Oil Pressure Gauge pinned while at stop

[fm1]

Yesterday my wife and I took the vette (1980 L82 ) out for its first ride of the new season. Everything is working fine. Even the clock decided that it was a good day to work properly. However, I noticed that while I am at a stop, in drive, the oil pressure gauge pins itself at 80. It may jump erratically for a second, but then still pins at 80.If I let off the brake it operates normally, and if I pop it into neutral it works normally. ( 40-60 reading ) If I am on the brake in reverse, it works normally. Driving at any speed or in park the gauge is fine. Really weird huh ?
Might anyone have any idea what is causing this ? :duh

 

[Hib Halverson]

I'm going to guess there's a problem in the wiring harness somewhere. Start tracing the wires from the oil pressure gauge. I'll bet you'll find a wire with worn insulation somewhere.

 

[73shark]

You can pull the connector off the sender and short it to ground and if it pegs the needle, then like Hib said you have a problem in the wiring and most likely its shorting to ground somewhere.

If it pegs when you remove the connector and before shorting to ground, then the wire is opening up somewhere.

 

[fm1]

I checked the wire lead on the sending unit today and it seemed to have a solid connection. I most likely will not have a chance to dig into this issue further for another day or so. It still puzzles me why this only happens while in drive at a stop. If I stay on the brake but put the car in neutral, the gauge reads normally. If I let off the brake, as soon as the car moves one inch, the gauge reads normally. I will follow both suggestions posted so far. Could be possible that I have a wire that is pulling during the torque over during the stop, now that you guys are making me think about it.

 

[73shark]

What happens if you tap the brake while you are moving? Starting to sound like you may have some grounding issues.

 

[fm1]

What happens if you tap the brake while you are moving? Starting to sound like you may have some grounding issues.

I tested that scenario, and the gauge reads fine. Only pins when stopped in drive.

 

[fm1]

Just came in from the garage. This problem was in the back of my mind all day. I traced the orange wire from the sending unit. The connection on the sending unit was solid, tight & clean. I followed & pulled up the orange wire to discover that 6 inches down the line is a plug (connector) that connnects into the main wiring harness. Standard GM plug, however it looks like heat is the culprit here. The plug looks somewhat melted, more brittle than anything, as it must have been stuck on the backside of the head or valve cover. The connection there was not tight. It must have been pulling apart ever so slightly to causing the gauge to pin. I tightened up on this connector, started the car and the gauge was reading normally . I put the car in drive, foot on the brake, and the gauge was reading accurately. I let the car get up to temperature and repeated this process a few more times and the gauge never pinned. I did not take it out for a road test, just threw it in and out of gear in the garage. Tomorrow I will stop by the Auto Parts store, pick up a new connector splice it in and replace the brittle one. Hopefully this will solve the issue.

Thanks for your help Hib & 73Shark, you guys pointed me in the right direction.

 

[fm1]

Thread update - Local parts store doesn't carry this wire anymore. PepBoys doesn't have it either. Corvette America lists this part as " Oil Pressure Sender Jumper Wire ", part # 29495. Corvette America has this part on back order. I should see it in about 10 days.

 

[Rebelrob]

Good Job on the troubleshooting...

 

[Bobplane777]

Sending unit

My 79 was doing pretty much the exact same thing. I replaced the oil sending unit (near the oil filter on 79) ... NOT the oil switch (as some mistake it) and it has worked perfectly for 2 weeks now. I bought it from Advanced Auto for $18.

 

[Hib Halverson]

Good Job on the troubleshooting...

I agree.
Glad you got the problem fixed.

 

[compyelc4]

Doesn't it feel good when the old gal "allows" you a successful diagnosis and repair?:cool

 

[fm1]

Doesn't it feel good when the old gal "allows" you a successful diagnosis and repair?:cool

Most definetely !

Good Job on the troubleshooting...

Thanks !

I agree.
Glad you got the problem fixed.

Thanks for your guidance !

 

[Mr. Chuck]

Once you have replaced the old connector and to avoid the same problem later on, try to relocate / tie wrap the wire /connector away from any major heat source like the exhaust manifold or any direct contact with hot engine surface. Better yet, wrap the wire / connector with heat shield wrap (same thing used to insulate the floor pan in the passenger compartment during carpeting replacement jobs) in the hottest exposure areas.