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I have a customer with a 04 F-150 (5.4L 3v) that is running very rich and throwing P0172 and P0175. The engine runs slightly rough at idle but drives and cruises fine. I still need to figure out how to upload data graphs but here is some info I pulled from my scanner, as well as some tests I have performed.
-Fuel pressure PID is 40psi (confirmed with mechanical gauge). This particular system is returnless.
-LTFT's on both banks jump very quickly to -27 / -30 as soon as vehicle enters CL.
-Vacuum is 20in-hg at idle as well as 2500 RPM with no flutters or erratic needle movement
-MAF is ~6.5 g/s at idle
-BARO is 29 in-hg
-spark advance at idle is 15 degrees plus or minus 2
-back pressure measured at 02 sensor port less than 1psi at idle, as well as 2500 RPM
-compression is 200 psi across all cylinders
Before the customer brought the vehicle to me, the customer changed out all the oxygen sensors, plugs, and coils in an attempt to remedy the problem. This truck has me scratching my head so far, as I cannot put my finger on a particular part or system. I figured I would give a shout out to you guys and see if you had any advice on what diagnostic route I should take next. Thanks!
hi not a lot of experience here I would do an amperage on the fuel pump see what that should be also a volume test on fuel pump might have a better idea of whats going on and also stft is important in relation to ltft so it would be good to know that to geta better picture of what happening ltft tends to be an integrator so something is knocking trims off but we need more info I think ben and tyler and graywave are really good
LTFTs do zero out quickly as the engine is revved up. I did check the vacuum line going to the fuel pressure sensor and I did not notice any raw fuel being sucked through.
Also, I forgot to add, I did check to make sure the purge valve was not stuck open, it is operating correctly.
As far as I can tell, the ECU infers its data from a cylinder head temp sensor, rather than a conventional ECT. The cyl head temp sensor is reading ambient at startup, and moves smoothly to operating temp once the engine is running with no spikes or drop outs.
I'll create an artificial vacuum leak when I get in the shop tomorrow and let you know what the O2's do, thanks.
I did disconnect and cap the vacuum line for the PCV to make sure it wasn't huffing fumes from the crank case and did not notice any change in the fuel trims.
No worries, I'm right there with you. I did check the intake gaskets and all the vacuum connections to the manifold and everything seems to be sealed very well.
Just some of my gut thoughts: when its idling it feels like a motor with the EGR valve stuck open, or severely retarded ignition timing. This particular motor uses them cam phasers to regulate EGR, however both cams seemed to be indexed perfectly relative to the crank. Maybe one of you Ford guys could chime in on some of the variable timing related PIDS; however the desired cam positon vs the actual cam positon are in agreement.
Also, could it be possible to have weak spark at idle, but be fine at high speeds and higher loads? In my experience the latter problems tend to be exaggerated with high loads.
I'm having to use a lot of my will power right now to resist throwing parts at this thing.
1. Does the Fuel Pressure drop on snap throttle?
2. Once in CL what are LTFT's @ idle, 1500, and 3500 rpm? Also, are both banks identical or different? ( Do the trims go positive as rpm is increased?)
3. On snap throttle does your Vac guage return to 20 in HG quickly or slowly?
4. On snap throttle, what is the highest g/s the MAF can achieve?
5. Do you smell raw, unburnt fuel at the tailpipe?
6. What are your MAP PID values at idle, 1500 and 3500 rpm?
7. What are your CALC Load values at idle, 1500 and 3500 rpm?
If you scan tool has Bi-directional control, command the EGR to open at idle, engine should stall.
I agree with Weycraze.
Just make sure there are no vacuum leaks on the engine. I've had the back of the intake leak cause me problems such as this before.
I would recommend a closer look at maf sensor - 6 grams at idle fully warmed up is a little high ... Not way out of spec but since nothing else is suspect I would start there. With negative fuel trims you are not looking for vacuum leak. O2 sensor when it sees a vacuum leak (extra oxygen in exhaust) it will add fuel to compensate so u will see high fuel trim not negative. May start with cleaning maf.
-After some more digging around, I found that the intake manifold runner control actuator was hooked up backwards. Since the runners are supposed to be in the "choked" position at idle, I thought it was a bit of a red herring, but hooked it back up the correct way anyways. This did not seem to affect anything.
-I was able to find a small hairline crack in the right side exhaust manifold (replaced manifold).
-The pigtail on the cylinder head temp sensor in the valley was barley making contact and showed very high resistance, even though the engine temp PID on my scan tool showed everything was fine. I repaired the connection (I thought for sure I had nailed the problem).
-The Cylinder contribution test on my scan tool shows number 8 contributing 10% less than the others at idle, however no misfire codes are set. There is still a slight stumble at idle, but no misses at loads or higher RPM's. Nothing jumped out at me when I scoped voltage and current wave forms on the #8 coil and injector. They also looked identical to other cylinders.
-My original MAF report was not when fully warmed up, when fully warmed up g/s is below 6 and voltage is at .9-1.0. My Shopkey program says idle voltage should be .7-1.0, (I did go ahead and clean the MAF anyway)
-In response to some of Weycraze's questions: LTFT's do get higher (better) with more RPM. At idle they will be in the mid negative 20's, at 1500 RPM they will go into the negative teens, and at 2500 and high closer to negative 10. Bank 2 is always about 2 points more rich than bank 1.
-Vac will quickly return to 20 in hg after throttle snap. Back pressure measurements at the primary 02 port didn't even register on the gauge. (less than 1 psi).
-I also checked the battery voltage at the PCM, battery itself, and injectors. Battery voltage at the PCM vs the battery matched within a hundredth of a volt. Supply at the injectors was within 3 hundredths of a volt.
Any thoughts or advice would be greatly appreciated, thanks!
Last edit: 5 years 2 months ago by Tacitus043. Reason: more info
I drove it around some more today, LTFT's still in the -20's on both banks. It does seem a bit low on power, almost like a plugged exhaust, however back pressure test and manifold vacuum show otherwise. Fuel trims do get better under load.
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