can be liars without a code.

jordan96xj

Negative is computer reducing fuel due to a shortage of free oxygen in the exhaust stream (i.e. compensating for a rich condition).
Positive is computer adding fuel due to an abundance of free oxygen in the exhaust stream (i.e. compensating for a lean condition).

Control of fuel introduction is achieved by the computer by increasing or decreasing the pulse width of the fuel injectors.

All of this is heavily dependent on the oxygen sensors functioning correctly and accurately reporting their measurement of free oxygen in the exhaust stream back to the computer in the form of a voltage signal.

97grand4.0

I think I got it backwards then in my prev post. If so you're looking at a massive vacuum leak or a bad sensor.

I actually was just checking everyone's alertness.