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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: JimE on June 14, 2013, 11:23:44 am

Title: Oil Pressure & volt meter Problems
Post by: JimE on June 14, 2013, 11:23:44 am
I have a 1986 C10 Silverado with 4bbl carb. My oil pressure sending unit blew out and I replaced it, but now when ever I put the auto tranny in gear the oil pressure drops to minus pressure and the amp meter goes to -13 volts. When I put the tranny back in park the gauges return to normal.

I have tried switching wire connectors on the oil sending unit, there are no wires near the shifting linkage.

Does anyone have any idea what the fix may be?
Title: Re: Oil Pressure & volt meter Problems
Post by: Captkaos on June 14, 2013, 11:36:17 pm
Sounds like shorted wires
Title: Re: Oil Pressure & volt meter Problems
Post by: Irish_Alley on June 14, 2013, 11:55:55 pm
neutral safety switch problem? does it still act funny in neutral or anything besides Park?
Title: Re: Oil Pressure & volt meter Problems
Post by: JimE on June 15, 2013, 10:41:31 am
The only time the gauges return to normal is when it is in park. I did notice that when I hit the brake the needles fluctuate, so I'm going to check that out.

Thanks for the help.
Title: Re: Oil Pressure & volt meter Problems
Post by: rich weyand on June 15, 2013, 12:25:14 pm
A multi-system electrical failure is almost always grounding issues.  Check your ground straps.
http://forum.73-87chevytrucks.com/smforum/index.php/topic,26163.0.html
Title: Re: Oil Pressure & volt meter Problems
Post by: Irish_Alley on June 15, 2013, 11:19:03 pm
rich how can putting a truck in gear and causing problems be a ground issue? not questioning your suggestion but curious. the only thing that i can think of that gets power by the shifter is the nss, but then how does that feed back to the dash?
Title: Re: Oil Pressure & volt meter Problems
Post by: jaredts on June 15, 2013, 11:27:05 pm
I had a friend once with a vw that had electrical problems when you put it in gear.  It was grounds between the engine and firewall.  When you put it in gear the engine would shift and loose connection.
Title: Re: Oil Pressure & volt meter Problems
Post by: rich weyand on June 15, 2013, 11:28:01 pm
When you put a car in gear, the rpms go down from idle-in-neutral, the output of the alternator goes down, as one example.  You go through reverse to go into gear, and the reverse lights go on.  There is a "Park sensor" to allow the engine to be started -- maybe that provides the missing ground to make things work when in Park, but not otherwise.  There's three possibilities. 

Basic message: crazy things happen when the grounds are missing.  Check them.
Title: Re: Oil Pressure & volt meter Problems
Post by: Irish_Alley on June 15, 2013, 11:36:50 pm
see that why i was saying nss its the only thing i could think of that would give power in gear but the gauges so return to normal when in neutral
Title: Re: Oil Pressure & volt meter Problems
Post by: Irish_Alley on June 15, 2013, 11:44:33 pm
my brothers 89 iroc was doing something like this. his problem was a loose wire that went to the ecm if you wiggles it it would fix the problem. but this would be a constant problem not just while in gear
Title: Re: Oil Pressure & volt meter Problems
Post by: bd on June 16, 2013, 11:40:31 am
A multi-system electrical failure is almost always grounding issues.  Check your ground straps.
http://forum.73-87chevytrucks.com/smforum/index.php/topic,26163.0.html

I agree - this is the best starting point.


rich how can putting a truck in gear and causing problems be a ground issue? not questioning your suggestion but curious. the only thing that i can think of that gets power by the shifter is the nss, but then how does that feed back to the dash?

The cab "might" be finding an alternate ground path through the shift linkage.
Title: Re: Oil Pressure & volt meter Problems
Post by: rich weyand on June 16, 2013, 12:04:54 pm
The cab "might" be finding an alternate ground path through the shift linkage.

Or the parking pawl.
Title: Oil Pressure & volt meter Problems
Post by: diphthong on July 03, 2013, 11:51:44 am
When the problem happens, Isn't this the position of the two gauges the same when the ignition is off.

It's almost as if he's describing losing power to these gauges.  These gauges are simple grounding circuits, You eliminate the power (+) or the ground (-) you eliminate the circuit.  If I'm Correct, and the gauges are mimicking an engine off condition, Because there's two independent circuit, I would start looking for the problem with the positive (+) side not the negative (-) side.










I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)