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Discussion Starter #1
Hello everyone, I bought this truck a few weeks ago and have been reading and trying to trouble shoot a fuel issue. The truck can idle for extended periods of time with no issues and rev smoothly. But as can be seen in the video, if I hold the rpm around 2k it begins to smoke, then miss, then smoke more, then bog down and if you let off the throttle it will die.
I can then restart the truck and it will idle again just fine but it is not driveable and the problem has not changed with the changes I have made.

video here .............. --------> copy and paste

I have replaced the fuel lines with the leroy diesel marine hose
deleted the fuel heater
new lift pump
new torqtek overflow valve
turbo is good
truck is straight pipe
I have also removed the afc housing and checked the fuel rack seems to be moving back and forth correctly. while i was in there i removed the fuel plate and slid afc foward in a attempt to see if more fuel would make a change. this was the last thing i did before the video. no change. except more smoke on the restart.
 

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Sounds like possible leak in suction side of fuel system to me. Pin the motor and pin the pump if you think it’s timing. Only takes 3 minutes to check


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Discussion Starter #4
Sounds like possible leak in suction side of fuel system to me. Pin the motor and pin the pump if you think it’s timing. Only takes 3 minutes to check


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thanks for the reply, ill have to read how the suction side works.
It should also be mentioned the previous owner took the truck to a shop where they replaced the seal on the side of the block and he said it hasnt ran since then
 

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Discussion Starter #5
Could be cracked pick up tube. How much fuel in the tank?


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About a half a tank. when i replaced the fuel line I raised the bed and pulled the sending unit to clean the screen. i tried to inspect the pickup tube and it seemed normal to me.
 

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thanks for the reply, ill have to read how the suction side works.
It should also be mentioned the previous owner took the truck to a shop where they replaced the seal on the side of the block and he said it hasnt ran since then
There is a brass nut to the left of the lift pump. Check it for tightness. I’ll bet that’s your leak.


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The nut is non the line that runs up to the left of the pump. Very common for people to forget to tighten that one and the one on top of the lift pump when doing a tappet cover seal.


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Discussion Starter #9
This being my first 12 valve I don't know the complete p pump operation. Based on other cars I have worked on it seems like there is definitely a fuel supply issue. Seems the injection pump has a small reserve supply enough to idle and rev smooth, then once that is used it is starved for fuel stumbles and dies. Any advice on the fuel enrichment part of the pump or maybe some other things to look at? Diaphragm maybe?
Also, the air filter and primary fuel filter cartridge after the lift pump is new.
 

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If previous owner had someone replace the tappet cover gasket then the p-pump would been removed so I’d bet when it was reinstalled the timing was not set back right
 

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In my experience improperly set or slipped timing; the truck wont start.
 

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Discussion Starter #12
Has anyone bypassed the primary fuel filter to diagnose if there is a restriction or air suction problem between injection pump and fuel filter? I have installed a spin on fuel filter on the frame to serve as the pre filter. Tank ---> pre filter (spin on) ---> lift pump ---> factory cartridge fuel filter ----> injection pump
 

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Has anyone bypassed the primary fuel filter to diagnose if there is a restriction or air suction problem between injection pump and fuel filter? I have installed a spin on fuel filter on the frame to serve as the pre filter. Tank ---> pre filter (spin on) ---> lift pump ---> factory cartridge fuel filter ----> injection pump
Try bypassing your aftermarket spin on pre-filter. I'd bet it casing a restriction in fuel flow that would rise in an exponential fashion as flow increases.

The stock lift pump is great, its simple and amazingly reliable, but, it can't deal with a lot of inlet restriction. If you really want to run a spin on pre-filter , then you need some kind of booster pump to compensate for the restriction.

Personally I would remove the spin on pre-filter and put the stock pre-filter back on (assuming you've removed it). The stock pre-filter only catches big stuff, but it doesn't have much restriction to flow. And the service interval on the stock pre-filter is in the 100K mile range. Let the post lift pump fuel filter do the fine filtering job. The stock lift pump is WAY better at pushing fuel than pulling it..
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Discussion Starter #14
Try bypassing your aftermarket spin on pre-filter. I'd bet it casing a restriction in fuel flow that would rise in an exponential fashion as flow increases.

The stock lift pump is great, its simple and amazingly reliable, but, it can't deal with a lot of inlet restriction. If you really want to run a spin on pre-filter , then you need some kind of booster pump to compensate for the restriction.

Personally I would remove the spin on pre-filter and put the stock pre-filter back on (assuming you've removed it). The stock pre-filter only catches big stuff, but it doesn't have much restriction to flow. And the service interval on the stock pre-filter is in the 100K mile range. Let the post lift pump fuel filter do the fine filtering job. The stock lift pump is WAY better at pushing fuel than pulling it..
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Before i installed the spin on filter, i deleted the fuel heater (possible air leak) and cleaned the metal screen. At the same time I installed the new cartridge fuel filter and air filter.
After doing this the truck did the same thing. So that is when i ordered the Larry B marine fuel line and spin on kit along with a torqtek over flow valve.
The spin on fuel filter is a wix 33528 with a wix 24770 mounting base. the filter is rated at 12-15 gpm. A google search on lift pump fuel flow came up with this link Cummins Fuel Fuel System - The Cummins Lift Pump
where they are saying the lift pump only flows 0.5 gpm (rounded values) @800rpm and 1.5 gpm @ 2200 rpm if i am reading it correctly.
Also the previous owner had new injectors installed, appear to be rebuilt stocks.
 

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Whats your fuel pressure at idle, and where's it at when the truck starts missing at 2k rpm
 

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Before i installed the spin on filter, i deleted the fuel heater (possible air leak) and cleaned the metal screen. At the same time I installed the new cartridge fuel filter and air filter.
After doing this the truck did the same thing. So that is when i ordered the Larry B marine fuel line and spin on kit along with a torqtek over flow valve.
The spin on fuel filter is a wix 33528 with a wix 24770 mounting base. the filter is rated at 12-15 gpm. A google search on lift pump fuel flow came up with this link Cummins Fuel Fuel System - The Cummins Lift Pump
where they are saying the lift pump only flows 0.5 gpm (rounded values) @800rpm and 1.5 gpm @ 2200 rpm if i am reading it correctly.
Also the previous owner had new injectors installed, appear to be rebuilt stocks.
A filter rated flowrate number is meaningless without the differential pressure at that flowrate. Is is rated for 12 gpm at .01 psid or at 5000 psid?. Bottom line, the lift doesn't do well at pulling fuel (very few pumps do, hence the reason most fuel pumps are in the fuel tanks now). And adding restriction to the inlet is a really bad idea. If you're set on running a spin pre-filter then add an electric fuel pump in or near the tank to compensate for the filters resultant pressure drop.

Just curious , do you use a lot of farm fuel or fuel that has been stored for longs periods of time or is otherwise dirty? If you fill up at the pump like everyone else there really isn't a need for an extra fuel pre-filter. Plenty of people are over 500K miles and some well over a million miles with no extra fuel filtration. Just wondering what prompted the need for more fuel pre-filtration.
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I second Antonm Its a quick and easy diagnostic. Also that filter you listed above 33528, is a 2 micron.. which filters particles that are 2 micron and bigger basically. Your stock filter is a 7-10 micron filter (depending on brand).
 

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Discussion Starter #18
Whats your fuel pressure at idle, and where's it at when the truck starts missing at 2k rpm
I dont have a fuel pressure gauge at the moment, I would like to get rid of the factory cartridge filter and run a second spin on between lift pump and injection pump. But im not sure on that. Like I said this is my first 12 valve and I try and spend a little time searching what other people have done before I buy anything. I know not being able to see the fuel pressure makes diagnosing the problem more difficult. I suppose I could order one today.
 

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Discussion Starter #19
A filter rated flowrate number is meaningless without the differential pressure at that flowrate. Is is rated for 12 gpm at .01 psid or at 5000 psid?. Bottom line, the lift doesn't do well at pulling fuel (very few pumps do, hence the reason most fuel pumps are in the fuel tanks now). And adding restriction to the inlet is a really bad idea. If you're set on running a spin pre-filter then add an electric fuel pump in or near the tank to compensate for the filters resultant pressure drop.

Just curious , do you use a lot of farm fuel or fuel that has been stored for longs periods of time or is otherwise dirty? If you fill up at the pump like everyone else there really isn't a need for an extra fuel pre-filter. Plenty of people are over 500K miles and some well over a million miles with no extra fuel filtration. Just wondering what prompted the need for more fuel pre-filtration.
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I dont know what the previous owner used in the truck, I just purchased it about 2 months ago. my main reason for the spin on pre filter was to delete the fuel heater/ pre screen all together and eliminate the small fuel line sections between the pre filter and lift pump. at the same time i did want to run a filter before the lift pump like the original design.I have ran the same setup on my 6.5 TD silverado before with no issues so I kinda went back to the same setup. I like having the spin on filter under the truck, its easy to service and "simplifies" the system in my mind. But i could be completely wrong.
 
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