1987 Silverado V10 from the frozen north

[JohnnyPopper]

Good on you man, hope it works out that you O.P.  is sufficient to run her.

[nbarr7]

Got my tester in finally. Just to make sure, the sender is the unit that comes off the 90 degree piece just to the drivers side kind of underneath the distributor? Can't really tell if it has flat sides for using a wrench, or if you just need to use a tiny oil filter style strap wrench or?

[bd]

The dash gauge oil pressure sender will appear like...





...(although maybe painted black) and is more likely located just above the engine oil filter.  On TBI engines the switch located adjacent to the distributor, typically, is a failsafe to power the in-tank fuel pump in the event the fuel pump relay fails.

[nbarr7]

Thank you for clarifying. I found the spot, and hooked up my tester, and this is what I'm seeing with the truck running (video link below). Maybe about 33psi with old oil? Also, I was leaking oil at the connection point and when I went to undo the quick connect, it may have come undone a bit, so even this reading may be a little low. But maybe not. This was a cold start, and only running it for a minute due to oil spilling from the port (so much for the o rings that came with the oil tester kit).

https://youtu.be/aYIZ-vtjbeY


My next issue, assuming this is ok, is to find out why I can put 4 gallons in and the truck will run for like 3 minutes, and then run out of gas haha. Twice this has happened, and hitting the tank it sounds fairly empty. Wonder if it's somehow getting returned to the left hand tank or something? (right hand tank is brand new along with the rh pump and strainer and sending unit)

I also have basically no gauges except the amp meter. Looked for the dash ground near the emergency brake, but the old owner messed so much with the wiring I'm not sure where things are.

[JohnnyPopper]

Well she's not a flat girl after all!

33-35 seems low, but your oil may be completely spent with little viscosity left. The leaks might have cost you a few pounds, if they were pouring out.

How many miles is on the motor?

Use some motor flush on the current oil, and fill her with single viscosity oil, like 40w or even 50w.

[nbarr7]

The odometer says 108, but as the dash was completely disconnected, I have no way of knowing if those miles pertain to this truck. It was recommended to run something like rotella 15w40 by a friend, so I was looking at that 40 weight level anyway.

[JohnnyPopper]

Rotella is a good oil. I would start with a single vis oil first.

33 is low for a cold motor. But in this case, you don't know if it's loose bearings or shot-out oil.

If it jumps to 45, with new oil while cold, it means the bearings aren't shot, it will thin out as temp is gained.

If it drops to 30-35 I wouldn't lose sleep.

[Shifty]

Old rule of thumb...10lbs for every 1000 rpm after 30lbs.

[nbarr7]

Thanks for the help and opinions. I've removed the oil pressure sender - would you all replace that or just run a mechanical gauge for a while? I have one of those basic 3-pack gauge sets laying around anyway, but my long term goal is to use the in-dash gauge. Not sure how to troubleshoot it if it's not even hooked up...

[nbarr7]

Ok here we go. I did change the oil and filter (wix) and went with Rotella 15W40 as it was local, easy to get up here, and another friend runs it in his tbi suburban. I can always go to a straight 40wt later if needed. I installed a mechanical oil gauge for now, since I still have zero dash gauges excepting the amp meter. I'm now showing around 40 shortly after starting (cold) (see attached image)

The truck is still doing this thing where I'll put 4 or so gallons in (have done this twice now) and it will run for maybe 3 minutes, then act like it's out of fuel. It's a new tank, so I know you need a few gallons just to submerge the pump, but I've put 4 gallons in twice at least, so that means there should be 8-10 gallons in a 16 gallon tank which shouldn't run out in 3 minutes. And as a reminder it's a brand new fuel tank, new pump, new sending unit, new in-line filter, I used a dremel/sanding disc and ground a bare spot on the frame to re-ground the sender, and all hard lines have been blown out with an air compressor (except those 'aft' of the filter as I didn't mess with the selector valve yet and didn't want to blow compressed air through that). The throttle body and injector housing has also been disassembled and cleaned out with carb cleaner.

It's really weird. Even if I put fuel in the throttle body, it will only burn that much and then quit like it's empty. But 3 minutes before I had added 4 gallons, you know? Thoughts of what to check next? On either fuel delivery or factory gauge non-function?

[frotosride]

From personal experience, you can keep the engine running on a level surface with just over 1gallon. I would verify the return line routing. Hand over hand this item you'll thank yourself later. Tap the other tank and see if it's full, at this point you should only have to add 4 more gallons and the other tank will likely start to overflow.

The selector valve/switch can leak by but unless the internals are almost missing it wouldn't leak by that much that quick. The valve may have been replaced or at some point the returns swapped. I'll try and find a diagram but for reference the return is the 5/16" hose (the middle size) the smallest is a vent for the charcoal canister (if it still exists) and the larger line 3/8" is the fuel supply.

[nbarr7]

Sorry for the delay all - the truck is in my driveway (I don't have heated shop space - only a woodshop) and with temps at or below zero Farenheit, I haven't been able to make myself crawl underneath - my fingers just don't work at that temperature. I'm thinking of bypassing the selector valve for temporary (until spring) just so I know everything is good from the brand new tank, pump, and sending unit to the throttle body etc. We'll see what I can do later this week if/when it warms up.

[frotosride]

I don't blame you one bit. My garage is for tools, not parking vehicle, except maybe 🤔 a motorcycle or two. Way too many tools and parts for anything else.
Down here we've been in the 30-40 at night and 50 to low 60s during the day but that dang wind!!! 😬

[nbarr7]

Ok, I took the relative reprieve yesterday of double digits above zero and used double ended barbs to connect the RH tank directly to the send and return lines going to the throttle body. Tapping on the tanks themselves with wrench/stick, the LH tank does indeed sound full, and the RH tank sounds largely empty - must have been pumping fuel to the LH tank as well as a small amount to the throttle body, so that it died in 2 minutes or so.

Fun side note, when I disconnected the RH tank from the selector valve, something in the LH tank was allowing it to act like a little water tower or pressure tank and it started dripping gas slow, but steady for a while out of the selector valve itself. I filled up a whole ice cream bucket with gas dripping while I ran to the parts store to get some vacuum plugs to wire clamp over any fuel selector openings I left open during this process. I didn't think the LH fuel pump would allow fuel to just pass through. Turns out I got to get a free hand/down the arm gas shower instead.

Since yesterday, we're back down to like 3 degrees, so I'm going to wait a few days before trying to start the truck (also hoping some of the gas that got spilled around the ice cream pail gets dried up)

[frotosride]

Well that leaves two options: 1) lines are incorrect.
2) selector valve/switch is leaking by.
If you're not worried about the second tank and just want drive then keep your current set up bypassing the selector and drive to see if there are any other issues. This way when you take it down to fix the fuel tank issue you can fix anything else that come up while it's down.