No 4 low

[Cletus135]

I have a 99 4x4 xcab, former 4.0, with a 2000 mountaineer 5.0, 4r70w, and 4406e. I've had the truck on the road going on 3years and the only issue I've had is no 4 low. Shift motor is good, just no signal to engage. 4 hi works, but when it is engaged I have a random engine miss, actually a pretty bad bucking sometimes. on one occasion, it actually killed the engine at 60mph! Never get an engine light from it though. I'm thinking either the pinout from the 5.0 ecm is feeding some voltage where it shouldn't, or my GEM and/or 4wd module are the culprits. I'm ready to start digging into this being winter is coming, figured I'd see if anyone else has run into any issues like this after the swap. Thanks.

 

[franklin2]

Going into 4 low has special requirements. I don't know them all, but one of them is no signal from the speed sensor (you are stopped) and I believe you can't be in gear either, neutral would be a safe bet. There is a switch that verifies what gear you are in. The factory manual will have all the details, but I would verify conditions are all met for a shift to 4 low.

 

[RonD]

Welcome to TRS

1999 Ranger did use the GEM as the 4x4 Controller, and GEM and the Dual Relay box are working if you can shift to 4high and back to 2WD

GEM does need to see 0MPH, foot on brake pedal, and Transmission showing NEUTRAL before it will activate the shift motor for 4Low

Diagram below
Ignore electric clutch and PVH wiring as these are not required for operation of 4WD system and can't prevent it from shifting

Brake pedal sensor is part of brake light switch(but not for brake lights), and used by a few things so I doubt its the issue and wouldn't be touched in a V8 swap
I assume speedometer works, no P0500 code, and no changes to speed system?
So that leaves "In Neutral", not Park, Neutral
That is done by the GEMs Red/white wire(pin 22) being grounded by the DTR(transmission switch), pins 7 and 8


The GEM has no operational connection to Engine Computer(PCM) and PCM has no interest, or anyway to tell, if the vehicle is in 2WD or 4WD, it doesn't matter to run the engine
So being in 2WD or 4High should not effect engine operation
If you had crossed wires or sensor errors PCM would set codes and turn on the CEL(check engine light), for sure, at that time

Because Explorer PCMs got speed signal from the 4WABS unit not the GEM like a Ranger did, some swaps bypassed GEM for speed signal, no speed signal at GEM would disable 4Low