Suspicious lift pump road test

[EMDDIESEL]

Ok, i just took the truck out for a blast to check fuel pressures again thinking maybe they would change. with the new fuel pressure gauge, here is what i am getting:



When i start the engine it goes to 14-16psi, the drops to about 3psi.

Idle: 3-4psi



Cruising around town, 0psi. I went on the the highway and floored it, the gauge went to zero for about 5 seconds, then i let off the throttle at about 80mph and the pressure shot up to 15psi and stayed there for about 5 seconds, then i stepped on it again and it went to about 5psi for a few seconds, then back to zero.

Does this sound like the lift pump is going??. Should i drive the truck as little as possible till i get it fixed?. Its going to the dealer monday for the clockspring, but i DOUBT they will have a lift pump in stock. What can i do in the meantime? should i just buy the pump and do it myself?, how hard is it and how much. I heard it was easy. Sorry for all the posts on this, i am just freaked since i have no back up car. Any help would be GREATLY appreciated.

 

[DAWG-1]

I read on your prior post that you installed a mechanical gauge. How did you bleed the line to your gauge? I was thinking you might have air in the line, creating a false reading.

 

[Archive]

If those readings are correct, it certainly sounds like your lift pump is going south.



If memory is correct, a new lift pump from dodge is over two hundred bucks(closer to three)... from Cummins about 139. Putting a new one on shouldn't be too bad... I would remove the fuel filter, and reach down there and do it. You could probably do it from the bottom, with some very long, skinny arms. Seems like I remember you not being the "skinny" type.

 

[illflem]

EMD, I doubt air in the line would give that much of a false reading. One way to look at it is that your pump most likely was putting out low pressure long before you installed the gauge, whether you drive it more is your call, but I wouldn't be going on any long trips quite yet.

 

[DRR-24V]

I would have it replaced under warrantee. You can buy some more Bomber parts for the $200-300 bucks.

 

[Evan A. Beck]

EMD...



It definatley sounds like your lift pump is on the fritz. Erratic performance (like you are having) is a sure indication of a pump on its way out.



Don't get the pump from Dodge... They are $395.



My advice to you, is buy a pump from Cummins and install it yourself. Yeah, it'll cost $120+, but it sure beats letting the Dodge techs get ahold of your precious Ram. See what the pressure readings are after the new pump is in. Should be improved... One thing to keep in mind, is the pumps can be bad right out of the box. I have seen it happen about a half dozen times or so. Changing the pump is easy. You don't need to remove the fuel filter, or anything else for that matter. Do it from the top, it makes it much easier. Takes about 45 mins to change, if you take your time.



Your pressure at idle seems ok, but when you get on it at all, it goes in the can. What's that mean? Bad output from the pump. It just can't keep up when the fuel demand is higher. That's why it goes back up when you let off the throttle. I think a new pump will take care of your problem.



If you want to go a different route, you can install an aftermarket pump. I am building a custom fuel system for my truck using a Carter 4601HP 14-16 psi pump. I will be using 1/2" supply, and 3/8" to the filter & injection pump. The pump will be located aft of the transmission crossmember, and forward of the fuel tank. I am building an isolated mounting bracket for the pump as well.



So why the 1/2" supply you ask?



Well, I have done a lot of reasearch on fuel systems on the ISB engine, and have found the supply line is a big cariable when it comes to fuel pressure. For example, lots of the big 30,000 lb motorhomes I work on are equipped with the ISB. Yeah, they are a 260 or 275 HP version, but basically the same as the one in the pickups. The lift pump is the same, the fuel filter is the same, the lines from the lift pump to the injection pump are the same, and the injection pump is virtually the same. BUT... The supply line to the lift pump is ALWAYS 1/2". Fuel pressure tests going uphill under load in one of these big diesel pushers, never goes under 9 or 10 lbs. The pickups are another story. They are being starved of fuel because of poor supply volume to the lift pump. Distance between the lift pump and fuel tank on the pushers is greater than that on the pickups. The supply line on the pickups is 5/16", far too small IMO. And you gotta remember, that pump has to suck fuel UP from the bottom of the tank, all along the frame rail, and UP to the lift pump. The small ID of the supply line is causing a major restriction. Think of it as running a 1/2" water main to your house... It's just not going to perform well.



I looked into the lift pump for the ISC, and it is identical to the one on the ISB except for one part. It uses a 3/4" supply. Same Carter pump body, same electrical plug too.



As soon as I get the system done, I will be posting detailed results. I am going to have to drop the tank for this project, but that's no big deal... Gotta change out the sending unit anyways.

 

[swamp rat]

5/16" supply line?

1/16" isn't much to speak of, but I thought the supply line was 3/8"OD and the return line was 5/16"OD?? If I am wrong then that may be the answer to a problem I'm having!



Looks like I may be in search of some nylon QD lines to the sending/pickup unit.

 

[Evan A. Beck]

Swamprat,



The supply line is 5/16" ID, and is 1/2" on the motorhomes and such... Other than that, the system is the same. Sounds pretty restrictive, eh?

 

[John]

.....however

Evan, the Diesel pusher motorhomes equipped with the ISBs are also helped by gravity feed (i. e. , the fuel tank is mounted forward of the engine... the reverse of what we have, thus creating an aid to fuel delivery), thereby not making this a seemingly apples to apples comparison.

 

[Tom W]

You probably know this. The pump is covered under the emissions warranty until 100k miles. Mine was replaced 25K miles ago and works fine, 13-14lbs at idle and cruising, never drops below 12lbs.

 

[B9Mile]

The Lift Pump

I would have it replaced under warranty.



If your VP44 takes a dump before you get to 100k miles, then its in the DC computer system that you had a defective lift pump. This will make it harder for the DC people to deny warranty replacement of the VP44 due to "something YOU did" to the truck.



Just make it clear to the service people that you don't want any reflashes of the "latest" software upgrade.



My lift pump was replaced under warranty at 46k miles. I think the charge to DC for the new pump was about $359. Its been in for about 25K miles now. I get 13 to 14 psig at idle, 11. 5 at 65 mph with 5 psi of boost (its bone stock, I like my 22 to 23 mpg on the hiway), and 10 at WOT.

 

[EMDDIESEL]

Thanks for all the responses guys. I will play it by ear and see whent i bring it in tommorow about how long it will take to get the pump. I did not bleed the line, totally slipped my mind. But even still, i dont think that would cause the readings i am getting.

The thing is, the truck runs great, it accelerates fine even when the gauge is showing ZERO. I dont get it? I have the Enterprise pusher pump kit but i dont want to install that untill i fix the stock pump. After its all done, then i will have both pumps which should help. One last thing, which connector do they use to Reflash? i want to lock it somehow so they dont mess with it.

 

[Evan A. Beck]

All the more reason to go with 1/2" supply...

Good point John. However, more often than not, the fuel line goes from the tank to the very BACk of the rig, and then the opposite direction. This is because there is a filter on the suction side, and it is usually mounted at the rear access opening on the motorhome. Also, the pickup line in the tank is longer, and therefore has to go a further distance up while inside the tank. Gravity would only play a small role, and its effects would be negated by the rear-mounted filter setup.

 

[B9Mile]

VP44 / Reflash

The VP44 is actually two pumps within the same body. There is a ow pressure pump which supplies fuel to the high pressure injection pump. The lift pump ensures the LP pump always has a positive suction head.



The VP37 pump on my TDI Jetta does not have a lift pump. Actually, it develops a slight vacuum in the suction line. That's another story.



The ECM reflashing is done through that computer serial cable looking connector under the lower lip of the panels below the steering wheel. The dealer's technician will need to access this to check for any fault codes from a failed lift pump.



Your VP44 should be getting lots of fuel right now. If it weren't, the fuel temp inside the pump would increase quite a bit causing the ECM to reduce your fueling rate. When you do your full power runs to check the gauge readings, this is when you would notce the defueling signal.



Your VP44 should be OK. I would think it would take some serious towing to cause it to overheat.



I never knew my lift pump died until I tried to refill the fuel filter to bleed the system after I installed my Westach gauges last summer. The pump would run just fine, but it didn't pump any fuel. I ended up adding fuel to the inlet vent port of the fuel filter housing with a turkey baster. After a little cranking, it started right up.



Then I had about 0. 5 psig fuel pressure at idle and loss than 0 at anything above an idle. There weren't any fault codes in the ECM when I had the lift pump replaced. By the way, that $359 figure for the pump didn't include the laobr.



Its a good thing for DC management that Lee Iacocca isn't in charge anymore.

 

[EMDDIESEL]

So basically if i show them the gauge and that is shows 4psi at idle they wont fix it uder warranty since there is no fault code tripped?

 

[B9Mile]

Lift Pump Replacement

The easiest way to get any work done under warranty or a TSB is to get a copy of the TSB. Then look at the "symptoms/condition" section and complain to the dealer by using those "symptoms/conditions"



Here is the TSB for the lift pump replacement:

http://www.dodgeram.org/tech/tsb/2000/Sa_00-11.htm



Now, word has it that you were changing your fuel filter. You couldn't get the truck restarted because of VERY low (read ZERO) lift pump output. That should do it.



Some dealers may consider 4 psig at idle to be PLENTY of fuel pressure and deny warranty coverage. Others might recognize the real problem and change the pump. I would not have a gauge on it when taking it to the dealer and then complain of hard starting.

 

[EMDDIESEL]

Thanks for the TSB, i printed and will be bringing it with me. But what am i supposed to do with my installed Fuel pressure gauge?. You said i should not have it installed when i go, why? your saying i should take all the stuff out?. I cant see how they can void my warranty for having a fuel pressure gauge.

Is there somehwere in writing online that says the correct fuel pressure readings that i can show them so when they say 4psi is fine, i can say "not according the service manual"

The only thing i took out of the truck today was the EX box. I am leaving the Psychotty in, i cant see how they are going to say that is hurting my fuel pressure, should i put the stock airbox back too?

 

[B9Mile]

Lift Pump

EMD, I jumped the gun a little with that pressure gauge statement. Some techs at dealers might just look at your gauge and say... "that looks fine with me!", and not use their dealer's gauges to test the pump's output. They need to verify the lift pump's output to authorize a replacement.



Of course we know that, but some dealers are a little skittish of warranty work due to the reduced labor rates and any possible "Warranty" audits by DC.



When I get home in about 3 hours, I'll look up the required pressures in my shop manual. There are two stated pressures. One is for idle, and the other on is at 2,500 RPM, I think.



From what I can remember, your idle pressure is way below their minimum. I think it was something like 7 to 10 psig at idle.



The 2,500 RPM (?) requirement is not specified in the manual as being taken while the engine is under load, or with the transmission in neutral.



I think once your dealer looks at your pressure at idle, you should be getting a new pump on DC. The manual is quite specific. I'll e-mail you a picture of the page later on this evening.

 

[B9Mile]

Here are the lift pump minimum acceptable pressures from page 14-39 of the 24 Valve Engine Supplement of my '98 shop manual:



... with engine running (no RPM specified) ... ... ... 10 psi

... with engine cranking... ... ... ... ... ... ... ... ... ... ... ... ... . 7 psi





This is where the 2,500 RPM stuff I mentioned comes in:

... Overflow valve release pressure... ... ... ... ... ... ... ... ... ... ... . 14 psi @ 2,500 RPM

... Fuel pressure drop across fuel filter test ports... ... . 5 psi max. @ 2,500 RPM

 

[Rambling]

B9 is correct.



The '99 manual says the prefilter pressure should be 10psi during idle. After that, they switch the guage to post-filter and perform a second check at idle. If the pressure drops more than 5 psi, change the filter. There is no other pressure test listed.



There is however, a vacuum test performed with a guage mounted in the fuel supply line (pre-lift pump?) at full throttle and no load. Minimum is 6in/HG.



Guess this is to prove the lift pump sucks.



Doesn't that seem backwards? If it's working, it sucks. If it isn't, it doesn't. I think anyone that has had a failure would agree that when it's broke it really sucks.



Anyway EMD, like the others have said it sounds like there's a serious problem with your lift pump. No hard driving and keep it to a minimum when do.



Good luck!!