Priming fuel filter - HELP

[hump]

Changing out fuel filter the way I have in the past. Attached suction gun to petcock, loosened cap on top of filter and sucked the bowl dry of fuel. new filter installed but I cant activate Lift pump by keying the ignition switch like I could before. I drained off a cup of fuel with truck running beforehand no problem. Any ideas? can I pump clean fuel back in through petcock? Any help would be appreciated as I have to get to work tomorrow.

[HowieE]

For a get to work solution. Nick the Gray wire coming up from the Oil Pressure switch and apply 12 volts to the nicked wire. That will supply voltage directly to the fuel pump. Open the pet cock while the pump is running and bleed off the air.
If you want to see the fuel pump circuit look at my web page for the OPS relay upgrade.

[hump]

Thanks Howie,
So with the engine going, would the lp run if OPS is shot?

[HowieE]

No. If the OPS fails the fuel pump will not after startup. However your OPS is not in the circuit while tring to prime the filter with the ign. key. The OPS only completes the circuit to the fuel pump after the engine is running and the oil pressure has gone above 4lbs.
The reason for the OPS mode shown in my web site is to prolong the life of the OPS. GM designed a switch that is rated at 1 amp. while the fuel pump draws 4 amps. "Planned Failure" to sell parts.

[hump]

Did a search and tried Dick Wells trick of jumping 85 & 86 contacts under the fuel pump relay in the fuse box. Worked like a charm, makes the job a lot easier when you can activate lp from under the hood (only a cup of fuel on drveway rather than a pint!)

Funny thing is, ignition will now activate lp. What's that all about? Just another electrical gremlin to cause me grief I guess. Once again the Diesel Page helps out. Thanks Howie, your idea looks good as well, nice site.

Any thoughts on draining the filter bowl before changing filter? Seems to me that few techs will take the time to do it(who would know) or to clean out any accumulated crud. Possible source of injection pump wear and failure. Crud stirred up will settle in intake tube if my thinking is right. Doesn't take much to screw up these pumps.

[332bill]

When I changed the filter on my burb after I bought it, the old filter was black and there was some crud lying on the bottom of the filter bowl. I siphoned out the remaining fuel, and sprayed some brake cleaner in to loosen up the crud. I then sucked it dry with the shop-vac. Clean as a whistle!!

Bill

[MTTwister]

HowieE - "The reason for the OPS mode shown in my web site is to prolong the life of the OPS. GM designed a switch that is rated at 1 amp. while the fuel pump draws 4 amps"

I was under the impression that '96 up already had a LP Relay in the Fuse Box. Does this not take the load off the contact points?

I had some 30 relays (headlight, driving light type). would one of these be sufficient to wire in, if needed? If ot, I believe you got your HDuty at Radio Shack - don't remember the part number, I suppose? smile.gif

[HowieE]

Yes there is a relay in the 96s but that relay only supplies voltage during the Glow Plug Cycle and drops out of the circuit once the engine starts and the OPS makes with 4 lbs pressure.
Any auto parts should have a general purpose 30 amp relay. If you can't find them there I get mine from Bully Dog.

[CareyWeber]

Originally posted by hump:
Did a search and tried Dick Wells trick of jumping 85 & 86 contacts under the fuel pump relay in the fuse box. Worked like a charm, makes the job a lot easier when you can activate lp from under the hood (only a cup of fuel on drveway rather than a pint!)

Funny thing is, ignition will now activate lp. What's that all about? Just another electrical gremlin to cause me grief I guess. Once again the Diesel Page helps out. Thanks Howie, your idea looks good as well, nice site.

Any thoughts on draining the filter bowl before changing filter? Seems to me that few techs will take the time to do it(who would know) or to clean out any accumulated crud. Possible source of injection pump wear and failure. Crud stirred up will settle in intake tube if my thinking is right. Doesn't take much to screw up these pumps. hump,

On the 97's and up there is a red single wire coming off the engine Electric center (when looking from the drivers side it coming off the upper right corner) that when 12 volts is applied to it runs the lift pump.

I mounted a momentary switch on the passenger side of the engine Electric center and now priming the filter is so easy. :cool:

Carey

[HowieE]

That red wire is the fuel pump prime connection, factor installed for that purpose. As many times as I have posted on the OPS and it's modes I had never noted that wire on the diagrams. The wire goes to the NC contacts on the fuel pump relay.