Crazy acting 98 Z71

[rcolley]

The last two days on my way to work my speedometer has been jumping all over the place, the transmission shifting in unusally ways, and the abs acting unusual. It started yesterday when the cruise wouldnt stay set. It has progressed to where the truck is barely drivable. My first thought was a computer problem, but I dont really know and dont want to throw parts at it. Any ideas. Thanks. Its a 1998 k1500 z71 with 5.7 and 4l60.

 

[Scrufdog]

first thing I'd figure is the VSS. Thats the common component of the trans, speedo and abs

 

[rcolley]

That makes sense. Im not exactly sure where it is. Im guess its in either the transmission or the transfer case. Seems to also work with the cruise. All these systems seem to be very interrelated

 

[1997chevydriver]

Vss is on the output shaft of t case

 

[Amp24 7]

If not vss I'm willing to bet it's the wiring harness that runs under neath the steering wheel. There's a wire in there that runs power to the transmission and if it goes bad your trans goes to limp home mode.


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[tattooed4life]

Check to see if it threw any codes when it went crazy on you. Possibly help you narrow down the problem.

 

[sbdblyss]

I had the same problem and put a lot of money into replacing things. My speedometer would jump and shifting would be crazy. It worsened and it started backfiring and missing, running hot and stalling out. Sometimes it would run fine. I replaced the distributor twice, burned through 3 coils, replaced the battery and alternator, all vaccum lines, most sensors, new throttle body, new computer and chip, and the drac. No luck, same problems. Finally a friend reached up to wiggle the wiring harness the runs the the front of the intake manifold and the truck shut off. It was the ground wire running from the harness to the front of the intake manifold. There is an alternator support bracket that mounts to the manifold and it had slowly backed out. The ground is attached to the same bolt. Everything runs perfect now. Check your grounds! It may save you hundreds of dollars. If you want to see how my truck was behaving, search YouTube for "1995 gmc sierra acting odd." It is under my youtube username sbdblyss. Good luck!

 

[sbdblyss]

Sorry, it's "1992 gmc odd behavior" on YouTube. I deal with a 95 and a 92 and I get them mixed up.