Alright the problem comes into play when I get off the highway. When I get to a stop the oil pressure drops quick and picks back back up. First thought was the sending unit, but today it acted like it was going to stall out. Engine lights came on for the duration of the drop. I listened for a ticking but heard nothing. Could it be the pump or is this the sending unit? Is the sending unit tied into the computer in any way to shut the motor down in the event of oil pressure loss. Truck is an 89 F250 4x4, 351w, zf5 speed. Thanks

 

nope if u have no oil pressure the engine light will just be on

i know this because i put my aftermarket gauges in sunday and i started it to be sure it wasnt leaking and i didnt have the factory sensor plugged in yet and it ran like it always has except the engine light was on

 

first, the oil gauge is a glorified idiot light.

it only moves if the pressure drops below 7 psi.

you need to check the oil pressure with a mech. gauge ASAP.

 

Yeah I know the sending units are notorious for going bad. If it helps the needle was flickering between L and normal. Kinda like it was trying to figure which one to go to

 

Ok, read a thread that said to test the sensor you just ground it out. Grounded it should read max and ungrounded should be low. Well grounded only went to half ( normal ) and ungrounded went to low. Does that for sure mean that the sensor is bad. Checked the oil and it is only 1 quart low

 

uhm when its completely grounded it should be about 3/4 of the way to the high side

 

Never went past half. Tried it a couple times. So does that for sure mean the sensor is bad. If not I'm going to get a ride to work and pull the pan tomorrow. Also, where is it that you hook an aftermarket guage to. If I unplug the sensor and use that port then I'll have a check engine light.

 

The red engine light is just a warning for low oil pressure and/or high water temperature. The Check engine light for the computer is yellow and will not come on due to low oil pressure. The gauge and pressure switch seem to be functioning normally from what you have described. The only way to know the true oil pressure is to install a mechanical or electronic gauge sender in its place. You may never lose oil pressure completely - it might be right at the switching point of the stock pressure switch, causing the gauge to bounce between normal and nothing, when in reality the pressure may have only changed a 1/2 psi.

 

I have an 88 f-250 351 that does the same exact thing. When I first bought the truck it leaked a ton of oil and both head gaskets were blown. I put a different engine in with good head gaskets thinking it would correct the problem. but the oil pressure gauge still has a problem whether its low on oil or completly full. And occasionally it will sputter out/stall on me when stopping at an intersection after going 55. It seems to get better when the truck is warmed up. I just live with it.

 

<i>comes into play when I get off the highway. When I get to a stop the oil pressure drops quick and picks back back up.

First thought was the sending unit, but today it acted like it was going to stall out. Engine lights came on for the duration of the drop.</i>

Doesn't sound like you have a oil pressure/monitoring system problem, sounds like you have problem in the way the motor is controlled under certain conditions.

If the motor all but stalls out when letting off the gas it's rpms drop dramatically, the oil pumps speed falls with it. If the pump just about stops spinning the amount of oil it pushes drops with it causing the gauge reading to drop accordingly.

When suddenly letting off the throttle, say when exiting the highway for example, several things happen the most important of which is the IAC valve beginning to cycle rapidly to keep the motor from stalling out from the sudden loss of intake air when that butterfly slaps shut.

If it where me I'd clean and inspect that valve/system, likely just replace it, especially if its original to the truck/motor.

 

exactly.

 

I thank you all for the help. Unfortunatly I am paraniod about oil. Bought a new pump and oil pan gasket. Also got a new rear main seal. When I got the truck, I replaced all the upper side gaskets. Oil was all over everything. Now the only leak is the rear main so I figure I'll fix that wile I'm in there. Also gonna pull my auto meter electric guage from another truck and use that in the factory spot. Is there a way to terminate the factory circuit so I don't have a red engine light on?

 

put a new pickup screen in and use the felpro blue one piece gasket and holders.

and, check with a real oil pressure gauge before you do all this.

 

You can either use a T-fitting to attach both the stock switch and the sender for the autometer gauge, or you could just ground the stock sender wire and the gauge will remain mid-sweep no matter what oil pressure you have.

 

Droped the pan last night. Seems like everytime it's harder than I remember. Had to pull both headers and the upper intake. Found a lot of pebbles and one rock inside the pan and screen. At least they were bigger than the holes in the screen. Can't really figure how that crap would get in there