Engine/Transmission (1998.5 - 2002) 12V Lift Pump on a 24V

[Mr. Brewski]

After installing the proper cam I decided to rid myself of that awful stock electric lift pump. I installed a Cummins part# 3936317 with spacer plate and gaskets, replumbed all the banjo's with 3/8" Push-Lok -6an fittings and hose, and added a huge Mallory Bypass fuel pressure regulator between the pump and the stock fuel filter. I'm reading fuel pressure from the outlet of the filter canister. At idle I can adjust my fuel pressure from 4psi to somewheres around 25psi. I have it adjusted to 15psi.



I took the truck for a spin around the block and after she warmed up, I put the comp on 5X5 to see how far I could drag down the pressure. It came down to 6spi. Later I took it to the store and gave it another couple of 5X5 blasts and my FP was down to 12psi at idle.



Just to make sure that it isnt my Westach electric FP guage, I'm going to hook a cheapo 0-100psi full sweep oil pressure guage and try it again. I'll also do some troubleshooting and take the regualator out of the equation.



I have a couple of questions:



1) Even though I lubed the end of the pushrod on the fuel pump with cam lube before installing it, how much of a chance is there that I either wore down the pushrod or wiped out the cam lobe? It doesnt look like it's possible to misalign the pump, but I've never installed a 12V pump before, just many 24v pumps :-laf



2) How often has one of these pumps been bad right out of the box?



3) I hear that the VP will take incoming pressures exceeding 50psi. Whats everyone's oppinion about that?



4) Because I havent ever plumbed or installed a 12V lift pump, I assumed the the suction side was the port above the primer bulb and the pressure side was the horizonal port - is that the case or do I have it backwards?



Any comments and suggestions are apprciated in advance! Thanks!

 

[DavidC]

Maybe it is not the pressure side that is giving you problems. Could be the suction side. Check this post.

http://turbodieselregister.com/forums/showthread.php?t=162110



Dave

 

[Mr. Brewski]

Thanks for the reply, that could be the issue, how well did blowing air backwards through the lines work for you in the long run?

 

[DavidC]

Blowing the air was short term but showed me the pressure problem was behind the pump. About 1 mile tops. I wound up cutting the strainer from the in tank unit and installing an external unit. It is clear plastic that you can visually check and has a stainless screen and opens up to service. Pressure at idle is a constant 13-14 now compared to a dropping at least to 9 at idle with the in tank unit. A Rasp or Mitusa is next.



Dave

 

[The patriot]

To answer question #1.....

I was told dont bother lubing the pushrod.

"There's plenty oil in there". :-laf

I dont know what you incorrectly valved trucks are supposed to run, but my 215 Hp engine with 370 injectors has no problem with fuel pressure.

Under full load with the TT on going up hill I rarley see it under 20 PSI even mashing it hard.

Piers estimated my engine to be about 260 Hp with the injectors.

Eric

 

[Mr. Brewski]

A little more information... .



I hooked up a el-cheapo Equs oil pressure guage to the clean side of the filter and set the regulator at 20psi. Normal driving = rock solid. 5X5 blowing coal = 0 psi or close to it. I put the guage on the dirty side of the filter and had pretty much the same results - a little loss over the filter but with as much oscillating as the guage is doing it's hard to tell. I then left the guage on the dirty side and took the pump line off the regulator and hooked it directly to the fuel canister. The guage was oscilating from about 5psi to 95psi.....



Took it out for another run on 5X5 and smoked some of my neighbors out (I'm really sorry... ) and the guage would oscilate from 0 to 60psi. I'm kinda wondering if the fitting that screws into the output of the fuel pump is set too deep and interfering with the check valve. Also, I need to borrow Fishn2deeps oil filled guage and see if I can get a more accrate representation. My elcheapo guage is now shot I'll bet...



Hooked it all back up the way I meant it to be with the regulator...



Your suggestion that I put 125psi air pressure through the lines from the tank and blow all the crud out of the screen on the pickup is a valid next step - I might try that... But it looks like I'll be giving Eric from Vulcan a call and upgrading my fuel lines to 3/8" -6an all the way from the tank and putting a stand pipe in. We will see. I think it's good to go as far as driving is concerned though.

 

[Fishin Guide]

My setup has no issue making pressure. In fact, I cannot pull it below 38 psi with my new Vulcan DRAW STRAW and -8 lines from the tank to the pump.



And I know nothing is wrong with the lobe on that cam. I have personally inspected it with a 32 oz ball peen...



The pressure issue is in the regulator. It should make 40-50 psi unregulated at idle.



So, here's the next step. Stop by, let's hook up the good gauge and figure out exactly what the pressure is without the regulator inline. Then, lets set the pressure you want to see with shop air. We'll add some pressure on the bench to help counter the huge fuel pulses.



And at the end of the day, Mr Brewski will be home cracking a few cold homebrews and pondering the significance of haveing such an ace troubleshooter so close to home...



Dave

 

[Mr. Brewski]

the regulator stays holmes...



troublshooting with a pressure guage in multiple locations indicates tank issues - same as yours. I can pull the pump output to zero (Or really close. . ) without the need of a regulator.



and if you remember, I had a load of bad Bio Diesel with a good portion of that soap, my bets is that the little cloth at the bottom of the fuel tank module is full of crud...

 

[Mr. Brewski]

So, here's the next step. Stop by, let's hook up the good gauge and figure out exactly what the pressure is without the regulator inline.

been there, done that...

 

[Fishin Guide]

been there, done that...

You need a more stable gauge to get accurate readings. Once you know what you are dealing with, the rest is gravy.





Dave

 

[RonA]

Do the vp pumps have an overflow valve like the P7100? I bought an 8 dollar oil pressure gauge to check the fp. I only check it every 3 months. It bounces a little, but not that bad.

 

[Fishin Guide]

Do the vp pumps have an overflow valve like the P7100? I bought an 8 dollar oil pressure gauge to check the fp. I only check it every 3 months. It bounces a little, but not that bad.

Yes they do. It is set to a lower pressure (14psi approx).



However, the VP does not have the internal leakage of your pump. So, all that volume is backed up in the front of the VP resulting in much higher pressures than you will see.



This is why he and I are looking at using regulators to get pressures around 20 psi.



In the VP trucks, the pressure spikes are nuts. 5-10 psi a stroke. The regulator acts as a cushion for the VP and any gauges downstream. However, without a snubber, it still quickly kills them.



Dave