97 Auto 4x4 slippage- PCM question

[sk1er17]

My buddy has a 97 sport with electronic t-case. while in auto the 4x4 wont engine and he can spin the rear tires. He did do the brown wire mod and didnt use a relay, so i think he may have messed up his PCM. (the switch he installed has an LED, it used to get bright when he hit the gas- now it just blinks irradically)

So i have a 98 sport that i put a manual t-case in... both of us have SOHC's. Can i swap in my PCM or do i need one from a 1997?

 

[Jefe]

The PCM has nothing to do with the Auto-4x4. That is the job of the GEM and other external relays.
And before trying to swap out the GEM I would check all of his wiring (stock and modified) and fuses so that you don't blow up a second one (assuming it is the GEM)

As for whether the GEM will swap out, I do not know. I do know you have to have similar options between trucks (power windows, etc) but I wouldn't be surprised if the GEM changed in 98

 

[sk1er17]

yea you know what, that was a brain fart right there- i meant to say GEM...

Thats a good point about checking the rest of the wiring. I may also hook the scanner up at work- i remember there being a KOEO self test that would diagnose such a problem...

 

[gijoecam]

The GEM has nothing to do with the Control Trac automatic engagement. The Torque On Demand relay controls the clutch engagement in automatic mode. It's possible that the TOD relay went south or the connections on his switch for his brown wire mod are bad. Either way, it's got nothing to do with the GEM.

It's also possible that the clutch itself is not grounding properly.... that would prevent the 4wd from working properly. If he engages the 4wd with the knob on the dash, does it work?

IMHO, there is no need for a relay on the brown wire. I've got a 15A fuse on mine, and it doesn't blow when engaged full-time, so the 30A switch I'm using for it won't melt down.

-Joe

 

[sk1er17]

Yea we disconnected the switch from the brown wire mod, reconnected the wires and tested everything out. the GEM was working fine and not throwing any codes.

we lifted the truck in the air and the front tires would engage in auto/4hi/4low so we know its getting some power. I think it's just a matter of his clutch slipping.. it is a used transfer case and we're not sure of the abuse it had before we got ahold of it.

I just sold my truck (i think ), so if the guy doesnt want my spare t-case we'll most likely throw that in there.

 

[gijoecam]

If it was a clutch slipping, it should slip when you engage 4 hi as well... When you flip the switch to 4 hi or 4 low, the GEM bypasses the TOD relay and sends power directly to the clutch coil.

If it only slips in auto, I'd have to say that the TOD relay is going south.

Where exactly did he splice the wires for the brown wire mod? Right or left side of the stereo opening or under the seat?

-Joe

 

[sk1er17]

it slips in all modes- thats why i think its the clutch

 

[gijoecam]

Aaah, indeed. It'll either be the clutch, or possibly a coil grounding problem, but I'm not entirely sure it's worth trying to troubleshoot them if a replacement is available.

Here's two more thoughts: Double-check the plug on the t-case for a solid connection. Second, maybe try bypassing the brown wire all together and run a solid 12-v jumper (I'd use a 15A fuse just in case) direct from the battery to the brown wire connection on the t-case. That'll ensure it's not a wiring problem.... I'd hate to see you guys replace the t-case and have the same problem.

Let us know what you find.

-Joe