79 20R Fuel Pump Cuts Off

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David3283

David3283

10 Year
Joined
Aug 4, 2013
Threads
6
Messages
23
OK guys,

I've searched and searched, but havent been able to find much info on the issue I'm having.

When my truck is at running temp, the oil light slowly illuminates, and the fuel pump (electric on my truck) cuts off, obviously causing the truck to stall.

From what I've read, if the oil pressure drops, the electrical system shut off the fuel pump to avoid damage. Is this right?

I changed the Oil Pressure Switch, but had the same problem.

My next step is to get ahold of an oil pressure tester and test the pressure. I'm thinking this will eliminate a true pressure issue vs. an electrical issue. Am I on the right track here?

However, this is where my true quesitons come in... I've heard people talk about fuel pump relays, and fuel cutoff solenoids but cant seem to locate either. Are there other electrical components I should check before buying an oil pressure tester?

I appreciate the help,

:beer:
 
Are you confident that it's in the oil pressure wiring? I would try a jumper wire directly from the battery to the pump, see if it keeps running.

If it is something in the oil pressure wiring, I would be more concerned with the dropping oil pressure. Might be time for a new oil pump. The pressure regulator is built into the pump, they do wear out, as do the crescent pump gears.
 
I'm pretty sure I have a wiring issue and here is why.....

The fuel pump was previously wired directly to the battery (previous owner's set up). I obviously wasn't happy with this set up so, I found the old wiring for the internal tank pump (the current pump is an inline pump) and rewired it to the new inline pump. This is exactly when I realized I had this issue.

Today I used an oil pressure tester and connected it directly to where the oil pressure switch was, I had perfect pressure (Haynes says at idle = 4.3 psi minimum, at 3000rpm = 36-71psi).

At this point I started poking around with the wiring near the oil pressure switch, here is what I found, and where I could use some help.

I disconnected what looks like a ground wire attached to the engine (black/yellow). The wiring diagram shows this wire running to the fuel cut solenoid (not sure what this looks like). When I disconnected this wire, my oil light no longer illuminated and my fuel pump never cut off.

When this wire is attached (or touching any metal), my oil light illuminates, my temp gauge spikes quick, and my fuel pump then cuts off.

So, I disconnected it again and took it for a quick test drive. No oil light illuminated, my fuel pump ran fine, and my temp registered as normal.

My truck is very close to road ready after a considerable about of work, but I'd like for the oil light and cut off to function normally, especially given that my truck does not have a permanent oil pressure gauge.

Keep in mind that I don't have this issue until the engine is at normal operating temp.

Any thoughts on issue would be greatly appreciated. Also, if needed I'm happy to take some pics.

Thanks,
 
Last edited:
David3283 said:
I'm pretty sure I have a wiring issue and here is why.....

The fuel pump was previously wired directly to the battery (previous owner's set up). I obviously wasn't happy with this set up so, I found the old wiring for the internal tank pump (the current pump is an inline pump) and rewired it to the new inline pump. This is exactly when I realized I had this issue.

Today I used an oil pressure tester and connected it directly to where the oil pressure switch was, I had perfect pressure (Haynes says at idle = 4.3 psi minimum, at 3000rpm = 36-71psi).

At this point I started poking around with the wiring near the oil pressure switch, here is what I found, and where I could use some help.

I disconnected what looks like a ground wire attached to the engine (black/yellow). The wiring diagram shows this wire running to the fuel cut solenoid (not sure what this looks like). When I disconnected this wire, my oil light no longer illuminated and my fuel pump never cut off.

When this wire is attached (or touching any metal), my oil light illuminates, my temp gauge spikes quick, and my fuel pump then cuts off.

So, I disconnected it again and took it for a quick test drive. No oil light illuminated, my fuel pump ran fine, and my temp registered as normal.

My truck is very close to road ready after a considerable about of work, but I'd like for the oil light and cut off to function normally, especially given that my truck does not have a permanent oil pressure gauge.

Keep in mind that I don't have this issue until the engine is at normal operating temp.

Any thoughts on issue would be greatly appreciated. Also, if needed I'm happy to take some pics.

Thanks,
Click to expand...

How would you like to have a stock oil and voltage meter? The type that goes by the heater blower.
I might source one if you want one.
 
I'll likely add one, my interior is blue so if you have one that matches I'd be interested. However, I'd like to solve the problem either way. I currently have the cut off solenoid disconnected b/c I know I'm getting adequate pressure.
 
David3283 said:
I'll likely add one, my interior is blue so if you have one that matches I'd be interested. However, I'd like to solve the problem either way. I currently have the cut off solenoid disconnected b/c I know I'm getting adequate pressure.
Click to expand...

Alright David, blue is a hard color to get. But I can get a black one. I'll try to get some pictures by tomorrow.
 
1980 20R Fuel pump issues.

I am having some issues installing my mechanical fuel pump in my 20R. The rocker arm on the fuel pump is to long, it is not installing. I may have the wrong fuel pump. Can someone give me some insight on this? Sorry for posting on your convo, I could not find any other thread that was similar.
 
There is supposed to be a spacer "insulator" between the pump and the cylinder head, do you have this installed?
 
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