OPC, lift pump - new quirk Lift pump stays running 96 Suburban

[jrsavoie]

Wife was going to work yesterday and the battery was dead.

I put the charger on it for a short period of time and it started right up.

I was checking the usual dome lights and whatever. Didn't find anything.

When I turned the truck off the lift pump stayed running much longer than usual and the gauge still read 40 lbs.

I'm letting it warm up no to see if when the oil is warm the pressure bleeds off faster.

It's not near as cold now - 38 degrees as it was Sunday night.

Has anybody heard of anything like this?

Any ideas on why the oil pressure isn't going down?

5w30 Amsoil. Not that it matters but I had the oil tested a 1000 miles ago at 11,000 on the oil change. They said the oil was still good to go. I changed the engine oil cooler lines and the oil then.

After it was running and warmed up the lift pump shut down as it should.

 

[Brooklyn Tow]

Maybe your Oil Pressure Switch is pooched and some how fooling with LP circut?

 

[ak diesel driver]

maybe the contacts stuck

 

[WarWagon]

That isn't the lift pump you hear...

That is the Suburban shivering :hihi:

What does the oil look and feel like? (Coolant turns it into pressure holding sludge quick.) Otherwise I would say normal holding pressure for cold oil and tight bearings a good engine will have. OPS has 2 sensors, but, if it sticks at 40 PSI the LP will be running too. Cold oil makes sense, a sticking OPS would be unusual.

Otherwise check glove box light, current drain test, battery failed... Failing dome light switch and intermittent with cold weather turning it on to make it fun to track down.

 

[JMJNet]

I think that is normal. Mine did the same thing. The problem is I don't know when it is going like that.

Actually, I would check the LP and make sure it is still pumping. Sometimes, it is purring but not pumping.

OPS does not go down as soon as the engine shut off. At least not in mine.

 

[ak diesel driver]

mine never runs after shut down. ECM control?

 

[jrsavoie]

mine never runs after shut down. ECM control?

If on your 96, your OPC could be bad.
That's given that it's running while the vehicle is running.
I'm assuming the vehicle stays running when you open the drain T valve?

 

[Turbine Doc]

Could be the "brain" in the pump itself, or stuck contacts on the lift pump relay under hood.

96 is OBD-II, (2) power sources OPS & PCM so if unplugging OPS does not make it quit I suspect relay or pump itself. Disconnect OPS and see if problem persists, lift will run on PCM control if OPS is not present

 

[jrsavoie]

I would say with the cold, stuck contacts in the relay is a good bet. Warming the engine could've cured that also.