98 Expedition stalling when shifting into reverse

[Fitz98]

I have recently changed/rebuilt my transfer case and since the exchange, my truck stalls (most of the time) when shifting into reverse with foot on the brake and vehicle sitting still. 98 Expedition 5.4 4x4.
It is clear that it happens as the transmission engages into reverse gears and I can hear the engine start to ping a little and the RPS drop as it engages and sometimes it stalls and sometimes it will come back up to speed.
Once engaged, there is no problem with vehicle moving.
I should mention that my transfer case was removed for a couple weeks and as it was jacked up, about 1 quart of fluid slowly drained out of the rear of the transmission, because of the front being jacked up. I refilled and checked levels, all filled up now and at proper levels.
Also the battery was disconnected for that duration as well. I thought originally that the computer needed to relearn itself, but I have been driving for about a week now, so it has had plenty of time to relearn.
No check engine lights.
Any ideas on what the problem may be?

 

[eljefino]

Maybe it's your range switch needs adjusting? If the computer doesn't "know" it's going into reverse, it isn't ready to bump the idle proactively. So it's trying to do it reactively, when it sees the dip.

A tranny shop has a gizmo that tells you what gear the computer thinks the car is in. But you can check it yourself with an ohm-meter.

This is a mostly-ford thing.

I presume things work fine if the t-case is in neutral?

 

[Fitz98]

That is correct, no issues in N or when driving. Most notable when shifting into reverse.

 

[SwampSurvivor]

What if you shift into R from Neutral?

I had a loose linkage on my Taurus and it did some weird things with the needle on the dash.

 

[Roadkingnc]

Something is making the torque converter lock up, if the fluid level is correct there is a problem with the valve body, solenoids or hydraulic circuit leak

 

[Fitz98]

This sounds like it makes sense. I am wondering if it is possible that something got affected by being dry and not bathed in fluid during the 2 weeks that the fluid was leaking out while the t-case was out.
Could there be an air pocket or something? Is there any bleeding proceedure that should be done?
What about some additive or proceedure to free up a stuck valve?

 

[SHOZ]

I'd second or third the Transmission Range Sensor on a 1990's Ford.

 

[Fitz98]

Can you expand on the testing for that? Can you explaing how the range sensor would cause this condition?
Agin, what I find curious is how there was not a problem before doing the TCase work, now there is. I did not touch the range sensor at all during the procedure, but perhaps there are other ways it can be affected?

 

[Fitz98]

Just went to check all gears. Happens in L as well, so L and reverse are the worst to stalling or almost stalling point. The others I notice RPM's slightly decrease, but not enough to try to stall.

 

[punisher]

Before you spend a dime, reset idle strategy. MLP can be checked with any scantool with a data function.

 

[Fitz98]

So if I am understanding correctly if it was the range switch adjustment, the computer would think the vehicle is in neutral, so it does not adjust the idle speed on advance, even though it is shifted into gear?
Would this still make sense if it is happening mostly with Reverse AND L1 with almost the same condition?

 

[punisher]

Originally Posted By: Fitz98
So if I am understanding correctly if it was the range switch adjustment, the computer would think the vehicle is in neutral, so it does not adjust the idle speed on advance, even though it is shifted into gear?
Would this still make sense if it is happening mostly with Reverse AND L1 with almost the same condition?


Yes.

All I can tell you is based on a decade plus doing engine performance/electrical at a Ford dealership. Your problem is textbook idle strategy concern. Sometimes PCM's just have a tough time learning an idle. It is aggravated by vac leaks (especially on early 4.0 OHC engines).

If no vac leaks, get engine to normal op temp, disconnect battery, have a cup of coffee, or a beer. Give it 15 minutes to be on the safe side. Hook up battery. Switch AC to off, put gear selector in "P". Start engine, let idle stabilize (up to 30 seconds), foot on brake, cycle through gears, pausing each time to let idle stabilize. Repeat with AC on, fan on high to make sure compressor remains on.

Although minor, there is technically more drag on the engine in reverse due to increased trans line pressure. I can't see it having effect, but..........

The MLP/trans range sensor has alignment marks on it. The two hash marks line up in N. Except for the early MLPs, with the water intrusion/connector TSB, I never ran across a lot of problems. A bad MLP will cause oddball shift/lockup concerns a lot of the time.

 

[Warstud]

Check your fluid level again on level ground. Could be a plugged filter.

 

[Fitz98]

I have checked fuses and I cannot get test light to read power at the DTR Sensor Fuse on either side of the fuse.
Fuse 21. There are others with that same condition.
What could cause this issue?
Fuse is O.K, just no power at the fuse terminal

 

[Warstud]

See if you can drive the truck in reverse with the MLP unplugged.

 

[Fitz98]

What is the MLP? and where is it?

 

[Fitz98]

The alignment marks are lined up in N.
I just went out and started vehicle, and then unplugged sensor.
No noticable change, other than it seems to take a little longer for PCM to correct idle once in gear.
Is there a way to test this at the connector before replacing the part?
Is the concesus that it is a bad sensor?

 

[Fitz98]

Did reset as described, and rechecked tranny fluid levels.
Fluid was down about a quart, but there are no apparent leaks.
I had checked the fluids after finalizing th etransfer case install and brought them up to full.
Is it possible that it just took that long to fill in the fluid voids from when the fluid slowly leaked out of the rear of the transmission during the transfer case work?

 

[Krishna_R]

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