Cummins p pump question

[Fritz Maurer]

Have the pump off the engine. The rack is moving about .250” as viewed through the end plug. Pressurized the head and all six delivery valves are leaking… will not even hold 5> psi. Should they not hold at least a little bit?
The engine had been idling and just quit ( after fuel filter change). Had not been able to start since. Thank you.

 

[Destroked 450]

I’ve never pressurized my pump with the lines disconnected so not sure what the delivery valves will hold, it takes over 3000 psi to pop the injectors so a few psi getting past the delivery valves shouldn’t be a issue
The fuel rack will only travel a small amount until the engine starts and the governor raises the arm above the step in the fuel plate
Sounds like you induced air into the system

 

[Dieseltech]

The .250 is just over 6 MM rack travel, MOST Bosch pumps FULL rack travel is 20-21 MM. Depends what governor it has, RSV ag governor will allow full travel for starting, RQ and RQV won't UNLESS it's set up to do that. USUALLY delivery valves won't leak, BUT there are some that are designed to like some VE pumps have. What is engine application, and what governor is on pump?

 

[Fritz Maurer]

The .250 is just over 6 MM rack travel, MOST Bosch pumps FULL rack travel is 20-21 MM. Depends what governor it has, RSV ag governor will allow full travel for starting, RQ and RQV won't UNLESS it's set up to do that. USUALLY delivery valves won't leak, BUT there are some that are designed to like some VE pumps have. What is engine application, and what governor is on pump?

The travel I noted was simply moving the stop lever. What governor it has is probably on the tag which I understand is underneath the throttle linkage bracket which I haven’t taken off yet. Application is 1996 dodge one-ton dump.

I had a similar no-start after filter change on a 3 cylinder Deutz… primer would pump fuel all the way up to the injectors , but it would not build injection pressure. Pump guy said it was short hair- like debris ( Which looked like it could have come from the braided covering of the fuel lines, although that was never ascertained)stuck in the delivery valves. I was just wondering if we had the same situation here, with all the rust and garbage that they cleaned out of the system.

 

[Dieseltech]

That's the RQV governor, on most Dodge trucks the throttle MUST be bumped a bit right after starting cranking so the rack will travel forward more for easier starting. Rack needs to be AT LEAST 12 MM or more for starting, 6 MM is not enough. See if the rack will move further by moving BOTH stop and throttle levers. Rack MIGHT NOT move forward further until the starter is bumped.

 

[Fritz Maurer]

Diesel tech, I posted pics of the actual rack travel. Not quite 12mm, possibly fuel ratio control holding it back? Turning the pump with both levers at maximum doesn’t make the rack move any further. The rack just passes the forward surface of the pump body maybe 1mm.
Something else occurred to me, regarding the return line… is there supposed to be any restriction to keep some pressure around the plungers? Just found out that they changed the lift pump as well. However, they did have it running so that theory doesn’t seem viable.

 

[Dieseltech]

If the rack moves in/out easily then one or more plungers are NOT stuck which WILL keep rack from moving. The return PRESSURIZING bolt valve DOES fail on that application, shop I used to work at that was the FIRST part replaced on that pump whenever there was a starting/running complaint on any P7100 pump. Inline pumps NEED gallery supply pressure to work right or plungers can't fill on the charging cycle. The Bosch number is 2 417 413 101 for that valve. We always used the Zexel valve 131424 1520 as it cost a lot less. I sure HOPE that pump was not removed just for a bad return valve bolt...

 

[Fritz Maurer]

If that is really what is wrong with it , I’d gladly unbolt that thing in lieu of a new pump.

 

[Destroked 450]

If the rack moves in/out easily then one or more plungers are NOT stuck which WILL keep rack from moving. The return PRESSURIZING bolt valve DOES fail on that application, shop I used to work at that was the FIRST part replaced on that pump whenever there was a starting/running complaint on any P7100 pump. Inline pumps NEED gallery supply pressure to work right or plungers can't fill on the charging cycle. The Bosch number is 2 417 413 101 for that valve. We always used the Zexel valve 131424 1520 as it cost a lot less. I sure HOPE that pump was not removed just for a bad return valve bolt...

I think what your calling the return pressurizing bolt valve is what most 5.9 12v Cummins owners call the overflow valve
I have an adjustable one from TorqTek on my 5.9
And yes that is the fist thing to check on a p pump, I have a fuel pressure gauge in my truck to monitor full pressure, stuck a plunger in a 160 pump due to low fuel pressure

 

[Destroked 450]

Diesel tech, I posted pics of the actual rack travel. Not quite 12mm, possibly fuel ratio control holding it back? Turning the pump with both levers at maximum doesn’t make the rack move any further. The rack just passes the forward surface of the pump body maybe 1mm.
Something else occurred to me, regarding the return line… is there supposed to be any restriction to keep some pressure around the plungers? Just found out that they changed the lift pump as well. However, they did have it running so that theory doesn’t seem viable.
View attachment 68913View attachment 68915

I’m not sure what the issue is but the rack never extends as far as your measuring, the rack plug prevents it from coming that far forward
Some Mack’s with p pumps had hollow plugs that allowed more travel but those plugs didn’t come in pumps in Dodge trucks
Performance people swap them out for more rack travel in high performance apps

 

[Fritz Maurer]

I’m not sure what the issue is but the rack never extends as far as your measuring, the rack plug prevents it from coming that far forward
Some Mack’s with p pumps had hollow plugs that allowed more travel but those plugs didn’t come in pumps in Dodge trucks
Performance people swap them out for more rack travel in high performance apps

That is a Dodge truck and that is a hollow plug. The travel I have is coming nowhere near bottoming on that plug. Whether it’s original or not I have no idea.

 

[Dieseltech]

I think what your calling the return pressurizing bolt valve is what most 5.9 12v Cummins owners call the overflow valve
I have an adjustable one from TorqTek on my 5.9
And yes that is the fist thing to check on a p pump, I have a fuel pressure gauge in my truck to monitor full pressure, stuck a plunger in a 160 pump due to low fuel pressure

Yup, overflow valve is another term. In all my years in diesel injection I've never heard of a plunger sticking like that. The electronic JD P7100 pumps actually shut down by stopping fuel flow into the pump with an electric solenoid, no fuel in means no fuel out, and they never stick a plunger. Ford/Simms only use 3-5 PSI feed pressure and I've never seen a stuck plunger on them either. Any chance a slug of water entered the gallery? That would stick them for sure.

 

[Dieseltech]

I’m not sure what the issue is but the rack never extends as far as your measuring, the rack plug prevents it from coming that far forward
Some Mack’s with p pumps had hollow plugs that allowed more travel but those plugs didn’t come in pumps in Dodge trucks
Performance people swap them out for more rack travel in high performance apps

The Dodge rack plug will still allow 12/14 MM travel, just not the full 21 MM like other pumps can with their longer hollow plug. The 12/14 MM is USUALLY where the full load balance check is done.

 

[Destroked 450]

Yup, overflow valve is another term. In all my years in diesel injection I've never heard of a plunger sticking like that. The electronic JD P7100 pumps actually shut down by stopping fuel flow into the pump with an electric solenoid, no fuel in means no fuel out, and they never stick a plunger. Ford/Simms only use 3-5 PSI feed pressure and I've never seen a stuck plunger on them either. Any chance a slug of water entered the gallery? That would stick them for sure.

The 94/95 160 hp 5.9 p pump has what is referred to as the slow fill cam, this cam was also used in the 11mm 190hp industrial engines
With fueling mods done to increase power if good fuel pressure wasn’t maintained they were know to stick a plunger on a hot pump
I had a check valve come loose it the lift pump and on a hard pull fuel pressure dropped to 5 psi, just before topping a mile long 8 percent grade it started rattling and dropped a cylinder
After topping the hill we had about 1 1/2 miles of light down grade giving the engine compartment time to cold down, before we got to the bottom of the grade the rattling stop and the cylinder picked up again, after replacing the lift pump regaining good fuel pressure it didn’t happen again
The later 96/97/early 98 pumps use the quick fill cam that isn’t known to have the plunger issue
My current engine has the 215 pump, recently the rack plug came out allowing the rack bushing to slide out and rotate blocking rack travel, thus limiting the engine to around 1500 rpm
I’m going to try taking the pump loose and get it to tilt back enough to realign the bushing without pulling the gear

 

[Destroked 450]

That is a Dodge truck and that is a hollow plug. The travel I have is coming nowhere near bottoming on that plug. Whether it’s original or not I have no idea.

If it’s a hollow plug someone has added it
Been a member of the Cummins Diesel Forum for many years in the 12v section, been a good bit of talk about the hollow (Mack) rack plug but haven’t hear anyone claim their Dodge came with the hollow plug

 

[Fritz Maurer]

I’m not sure what the issue is but the rack never extends as far as your measuring, the rack plug prevents it from coming that far forward
Some Mack’s with p pumps had hollow plugs that allowed more travel but those plugs didn’t come in pumps in Dodge trucks
Performance people swap them out for more rack travel in high performance apps

If my pump had a solid plug, it would screw in right up to the rack bushing by time the gasket contacts the housing. How would it run with 6mm> of rack travel?

 

[Dieseltech]

The 94/95 160 hp 5.9 p pump has what is referred to as the slow fill cam, this cam was also used in the 11mm 190hp industrial engines
With fueling mods done to increase power if good fuel pressure wasn’t maintained they were know to stick a plunger on a hot pump
I had a check valve come loose it the lift pump and on a hard pull fuel pressure dropped to 5 psi, just before topping a mile long 8 percent grade it started rattling and dropped a cylinder
After topping the hill we had about 1 1/2 miles of light down grade giving the engine compartment time to cold down, before we got to the bottom of the grade the rattling stop and the cylinder picked up again, after replacing the lift pump regaining good fuel pressure it didn’t happen again
The later 96/97/early 98 pumps use the quick fill cam that isn’t known to have the plunger issue
My current engine has the 215 pump, recently the rack plug came out allowing the rack bushing to slide out and rotate blocking rack travel, thus limiting the engine to around 1500 rpm
I’m going to try taking the pump loose and get it to tilt back enough to realign the bushing without pulling the gear

I still don't buy the stuck plunger story, low fuel pressure gallery filling, yes that can cause a problem. The reason is whenever a plunger is REALLY stuck/seized it WILL keep the rack from ever moving again, and if rack is stuck at full load going uphill it will stay stuck going downhill as the governor CAN'T move a stuck rack, and that would be a real thrill going downhill with no way to shut the engine down. A stuck plunger won't deliver fuel, so what would cause the rattle noise? Possibly tight valves contacting the piston tops on a HOT engine? The Bosch service school never mentioned any complaints about the earlier pumps in all the classes I attended.

 

[Fritz Maurer]

Diesel tech, that was it . That regulator was like blowing through an empty banjo bolt. Many thanks. This was a harrowing experience for all involved.