Oil pressure gauge playing up

[Tiny Trucker]

Just today noticed my oil pressure gauge would start diving to full any time any throttle was given. Doesnt matter if its in gear or in neutral. No "check gages" light and I was under the impression the ecu would stop giving fuel if starved of oil (maybe thats the other sender unit?), but shestill runs.

I also noticed some time ago the gauge would bank hard right if I gave it full beans and in the past the truck not start (gauge to the right again) if it soaked enough heat in the summer and leave me stranded for and hour or two until it had cooled down...

Maybe its time to replace the sender unit by the distributor? Hopefully its not the pump as it seems electrical (like a short).

Any advice appreciated.

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[bigfutz]

Replying to an older post, but similar symptoms... I added some Sea Foam to my oil (not after fresh oil change) and noticed I’m getting more response from my oil pressure gauge to throttle. Did I mess something up? Or is the Sea Foam just exposing a problem I didn’t know I had? Here’s a short video in park. Notice also the needle is a little jumpy. Am I seeing exhaust getting into the crankcase?

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[Pinger]

I'm pitching in here looking for confirmation that fuel is deprived until sufficient oil pressure has been reached (a product of its emergency shutdown if the motor unexpectedly stops?) as I'm having occasional starting problems and even when it will start, it takes a few seconds of cranking.

Re post#2. If you suspect exhaust in the crankcase, removing the PCV hose on the passenger side should let you see any pressurisation.
My 1999 350 doesn't show such high oil pressure (assuming both our gauges are calibrated the same - psi not mPascals? - my speedo is in km). The highest I see is 60 and usually 40 in normal driving and not much more than 20 idling when hot. I see 60 driving when cold (and guess the oil is near correct temp when I see it fall to 40).

Presumably there is a pressure relief valve. Seafoam dislodged some dirt that is causing it to stick (closed)?

 

[Schurkey]

1. The oil pressure switch can turn the fuel pump ON if the fuel pump relay or the relay wire harness, or the ECM circuitry that drives the fuel pump relay has failed. The oil pressure switch CAN NOT turn the fuel pump OFF if the fuel pump relay is working like it's supposed to.

2A. A failed fuel pump relay/harness/ECM can cause a long-crank situation, because the engine will have to build oil pressure for the oil pressure sensor to power the fuel pump. Engine will not start until it's cranked a long time.
2B. Test the fuel pump relay, harness, and (some of the) ECM circuitry by verifying that the fuel pump will prime for at least two seconds when turning the key from "Off" to "On/Run". Vehicles with a "Hot Fuel Module" may prime longer than two seconds--perhaps twenty seconds.

3. On my '88, when the oil pressure gauge is erratic--generally too high, generally too low, bouncing high/low pressure reading--the oil pressure sending unit on the block above the oil filter mount has partially-failed. The '88 and '89 trucks use this sending unit, I don't know about newer trucks. The '88--'89-style sending unit is a HIGH FAILURE ITEM. I've gone through four of 'em in less than 150,000 miles, and I know other folks who have failed at least one. Far as I can tell, they're sold under multiple brand names, at varying prices--but it's the same sending unit made in the same factory in Asia.

 

[Pinger]

Thanks Schurkey - much appreciated.

I think mine may be starting from the oil pressure. When it fails to start I don't persevere for fear of flattening the battery so immediately 'force' a start on LPG(propane). (The LPG is enabled via the tach not oil pressure AFAIK).If I change back to gasoline on the hoof with plenty oil pressure it runs faultlessly. If I change back to gasoline when it's idling it will often stumble, sometimes dying (but will usually restart on the key). A combination of lowish oil pressure (at idle) and latency in the electronics perhaps?

I also need to revisit what HWB has said re PassLock. I think I read it cuts fuel (but allows sparks?).