Hello, I have a 2001 Navigator with the 5.4 v8. Consistent codes are P0171 (lean bank one), and P0300 (random multi-cylinder mis). So far, We have replaced fuel pump, filter, and regulator, because the fuel pressure was 6psi below spec. Now KOER pressure is back to 33psi, 2psi low, but better and the long start issue is fixed. Codes remain. Have tested and changed B1S1 o2 sensor, vacuum lines for pressure reg / AIR system, PCV valve, cleaned out EGR valve, and tested function via scan tool, cleaned MAF sensor. MAF sensor voltage spec Idle fully warmed up is .70-.90 volts, and it's sitting at .96. A touch high, but shouldn't be enough to kill power and random mis throughout the rpm band. Have smoke tested intake and EVAP system, no leaks, also did the old fashioned Ether spray to no effect. Randomly a single cylinder will call out a mis, be it 8, 4, 7, 2, different one each time, compression test on those cylinders is 155psi +/- 5psi. About to smash this car, anyone have any good ideas? oh, also did the ford cam-phaser test, appears to be working fine. Any ideas, no matter how crazy, would be welcomed. Thanks
Thomas

 

Please tells us that you have changed the plugs. It looks like you've covered most of the common issues but the obvious.

 

How about the COPS are they original and have you tried changing the COP boots?

 

Yes, it came in with AC Delco plugs, and i changed them to the propper MotoCraft plugs, and gapped each one before installing. Changed coils around, and replaced #8, but still get misfires on 8 randomly, and the p0300.

 

No moisture in the plug tubes? Antifreeze is culprit when the intake manifold leaks a bit, grounding out the spark.
Also, you said that you flipped around the COP's, but to alloro's point, the boots crack and allow the spark to ground out to the plug hole walls, creating the same thing.
I'd pull an easy to get at, COP and really look closely at the boot.

Here's one of mine.

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Friday, p0300 and p0308. this morning, cleared codes, p0307. just now, cleared codes, p0304. .. and i'll take another close look at the boots, check them out.

 

But if the plugs were grounding out like that, wouldn't there be a bunch of un-burnt fuel going through? it doesn't smell like a fuel soaked cat, and there is still the lean B1 code.

 

Checked all coil boots, all seem to be fairly new. no cracks, nice rubber.

 

Any significant loss of power over the last 30-60 days? Maybe your cat, although you would expect a possible downstream fault but not always.

How about checking your cam position sensors too?

 

Tested the cam position sensor (only one on left bank), it's fine, as it the cam phaser. It does have significant power loss right now, and finally starting to get that wonderful fuel soaked cat smell. No o2 or cat efficiency codes though. Going to pop the pipe off and scope the cats once it cools off. I am an ASE mastertech at an independant shop by the way, just never seen anything like this before, that's why i was looking to the forums for weird problems and fices others have had, you guys are usually a better resource than mitchell1 when it comes to your not every day problems.

 

the only abberent sensor readings are the MAF, .1v above where it should be, tested with 2 different MAFs, anf the ECT, wich has not gotten above 180F, even though it shows CL fuel status.

 

I know some guys talk about the ecu creating erratic spark as you describe but I'm not personally aware of it.

 

Your not going to be able to test the cam phaser on an '01 Navi.

Take a look at the fuel trims. If the STFT + LTFT is above 28% you are running lean, causing the P0171.

(Look at the FF data to determine which STFT cell was active when the CEL tripped.)

When you smoked the intake did you smoke it all the way up to the MAF, including the PCV valve's fresh air intake tube running from the air box back to the rear of the driver's side cam cover on that Intech V-8?

I think your running lean causing the random misfires. The O2 sensors don't see the unburned fuel, they see the unburned Oxygen and the PCM tries to go richer, ergo the gas smell.

I'd also do a voltage drop test on the ground side of the fuel pump to be sure it has an adequate ground or it will run slow.

What ever you do, don't "smash this car"!

 

Hey tmuther ,what was causing the long start issue one your navi? mines doing something similar I'm going to check my fuel pressure tomorrow.....

BOT:What if the exhaust valve bent/not closing on #8 cylinder causing the codes???

 

Fuel pumps with a return line to control fuel pressure, versus those without and the regulator pulses the pump to get proper pressure, have a check valve to keep fuel pressure in the fuel rail. If that check valve goes bad, the fuel drains out of the rail, and you have to pump all the way from the tank before it'll start.

I considered a bent/stuck valve, but compression is the same on every cylinder, 155psi +/- 5, so it seems unlikely.