working on an 86 f150 w/5.0. oil pressure gauge was reading low, mechanical gauge said it was fine (50psi). grounded the sender wire and the gauge pegged. so installed a new sensor and didn't get a change.

I thought it was in 87 that they supposedly went to a dummy gauge with a pressure switch. (however my 88 had a switch put in it and it just pegs the gauge).

this truck has the larger sending unit, I put a napa op6091 into it.

anybody have any insight?

 

When you ground the sender wire it will let the gauge. That is the way the gauges are supposed to work. So I don't understand the problem.

 

with a new sending unit, the oil pressure gauge still reads low, not even in the "normal" range.

 

Make sure you do not put hardly any type of sealer on the threads. It needs to ground through the threads into the block to operate properly.

You can take the sending unit wire, and with the key in run, touch the wire to ground and then take the wire off ground, this should make your gauge swing full scale low and high.

You have the large sending unit, so you have the "real" guage.

If your gauge is reading low after all this, maybe you have low pressure. Who knows? Why does anyone spend any time or money getting the original gauges to work, they tell you nothing.

My 89 has the "fake" gauge. I don't care. I put a set of real gauges under the dash for it.

 

What he said - x2. But, for testing, ground the case of the sending unit with a wire to a known ground and see if that causes the gauge's reading to increase. If so, you have too much sealer/tape on the threads.

 

well, its not my truck, I would just run aftermarket gauges he bought the truck to give to his dad, who bought it new. and roped me into doing the work.

I touched the wire to ground and got the gauge to do the "full swing", I also tested the pressure with a mechanical gauge, got 50psi, so its not like it doesn't have the pressure.

didn't think about the thread sealer, it came with the sealer already on the threads, so I will try grounding the sender case like gary said.

 

grounding the sending unit didn't do anything. guage is hovering between the line and the N, but i also noticed that it doesn't change with rpms, and chance its a dummy guage that somebody put a sending unit on?

 

Next question. Does the temp gauge and fuel gauge work? The three are run by the same "voltage regulator" that is notorious for going wonky. So if the other two anernt reading right it may be the ICVR.

 

temp gauge is definitely ok, fuel gauge isn't showing any strange signs. but it hasn't been driven enough to see it over time.

 

I tore the dash apart and hooked my fluke up to the regulator. it looks to be fluctuating from 0 to around 8.5 rather than staying constant, on its power side its doing the same, but from nine up to battery voltage. i can't get a straight reading. any chance this might be the problem? only thing i'm wondering is that if it is, shouldn't it affect the other gauges as well?

 

Lol! Remember me putting "voltage regulator" in quotes?? That's because calling the ICVR a voltage regulator is like calling a Pinto a sports car. Not even close. Go read this link. That'll tell you what you are dealing with.

But, if the temp gauge is working right it isn't the ICVR since it serves that plus the fuel and oil pressure gauges.

 

And then, if you want a real voltage regulator read this how-to.

 

a waveform says a thousand words... and i think i missed thje quotation marks. good stuff to know though. sucks that it leaves me searching.

 

Here's the wiring diagram if that helps.

 

Take the sensor back. Everyting else is working.