Hello everyone. I'm new here and need some help. Maybe just reassurance that I'm heading in the right direction.
I picked up a 97 f150 4x4. Couple hundred thousand miles. 4.6 automatic. Not the prettiest but, runs like a champ. And,I got it as payment for labor so, I wasn't passing it up.
Problem is that the 4x4 isn't working. I put a transfer case motor in it. No difference. I checked the switch on the dash and it's good. Checked all fuses and they are good. I'm thinking it's the GEM. The 4lo lights have been lit on the dash on occasion. The door chime works, when it decides to. No radio but, idk if it worked before or not. AND I discovered the weirdest damn thing I've seen on a vehicle yesterday... with it idling I hit the high beam lever(pulled it back to flash high beams) and the idle dropped momentarily and then revved to about 1500rpms and backed right back to normal after a couple seconds.
I'm gonna go nuts on this thing... Lol
Any suggestions? I pulled the gem to check the numbers and then realized how expensive they are and how hard the one I need is to find used. Anyone have a known good gem I could use to test with? Lol
Thanks in advance!

 

I don't necessarily believe the light switch/idle condition is related to anything else. It's just something that I noticed while checking things out.

 

Just to clarify... it was the gem module. I found one at a local u pull yard for $5. It was even the updated version.

 

Good deal!

 

Now I have four wheel drive but, when I went to test drive, in two wheel drive, I believe it's in limp mode. Won't go over 3,000 rpm. The truck sat for many months before I got it. Could bad gas cause that? It fits have some (quite a bit) of exhaust smoke when guy rev it while sitting in neutral/park. I haven't had a chance to talk to my buddy who was the PO to find out if it smoked before or not. I'm just curious what to look for if good gas didn't take care of it.

 

What color is the smoke and what does it smell like?

 

Looks to be black from what I can see. Can't get smell cuz by the time I get to the back of the truck, the smoke has dissipated. I'll give it another shot today when I get home to see if I can get a whiff.

 

It also stumbles and falls all over itself horrible when it's cold. Seems to get better when it gets warm. No check engine light had come on yet. Going to disconnect the battery to reset the system and start fresh.

 

Have someone else start the truck and hold your hand over the tailpipe and see what winds up on your hand and smell it. Black is usually too much fuel. You may have leaky injectors.

 

A limit like that on RPM's could be gasping for air, low fuel pressure, or plugged cats.

You said it sat for awhile, maybe a critter made a home in the air intake system, or debris before the air filter.

But like glc said it could have a leaking injector causing too much gas. The black smoke is unburnt fuel from either too much gas or not enough air.

 

Starting to think it's a transfer case issue. Finally got to take it out for a decent test drive and it made it about a half mile and stopped. No movement at all. Flipped the transfer case switch and got it to go again. Drive a little more and it happened again. Acting like it's stuck in 4lo and jumping out of 4lo but not into another gear but neutral instead.