Lean Banks 1&2

[Lowridin67]

This is a little long, but it what I posted on another forum with no responses. I have been watching your videos to try and diagnose, but each time I feel like I’ve found something and fixed it I get a new problem. So here goes.

First post:
About a year ago my wife’s truck, 2002 F150 4×4 5.4, began showing CEL and gave codes for Lean Banks 1&2. I began by replacing all the vacuum lines. No more CEL for about a month. When it came up again I began using my OBD2 scanner and Torque app to diagnose. The LTFT was sitting at about 20% on both banks. STFT would go negative under load and return positive when vacuum came back up. I suspected an intake gasket leak. She continued to drive the truck with the CEL on because I didn’t have time to get to it. Other than the CEL there were no problems. It ran fine.
Then, about 3 weeks ago, it died on her while sitting in traffic on the interstate. It eventually restarted and she made it home. I couldn’t duplicate the problem and it was running fine again so she continued to drive it. A week later she was idling while picking our son up from school and it died again. That weekend I replaced the intake gaskets. The truck ran great and the fuel trims were sitting at about 10%. I considered it done until it died on her in traffic again. I watched the fuel trim and it was at about 10% but creeped up at idle. Eventually it maxed out the LTFT at 29.69% and STFT continued to climb until it reached about 50%. Then it would die. Once I got it started again I drove it and it was ok. When I got home I let it idle and it did the same thing. The only other thing I could think of that would affect fuel trim at idle only is the MAF sensor. I replaced it last Friday. The LTFT dropped to about 4-7% while driving and I let it idle for 20 minutes and it didn’t move. Perfect. Should be good to go.
Then this morning when she went to leave for work it would not idle. It would run if you kept it at about 2000RPM but every 10 seconds or so it would stumble. If I let off the gas it would die. LTFT was at 0 at 2000RPM but STFT would flash up to 99% when it stumbled. I suspected the IAT but it read 42 deg. and did not fluctuate at all. Ambient temp was 39 deg.
I am now completely stumped. What else could it be? Thanks in advance for your help.

Second post:
Still stumped. After all the above I decided to replace the IAT sensor. I didn’t think that was the problem, but I was still stumped. Ran great for me for about 15 minutes. then it started showing LTFT in the 20’s again.But now the downstream O2 voltage on both banks was sitting at .7-.8V. That was the first time for that. I drove it again the next day and it died on me while just driving down the highway at about 60mph. Wouldn’t restart. had to call AAA for a tow.
A new code showed up. Low voltage from TPS. Ok. Now I start looking at the TPS. It shows open 19% at idle. Is that normal? I can’t find an answer to that so I assume it should be at 0% with throttle closed. So if the throttle is closed but TPS is telling the PCM it’s at 19%, does that make the PCM think it’s getting more air than it is? So it increases fuel trim. Huh. Order a new TPS.
Installed the new TPS today. Cranked right up. Drove it around the block. Shows 70% load under light acceleration. Down on power. LTFT 20%+ both banks. Downstream O2 .7-.8V both banks. Just over idle and pulling into the driveway it showed 65% load? Something is not right.

I refuse to replace anything else unless I have proof of what it is. I’ve tried not to just throw money at it. But that seems to be what I’m doing now.
I’m beginning to think the cats are no good. But how do I prove it? What about the Idle Air Control? EGR?

[KamiWolf93]

To test for exhaust restriction you can use an exhaust backpressure guage. It appears your engine’s running quite rich at .7 and .8 volts. Throttle position sensor values from car to car. It appears maybe there’s a wiring fault somewhere. Keep an eye and see if that code comes back. I would try resetting your cars ecu now you’ve changed some parts plus it’ll reset your fuel trims. Seems like the TPS is putting out the wrong voltage and affecting your trims as a consequence. Do you have a multimeter? Perhaps you could run a continuity test by backprobing the connector and the associated pins on the ecu plug. Running so rich won’t be helping the engine to keep running either, another thing you can do just to rule out vacuum leaks is pour water over your vacuum lines, if there’s a leak the engine will stumble. Focus on the TPS for now as that’s very likely causing your issues. Hope this helped

[KamiWolf93]

There may be a way to calibrate the TPS on ford also. Be worth a try to see if it helps.

[KamiWolf93]

An easier way with the multi-meter would actually be to put the ground lead on your multi meter to battery negative then use the positive to probe the connector for 5 volt reference.

[Lowridin67]

“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.

[KamiWolf93]

I’m not familiar with your vehicle. Although i’d agree your cat is showing a rich reading. Probably from the positive trims. Would definitely start checking for that 5 volt reference. ScannerDanner has a channel on youtube full of diagnostic information regarding lean conditions. Pour some water on the engine in different places and listen for a stumble, just to double check there’s no vacuum leaks. Or perhaps have it smoke tested by the mechanic. You need to have the key in the on position without the engine running in order to get the signal from the TPS connector.

[Lowridin67]

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.

[KamiWolf93]

What makes you think it’s the cats? Surely the 20% positive fuel trim is what’s causing a rich reading from the downstream sensor. Could try a different o2 sensor in place of one of the upstream ones and see if the readings change. I had this problem when one of my o2’s got damaged and would only put out low voltage. I would say swap them round if both banks read different trims but it seems that’s not the case. Do your trims return to 0 under load or do they stay positive?

[Lowridin67]

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.

[Schrodinger’s Box]

Just a thought, but when it goes crazy it goes completely mad, what we used to call full scale deflection. Have you looked at the earth/ground leads. It’s almost as if the earth/ground fails and then it tries to ground out through whatever is avaliable to pass current. This is just a wild guess without thinking about it too much.

Back in the day, there used to be a small earth lead on the back of the block, this went to the chassis. It was very much a minor item, but, leave it undone when doing a motor changeover or similar and the engine would earth out through the nylon lined clutch cable. This would go really hot and melt the steel clutch cable to the nylon liner. Technically this could be called a real bitch.

[Schrodinger’s Box]

It would’nt cost anything to pull the EGR valve, clean it and put it back. Ignoring everything else previous to this if it stuck open at idle the engine would stall. It’s worth a shot and things are getting desperate.

[Lowridin67]

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.

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