'95 5.7 auto - non working tach & speedo

[PikesPeakMtnMan]

I have a 1995 GMC 1500, 5.7L, auto, 4x4.

A lot of the times I start my truck the speedo and tach and the little light showing which gear I'm in (P, R, D, etc) don't work. If I shift into reverse it shifts fine but it "clunks" into Drive. When I drive, the truck accelerates like the parking brake is on (seemingly more RPMs than necessary and very little speed to show for it) and the shift points seem off (though the engine doesn't rev noticably or anything). Occasionally, while I'm driving everything "magically" starts working normally again.

All the other gauges and lights work normally and not only are all gauges within normal ranges, there are no odd sounds, smells, leaks, etc.

I haven't noticed any correlation between cold vs. warm engine, ambient temp, etc, etc.

Most of the time when I start my truck and notice the problem I will... A) not drive...B) turn it off and restart it until the problem "goes away"...C) drive anyway (because I have to get back to work or some other "urgent" circumstance) and hope for the best.

This is a new problem for my truck. However I have some problems that I haven't fixed yet because they are mostly nuisances and not major issues. I doubt any of this caused my current problem but I'll explain just on the off chance it is related.

I have what's been explained to me as a "short on the ground side of the circuit" somewhere deep in the electical bowels of my truck.

--My 4-way flashers will drain the battery in about 5 minutes if the engine is off...

--My interior dome light doesn't work via the doors, only with the manual switch, my cargo light doesn't come on unless the dome light is also on. (I put in a LED hi-mount brake light and realized the cargo light worked just as it should but the brake light would flash and quickly fade out when the brakes were on.)...

--I notice LOTS of voltage draw with multiple accesories going (radio, headlights, fan blower on HIGH, windshield wipers all at once)...if I keep my blower motor on anything but HIGH then I'm okay.

So far everyone I've talked to about my tach/speedo problem has been stumped so hopefully someone here can help me.

[Jeremy-WI]

Sounds like your ignition switch might be bad, when it acts like the parking brake is on try manually shifting into first and see if its better. There have been quite a few bad ignition switchs(electrical portion) and the symptoms are usually no shifting, no PRNDL, no tach and no speedo along with a few codes. Another thing to check when it acts up is voltage at the trans fuse in the interior fuse panel, it should have the same voltage as the battery and a test lamp may be a better indicator since corrosion or dirt on the ignition contacts may show the same voltage but not be able to handle the amp load

[PikesPeakMtnMan]

Thanks....shifting into 1st does help with the acceleration.

I was also told today that it could possibly be one of the two speed sensors in the transmission.

I don't have a code checker but will probably pick one up soon since the two places I went to today couldn't check the codes because there are too many newer trucks out there now and no one has the "old style" plug-in

Another couple things I've noticed is the "check gauges" light comes and goes. It generally is on when I'm stopped but goes off once I start driving. I only noticed this a couple nights ago since typically my view of it is blocked by the steering wheel so I don't know if it's always been doing it or not.

The other thing is my engine RPMs go up and down. Typical idle speed in gear is 600 RPM and 800 idling out of gear. Every couple seconds the RPMs drop by 100 and then go up 200 before going back to normall (ie. idle at 600 at a stoplight then drops to 500 then goes up to 700 before returning to 600) . Just FYI, I'm pretty sure 600 RPM is low but it's been like that since I bought the truck and never posed any problem.

[Jeremy-WI]

Since you have a 1500, you should have the 4L60E trans and it has only 1 speed sensor and if it failed you would likely have only first gear, the computer controls shifting and if it doesn't see anything from the speed sensor it won't shift out of first.

The revving could be caused by an A/C problem if you are low on freon or have the A/C pump clutch disconnected. The A/C will try to run with climate controls in A/C or defrost mode.

Do a search on checking OBD 1 gm codes and you should be able to find info on how to use a paperclip to check the codes, if its a ign switch or trans wiring problem, the codes should all be solenoid electrical and I think OBD 1 had one for low voltage

[PikesPeakMtnMan]

OK, thanks....I know just what happens when the speed sensor is inoperable because last time I took it to the mechanic they forgot to reconnect it.....my current problem is not like that.

I'll try the paper clip method you suggested, thanks.

Well, I did the paper clip thing (info from troublecodes.net) and got a Code 12 (1 flash, pause, then 2 flashes) which apparently means "system normal" (I double-checked and counted the code 3x)....so I guess I'm back to square one...??

[Johnny Mullet]

You could also have a ground issue. Start with the battery connections and then follow the grounds and make sure they are good. Was there any recent work done before this problem showed up?

[will6158]

I have the same truck with the exact same problem and for the life of me can't figure it out, my problem started happening after i changed my alternator and serpentine belt, if you figure it out i would appreciate it if you let me know, thanks

[cudock]

Originally Posted by Johnny Mullet

You could also have a ground issue. Start with the battery connections and then follow the grounds and make sure they are good. Was there any recent work done before this problem showed up?

{{{{{{{i have the same prob, changed speed sensor once, and it worked for prob 3,4 years, started again this time ignition switch, changed it, worked about, 2 months, now same prob,could something knock out the switch?

[Schurkey]

Originally Posted by PikesPeakMtnMan

--My 4-way flashers will drain the battery in about 5 minutes if the engine is off...

--I notice LOTS of voltage draw with multiple accesories going (radio, headlights, fan blower on HIGH, windshield wipers all at once)...if I keep my blower motor on anything but HIGH then I'm okay.

FIRST thing I'd do is to figure out how a few small light bulbs can drain your battery in five minutes.

First Guess: Extremely discharged or defective battery. No way can a fully-charged battery be drained in five minutes without big cables melting.

When the battery is both "good" and "charged", see what happens with the rest of the electrical problems.

[TorchRed77Vette]

Same exact issue. The ignition switch comment was intriguing. I can't find any other references to this issue with those symptoms, but symptoms are dead on. Truck cranks fine but stays in second and will only go into first if you shift it manually buy never above 2nd. Speedo tach and shift light out with the check gages light illuminated.

[ChevyBoy_88]

I have a 1995 chevrolet suburban k1500 and my speedometer, rpm, mileage & my gear lights does not work anymore and my truck only drives in first gear. It takes off slow but then gradually picksup speed. I would like to know whats your diagnose?

[Schurkey]

Originally Posted by ChevyBoy_88

I have a 1995 chevrolet suburban k1500 and my speedometer, rpm, mileage & my gear lights does not work anymore and my truck only drives in first gear. It takes off slow but then gradually picksup speed. I would like to know whats your diagnose?

It's broken. Find a competent service facility, and give them money to fix it.

[EasyHangIt95]

Hello I have read a lot of posts about SOME of my problem. I could really use some tech help. Please!
I have a 1995 K1500 GMC z71,5.7 stepside. It was sitting for 14 months but runs ok. I bought it because of the way looks. I havent seen too many here in NYC. All of this was not working when they dropped the truck off.

A)The Odometer, Speedometer, tach and prnd don't work. I
I have replaced the VSS $82.00 no change.
People have said its just a ground wire. OK, But where?

B)I was having a problem with the brakes so i changed all the way to the hoses including MC. The bakes seem to be fine until i have a slight down grade to a stop. All of a sudden the brake pedal goes soft then it feels like someone is hitting the brake pedal with a hammer real fast! The truck stops but what the heck is that? It was quite scary.
Oh . I forgot one thing. The ABS light was on. I checked the front ABS sensor and the wire was broken so i soldered it. The ABS light then went off for awhile.

Here is the main question: Can all this be related to just a little stepper motor in the instrument panel that tells the computer how fast your going? If so, The odometer could be fixed and the speedometer but what about the Tachometer??
I realize this is a lot but my kid's think daddy can fix anything and its been two weeks! I didn't want to take apart the dash for no reason But i will if some one can guide me.
PS: I have been working on cars since i was 15 and this is killing me.

[EasyHangIt95]

Sorry I just saw a post about an IGNITION SWITCH being the culprit.$135.00. I will get it monday if no one tells me not to.
@sierra

[Schurkey]

1. You need a REAL service manual for this vehicle. eBay is a reasonable source.

2. IF (big IF) your '95 is set-up like my '88, the instrument cluster may be faulty. I spent about two years on-and-off trying to fix my intermittent speedo/odometer. When it worked, it worked OK. Then the speedo would drop to zero, the odometer would quit, the cruise control and ABS would quit, and I'd get a MIL light on the dash. My truck doesn't have a tach--I suppose it would have quit, too. The speedo and all the rest would be non-functional for five miles or five days--no telling until it suddenly came back to life. I replaced the VSS and the speedo gauge with no change. Eventually, I installed an entire instrument cluster from a salvage yard, and it's worked reliably ever since.