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94-98 Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect...NO ADVERTISING

Thread: Oil and fuel mixing in ppump Reply to Thread
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  Topic Review (Newest First)
Yesterday 08:51 AM
GAmes
Quote:
Originally Posted by Dieseldave94 View Post
I ended up bleeding the lines to the injectors some more...........
You lost me. What did you bleed them of? Any small amount of air in the injector lines is pushed out less than 30 seconds after starting the engine.

There is a good possibility that the gauge was ruined by not installing the needle valve in the beginning. A good lift pump with a functioning OFV should give you more than 20 psi of pressure.

I suggest you drop the tank and check the module for damage and crud build up.
07-17-2019 11:08 PM
Dieseldave94
Quote:
Originally Posted by Antonm View Post
This doesn't make a lot of sense to me. My stock OFV ran at 10psi and the truck started/ drove fine with none of the issues you're seeing (the only benefit I saw replacing the OFV and setting it at 28psi is a possible increase in power, but that may be just in my head idk). Also if it was a suction restriction like a clogged draw tube, wouldn't the issue be more present at high RPM / under heavy load when fuel demand is higher, not at idle and 1100 RPM like you're seeing?
I think if you have positive pressure to the injection pump (which you do) and no air leaks (which you've verified with the clear hose) that your low pressure fuel system is not the cause and start looking other places.
Yeah I was thinking about and it and came to the same conclusion. I ended up bleeding the lines to the injectors some more to see if it did anything and now the fuel pressure rises with rpm. It still drops after a second a second or two of staying at a certain rpm but it seems to be a lot closer to the correct pressure range. The truck still runs the same though.
07-16-2019 09:46 PM
Antonm
Quote:
Originally Posted by Dieseldave94 View Post
So I have fuel pressure gauge but never really could read it properly because it was bouncing around a lot due to not having a needle valve. Today I installed a needle valve and noticed the pressure is at 20 psi at idle but never really rises above that. It would actually drop by as much as 5 psi when increasing rpm. When I let off the throttle it will spike back up to a little over 20 and then rest at 20 again. I recently replaced the lift pump with a dcec cummins one and when I pinch the return line the pressure goes up to about 40 psi. So at this point im think maybe there is a restriction in flow like a clogged draw tube in the tank. Im going to test it later by running a hose directly from a jug of diesel to the lift pump but is there anything else that would cause dropping fuel pressure?
This doesn't make a lot of sense to me. My stock OFV ran at 10psi and the truck started/ drove fine with none of the issues you're seeing (the only benefit I saw replacing the OFV and setting it at 28psi is a possible increase in power, but that may be just in my head idk). Also if it was a suction restriction like a clogged draw tube, wouldn't the issue be more present at high RPM / under heavy load when fuel demand is higher, not at idle and 1100 RPM like you're seeing?
I think if you have positive pressure to the injection pump (which you do) and no air leaks (which you've verified with the clear hose) that your low pressure fuel system is not the cause and start looking other places.
07-13-2019 02:03 PM
Dieseldave94 So I have fuel pressure gauge but never really could read it properly because it was bouncing around a lot due to not having a needle valve. Today I installed a needle valve and noticed the pressure is at 20 psi at idle but never really rises above that. It would actually drop by as much as 5 psi when increasing rpm. When I let off the throttle it will spike back up to a little over 20 and then rest at 20 again. I recently replaced the lift pump with a dcec cummins one and when I pinch the return line the pressure goes up to about 40 psi. So at this point im think maybe there is a restriction in flow like a clogged draw tube in the tank. Im going to test it later by running a hose directly from a jug of diesel to the lift pump but is there anything else that would cause dropping fuel pressure?
07-13-2019 01:46 PM
Dieseldave94
Quote:
Originally Posted by 9297oldram View Post
Were they Bosch injectors, seen to many people buy off brand injectors only to find out they weren't popped to spec.
Yep they were oem bosch specifically for my model year
07-13-2019 01:45 PM
Dieseldave94
Quote:
Originally Posted by GAmes View Post
Unlike the VP44, running with 0 pressure won't damage a p-pump. Have you done a search and read the symptoms other members have had with their '94 pumps?
Ok at least thats good to know. Did a search but none of the symptoms I have seem to exactly match other members. It seems like in most cases ive read the truck will have a hard time starting or the problem will come and go but with mine it seems to be constant and it starts up fine every time.
07-02-2019 06:30 PM
9297oldram
Quote:
Originally Posted by Dieseldave94 View Post
Yeah rockauto only had two so I actually ended up ordering all of them from summit racing. They also had $12 next day shipping which was nice
Were they Bosch injectors, seen to many people buy off brand injectors only to find out they weren't popped to spec.
07-02-2019 06:15 PM
GAmes Unlike the VP44, running with 0 pressure won't damage a p-pump. Have you done a search and read the symptoms other members have had with their '94 pumps?
07-02-2019 02:56 PM
Dieseldave94 So I replaced the injectors and the issue is still there. Its definitely not smoking as much but still sounds like it has a slight misfire and has a bad vibration around 1100 rpm. At this point I think it has to be either a burnt valve or something with the injection pump. Would a burnt valve cause a significant difference in readings on a compression test? Im leaning more towards the pump because when I bought the truck the overflow valve was bad and it was running 0 psi. Im not sure how long it was running like that so I think it may have damaged the pump. Anyone have any recommendations for shops to have a pump rebuilt or buy a reman one from?
07-02-2019 02:47 PM
Dieseldave94
Quote:
Originally Posted by texasprd View Post
If Rock Auto doesn't have them, check Summit Racing. When I replaced mine, Rock Auto only had 5 - Summit was the next cheapest I could find, so I got the 6th one from them. Though a little more than Rock Auto, Summit was still cheaper than getting one rebuilt by the Bosch pump shop I went to. That was nearly two years ago - so things may have changed since, but still worth checking into.
Yeah rockauto only had two so I actually ended up ordering all of them from summit racing. They also had $12 next day shipping which was nice
06-27-2019 04:01 PM
texasprd If Rock Auto doesn't have them, check Summit Racing. When I replaced mine, Rock Auto only had 5 - Summit was the next cheapest I could find, so I got the 6th one from them. Though a little more than Rock Auto, Summit was still cheaper than getting one rebuilt by the Bosch pump shop I went to. That was nearly two years ago - so things may have changed since, but still worth checking into.
06-26-2019 07:34 PM
GAmes The best prices on new stock Bosch injectors is at Rock Auto when they have them in stock.
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