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Discussion Starter #1 (Edited)
My gauges have been acting crazy today. The tach mainly, but all the gauges have been jumping around. The voltage gauge has been steadily showing 17 volts....at least I think that is what it's at, kind of hard to tell on this gauge. Towards the end of the video I floor my truck and all the gauges start working properly. But a few miles down the road it started doing this again. The truck still runs fine by the way.

I got the video working....
 

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Discussion Starter #2
The MIL came on today too, my scanner says it's high voltage in the bank 1 O2 sensor.
 

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Nano brain
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Your video didnt work

Really sounds like you have a short some where, i cant see why the O2 sensor would throw off your gauges if they are getting screwy.

Have you tried resetting the PCM and unhooking the battery?

Check all the plugs at trans and clean them you may want check and clean all the grounds, and then check your Vehicle speed sensor. I would try these first before replacing anything.
 

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Discussion Starter #4
I don't know whats up with the video, Youtube wont let me post the video because it goes against their code of conduct....how they would know that before I even posted the video is beyond me, so I don't know how else to post the video.

I was just out doing a little diag, meter showed 12.8v with the key off and 14.3 with it running, so I know it's not over charging like the gauge was showing me. I checked that first because I remember reading a post somewhere that a bad PCM would cause gauges to fluctuate like this....so I thought maybe I was overcharging and it was frying my PCM.

Anywho, I unhooked my battery for a couple of minutes, hooked it all back up and as soon as I fired the truck up the tach went all haywire again, but evened out after a couple of seconds. I only let it run for about 30 seconds though before I shut it back down.

I'm about to crawl under it now to check all the connections.
 

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Discussion Starter #5
Alright, I got the video working. Had to upload it through IE, apparently YouTube doesn't like Firefox. (uploaded back to first post)
 

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1988 Dodge Dakota LWB RC 3.9V6 3 speed auto
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For the gauges, I'd be checking the gauge voltage regulator (module hung off the back of the instrument cluster) and seeing if that's what the problem is. Could just be a bad connection.

Out of three clusters I've been through getting a good odometer for the stepson's '88, one had a VR that did that with bumps in the road. I opened the case and found some bad solder joints inside.

Tossed it anyway - I had two good ones, one to go and one for show *grins*

RwP
 

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Nano brain
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Yeah thats also possible. Thoze cluters are pretty easy to take out too.
 

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Discussion Starter #9
Sorry I was out so long, Ive been moving....

Anywho, my truck is down (again!) and I'm thinking it was the PCM causing the gauges to go crazy. Here me out here and tell me what you think. The MIL in the original video was an O2 sensor code, I cleared it, the next day a different code popped, cleared it, then the next day a different code. Literally every day Im getting a new fault code for a different sensor. Then today my truck kicks out of overdrive, all the gauges go more crazy than usual, the MIL flashes, the truck backfires, bogs down the dies. I plug in my scan tool, and I cant a signal from the PCM. I have a cheap scanner that gets power from the ALDL. With the key off, the scan tool powers up and tries to communicate, but when I turn the key on the scan tool just shuts off. Also while the key is on I can hear what sounds like every relay under the hood clicking on and off, the IAC is making a bunch of noise and the GEN "dummy light" is lit up on my dash too.

After about 15 minutes my buddy arrives to get me, I turn the key on so i can roll up the windows and everything is quiet, no clicking relays or tapping IAC, no lights on the dash. Everything seems normal. So I try to start it, and it fires right up and runs and idles just fine. And drove the 30 miles home with no problems. At home I'm able to get my scan tool to communicate, no codes are being thrown and it seems great. Then about 15 minutes ago I went to go back it up so I can get the bike out and it started acting up all over again. No start, clicking everywhere under the hood, and no communication from the scan tool.

I'm a decent mechanic and can fix most things, but diag isn't my strong suit and I don't even know where to begin on this problem.
 

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I'd start by checking grounds. Clean the pcm ground, ground straps, battery cables and terminals, and keep an eye out for any corrosion. Also check and clean under hood fuses and relays. If it's not any of that I'd suspect a very oddly failing pcm.
 
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Discussion Starter #11
I checked the major grounds, or at least the ones I could find. They are all tight and appear to be on some solid metal with no rust or corrosion. Positive cable and both terminals are new(ish) at about 6 months old.

This morning the truck started right up, I made it about half way out of my drive way then it just died. I tried to restart it but it did nothing when I turned the key, didn't try to crank, didn't make the starter-solenoid-clicking-noise, just nothing happened. I pushed it back up to the garage....then it fired right up. Battery is still showing 12.4 volts, 13~15v running.

I put a fuel pump in about a month ago, and I broke that plastic nipple off the roll over valve. Could that cause this problem? It's been running fine up until now with it broken....so I don't know. I'm just running out of things to rule out here.

Also, when it is running the MIL is on but wont show any codes. Then GEN dummy light came on right before it died too. I'm at a complete loss here.
 

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Discussion Starter #12
Well lads, I think I got 'er fingered out.

Nitrohog, you were right about the PCM ground. It passed the "wiggle test" by hand to make sure it was tight. Then I tried it again while the truck was running and the "wiggle test" made the truck die this time. The threads in the alternator bracket where the stud goes was stripped out. I moved the grounds back to the intake where that support arm thing bolts to and the truck has been running fine....so far. I only test drove it about a mile, but it kept running the whole time since.

I guess the drive to work tonight will be the real test.

Thanks for all the help and suggestions guys.
 
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