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For some reason my post I submitted yesterday isn’t showing. I’ll give a rundown on it and then my newest findings:
While checking the fuel pressure I bumped the PCV valve and it started rattling. I had heard this before but could never track it down because it was intermittent. So I replaced the PCV. I then drove it for about 20 minutes or so. All was great. At idle the STFT would creep up to 20, but it would drop under load. I checked for vacuum leaks again. Nothing. But it was running much better. I let it sit and idle for 15 minutes and still never died. Finally.
Then, something told me to check the fuel pressure again. It was good. I moved the gauge to where I could see it from the cab. I was going to see what it did under load. Before I even put my foot on the pedal the pressure started to drop. It stumbled and died when pressure dropped below about 7 psi. I tried to restart but there was no pressure. I cycled the key several times and nothing.
I did not expect a fuel pump issue because it is less than 3 years old. And pressure was fine when I had checked it earlier. I just got lucky and had the gauge on it when it died this time. I paid a shop to replace it last time. I think he used the cheapest pump he could get from AutoZone. I couldn’t find a Motorcraft so I ordered a Carter from Rock Auto. Hopefully this will fix my problems, and last a little longer.
Thanks for all your ideas. This one really had me stumped. That is why this is the only OBD2 vehicle we own and the average age of all our cars/trucks is 45 years.So I got it to shut down again last night while watching everything. I thought I had gotten Torque Pro to log it but I was using my tablet this time instead of my phone, and didn’t have the settings right.
But here’s what I can remember. It was running good with LTFT at 20 and 16. It would drop below 10 under load. I have verified no vacuum leaks. O2 sensor 1 on both banks were oscillating .1-.8V. O2 sensor 2 on both banks was just above 0. It ran like this for 15-20 minutes. I was sitting and idling for 5 minutes after that and then all of a sudden one upstream O2 sensor stayed at zero and the other right behind it. STFT jumped above 50 on both banks. The downstream sensors started oscillating from 0-.8V. STFT dropped and then engine died.
I will try to log again tonight so I can see if O2 is reacting to fuel trim or vice versa. Then I will have to figure out how to post it.
I did find a source that confirms the TPS should show .9V at closed. This would be just under 20%. I will still confirm the 5V supply, but that seems to be ruled out with this confirmation. I have checked for vacuum leaks with carb cleaner, brake cleaner and propane. Since I replaced the intake gaskets and almost all the vacuum related hoses I have not verified any more vacuum leaks.
I am now leaning toward an issue with the cats. But I’m looking at $700 to replace them myself. I want to make sure they need to be replaced. I will start looking at back pressure.
“It appears your engine’s running quite rich at .7 and .8 volts.”
That is the downstream sensors. The upstream are properly cycling from .1-.9. And LTFT is 20+. So if anything, it just means the cats are not doing their job. But to have both banks go bad at the same time? I never got high downstream readings before making any changes.
“I would try resetting your cars ecu now you’ve changed some parts plus it’ll reset your fuel trims.”
I cleared the codes after putting in the new TPS. Fuel trims started at zero and went up to 20+ while driving.
“Seems like the TPS is putting out the wrong voltage and affecting your trims as a consequence.”
I will check for 5 volts at TPS after work.
“Perhaps you could run a continuity test by backprobing the connector and the associated pins on the ecu plug.”
I will see if my manual has a diagram for the PCM I don’t think it does.
“There may be a way to calibrate the TPS on ford also. Be worth a try to see if it helps.”
It is not adjustable. From my understanding the F150 zeros the TPS at idle on every new cycle. But if the reference voltage is off that could be the problem. I just don’t know if zeros means it should read zero or just that it takes the voltage reading it gets and considers that zero. I will research that more. I am kinda leaning toward TPS problem.
