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post #1 of 14 (permalink) Old 05-10-2019, 06:49 PM Thread Starter
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Electrical gremlin

So recently I installed LED dash lights, and since they turn on instantly, I noticed my check engine light flicker... everything seemed to work fine for a long time so I never bothered with it

Recently, it's got some charging and electrical issues... doesn't charge, voltage jumps all over the place (never overcharge, just under), CEL comes on when it's not charging, oil pressure is much higher than normal (3/4 gauge, always used to be 1/2).. the strangest thing is it's only when the truck is moving, so it's dang near impossible to troubleshoot, I've wiggled all sorts of wires, put a jumper cable from the block to the battery (-) etc trying to find a grounding issue.. hasn't helped any.. If only I could make it fail while not moving I'd have a chance.

93 XCLB auto diesel truck

Any ideas?


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'93 XCLB Auto 4x4, '92 XCLB Auto 4x4 (Dads)
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post #2 of 14 (permalink) Old 05-10-2019, 07:37 PM
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Extra jumper to the body, clean both battery cable on both ends.

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post #3 of 14 (permalink) Old 05-10-2019, 07:38 PM
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Most likely a ground issue check the body ground but also check or replace the crank position sensor. Do you loose overdrive at the same time?
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post #4 of 14 (permalink) Old 05-10-2019, 07:38 PM
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Quote:
Originally Posted by 9297oldram View Post
Extra jumper to the body, clean both battery cable on both ends.
Every time..... great minds think alike haha
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post #5 of 14 (permalink) Old 05-11-2019, 04:20 AM Thread Starter
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battery connections are mint, new cables and ends, cranks great.. bad ground was my first thought which is why I put the booster cables on the block to the chassis to test


I can't say if OD is kicking out at the same time, truck isn't currently insured so it's just doing farm work.
I did have a bad connection on my 2nd gen crank sensor, I tweaked the pins a bit and it fixed it, did the same to the first gen and it hasn't changed anything

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post #6 of 14 (permalink) Old 05-11-2019, 07:03 AM
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Did you check the gap on the CPS? Should be .050

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post #7 of 14 (permalink) Old 05-11-2019, 01:07 PM Thread Starter
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I'll do that here next time I run it... I kinda doubt that's the problem but worth a shot...

I'm thinking it's a wire that's fatigued inside the casing somewhere and the vibration makes it have contact or not, and it just happens to be while it's stopped it works... but which wire???

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'93 XCLB Auto 4x4, '92 XCLB Auto 4x4 (Dads)
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post #8 of 14 (permalink) Old 05-11-2019, 01:29 PM
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perhaps the alternator brushes are at the end of their life.
if your ac works that will tell you if the cps is good. if not put a test light on the asd relay.

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post #9 of 14 (permalink) Old 05-11-2019, 11:03 PM Thread Starter
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Fiddled a little with it, disconnected the alternator at the air box connection, checked everything there, looks good, same with the bulkhead connector and PCM connector. ran it with no alternator and my voltage still significantly dips at times.. Looking like there's a short to ground somewhere,.. probably a wire rubbed through.. going to have to pull fuses to narrow down what circuit it could be.. Fiddled with the underdash wiring, trailer/tail light wiring.. moving things a bit here and a bit there but nothing is jumping out at me yet. AC is working properly.

Won't have time to play with it much more for a bit, I'll try and take a video of what it's doing if I don't figure it out.. I'm going over the wiring diagrams trying to find a common link between a high oil pressure signal and everything else, sounding like either the gauge cluster is losing ground or something is shorting to the oil pressure sender circuit.. though that doesn't explain why the CEL comes on.. An analog multimeter would be nice for this, digitals don't show squat.

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'93 XCLB Auto 4x4, '92 XCLB Auto 4x4 (Dads)
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post #10 of 14 (permalink) Old 05-12-2019, 01:03 AM Thread Starter
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I'm going to get a voltage reading right off the battery when I get a chance, that should help me narrow it down a little, if the actual battery voltage doesn't fluctuate much but the in dash gauges does it's probably something goofy in the cluster

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'93 XCLB Auto 4x4, '92 XCLB Auto 4x4 (Dads)
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post #11 of 14 (permalink) Old 05-15-2019, 11:28 AM
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what bran LED lights did ya install when it all started? some of the cheaper led lights generate a ton of EMF and can interfere with electrical system... I learned bout it the hard way when I switched all my 03 Harley Fatboys lights to LED... turned out the LED tailight was interfering with the bikes voltage regulator... got rid of the Amazon $28 tail light and got a nice $75 one and erratic operation was cured... some people just put ferrit rings on effected circuits and keep running the cheap lights... your gauges are electronic.. the dash light wireing is running right along side your gauge wiring...
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post #12 of 14 (permalink) Old 05-16-2019, 12:37 PM Thread Starter
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happens even when no lights are on

I disconnected the oil pressure gauge and it's still doing it, going to disconnect the entire engine harness and hotwire the shutdown solenoid to the battery, rule that out or not.. maybe a wire rubbed through behind the fuel filter?

'94 SC 4x4 Dually flatdeck, ~500hp, 67mm HE351VE
'93 XCLB Auto 4x4, '92 XCLB Auto 4x4 (Dads)
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