1994 6.5 Hunting For Gears

[94blue]

Hi All,
Had my '94 suburban 6.5 since 1998 w/o any trouble except for the PMD. Last weekend it was running fine and all of a sudden riding along about 50mph the trans shifted from OD to Drive and started "hunting" back and forth between the two.It never went away and is parked in the driveway at the moment. Has something worn out or could it be electrical related to the tach??
Don't know where to start.
Truck has 258K on it, 4WD.
Oh, and a check gages light came on a week or so ago???

Any suggestions welcome.
Thanks,

[moondoggie]

Good Day!

Get the codes. There can be codes that don't light the SES light.

"Check gauges" light (I think) means the PCM thinks the oil pressure or coolant temp is out of range, so you should check your gauges.

This is a weird combination. I can't wait to hear what's causing your problem. I'm tempted to say verify/fix all grounds, as these problems don't sound otherwise interrelated.

Blessings!

[94blue]

Hi Moon,
Thanks,
I don't think they are realated but the shifting thing is a ??.
I need to research the code reading again. It's been a while.

Thanks,

[a5150nut]

On your 94 you use a jumper between the two upper right terminals in the connector just below the stearing columb. Turn the key on and watch the service engine light. Count the blinks in groups of three. 1, 1 2 is all clear, any others record and post.

[94blue]

Hi 5150,
Mine too is a 94, 4x4, w/ all stock stuff. 258k or so. Would the codes show a trans problem?
I'll look for them this weekend anyway and see what pops up.
Thanks to all,
94blue

[94blue]

Just a FYI ,
Drove this suburban for 2 hours around town today and out to the beach and back, Highway, and up to 80mph on highway and no gear hunting?????

Looks like an intermittant thing which really sucks for troubleshooting.
Ran out of time to check for codes but all seemed normal.

Thanks to all.

[moondoggie]

Good Day!

Yes, there are tranny codes, & yes, you might set some that don't light the SES light. The problem is, after a certain number of restarts (50?), the codes go away, so you might want to get on this, on the odd chance that the PCM caught anything.

Blessings!

[94blue]

Hey Moon,
Thanks for the input. I'll check the codes hopefully this weekend. Luckily I have a work truck so the 94blue is not the primary vehicle.
I'll get back with any codes or misbehavior ASAP.

Thanks agian,

[carymc]

I have seen your problem posted on other threads in this forum. I have a 1994 K2500 which started shifting between OD and Drive in 2003. The trans shop installed a new/reman transmission ($2800) and had the same problem with the new one. The ended up installing ground jumpers to several places which stopped the hunting problem. I saw one post which pointed to the trailer wiring as the problem, another the speed sensor was dirty.

After the transmission shop stopped the hunting with ground wires the check engine light comes on when the transmission shifts into drive from 2nd. Today 3 1/2 years and 40K miles after trans. replace it would not up shift into drive. I drove to parts place to get ecm, which they did not have. I started truck again and everything worked ok. I believe your problem is electrical. Maybe ECM or TCM or speed sensor.

[94blue]

Gotta love the 94's
I have'nt gotten around to fixing the wiper gremlins, extra relay for the headlight switch, loose fuse clips for the tail lights and dash lights, etc.
At least it it does'nt sound like a tran. just some greasy wire tracing. Is there a list of the grounds that are scattered around the vehicle?

Thanks to all,

[ronniejoe]

Did your transmission find its gears yet?


Couldn't resist! :D

[JohnC]

Ya know, a lot of folks mistake the TCC engagement/disengagement for a shift. It could be dropping in and out for something as simple as a bad brake light switch...

[94blue]

Hi guys,
Been out of town for last week. 2-21 saturday hunted for gears agian. 2-22 sunday it did'nt??

I had to leave town and just got back. No chance to check codes yet. I'll need to go through my troubleshooting guide to do a "refresher" on code checking.

I asked before if there is any "list" of grounds that can be looked for besides the obvious.

I'll try to get on it this weekend.

[94blue]

Just thought I would finish my thread.
My 1994 is a weekend driver or for fun these days. Company truck gets most duty (w/ free gas, thank gosh).
Any way the "hunting for gears" thread got me looking for grounds. During that period I had the 4year old batteries fad and die. Replaced both. During all this (weekends only), I checked any ground I could find and most seemed visiblely good but cleaned anyway. Wiggled the tranny position plugin's, etc. Also found the temp sender for the water temp pump manifold had corrodedd and was not really doing anything. Replaced that and POOF, the truck cranked normally but idled slower on startup and when took out for the weekend exercise the gears shifted normally all the way to OD. ??????????????? That had not happened for months, I'd just been too busy to really dig into the problem.

Not sure if the gounds got fixed. Not sure if it was a battery related issue?

All is good for the last 6 weeks and runs like a champ.
It's a love hate thing for sure.
Thannks to all and till next time, Comments please!
94Blue out!

[Robyn]

Howdy

The 94 feeds power to the truck off of the RH battery.
There is a small cable that ties into the large + cable and snakes down around the engine and then back up and into the junction block on the firewall right over the HVAC unit

This cable supplies all the power to the truck (other than the starter)
The side terminal cables can and do often get all corroded inside to the point that they will fail. This is usually under the red jacket and in the cable core where it can't be seen.

Now there is more.
The alternator ties into the LH battery which then feeds the cross over cable to the RH side.

The ground cables are notorious for going south and failing to provide a good connection.
This is commonly at the attachment point on the engine. I have seen the ground on the LH battery fail resulting in very poor charging and also no added power from the battery.

The end result is all sorts of troubles including shifting DTC's and such not counting slow cranking and balky starts.

The best thing you can do is build a set of new cables with soldered on copper eyes using some fine strand welding cable (#0 for the mains and a #4 for the truck feed line)

I recommend rerouting the feed line from the current position down under the engine to one that runs directly from the battery across the inner fender and under the air filter around the coolant tank and into the junction box.

This is very easy and will use far less cable.

The electonics on these trucks DONT like goofy grounds and screwy voltage.

I have been down this path witha few of these trucks and its well worth the time and a few $$$$ to do it.

Even a fresh set of cables from the local NAPA store will help the cause a lot but they are not near as good as a custom set made from welding cable.

Be sure to replace the little cable from the alternator to the LH battery too with a healthy sized one (#4)

Adding a fresh engine to chassis ground strap is not a bad idea either and be sure you get a good ground strap from the body to at least one of the batteries.

All the lighting and other equipment ground to the body or the frame and if the return ground is poor all sorts of nasty issues can pop up.

The factory had a ground strap on the RH battery that connected to the inner side of the fender, be sure you replace this with a good little strap.
A #8 is plenty on this one.

Good luck

Robyn

[94blue]

Thanks for the input Robyn. I appreciate the detailed input over all the posts I've seen from you and many others. The next thought is for the engine section, but I've seen you reply to my next question before.
Is there an easy way to see if the coolant I'm losing is from a hose leak or through the (gasp) heads/block?

Thanks
94Blue
4x4,loaded,stock,255k miles,6.5TD