1990 Crew Cab Dually

[TravisMartin]

I just picked up (rescued, really...it was being abused...) an R3500 with 454 and TH400 and most options. Drives pretty good but has been cowboyed almost to death. Planning to bring it back to nice if I live long enough.

It has had an aftermarket mechanical oil pressure gauge installed...I can't find the wire from engine harness for the oil pressure sender. I believe it is a tan wire, but the sender is gone...where should it be mounted? The mechanical gauge is connected just above the oil filter. Doesn't a TBI motor have to have an oil pressure switch to maintain the circuit to the fuel pump? It runs fine and I hear the fuel pump relay click after a few seconds after the starter has been operated so I'm assuming the oil pressure switch is there...but where?

Next question...it would be a far more enjoyable truck with a 4L80E in place of the TH400. Has anyone done this swap with original components, much like the fairly common retrofit of TBI into carbureted trucks? Looks like it shouldn't be a big deal if you had a 91 up donor. Is the transmission controlled out of the ECM or is there a separate box?

Thanks,

Travis

[clinebarger]

The oil sender wire whould be blue. factory 4L80Es were controled by the ECM
Some early 90s diesels had a TCM (transmission contol module). and there are aftermarket cotrollers you can buy. if it were mine id put a cummins 6BT diesel backed with a 5 speed manual. 20+ mpg

[TravisMartin]

Thanks for the quick response. I'll start looking for a blue wire that isn't connected...any idea where the sender should be?

Travis

[clinebarger]

Behind the driver side head was the place they used instead of above the oil filter on some models. if your truck does have the fuel pump relay bypass oil sendor on it it whould be three wires Orange, Gray, Blue

[TravisMartin]

Thanks; don't see anything there though. I did determine that apparently mine doesn't use the oil pressure switch...it dies when you unplug the fuel pump relay. The harness is in pretty bad shape; it's hard to tell where things should be. I have a 1990 shop manual ordered; maybe there will be some pictures that will help. I had assumed that if I knew where the sender was supposed to be, I'd be able to find the wire, but so far no luck. I have a couple of 1990 suburbans with 350 TBI's that I can steal parts from.

It's kind of an orphan situation; electrically it's probably more nearly like the 88 up pickups, even though it's a square body. Maybe I should pose the question on the 88-98 forum.

I appreciate the help.

Travis

[Keith Seymore]

"Cowboyed" to death...

(LOL) -

I can certainly relate to that.

Congrats on what sounds like a great purchase.

K