Lift pump problems

[20050627|3|008327|000043|65.183.99.20]

Had a new lift pump and OPS put in while on holidays (mid August) and it seems I still have lift pump problems. It worked for a while but has started hesitating and seems to have crapped out again.

What should I be checking for?

It really does not feel like it's running while idling.

Where is the OPS located?

And if I got work done at one dealership, should another be prepared to fix the mistakes of the first? I'm nowhere near where I got the work done.

[Kennedy]

Having seen way to many issues with the lift pump, I have developed a complete control harness setup that carries current to the lift pump independently of the OE OPS. It still uses an OPS and you must retain your current unit for dash gauge function, but my kit ads a "prime at start function as well as manual activation for easy filter bleeding. My OPS does not carry any of the load for the pump also.


It is difficult to say what happens in the OE system. The pump could short or start drawing excessive current, OR the OPS could deteriorate in connectivity to a point where it "browns out" harming the pump.

I also have a lift pump that promises to be the last one you will ever buy for your 6.5. It is not affected by contaminated fuel, and in the unlikely event that it stops running, it poses little or no measureable restriction...

[Kennedy]

I should add that opening the fuel filter water drain with engine idling is a sure fire way to tell if it is pumping. If fuel discharges then it is working. Otherwise it wil suck air and stall until you close the valve.

[20050627|3|008327|000043|65.183.99.20]

It's one of those dumb things that goes wrong when your 500 km's from home, with the wife and dogs, pulling a trailer, so I had GM fix it.

Given less of a time sensitive thing, I may have gone with your setup (and spent less then I did) but I'm pretty sure I can track this down.

BTW, while I have your attention, can I use your fan clutch without replacing the fan? On a 94 "S" engine.

[20050627|3|008327|000043|65.183.99.20]

Just looked at the pump on your site.

Ayup. Woulda been a lot cheaper. :(

[Kennedy]

You'll need to change the blade too as the blade hub diameter is much smaller on mine.

[20050627|3|008327|000043|65.183.99.20]

Back to the lift pump. I threw a vacuum/fuel pressure guage on the bleed line (this is the one mounted on the thermostat housing, right) and got a slight vacuum at idle.

I crawled under and tested the connector and got around 1 volt out of it.

As I said, both the OPS and the lift pump are brand new and I really think it is a connection somewhere. Where does the OPS connect up? The connector at the pump itself doesn't seem to be the problem.

[JohnC]

The current also goes through the NC contacts on the fuel pump relay and the fuse...

See if it pumps while cranking.

[C.K. Piquup]

What if it won`t start and when cranking only a weak amount of fuel exits the bleedera?

[20050627|3|008327|000043|65.183.99.20]

Well, I broke down and took it to a dealer. I really wanted to be fishing instead.

$55 to fix the OPS connection. She's back and running.

Still don't know where the thing is though. Is it possible I disconnected it while trying to fish out the PMD connection?

[JohnC]

Originally posted by Tacklewasher:
Still don't know where the thing is though.
On the back side of the block just below the driver's side head.