hello, new to this forum as just purchased a 1986 TD trooper and converted it to run svo/wvo/bio from "lovecraft" in LA. great people and a 1 tank system. was driving down the road @ about 65mph when the oil pressure gauge started to slowly go from about 70lbs to about 0. pulled over and stopped. oil light did not come on and no "knock" or noises to say of. let rest for awhile and was only about 1/4 mile from house so babied it home. next day, checked oil, was about maybe a 1/4-1/2 qt. low, topped it off and started it up. pressure came up to about 70 lbs. and i drove around the neighborhood for a few miles, the gauge seemed to do the same thing, start to slowley go down to 0. any idea where to start looking first to fix this ? and does anybody know of a good diesel mech. in the ventura county area ? thanks

It could be as simple as the by-pass valve in the oil filter.

Or perhaps the sender unit and or gauge is going out. I found the wire off on the latest Trooper I have. I put a new pushon connector on the wire and installed it, to no avail. I checked the schematic but it was unclear which connector on
the back of the gauge was supposed to be the resistive sense. So I was stopped there. i thought about trying the gauge from the other Trooper but I never did.
Brian Rodgers
.

Very common - look at the connector underneath the vehicle on the passenger side -it's a pin lug type connector.

Maybe install a mechanical gauge to it to get the actual reading then go from there?

Cheers,
Trong

was the sending unit. thanks for all the input

Mine turned out to be the gauge itself.
Swap proved it.
Brian Rodgers

I have an 86 tdtII doing very similar behavior. Starts up at ~60 psi and goes down to about 30 whlie drivning in town. It disconcertingly heads down to 0 when on the highway, however the idiot light stays off. Sometimes it starts reading again when back in town after a highway trip. I haven't been doing any highway miles because of this.
I looked at it today, and the sender has a small external 'condenser' held on w/ a pipe clamp & *****.
I also have an 88 2.6 trooper and a spare oil sending unit for it - anyone know if the sending units are interchangable between the two? I can't see why not, however the setup for the gas trooper never included the condenser.

Thanks for any help

THAT SENDING UNIT WILL WORK, IT MAY NOT READ THE EXACT SAME PRESSURE READIGN AS YOU OLD ONE BUT IT WILL AT LEAST SHOW YOU THAT IT IS MAKING PRESSURE , THE SMALL CAPACITOR IS JUST FOR RADIO NOISE SUPPRESSION, AS THE WIPER IN THE CANNISTER MOVES ACROSS THE RESISTANCE WIRE , IT WILL WORK FINE WITH OUT IT.. JERRY

Wow, the guru himself! Thanks Jerry. According to napa, they list identical sending units for the 86 diesel vs the 88 gas models, so there was no point in buying a new one from them. I swapped sending units yesterday and there's an improvement. I als replaced the filter a bit early in case it could have been bypassing and I refilled with rotella 15w-40 oil. It starts up at about 40 -50 psi. Once up to temp the pressure reads about half way across the 0-30 segment of the gague, an didn't drop any lower while running 3k rpm at about 65mph.
This still strikes me a somewhat low, but I know I've read here that this is fairly normal range for these motors. This one has 152k on the clock and was supposedly replaced by isuzu around 50k due to a "rod issue" (info from previous owner). Is there any concern that the bearings are loose with pressure readings like this?
I suppose the other thing to investigate is the turbo. The chilton manual I've got is worthless with respect to this. Anyone have good search terms for this forum regarding turbo specs & rebuilding?

Thanks again