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Old 01-23-2015, 05:19 PM
sundvl76 sundvl76 is offline
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5.4L Lean code head-scratcher

Vehicle is a '99 F150, 5.4L with 90K miles. Located in Central TX.

Background on the problem, I'll try to be brief: Apprx. 2 yrs. ago, fuel pump went south, had pump and check valve replaced. Fuel filter had been replaced not long prior to that. Sometime shortly after that I began getting a funky idle condition under specific conditions, i.e. winter-time or early spring, warmer than normal day (70F or above), hot-soak for 5 - 20 minutes. Barely idles, up-and-down on the rpms, but after approx. 1 min. it runs OK. Have not had a problem during colder weather, NOR during the summer (90 - 105F). Seemed to me that for some reason the winter blend on a hot day gave trouble. No MIL, no codes show up.

This week we had a day with temps up to 81F, and it did the same thing, BUT after a few errand stops, it started hiccuping while I was driving. This steadily progressed to being almost undriveable, like turning a switch off and on - surges, then almost dies, surges, almost dies. Load conditions don't seem to matter, as it will do it on a downhill coast. Had to limp home in "2" keeping rpms around 3K. Lumpy idle would not clear up either.

Next AM, it was much colder (40F), and it started and idled normally. I have not needed to take it out since, so I don't know what will happen once it warms up.

This time the MIL lit up, and it tells me there's a lean condition on both bank 1 and bank 2. The freeze-frame was taken at idle, and shows a short-term fuel trim of -18.75 on both banks, but a LTFT of +25 on both banks.

This leads one to think there is a severe vacuum leak of some sort, or a fuel delivery problem. I've inspected the hoses I can see, but all seem OK. MAF was cleaned not long ago as routine maintenance. Pulled the vacuum hose from the FPR, and it was dry, no sign of diaphragm leakage. (I know that's not definitive, but I'd think with this severe problem it would show up.)

From what I've seen on other sites, the 5.4L commonly has a problem with the PCV elbow connex on the back of the intake manifold, and also has a common issue with the MAF, as well as intake manifold leaks.

I could see the MAF being suspect if it were just running badly, but still drivable, and same with the intake manifold. The PCV elbow is a good possibility, but there's a lot of work involved to just "take a look". As far as I can feel it, it does not seem broken off, at least.

So, I'm looking for suggestions as to what to immediately check the next time it goes wonky. (Warm weather predicted for next week.) I know I can unplug the MAF to see if it clears the lumpy idle, but what else should I suspect or test at the time?

Thanks!
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Old 01-24-2015, 07:18 AM
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If you have or recorded any DTC's those would in infinitely helpful here...

The PCV tubing elbow you mention is almost the first culprit when the Lean Bank's 1 & 2 is noted. Regardless how much effort it takes inspecting and/or replacing that fitting is vital to beginning to solve your issues.

If your engine has an IAC and its defective or has failed that too should trigger a DTC however that's not always the case, still a big possibility.

Let us know the results of checking the PCV elbow.
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Old 01-24-2015, 08:55 AM
sundvl76 sundvl76 is offline
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Originally Posted by JWA View Post
If you have or recorded any DTC's those would in infinitely helpful here...
The DTCs are the usual P0171 & P0174, no other codes triggered. I'll start digging into the PCV connex, thanks. The IAC is in the same area so that can be at least cleaned at the same time.
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Old 01-24-2015, 07:12 PM
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Let us know the results of checking the PCV elbow.
Today I pulled the throttle body off to inspect the PCV line. There was nothing visually wrong with the fitting at the back of the intake manifold - it was still flexible and functional , but given the time involved in getting to it, I picked up and installed a new assembly from the dealer. Found 3 other vacuum lines that were deteriorating, and, while none of them were cracked or obviously leaking, I replaced all that were flaking.

I've also checked the resistance on the intake air temp sensor and it is reacting to varying air temps as designed.

Given that there don't seem to be any major vacuum leaks, I have to conclude that some component is failing. I'll check the voltage readings on the MAF, and also fuel pressure when it is back together & running.

While I have the throttle body off, I'll also clean out the IAC valve and check it per the Haynes procedure.

Any other ideas??

Still scratching my head. . .
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Old 01-25-2015, 06:52 PM
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Fuel pressure question

Throttle body, hoses, etc. back in place. Truck starts and idles just great at this point. Next I moved on to utilize my newly-purchased fuel pressure gauge, but ran into somewhat of a quandary: At idle (engine warm fwiw), pressure indicates 31psi. This is on the low end, as specs say 28 - 40psi is the range for this vehicle. Disconnecting the vacuum hose from the regulator brings the pressure up to about 42psi, as expected.

The puzzle is, if I shut off the engine with the vacuum hose connected to the FPR, the pressure immediately drops like a rock to zero; if I shut off the engine with the vacuum hose DISconnected, the pressure remains at about 40psi for at least 5 minutes.

The Haynes manual is unclear as to under which condition the reading should be taken.

So, what have i learned?? Is there an internal leak or is this normal behavior? I've read that a symptom of an internal leak is hard starting/long cranks, but I don't have that problem.

(Further, I connected a vacuum pump to the FPR and tested with the engine running: Result, higher vacuum = lower fuel pressure, as designed.)
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Old 01-26-2015, 07:38 AM
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When you shut the engine off and FP drops have you tried immediately turning the ignition switch back on to check for residual FP maintained in the lines?

Does the truck start, idle and drive as normal?

Unfortunately I can't offer anything helpful past this and don't want to misdirect your process here. I will say Haynes and Chilton manuals typically aren't very helpful when getting into diagnostic procedures such as this.

Best of luck---hope its nothing serious.
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Old 01-27-2015, 12:09 PM
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Originally Posted by sundvl76 View Post
The DTCs are the usual P0171 & P0174, no other codes triggered...
I just started getting these two codes as well, but my truck is running and idling just fine. I replaced the cyl-1 coil pack a few weeks ago, but it's been running great since then.

Edit: after a bit of research, it appears that my MAF sensor may need cleaning.
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Old 01-27-2015, 06:57 PM
sundvl76 sundvl76 is offline
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Originally Posted by FurdTurgeson View Post
Edit: after a bit of research, it appears that my MAF sensor may need cleaning.
From my research also, I have seen that is a possible trigger for the lean codes. I've cleaned mine a couple of times very recently, but it made no diff in the hot-soak-idle problem.

As it happens, I was doing some electrical checks on my MAF today, and it appears that there is an open circuit across the signal and ground pin sockets, which - if true - would mean a bad MAF. Not unheard-of on these trucks. Need to do further checking; I don't know if it is possible for that condition to exist on my engine and not throw a code.
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Old 01-27-2015, 06:57 PM
 
 
 
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