Hello I have a 98 gmc jimmy slt, I’ve been having some problems with for a couple months now. It started out with I was driving to work and all the sudden the gauges went haywire and the truck died on me so I got a ride to work and came back after I got off started up drove home perfectly fine. I tested the battery and alternator and tested fine 14.3v - 14.6v so I drove it again and same thing gauges when haywire then died on me got a ride to work came back started up drove home perfectly fine. So I replaced the alternator, spark plugs and wires just because I didn’t think they’d ever been replaced but did the same exact thing. So I replace the ignition control module and ignition coil and drove it all weekend drove perfect no problems so I thought I had it fixed so I drove it to work the next day I made it to work but when I got off it would crank but no start. I noticed that none of the dash lights pop up like usual the only light that would come on the dash is the battery light. Everything else worked dome lights, radio, windows etc. just the lights on the dash and guages. I jumped it and was able to get it home so I figured it was the battery got that replaced the next day tested it to make sure it was charged it tested 12.5v put it in and same thing only the battery light would come on the dash and crank but no start. After I tried starting it I tested the battery again and it tested 12.3v and with the key turned to the acc it tested 11.9v. At this point I’m lost I’m not sure if I have a parasitic draw or a ground issue or if it’s an ignition switch issue. Has anybody came across this or had this happen to them any input is greatly appreciated I’m losing my mind over this.

 

We have two choices:

1. Travel with a digital multimeter, spark tester and fuel pressure guage so that you can diagnose the problem when the truck fails so we can make a targeted fix.
2. Make some best guess fixes to try and get lucky and nail the problem

You said that you think you have a parasitic draw problem, thats easy to confirm or rule out. If the battery is new and known to be good (load test is the best confirmation) then get is charged to 12,6 volts and leave the truck overnight with everything locked and off. Measure the resting voltage in the morning and report back. You can also measure the draw after everything goes to sleep and see if your out of bounds. Let me know if you want to go that route.

When you say that the gauges go haywire do you mean turn off and turn back on operating normally or do you mean fluctuating needles with values that make no sense?

You might want to get one of those cigarete lighter voltmeters so you can watch your system voltages to see if they ever go out of bounds

When it will crank but not start check for spark while cranking and if thats ok test fuel pressure. If no spark check for 12v on the pink power wires for the ICM and the coil.

If your a parts cannon guy and you are sure that you have a good alternator and battery then replace the ignition switch. This is only my best educated guess, I prefer to diagnose the problem and do a targeted fix.

George

 

Thanks for the reply George, I believe I fixed the stalling while driving problem with the new icm and coil after I replaced those it drove fine didn’t stall or anything. Right now it’s just when I turn the key the guages don’t work and the dash lights don’t come on like normal only the battery light and mileage and it will crank no start. Everything else works like the windows, radio, headlights, etc. I just replaced the battery and alternator when it first did the crank no start with just the battery light on the dash I would hope they’re good but it wouldn’t hurt to get it load tested. I’m not for sure I have a parasitic draw because when I first got the battery it tested 12.6 I put it in tried starting it and same thing with the dash lights and crank no start after I tried to start it a couple times I tested the battery again and it tested 12.3 and it just sits at 12.3 it hasn’t fully drained the battery but I did test it with the key turned and it tested 11.9 so I’m not sure. When the guages would go haywire all the guages would like spike once and all the lights would come on the dash and the truck would just fall on its face. Sometimes it would do the haywire thing a couple of times before it would fully fall on its face like the guages would spike then go down and the dash lights would flash and it would almost die but it would catch and be good for a sec then it would do it again and fully die on me that’s what’s making me think it’s a ground or ignition switch problem. The weather didn’t wanna cooperate with me today it’s all rainy and I have to work but I think tomorrow I’m gonna charge up the battery try and check the grounds and fuses. Any advice is greatly appreciated thanks again.

 

Here’s a picture of the dash with the key turned that’s all I get and it will crank but won’t start.

 

the gauges going crazy sounds like a bad chassis/ dash ground.

A bad ignition switch can do strange things on an old vehicle.

Also look at the bulkhead connector on the firewall...is it loose or melted? Fuse block have any overhrated connections?