2005 f 150 4.6 has -20% LTFT'S on both banks

Tutti,

1lb = 453,6 gr

So, 0.01lb/s = 4,536 gr/s

Scannerjohn,

You're right about low temp. I would expect at idle negative trims and o2 sensors cycling as they should.

What to expect at wot? I think anyway it has to rise o2 voltage, ignoring o2 sensor and enriching the mixture.

Is this engine getting flooded at wot?

Patrick,

Is the o2 voltage steady above 0.8v at wot and at that dead aceleration you described?

You said trims are responding when you spray extra fuel. Does it mean trims become even more negative?

You replaced the MAF already. How is the wire integrity there? Are you able to scope the signal wire and compare to a known good?

I'm not dismissing that ECT, just thinking out loud a little on other options.

Nissan Technician

1lb/s to g/s = 453.592

453.6 x .01 = 4.5

.0022046 lb/s in 1 g/s x 4.6 = .01014 lb/s

at WOT the 02 no longer oscillate they go default rich. the fuel pump is working at full speed at all ranges, supplying too much fuel... pcm sees this and is compensating by taking away fuel. my theory anyway...

fuel pump would be at high rpm at WOT to keep up with fuel demand so it should not be flooding

Thanks for the reply , and no it's not flex fuel, and i understand your thought process, that ecu can miscalculate the alcohol content on flex fuel vehicles.

And I believe you are right scannerjohn, from my research the pump is pulse width modulated, and controlled by duty cycle from the fuel pump driver module. it has 12 volts with key on and the module supplies a ground, during cranking i believe the duty cycle command is to give it a full ground and not limit pump speed, after it starts up duty cycle changes to vary pump speed.( Im not sure what all imputes effect the duty cycle) I think you are suggesting to check the duty cycle during cranking, and compare it to engine running to see if it changes, you think its not changing duty cycle after it starts running, or that the temp being low is commanding a longer on time of the duty cycle? but if this were the case , wouldn't my fuel pressure be higher? Im not sure on that, far from an expert.

One piece of info I forgot to mention is smoke coming out of my exaust. To me it looks white almost like a head gasket failure, but I assure you I drive it 150 miles a day on the interstate and it never overheats and I never need to add coolant. Below I'll post a video of the exhaust smoke after it idles for a few minutes and then having the throttle pushed .

Ok, it wouldn't let me share a 6 second video, so here are some pictures of the exhaust smoke on a snap throttle after it's idled a few minutes

the -20% on LTFT's stays the same at all increments of rpm, (1000, 1500, 2000, 2500, 3000 rpms) and at 70 mph they are still around -20% . i just added propane into a vac line and the STFT's immediately go negative, so yes it can take even more fuel away, And if i pull a vacuum line the STFT's go positive immediately.
Yes, during WOT while driving down the road, the upstream 02's flatline at 0.8 volts
Yes i have changed the MAF 3 different times with junk yard parts (same truck and engine).The MAF voltage is around 0.8 volts at idle and increase to 3.6 volts on a WOT snap. I will go and check the signal voltage with my vantage pro now to see if it is the same as scan tool voltage ( I believe thats what you were suggesting?)

Does it smell like fuel out the tailpipe?

No, the exhaust smoke does not smell like raw fuel to me, comparing it to a V8 engine with no cats on a cold start up, its no where near as strong of a scent .but i could be wrong, and I am getting good gas mileage (15-18 mpg)
I changed the plugs (motercraft platinums) last year, and last week pulled all the plugs to see how they looked and they were all in great condition still new looking after 30,000 miles. (no black soot, or oil fouling) which i was very surprised to see, due to the exhaust smoke. I can pull them again and post pictures, but there was no signs of any excessive burning of anything.

fuel pressure will not be higher, but high all the time same as startup duty cycle of 50%. Should drop to about 25%. If coolant temp is low, it would be signaling pcm that engine is not at operating temp and to stay at 50%... bad temp sensor would do the same.

scantool fuel pressure readings will only show as high as 70... put a pressure gauge on it, should be around 90psi

that white exhaust has to be addressed first... transparent white smoke is usually coolant, opaque white transmission fluid... blue is oil and black is fuel. what ever it is, if its getting on the 02's your going to have wonky readings.

scanner john, you are right, I never even thought about it like that, That what ever it is, that i am burning is contaminating and skewing my 02 readings.
i have tried and tried to find the source of what ever is causing the white smoke. thought it was head gasket issues and have done compression readings multiple times, and each time, every cylinder had 205 psi across the board. have done leak down tests with less than 7% leak down on all cylinders. My research says 10% leak down is normal. removed coolant cap during testing and no bubbles at all, plus it doesn't over heat or need coolant added.
With the results of the above-mentioned tests, i attributed the smoke as un- burnt fuel. Then found scanner danners video ( titled -stuck open fuel injector ) and the smoke coming out of his car is identical to how mine looks, although his car was smoking all the time and mine only does it after idling for 5 minutes or more, but he described the smell as" being similar to dunking your head in gasoline"
so I am lost on this truck , and it has beat me up on this issue for a long time now. lol.
Below I posted a picture of danners white exhaust smoke in the video (stuck upen fuel injector ) and a picture of mine.
Again, I appreciate the responses

See if an injector balance test shows you a or some leaking injectors. It isn't impossible to have several. I bought a set of eight used ones for a BMW a few years ago and used to have a fuel injector test station where you could do numerous tests and watch them flow. One of the tests was a leak test and three out of eight were leaking.

Nissan Technician

I'd go with the injector leak down test as well... with that heavy amount of smoke, I can't imagine why no fuel smell. Leaking injector/s will cause the neg fuel trims.

Ok. I wish I could do an injector balance test, I just don't have the tool to do it. And these injectors did come from a junk yard.
I did check duty cycle on the signal wire of the FPDM, (fuel pump driver module) with initial key on it read 66.6% and after start up it went to 50% D/C.
the (FPDM) lives on a cross member under the bed of the truck and while i was under there testing it is definitely very rich smelling, to the point of giving me a head ache, I had someone else smell it today and they say it stinks also, I guess in am just used to it.
And yes, the upper radiator hose is definitely hot

I discovered that i was on the monitored signal and not the actual commanded duty cycle control signal, i got this straitened out in comments down below this.

IMO, the fuel pressure and the FPDM are not the issue. 40 PSI is 100% normal for these systems. The duty cycle that you're measuring isn't a good indication of what's going on at the FPDM, FYI. That's the feedback signal from the FPDM to the PCM, and it'll only change if the FPDM detects an issue. An 'issue' results in the duty cycle going to zero or 100%. Both generate codes in the PCM in the P12XX range, which you don't have.

I know it sucks to test for, but I agree with everyone else that an injector is your likely culprit. Little else accounts for the kind of exhaust you're seeing. :silly: If it's worth your time, you can remove the fuel rail from the intake and pressurize the rail. Any fuel leaking out of the injectors represents a failure.

Thanks everybody for the time, responses and information. Tyler, I was getting ready to do exactly as you suggested, by removing the rail and having all injectors spray into 20 oz bottles to measure actual volume. It's pretty easy on this engine as nothing else has to be removed. And then possibly replacing injectors with more used ones. I know it's not the best method, and that used injectors may be no better. I'm just working with what I have. I just found the balance test kit on Amazon for $32. Last time I looked they were $400 , So I'll go ahead and get one

If you get a chance and you can get a fuel pressure reading using a gauge, I would like to have it for my notes and study... your scantool FRP is 40psi and the voltage is 2.78 which is the voltage for 40psi, but you posted when you pulled vacuum you had 75psi on scantool. Reading are supposed to be same. Would like to know for sure.

Can't say that leaky fuel injectors are not the problem, but you have neg trims on both banks so you should have at least two bad injectors one one each side.

Please let me know what you find.

Is it possible that the timing is off on the truck? I think that would also fit all of your symptoms if it was only slightly off.

Nissan Technician