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Looking for a little help here. I had the CEL light come on a couple weeks back and had to drive my van (‘01 E250 5.4) about an hour before I could check it out. Found the PCV valve had come out and I had 0171 and 0174 codes and really rich fuel trims…makes sense. Got the PCV back into the valve cover and applied a fix so that it wouldn’t pop out again (basically extending the elbow so it wouldn’t put upward pressure on the PCV…hose from the pcv to the back of the intake is new). Thought I had smooth sailing ahead, but I’ve been getting a p0171 code but not the p0174 code. The code is getting thrown right when I start up after a few drive cycles since reset. The LTFT have been either negative or really close to zero. Rpm have been low on the freeze frame, but the engine load has been high, but I have not been stomping on the gas. I have sprayed carb cleaner and inspected for vacuum leaks. The two upstream O2 sensors were replaced before the last time I had a code. I cleaned the MAF sensor well with crc cleaner and the fuel pump was replaced last summer with a heigh quality one, which was probably only 3000 miles ago. Any ideas from the knowledgeable folks here?
I've never seen fuel trims go that negative before----hope its nothing too serious.
That confuses me. What I’ve read, is that fuel trims more than +/-20% off from baseline are a case for concern. -2% would be considered really good. Of course you can’t believe everything on the internet.
I should add that it’s been running greatb before I get the code and after.
Does anyone know how engine load is calculated for these engines? Both times now, the freeze frame data have shown a load close to 90%. Seems odd at 600 rpm and 0 mph. I wonder if it is a momentary bad signal from the MAF or TPS. Maybe one of these sensors is on its way to failure?
If a mod could move his thread that would be great.
I should add that it’s been running greatb before I get the code and after
The codes could be an error in the PCM but if it is that too needs to be determined and remedied I won't dispute what you've read on the 'net regarding fuel trims but I'm more than a bit skeptical that a LTFT of -20% would be considered within a normal range. I have no knowledge if my skepticism is warranted, don't pay that too much credibility.
Originally Posted by Mikerson
If a mod could move his thread that would be great.
Contact one of this sub-forum's moderators, they're listed at the bottom of the page when opening this sub-forum.
I've never seen fuel trims go that negative before----hope its nothing too serious.
It's tough to get solid information from Ford on their theory of operation, but I've been told single-digit fuel trims ± 10% were considered normal. I keep an eye on mine when towing using the Torque Pro app, and I've seen them swing ± 5% during my usual driving. My Expy hasn't set any codes, though. It won't set instantly, the code requires a certain amount of time running out of spec before it assumes a problem and sets the code.
Originally Posted by Mikerson
Looking for a little help here...
The P0171/174 codes are set when the PCM has to richen the mixture past a certain threshold that indicates it's not a normal operating condition. The overwhelming majority of these seem to be caused by vacuum leaks, and they can be a real headache to track down. I'm not familiar with common failure points on these engines, but anything between your throttle body and intake valves can be a source. Insufficient fuel pressure can also cause this because the injectors aren't moving as much fuel as they should per commanded pulse width. I PDF'd the Chilton's diagnostic chart for P0171; start at H40 and work your way down as needed. It jumps around a bit, so I'm including the entire document.
Which brand of fuel pump did you install? Aftermarket fuel pumps not made by major brands have notoriously bad reliability, so it's possible your pump is failing early.
Think this would cause my problem? That’s the stud broken off of the number 4 cylinder exhaust manifold. I don’t see a lot of soot around there, so maybe it’s not a really bad leak yet.
BTW, I went and rented a fuel pressure gauge. ~33 psi at idle and when I rev it up, the pressure jumps a bit then settles back to 33 psi. I didn’t drive it.
Think this would cause my problem? That’s the stud broken off of the number 4 cylinder exhaust manifold. I don’t see a lot of soot around there, so maybe it’s not a really bad leak yet.
BTW, I went and rented a fuel pressure gauge. ~33 psi at idle and when I rev it up, the pressure jumps a bit then settles back to 33 psi. I didn’t drive it.
Nope, the manifold stud is a red herring. It can cause a noisy exhaust leak that would fail a state inspection in a number of state, but it can’t cause a lean code because it has no bearing on the inputs the PCM uses to determine fuel trims. It would take a huge exhaust leak that would deafen your neighbors to cause a lean code on its own.
The fuel pressure may be the culprit, though. I can’t find a specific spec for this year and engine, but that same engine in my ‘04 spec’s 55 PSI. I’m going to try and find a more specific pressure spec, but that’s my biggest suspect. How does it idle? Any misfires to speak of? Does it start quickly when you crank the engine?
It would take a huge exhaust leak that would deafen your neighbors to cause a lean code on its own.
Yeah…that’s what I figured.
Originally Posted by Tom
How does it idle? Any misfires to speak of? Does it start quickly when you crank the engine?
Seems to idle just fine. I have no misfires or codes from misfires. It cranks and starts right away. Really have had no problems.
Doesn’t the lack of rich fuel trim seem strange for a supposedly lean running engine? I would expect for the ECM to start dumping more fuel to try to compensate for a lean condition. 89% load in park seems nearly impossible (codes seem to be triggered after startup when parked for a few minutes in hot weather…and all we’ve had is hot weather).
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