Chevy small block weird oil pressure readings.

[GH85Carrera]

Originally Posted by Zeke

When you turn the ignition to off and remove the key you know you fully shut the car down. There should not be any residual 12v anywhere except at the ECM and radio. I don't know what kind of ECM you are using, but if as old as the car, there should be no power to a sending unit.

On the ticking, I have problems with the manifold bolt under the alternator.

I'd check the dash gauge before throwing 35 bucks at the problem. OTOH, it's likely time for a new sending unit even if it doesn't solve the problem of reading pressure when the car is 'off'.

z

It always shows pressure when the key is off when turned off in an normal way.

I just went to the garage and took this photo. The car has not been running for at least an hour and as you can see, the tachometer and temp and oil pressure all still show the last reading as they lost power.

The oil pressure gauge behaved perfectly tonight after 50 or 60 miles of driving today.





The speedometer is of course dead on accurate since I was in park to turn off the ignition and it is cable operated. The engine temp is showing the operating temp when shut off, as is the oil pressure and gas gauge. And yes, the second the ignition is switched on, the temp will drop to 100 and the gas gauge often changes if I am on a hill. The voltage drops to zero as it should because I can't get the key out before it drops to zero.

Only the speedometer has a speed sensor that feeds info to the ECU for the fuel injection. I threw out the carb and went to the FI system 15 years ago and it is essentially the system put on the 6 cylinder El Camino. All the parts are the same except the injectors themselves and the computer map. I had a guy in NJ remap that for me. Now there are tons of full systems that bolt on, but not back when I was sick of the carburetor problems. Fuel injection rules!

[dad911]

Originally Posted by Zeke

Another idea: there's a crack somewhere in the manifold which closes when the block gets warm enough. OP and ticking are unrelated. OP is just the cold oil, and the reading on the gauge was faulty as in out of range.

My GMC pickup does that also. Started just out of warranty. Now at 14 years old and 100k miles. Sounds just like a lifter, but fine when the engine warms up.

[dad911]

Originally Posted by GH85Carrera

It always shows pressure when the key is off when turned off in an normal way.

I just went to the garage and took this photo. The car has not been running for at least an hour and as you can see, the tachometer and temp and oil pressure all still show the last reading as they lost power.
......

That is because they are mini stepper motors. I've changed a few in my GMC. They remain in place w/o power.

[GH85Carrera]

OK, just an update for the few Pelicans that might care at all.

It was the oil pressure sender.

I went to the local NAPA warehouse store. The line was 10 or 12 people deep. If the pressure sender was going to be free, I would not wait in that line. Off to an O'Reilly. Nothing in stock, and they can get in in a couple of days, and it is 50 bucks with taxes. Nope.

So back to the on-line ordering. 30 bucks gets it delivered to my door. I tried to support the local stores, but no luck this time.

The good news for me was that the near genius, handsome and very modest mechanic that installed the last oil pressure sender put in a 45 degree elbow and that makes getting to the sender a ton easier and all I had to do was remove the cruise control vacuum module, and there it was. Well, I had to move a vacuum hose and the fuel hose is kinda in the way, but it was fairly easy to swap. I remembered doing that elbow when I installed it back when I swapped to the 350, back 70,000 miles ago.

Now the pressure drops to zero in a second or so before hitting the starter. It was already a little warm but stayed in normal and expected ranges. I will watch it close in the morning in cool weather.

The tap tap tap had to be an exhaust leak.

Another simple project fixed.

[LEAKYSEALS951]

Thanks for the update. This has been a good thread to follow.

[Scott Douglas]

Appreciate the follow-up Glen. Thanks. I was wondering how this worked out.

[LWJ]

Cool. The gearhead in me is pleased.

[Bob Kontak]

Originally Posted by GH85Carrera

The good news for me was that the near genius, handsome and very modest mechanic that installed the last oil pressure sender put in a 45 degree elbow and that makes getting to the sender a ton easier

He'd been through that before.

Good news!

[hcoles]

Good thread and glad you found the solution.