Hi everyone,

I installed a DELPHI low pressure piston lift pump on my 1991.0 Cummins. I haven't run the truck with it yet but started to prime the system today after getting the fuel lines hooked back up.

Priming went ok, got a lot of air out and fuel was coming out of the return line as well, but then the resistance started to get very high, and I continued to prime it a couple more times, pressing VERY hard. (bad mistake) THEN the IP started to weep/drip a little bit from the top cover/manual shutoff valve. This is strange because I resealed most of the pump, and ALL of the top cover.

Question is, did I overpressure the IP? Will it be ok running as normal? Or should I pull the IP again and take a look to see what is going on. I know on these piston pumps, the pressure is made from the spring return, not the cam lobe lift, and that is how pressure is set. I may have spiked the pressure on it, but not sure if I blew out an oring, or not.

I may just run it and see what happens and let you know. I can easily pull the IP anytime later on.

 

I have a Delphi low pressure lift pump on my motor as well. Been using it for at least 4 years now. I have never ran into a situation like you describe. Unless something in your return line plugged up and was stopping the pressure from releasing, you should not be able to over pressurize the system.

 

cool thanks that answers my question. The return line goes from stock 1/4" to 5/16" steel braided all the way back. Guess I need to look into it a bit more and reseal/repair as necessary before moving forward.

Edit:

Well now I'm really confused. I manually pumped the lift pump again and this time in addition to weeping from the shutoff lever, (looks like I need to pull the pump top to reseal) I heard a weezing of air release on the exhaust side and every one of the injectors were soaked at their base. I guess it could be worn saddle washers/seals on the return line but wow, this is very strange now. I never touched the hold down nuts on these injectors either. Lots of fuel on the ground, looks like i shouldn't have messed with the priming lever. I will have to check my return line for blockage as well.

 

This is odd.

I'd try turning the motor over by hand and see if anything sort of "catches" in the IP. If not I'd probably try to fire it but I wouldn't want you to do it on my recommendation and have something bad happen lol

Also, the IP return is a banjo bolt but it only has a really tiny bleeder hole in it. It's still possible to spike the pressure I'm sure.

 

In my experience with delphi pumps is they are Gooofy.

Pump #1 sent out 20+ PSI blew the seal on IP. Took the pumps off went back to H&H to get new seal and IP rekeyed and a new lift pump.

Seal & rekey no problem now the funny part Keith the guy that worked there at the time just took the lift pump and toss it in the trash and gave me another one. He said the paper work is way to much of a PITA to go thought to get a reimburse. Kind put a what did I buy feelling in the gut

LP #2 put out 6 PSI and sucks down to 1 psi.

Called Keith told him the PSI change he was shacking his head and just said junk. He ended up selling me a carter low PSI pump for some really low price.

That was about six++ years ago the carter is still sitting on a shelf. I sold that truck 4+ years ago pulled all the gauges they are sitting on the shelf also maybe one day I;ll get around to putting them on

 

I ran a Delphi pump on my old 91 with no problems. It will be going on my 92 if I ever get round to it. Sound like you have a return problem.

 

Thanks guys yeah I agree. I'll check into it this morning. I've run 3 other delphi's with no issues. I haven't messed around with priming it too much though. I just have a feeling that the prime button puts out much higher unregulated pressure than the main pump cylinder. So that in conjunction with my return line restriction could be my issue.

I have a 100 gallon transfer tank in the bed that the 5/16" line travels up to, so none of this is stock. I'll check that the fuel vent setup isn't clogged and also the return line itself. I have some new saddle washers to throw on there and looks like the manual shutoff oring can be replaced without removing the pump or top.

 

Just for FYI. The IP has a small hole in the return banjo fitting. It clogs easily especially when you blow the rubber tip off the shutdown solenoid. It that clogs it is easy to over press the IP.

 

Thanks for the info. So my problem turned out to be an overfull 100 gallon fuel tank. The vent line and return line as well were hydrolocked and that made it act like the return line was blocked. The air/fuel I was priming had nowhere to go. So I pumped 10 gallons out and now it is good to go. Was a good inadvertent pressure test of the system though. I'm sure it will be good to go now 100%.

 

Would have never though ov that off the top of my head. Oood it wwas somthing simple.

 

Thanks guys. I ordered the dieseltuff pump. I have been smelling diesel. I just got back from town and smelled it again. Sure enough the bottom of the stock pump is damp with diesel.