Engine/Transmission (1998.5 - 2002) Pusher pump too strong?

[azcummins]

My carter pusher pump is showing 22 psi idle, 18 psi WOT through Briar's gauge. These #'s are the same for before and after the filter.



The other day my truck started hard like it was out of fuel for no reason so I thought the VP-44 might be dying so I took it in to the friendly stealer. They ran some diagnostic tests on it and said it is starting hard b/c it is getting drowned out by fuel due to my pusher pump.



I find that hard to believe as the pressure relief valve in the Vp-44 kicks open @ 14 psi to send fuel back to the tank. Perhaps my valve is left shut drowning the Vp-44 out?



I'll be interested to hear what you guys have to say to determine whether I go get the truck, remove the pusher or leave it. Whatd'ya think?

 

[TxDieselKid]

You need to get a hold of Merrick(MCummings). He had the same problem all the way to Munice. Trust me, I had to put up with it.



Andrew

 

[azcummins]

BTW... truck has had the pump on there for 3 months w/out any problems until now.

 

[DEZLPWR]

I think the stealer is F. O. S. (gee what a surprise!)I'm sure Steve St. Laurent will chime in here. He has had the exact same setup on his truck for over 1yr with no problems. I have had the same setup on my truck for 4 months with NO problems. I am seeing 23psi @ idle and no less than 19psi @ WOT with Comp on 5-5... .



Your overflow valve may be stuck closed. I would try a new one. They should be cheap from Cummins.

 

[AggieJustin]

azcummins-



How long do your pumps run when you turn the key on? And does the hard start only occur if you're cranking while the pumps are running, or does it happen even after they've stopped?



**The remainder of this post is just speculation based on previous reading **



I know I've seen posts about the dealer reflash that shortens the pump cycle time when the key is turned on to eliminate a hard start condition. And since you have one of the first 24V engines, I was thinking that perhaps you still had the long initial cycle.



Even though I don't have a pusher pump on mine, I can tell that if I crank immediately while the pump is still running that it turns over a couple of extra times before starting.



Could it be that the relief valve is not open at startup and that when you crank while the pumps are running the extra pressure "drowns" the VP44?



Of course this problem would only show itself during warm weather when you don't have to wait on the grid heaters to cycle and you start cranking sooner.



Just my $. 02... .

 

[azcummins]

AggieJustin-

My pumps run for about a second when I go to start the truck. They are long since turned off when the grid heater turns off and I start the truck.



The hard start has only occured once. It occured on a hot day after I had been on the interstate pulling horses all day. It seemingly came out of nowhere so I was kinda shookup that it even happened.



The dealer's "main" diesel tech is supposed to be back in tomorrow and they will let me know his ideas. I'm interested to hear what the TDR says so I can go in with some ammunition!

 

[Rob Thomas]

I dunno about "To much pressure", I have the same pressures as you az, on 2 gauges pre and post filter, mine starts just fine. It hardly even cranks, and it fires. I haven't had a re-flash, and don't plan to. Not sure about the valve, is it replacable, or does it require a new pump?



Later, Rob

 

[azcummins]

Rob-

Dunno where the valve is and how to replace it. I hope it isn't internal and needs a whole new VP-44. I hope it is easy b/c I'm getting this feeling they are going to void my warranty on behalf of the pusher pump.

 

[KatDiesel]

Do you have the pusher pump wired with a relay and tapped into the stock lift pump power wire?



Too much fuel pressure at startup can cause a hard to start condition, thats why its important to tap into the stock lift pump wiring to get the command to cycle the lift pump instead of running it.

 

[jerryrigg]

The Overflow Valve

You might want to look at this thread



https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=50483



It was my understanding that the 14psi overflow was in ref to the fuel pump but Royal has pointed out that the overflow is for the internal pump pressures from fuel leaking past the piston etc. I don't know for sure yet, I'm ordering the VP44 book from Bosch to figure this geezwhizbangdohickey out once and for all.



Good Luck

-Matt

 

[azcummins]

Kat-

it's wired with a relay from the stock wire. It runs exactly as much as the stock pump.

 

[RADdodge]

Katdiesel is right. The factory lift pump is run at only 25% duty cycle on starting. This is to prevent hard starting. I'm afraid the stealer is right on this one. After the starter is disengaged, the ECM ramps the voltage up to 12v nominal (whatever you system voltage is (12-14. 5v). If you just use the ECM's connection to the lift pump to fire a second relay to the secondary lift pump, you may get "chatter" in the relay. Some have reported this. The reason is at 25% the relay doesn't fully engage the relay, but turns off/on as the voltage to the lift pump is massaged for starting. I published some diagrams that could help, but I haven’t tried to find them. Sometime last year. Basically, I powered the lift pump from the starter relay from the normally open contact. That way, when the start is not engaged, the secondary pump runs, when the starter is engaged, the secondary lift pump is off.

 

[azcummins]

RAD-

The pusher pump is on a relay that is wired to the stock lift pump wire like Kat said it should be. When I put the truck to "on" the pumps run for just a split second together then are off. Sometimes I don't hear them both start running again for several seconds.

 

[RADdodge]

Mine does the same, but if you look at the pressure you build up, it's in the neighborhood to 20psi. I cannot see what it drops to when I engage the starter, but I know it has to drop. Not everyone experiences problems, but the problem was manifested to the engineers that decided to limit the amount of fuel to the injection pump to "aid" starting.



I also have remote start on my truck that work's wonderfully, and the starter on time is 0. 3 sec. It starts the first time every time (unless the batteries are down - happened once, couldn't get the truck started until I disconnected the heater relays!). What I'm saying is the truck should start almost instantly after the heaters have had their turn. Anyway, there has been info posted about this in the past. If you want to see the diagram I posted, it's at #ad


p. s. The switch in the Cab is off in the center position.



Also, the thread it was on was: TDR Roundtable > Turbo Diesel Topics, 2nd Generation (1994 - 2002) > 24 Valve Engine and Drivetrain (1998. 5 - 2002) > Another Lift Pump Picture (sigh!)

 

[azcummins]

Rad-

I understand what you're saying and it sounds like that might be the issue. I'm still wondering why after 3 months of perfect starts, one day, in the middle of the day, it wouldn't start.



Another point ot prove your idea... the tech @ the dealer said the truck wasn't starting hard, but it was throwing a fair amount of black smoke out.

 

[WeirCummin]

AZ,

RADdodge is right on the duty cycle of the lift/transfer pump. Useing the stock wiring form the ECM to trigger the relay does not change the duty cycle of the pump. I'm sure that the nominal voltage needed to energize the coil of the relay is not above the 25% duty cycle and it wouldn't matter anyway. When the ECM commands the the stock lift pump @ 25% duty cycle, it is putting out less than it's 100% duty cycle voltage, which has a result of a slower speed from the pump and lower inlet pressure on the VP44.



The hard starting is a result of to much pressure in the VP44. I'll try to explain. During initial start up the injector pump has a default for timing and injector pulse. The timing control device receives fuel pressure from the vane pump (low pressure) if the pressure is to high then the timing at start up is changed and the hotter the fuel, the more dramatic the problem is.



Dean

 

[azcummins]

Weir-

I think the 25% nominal voltage is enough to run it b/c I can hear the pusher pump kick on for just a sec before I start the truck. Maybe I'm misunderstanding you that the pusher pump shouldn't be running before the truck starts?



Again though, If this is the problem, I'm wondering why it all of the sudden started having this issue. It's been fine for 3 months. Also, why would the truck have not started, then suddenly started fine like there never was a problem? Lots of questions here but they are good ones!

 

[KatDiesel]

Have you checked pressures yet out of curiosity?



Was your stock pump new when you installed the pusher? Could it have died?

 

[WeirCummin]

AZ,

In the stock configuration the ECM commands the lift pump to run at 25% duty cucle, meaning that it is only putting out 25% of it's rated fuel pressure. When we change over to a relay energized transfer pump we have effectively removed the ECMs ability to adjust duty cycle of the pump.



Kat has a point. what is your FP?

 

[WeirCummin]

Perhaps my valve is left shut drowning the Vp-44 out?

Or maybe it's wide open and not letting pressure build in the pump.