Need Help Diagnosing a Lean Long Term Fuel Trim

[bobinyelm]

2003 Ranger 4.0 liter 64,000mi since new

I posted a question a while back but didn't have all the PIN readins (Live Data) to assist in diagnosing for a LEAN BANK 1 & 2 Long Term Fuel Trim codes (P0171 and P0174). Bank 1 and 2 LTFT are BOTH 25

I now have every reading imaginable that the scanner could provide, so if any of you could help me diagnose the problem I would most appreciate it. I photographed the screen and can list whatever numbers you might think helpful.

Let me start by saying that the truck runs well, with no discernable poor running conditions under any circumstances. I sprayed EVERYTHING with flammable brake cleaner to try to find a possible air leak. With only 64k on the truck, all lines (plastic/rubber) look GREAT, and no leaks could be found.

Erasing the codes and running the truck takes maybe 500mi for the codes to return (but the LTFT readings are immediately evident). The STFT is also 25% now (the graphed readings bounce between 22-26).

Readings: (All taken at idle, 55 def F at 300ft Above Sea Level)

LTFT #1 25%
LTFT #2 25%
Manifold Pressure 0 psi (shouldn't it read atmospheric, or a vacuum like 20 or so in at idle?)
Mass Airlfow Status: "No Error"
Mass Air Flow 5.1 gr/sec or 0.66 lb/min
Mass Airflow Volts: 0.91v
Baro Pressure: 13.38psi
Engine Misfire Detected: NO
EGR Status: "No Error"
EGR Evaluated: YES
EGR Sys Eval Test Ready: "Not Ready"
EGR Vac Regulator Fault: "No Error" (Is this the DPFE?)
STFT #1 29% +/- 4% variable
STFT #2 28% +/- 3% variable

I DO now have a DTC P1000 OBD Readiness Test Incomplete which I suspect is just because I reset the previous codes, and the Readiness Monitors have not completed their drive cycles.

Questions/Comments/Ideas uch Appreciated?


Thanks,
Bob

 

[Dirtman]

You don't have a MAP sensor so a reading of zero would be a good thing. Its just showing a value for something that isn't there, ignore it.

Also P1000 code is nothing, ignore it.

Check fuel pressure, should be 65psi. Lower than 55 and your pump is failing or a clogged fuel filter is causing the lean condition.

Inspect your exhaust manifolds and downpipes. Any leak in the exhaust system before the upstream o2 sensors can cause a lean reading. ( this is unlikely since its an issue on both banks but still worth checking ).

I would also do a smoke test, the "spray test" works but its easy to miss something. Smoke goes everywhere. You can make a nice DIY smoke tester for about 15 bucks.

 

[bobinyelm]

Absolutely not a hint of exhaust leakage. I used a tube in my ear moved everywhere looking for exhaust or vacuum leaks by sound. The vehicle, which was purchased 2mo ago, was owned by a guy that even refused to drive it in the rain (in Seattle that's tough which is why he only put 4300mi/yr on the vehicle I guess) and kept it garaged, so not a hint of rust or any dirt on the exhaust manifolds you can't scrape off with a fingernail, so no corrosion/rusting issues causing leakage. I don't know why he owned a truck he wouldn't get wet., but the benefit was it looked nearly showroom with only dealer service (even bought Ford batteries).

I have a shop owner friend with a smoke machine. Usually he checks the Evap system, but in this case I guess we'd try to block the intake pipe with foam and use a tube stuck into the foam to pressurize the intake system while plugging the exhaust pipe (so as not to lose smoke pressure through an open intake valve?).

As you say BOTH banks are involved, so whatever is causing has to be common to both banks (hence the intake plumbing).

I hear you on fuel pressure, but I doubt it's a clogged filter as it would likely starve for fuel or misfire at 75mph as evidence of clogging as consumption is so much higher than at idle. I don't have a manual, but hopefully there is a Schraeder valve for checking fuel pressure on one of the fuel rails on this engine (I didn't see one)? The scanner had a Fuel Pump parameter but it just said "No Fault," which I guess it meant it was operating

Strange, when I looked online, it said Ford din NOT build a FX-4 model in 2003, only the Edge, but this is an FX-4. Hmmm... I was also surprised the towing limits showed only 3600 pounds for what looks like a beefy vehicle. With a 4.1 axle ration, it should have enough torque. Maybe the brakes are deficient for more? Just curious...

Bob

 

[Dirtman]

There is a schrader valve, its on (I think) the drivers side fuel rail usually in a very inconvenient place. The computer can only tell that the fuel pump is on it has no way to measure the pressure its creating so there is no PID for that, must use a mechanical guage.

 

[bobinyelm]

Thanks, I'll check tomorrow. I gave it a cursory look, but I didn't poke around.

Given all the useless things that are often monitored, I would think a fuel pressure sensor would be useful. I have a friend with a MB ML350 that had a MIL code of "Right rear door window switch sticking". I'd much rather have a fuel pressure sensor monitored

 

[Dirtman]

I agree that a fuel pressure PID would be handy BUT, the sensors are there for the computer's use not for daignostics. Fuel pressure is really just redundant information as far as the computer is concerned. The proper operating fuel pressure is known to the computer, if the fuel pressure varies off of that the o2 sensors will see the difference and adjust the injector pulse width to compensate. (Pressure too low and the injectors need to open longer and you get a lean code). The computer doesn't need to know why there's a lean issue, that's your problem to figure out lol.

 

[adsm08]

On the passenger side of the intake there is a connection for the pcv hose right by the throttle. Inspect that elbow. It is a common point of failure that will set lean codes.

 

[PetroleumJunkie412]

I'm having a similar problem with my 2011. Fuel pump was getting lazy, so I replaced it with a massive assed aftermarket pump in anticipation of a supercharger. Since the pump, I no longer have lean codes.

However, I noticed on forscan that I have some really screwy MAP readings. My engine is also knocking at low rpm load, which shouldn't be possible due to a knock sensor.

@snoranger and I have been troubleshooting behind the scenes. Seems that the SOHC uses the egr system to determine MAP pressures (my vac gauge is reading 21.5-22 in/hg, pcm is reading 8-12). Don't know if your year has a similar sensor setup.

I'll update as parts come in.

First paragraph :

 

[Dirtman]

Your EGR valve is a computer controlled electric motor not the ole fashion vacuum valve. The computer is using that calculation to control the EGR valve, it has no bearing on the fuel trim.

 

[bobinyelm]

OK, problem discovered.

I managed to bend my hand around and got my fuel pressure gauge on the Schrader valve expecting to see low pressure, but it was 65-66psi so went over to my friend's shop to use his smoke machine, but he thought maybe the IAC motor gasket was leaking cuz the idle was hight a about 1050 rpm, and while the cover was off the top of the throttle body he shot some brake cleaner where I couldn't get earlier and found a small crack in the plastic intake manifold runner set. When the engine was cold, no crack, but let it sit and idle a while and pull on the trottle body for more leverage, and the brake cleaner made about a 75 rpm higher idle speed.

So it looks like I'll be replacing the runner set. About $200 so not too bad, and it looks like a reasonable job.

I would have thought it would have taken more that such as small crack, but any crack is too big, so we'll see if that fixes it I gess.

Thanks for the replies and ideas-
Bob