Gen1 LS V6 - Intermittent stalling when below 1500 RPM

[W126LS]

Hello and thank you in advance for any help you can offer.

I have a 2000 Lincoln LS V6 with ~110k miles that is near mint condition, everything works perfectly. Except...sometime last year the car stalled at an intersection. The stalling continued intermittently, but has been increasing in frequency over time. There are no codes thrown, no check engine light comes on. When it stalls I can sometimes keep it running by pumping the gas pedal, other times the gas pedal has seemingly no effect. So I gave the car a full tune-up, knowing it was near that time anyway. New plugs, COPs, IAC valve, EGR valve, upper and lower intake manifold gaskets, fuel filter, etc. Same stalling issue. Car drives like brand new 99% of the time, then stalls at seemingly random when below 1500 RPM. The car always start right up, but continues 'choking' or stalling until I can get it revved above 2000 RPM for a few seconds.

Numerous trips to dealers finally resulted in them telling me they detected a fault in the fuel pump circuit, but they couldn't diagnose or fix any further. They suggested fuel pump, fuel pump relay, front ECM, rear ECM, or PCM. I found a leak around my jet pump seal as well so I went ahead and replaced both the jet pump and fuel pump. No noticeable difference, still the exact same stalling problem. I can't find any info on a front or rear ECM. Relay is fine (swapped with fog lamp relay, same problem). Fuel pump fuse is fine. How can I test to see if it's the PCM or something else like maybe the fuel pressure sensor or bad fuel injectors? Or, what should my next step be in diagnosing the issue?

 

[joegr]

Did you replace the PCV valve and the elbow? How about the o-rings on the IMRCVs?

I'd drive around with a good scan tool connected and log the sensors that could be related. You'll probably have to do it in sets, until you see the ones that change.

Some terms for you...
REM = Rear Electronics Module. This is what drives the fuel pump. It is behind the trunk light.
PCM = Powertrain Control Module. This runs the engine and tell the REM how hard to drive the fuel pump.
FEM = Front Electronics Module. This is not related to any engine/stalling issues.

You can send the PCM to SAI for testing.
Lincoln LS ECM / ECU Repair & Return - SIA Electronics

You can get a REM from a junkyard LS that had the same options as yours and it should work. (Note that you can't do this with the PCM without having a tool that can "marry" the PCM to the cluster and your keys. This is why it is better to get your existing PCM tested/repaired.)

 

[W126LS]

Did you replace the PCV valve and the elbow? How about the o-rings on the IMRCVs?

I'd drive around with a good scan tool connected and log the sensors that could be related. You'll probably have to do it in sets, until you see the ones that change.

Some terms for you...
REM = Rear Electronics Module. This is what drives the fuel pump. It is behind the trunk light.
PCM = Powertrain Control Module. This runs the engine and tell the REM how hard to drive the fuel pump.
FEM = Front Electronics Module. This is not related to any engine/stalling issues.

You can send the PCM to SAI for testing.
Lincoln LS ECM / ECU Repair & Return - SIA Electronics

You can get a REM from a junkyard LS that had the same options as yours and it should work. (Note that you can't do this with the PCM without having a tool that can "marry" the PCM to the cluster and your keys. This is why it is better to get your existing PCM tested/repaired.)

Thanks for the quick reply!

I have changed the PCV valve and elbow. Elbow ripped last year and I change the valve while I was in there. Haven't checked the O-rings on the IMRCVs yet, but I certainly will. Great info on the control/electronics modules. I'll post my results once I get my hands on a decent scan tool and do some testing. Thanks again!

 

[W126LS]

I got my hands on a scan tool and hooked it up to torque pro. When the car stalls, the STFT jumps up above +30. Test results showed 'Not OK' for these two: 'TID: $30 CID: $12 - Max: 512, Current: 65,535' and 'TID: $41 CID: $12 - Max: 15,360, Current: 65,445'.

Any suggestions on how to proceed, what sensor data to look at, or what tests to conduct?

I'll be installing new o-rings on the IMRCVs tomorrow and will update the thread as to whether or not they made a difference.

 

[W126LS]

I replaced the o-ring on the IMRCV (IMTV) yesterday and it did make a noticeable difference, as I gained about -1.5 psi of vacuum (went from around -23.5 to a steady -25). The STFT seems more stable, but still bounces back and forth a bit. The car drove great last night, but then stalled again this afternoon. Moving on to the REM. I've found several for sale with part numbers that match mine (YW4T-13B520-AA), is that sufficient? Or will it potentially need to be reprogrammed by a dealer?

Thanks again for any help you can offer.

 

[joegr]

Shouldn't need any programming.

 

[W126LS]

New REM installed. Made no difference, same stalling issue.

I found the service guide for diagnosing the fuel pump circuit and it mentions two possible culprits, aside from the REM, that should be tested before replacing the PCM: the IFS (Inertia Fuel Shutoff) switch and the FPDM (Fuel Pump Driver Module). I'd like to perform the specified diagnostics on both before sending off my PCM. I tracked down the IFS switch, located below the hood release latch (near where driver's left foot rests).

What I haven't been able to find is the location of the FPDM. Anybody know where it's located?

 

[joegr]

...What I haven't been able to find is the location of the FPDM. Anybody know where it's located?

It's inside the REM (really, a part of the REM, not a separate component inside).

 

[W126LS]

Thank you. I looked closer at the service manual and it does indeed mention that in a note, as shown below:

Note: For LS6/LS8, the FPDM functions are incorporated in
the Rear Electronics Module (REM). In the following steps,
if directed to perform an action with the FPDM, complete
the action with the REM. Refer to the pin numbers in the
beginning of this pinpoint test.

 

[tireman]

I had the same problem,,solution was an air vacuum leak, check boots going to pcv from throttle body, the IAC valve is another culprit, i;m on my 4th valve, also check inside throttle body for carbon buildup. once i replaced main vacuum lines with good rubber hoses, no more problems.