Archived Changed LP and IP - No LP press with key ON!

[JAde]

Hey Guys,



After installing a fuel pressure gauge I found I sometimes had low or no fuel pressure. At first I thought it was the gauge but sure enough it turned out that the injector pump was on its way out. I changed the lift pump. Two days later I had a dead pedal. I guess I was too late with the lift pump! Ended up changing the injector pump. After the injector pump change, I lost fuel pressure with the key in the on position. The lift pump in from Cummins the injector pump is a rebuild from a Bosch authorized shop. I've spoke to a tech at our local Cummins shop. He believes it is an air leak. I've changed every o-ring, washer and rubber line in the system. Still no luck. Just for grins I plugged in the old pump and grouned it to the battery. It cycles for a couple of seconds as I believe it should. Again, just for grins, I reinsatlled this lift pump. Turned the key to ON - No pressure!!!!!



Please help. I'm running out of money and energy! The truck is a 98. 5 24V Automatic, 2WD, short bed, bright red MONEY PIT!!!!!

 

[Missouri Mule]

Are you sure you have fuel in the tank?



Turn key to start position,release, that should make the lift pump run 25 seconds.

If fuel pump works. Crack injector lines at injectors,starting with no. 1 injector crank engine when you see fuel come out close injector.



Just read on another thread that you should open drain to fuel filter first until clear fuel comes out while cranking. Then try to start it.

 

[JAde]

Plenty of fuel!



Yes, if I bump the starter the lift pump will cycle for approx 30 seconds. The problem is that the lift pump does not cycle on with the key in the ON position and the Wait light on. The system looses its prime. With the old lift pump and injector pump combo the lift pump would cycle for approx 15 -30 seconds (appox 10 psi) to prime the system. I now have to bump the starter 2 or 3 times just to get the truck started.



Can someone with a fuel pressure gauge let me know if it is normal for the lift pump to build pressure while the Wait light is on? My truck use to start every time now I either crank the starter two or three times for 10 - 15 seconds a shot or bump the starter and let it build pressure.



I've read other post that only spoke of the cycling of the lift pump after bumping the starter. "What's normal lift pump opertations with the key in the ON position waiting on the glow plugs?"



Today I tried disconnecting the batteries and then after awhile reconnecting them with the key in the ON position in hopes to reset the ECM. Still the same. No difference.



I've ordered an Air Dog unit and I am wondering if the supplied harness and relay use the lift pump feed to power up the relay or can it be ran to a keyed 12 volt source? I figure I could always use an oil pressure sending unit for safety.



Thanks Guys!

 

[JLandry]

Can someone with a fuel pressure gauge let me know if it is normal for the lift pump to build pressure while the Wait light is on?

Here is a description of normal lift pump operation...



When you first turn the ignition key to the run (not start) position, the lift pump will come on for approximately 2 seconds only, then it shuts off. As a result, it's completely normal not to have any fuel pressure while you pause for the "WAIT TO START" light to turn off. While cranking the starter, the lift pump does work, but at reduced pressure so as not to overwhelm the VP44 injection pump. Once you release the ignition key back to the run position (after cranking), the lift pump should stay running continuously and provide full pressure.



And as you've already indicated that you know, the lift pump should run for approximately 25 seconds then shut off if the engine is cranked but not started (i. e. bumping the starter).



If your lift pump isn't behaving as described above and you're sure it's fine, then the problem is with either the wiring harness between the ECM and the lift pump, or with the ECM itself. There is no fuse or relay between the ECM and lift pump.



Sometimes the ECM connector pins can become dirty or corroded leading to improper lift pump operation, or sometimes the ECM can have a bad ground to the engine block which also causes lift pump problems. To fix an ECM grounding problem, all you need do is remove it, wipe it clean with a solvent moistened rag, clean the mounting location on the block, and then reinstall.



Now if your lift pump is operating properly and the engine is hard to start, it could be you have other problems... like the injectors haven't been completely bled, etc.



Good luck,



John L.

 

[JAde]

Thanks for your help John,



What you are describing is exactly what the truck is doing now. Do you have a fuel pressure gauge? With my old LP and IP combo, fuel pressure would build to approx 10 psi while the wait light was on and the engine would start very quickly. With this new combo no fuel pressure will build and the engine will not start without excessive cranking. I have been bumping the starter a couple of times to avoid problems. I have confirmed that the lift pump does cycle for approx 2 seconds but does not build the pressure needed to prime the system. Is it possible for the new injector pump to change the lift pump time cycle? I know it seems like I'm grasping for ideas but the only thing that's been changed are both the pumps. For troubleshooting I reinstalled the old lift pump and confirmed that the lift pump cycles for just 2 seconds. This same lift pump used to cycle for at least 5 seconds and biuld 10 psi before starts!! What am I missing?



I plan on installing an Air Dog 100 but after reviewing the installation instructions it looks like it uses the lift pump lead to trigger its relay harness. I don't see the Air Dog fixing my starting problem. It seems to me that I have one of the following problems - an air leak, an ECM problem or an electrical issue with the new injector pump.



The truck runs great and fuel pressure never drops below 10 psi.



Any suggestions?

 

[JLandry]

Thanks for your help John?

You're welcome!

What you are describing is exactly what the truck is doing now.

Then you don't have a lift pump problem and it's not "losing prime" as you suggested in an earlier post.

Do you have a fuel pressure gauge?

Yes I do.



Here's an interesting observation from my truck, which has an Airtex lift mounted on the engine block (relaces the OEM lift pump)...



Usually when I turn the key on I see the fuel pressure jump up to about 10 to 15 pis, then immediately drop back to zero while I pause for the wait-to-start light to go out.



On the other hand, sometimes I see no pressure spike when I turn the key on, but this doesn't seem to matter as far as starting is concerned. When the wait-to-start light goes off and I turn the ignition key to start, my truck always starts immediately no matter what the fuel pressure did when I first turned the key on.



To be honest, I haven't taken the time to figure out under what conditions I don't see that initial pressure spike... for example if the truck hasn't been driven for a long period of time or if it has something to do with fuel temperature (fuel viscosity).



When I bump my starter, my lift pump always produces good pressure for about 25 seconds and I can hear it quietly running.

With my old LP and IP combo, fuel pressure would build to approx 10 psi while the wait light was on and the engine would start very quickly. With this new combo no fuel pressure will build and the engine will not start without excessive cranking. I have been bumping the starter a couple of times to avoid problems.

So you're saying that you have to crank the starter excessively if you don't bump the starter first to cycle the lift pump? That is not normal and my hunch the problem is with the VP44 injection pump or injector(s).



How much have you driven the truck since changing the VP44? I ask because I'm wondering if all the trapped air is out of the fuel filter and fuel injection system yet. Did you bleed the air out of the fuel supply line at the VP44, and also at several of the injectors? Once the engine starts, does it run smoothly and normally?



It's worth noting that the VP44 retains fuel inside in its accumulator after shut down, and assuming it's in proper working order, it should be capable of at least starting the truck briefly even with no fuel pressure from the lift pump beforehand. But if there's air trapped in any of the injector lines, then all bets are off.



Just curious, have you replaced your fuel filter recently? Did you replace the fuel filter cap o-ring and did you tighten it to the proper torque spec? A dirty fuel filter could contribute to lower pressure at the VP44 when the lift pump comes on for only 2 seconds. I've also read reports of an air leaks at the fuel filter cap o-ring causing annoying problems. I usually lubricate the fuel filter cap o-ring with a thin film of silicone grease before installation to make sure it doesn't bind up as the fuel filter cap is tightened.

Is it possible for the new injector pump to change the lift pump time cycle?

No. The ECM controls the lift pump as previously described.



Did you replace the VP44 yourself? If the Bosch shop did the install and you can't figure this problem out, I'd be tempted to take it back to them and let them deal with it... I mean it could be a problem with the VP44, but assuming it runs well once started, then I'd be tempted to think it's air trapped in the fuel system.



Best regards,



John L.

 

[JAde]

Thanks again John,



You asked - So you're saying that you have to crank the starter excessively if you don't bump the starter first to cycle the lift pump?



Yes, every time. Please keep in mind that I haven't driven the truck more then a couple hundred miles since the pump combo change. By the way, I have around a 1/4 tank of fuel. I had read elsewhere that a member always started having fuel delivery problems if he'd run it below a 1/2 tank.



Since the start of the work week, I've had no time to play with the truck (I have a company car). This Friday we take off on vacation for a week. I'll spend some time with the truck when we return. Since I know I've had the fuel system apart it would probably be a good idea to make sure all the air is bled. What's the correct proceedure? My VP44 is an early one without a schrader valve. I haven't thought much about air in the lines only because it runs great. I will be installing an Air Dog 100 but I'd like to figure out this problem before I muddy the waters with a new addition.



"As long as I own this truck, TDR will always have a member!"

 

[Bob Cochran]

Mine works just like JLandry said above when the OEM pump was good and with the AirDog installed the same. Some where you still have air or sucking air into the fuel system is all I can think it can be.

 

[JLandry]

Please keep in mind that I haven't driven the truck more then a couple hundred miles since the pump combo change. By the way, I have around a 1/4 tank of fuel. I had read elsewhere that a member always started having fuel delivery problems if he'd run it below a 1/2 tank.

Well it's sound troubleshooting practice to try and eliminate the potential causes one at a time.



It sure sounds like air is getting in the system somehow when the engine is shut down. But it's easy to get focused on the wrong thing and miss the real cause.



That said, before you try starting it again, I'd unscrew the top off the fuel filter and carefully examine the o-ring seal around the cap for defects. I'd then put a *thin* film of oil grease or oil on the o-ring to insure it doesn't get tweaked when tightening the cap. If you haven't changed the fuel filter recently, do that also.



Another thing to check out...



Try swapping out the VP44 injection pump relay in the PDC (Power DIstribution Center) with another relay. The PDC is under the hood on the driver's fender. The relay is labeled somewhat misleadingly as "FUEL PUMP. " I mention this because I'm wondering if maybe the injection pump could be getting lower than normal voltage during cranking due to a worn relay, which possibly could contribute to the difficult starts.



You asked about bleeding...



To properly bleed air from the low pressure side of the fuel system, you're supposed to loosen the fitting at the fuel supply on the VP44 (where a Schraider valve would be if you had one), hold a big wad of rags under it, and have someone bump the starter to get the lift pump running. Even if there's air in the line you'll still get a lot of fuel coming out, so let it run as long as you can (the rags will absorb) and have the person in the can turn the ignition key off to stop the lift pump. Immediately tighten the fitting. This will get rid of air in the fuel supply lines and fuel filter housing.



The above procedure will normally be adequate to get rid of air trapped in the low pressure fuel system, and no additional bleeding of the high pressure (injector) lines will be needed... unless of course the VP44 injection pump was replaced or the truck was run completely out of fuel. In those cases you'd also have air in the VP44, the high pressure lines, and the injectors. To bleed those components, after you bleed the low pressure fuel system, you crank the engine for up to 30 seconds to fill the VP44 with fuel, then if the engine doesn't start (and it may run like crap for awhile if it does start), you simply loosen several of the high pressure line connectors where they screw in the side of the cylinder head (usually on cylinder numbers 3, 4, and 5), place rags around the loose connectors. Crank the engine for up to 30 seconds to push fuel out of the loosened high pressure lines. The engine may start, so if it does shut it off and tighten the high pressure lines. Restart the engine and let it run until it smooths out.



Also, definitely fill up that tank to see if that changes anything. It's possible you have air getting sucked in at the fuel tank module.



Enjoy your vacation!



John L.

 

[KLockliear]

Just as a note, the last time (first time) I lost a lift pump, the first AND SECOND replacements, direct from Cummins, were bad. The 3rd one finally made stock pressure.

 

[JAde]

Thanks Guys,



I'll keep everyone posted.



Joe