I just swapped my 2.8 for a 3.1. now the oil gauge pegs as soon as the key is turned. any ideas? i did a search. no luck. thanks

 

What sending unit did you use? are they the same for the 2.8 and the 3.1? If so I would be looking for a pinched wire coming from the sending unit or possibly the sending unit itself is bad.

 

If I recall correctly , our oil gauges work in a similar fashion as our gas gauges in that , an open in the sender lead will send the gauge full scale , and a "pinched" (Short circuited to ground) sender lead would cause the gauge to remain at it's bottom reading (indicating 0 psi)

So , you've either got a bad sender , or an open in the sender circuit ....

 

And yet when I searched "oil gauge pegged" about 355 threads came up , and the answer I posted above was found in the first three entries .

Wondering just how extensive this "search" was

 

maybe i didnt use the word pegged........... next time show your badge.

 

There is one thing NOBODY every mentions in the swap threads:

THERE ARE 2 OIL PRESSURE UNITS ON THE 2.8. THERE IS ONLY ONE ON THE 3.1 AND LATER MODELS.

One is the oil pressure fuel pump relay bypass switch and the other is for the dash gauge.

The late model unit does both.

On my 3.1, there were indeed bores for 2 sending units, but one has a plug in it. I had to go out and get a harness connector AND the 3.1 sending unit to use the dash gauge. This will cost you approximately $50 now (that sender pigtail isn't cheap and the sender itself is like $30).

When the dash sender isn't plugged in, or is otherwise disconnected or the wire is grounded, the gauge will either peg (disconnected) or flatline (grounded wire). Either way, it won't work.

 

Hey maverick,
The sending unit in my car is the 3.1 running off the 2.8 ecm. So can you explain to me exactly what i need to do without hacking into my harness any more. Can I bypass the fuel pump relay bypass wiring? also i keep blowing fuel pump fuses. could this be related?

 

There shouldn't be any issues running a 3.1 on a 2.8 system provided you swapped over all of the parts necessary. If you keep blowing the inline fuse, your probably going to be looking for a wire pinched or cut somewhere and grounding out.

The oil pressure/fuel pump unit has NOTHING to do with the ECM. The only way it ties into the ECM system is via the orange power wire, which, if damaged and grounded out, kills both the fuel pump AND ECM constant power supply by blowing the fuse. (Well, as a side note, the output wire to the fuel pump is also monitored by the ECM...)

Other than the OPS being a different unit on the 3.1 as opposed to the 2.8, the systems are identical between the fuel tank and the engine.

 

its blowing the under dash fuse. And I have no idea what most of what you just said actually means. this is all new to me. my gauge is redlined and i just want it to work again.

 

Which fuse specifically is it blowing? The FP/INJ 2 fuse has NOTHING to do with the fuel pump (IDK why GM labeled it as they did but that fuse is ONLY for the fuel injectors).

 

all i know is its a 20 amp fuse under the dash. i avent actually got a chance to look at it yet. when this fuse blows the relay stops working and the pump doesnt prime. so wich sending unit do i need to go buy? a 2.8 or a 3.1?

 

You need the 3.1 sending unit...

And to tell at least where the fuse is in the dash that keeps blowing... If it's a 20 amp fuse, then someone probably messed with something in the past, as EVERY fuse, in the dash, for any given engine circuit (with the exception of the starting circuit) is a 10A fuse...

Only 20A fuses I can think of are for the power accessories, turn/backup lights, tail lights, the radiator fan/alternator, MAF sensor and fuel pump/ECM constant power (in the engine compartment).

 

with the 3.1 unit, i will need to splice wires? umm i know at least alf of my fuses are not 10amps. but i do no know which fuse keeps blowing but i can find out later when i get home.

 

Yes, you will need to splice wires.

 

why cant i just get the 2.8 stuff and hook it back up without having to splice up my harness?.

 

Better grab some scissors and get to cuttin.

 

If you think you can get the plug out of the 3.1 oil filter adapter... Go at it. You need to pull the plug above where the oil pressure switch is so that you can put in the sending unit for the gauge. Unless you plan on splicing in the 3.1 pigtail so you can use the 3.1 sender...