INCLUDES:
- Dropping, cleaning and inspecting the fuel tank and testing the fuel sender.
- Replacing the OPS and fuel strainer.

Having the lift pump mounted externally is a convenience thats routinely taken for granted by pro's and DIYrs alike..

When properly maintained and not routinely refueling behind wafflehouse, these lift pumps should last 100,000 miles OR more.

Frequent OPS and/or Lift Pump failures are often caused from being overworked, lift pump trying to draw fuel thru a clogged strainer (fuel restriction) that places more work on the LP which draws more amps across the tiny OPS switch.

Thats why you should replace the OPS and strainer with a new lift pump.


Excessive vacuum allows the fuel to release air aka fumes that arent readily reabsorbed or reconstituted, create an unwanted "air leak" even though theres no leaks in the system..

 

HeavyChevy95,

Reviewing threads I came to yours.

I have a 93 6.5L and strange fuel pressure issues

Likely needs glow plug relay, but once warmed up runs fine, in fact will run all day and get 14-15mpg.

By opening the T valve to drain any water, nothing came out, 10 seconds later the engine quit. Bled system, repeated, same.

I then removed the fuel pump relay from the firewall, placed on a hot point and can hear the LP buzzing. This is how I primed the system again with T valve open.

I then got a HF fuel gauge, $19. Placed at end of T hose, started engine, opened valve and gauge shows a vacuum.

To add: once running, I could not hear the LP running, used a stethoscope.

Question, how can I use the fuse and hear the LP buzzing, but can't seem to hear it running and have a vacuum?

Juan304

 

Are you asking how to activate the LP? If so you'll need about 6' of wire hook it to the positive terminal on the drivers side battery and other end into the G terminal on the ALDL port under the dash this will make the LP run.

https://www.google.com/search?q=aldl...34ebjEgWp5M%3A

 

Let me clarify:
With engine off I can manually activate the LP, via fuse to hot contact. But with engine running I cannot hear LP.

Also, a vacuum points to LP

Seems LP has failed, if so, would that then explain the vacuum, and perhaps no noise as engine is running?

 

A 93 requires a good OPS for lift pump operation. I don't quite understand how your jumping power to the pump but a bad OPS may explain why your losing power with the engine running.

You stated you primed it by jumping the lift pump, so it sounds like the pump is working.

 

Burnhedge,
I agree the issue must be the OPS. Forum mentions OPS as a common problem.

To double test, with engine running I took fuel relay fuse and touched hot spot, LP came on and fuel pressure gauge then showed 5 psi.

Doing so bypasses the OPS.

I'll double check power coming to the LP, but almost certain issue is the OPS.

Will order new OPS and advise once installed.

Thank you, and wishing everyone a good XMAS and good year.
John

 

Use only AC Delco for the oil pressure switch.

 

Just now replaced the OPS. Fuel pressure at constant 5 PSI, regardless of engine RPM.

When engine turned off the LP cycles for about 10 seconds then stops.

So that solves one problem.

Hopefully with corrected LP, and being cold, engine will start better with less smoke.

Will advise, and with best thanks,
Juan

 

Yesterday morning temperature was about 25, started and truck smoked terribly with engine laboring to idle. It was awful.

Yesterday afternoon replaced OPS. I got the special socket from O'Reilly's

This morning, and similar 25 weather, truck started very well, no smoke, and engine idled very well. I can hear the LP cycling, and also when engine turned off.
So that addresses one point.
I'll now replace the glow plugs before weather turns really cold.

Best to everyone for XMAS.
Juan