Well after getting the truck started and pulled into my bay, I noticed the engine ran kind of rough and has VERY slow acceleration, I flipped on the high idle switch and it SLOWLY went into high idle, the engine just doesn't run right. I decided to check a lot of the basics, air filter, oil, fuel tank, I ended up changing our the main filter and fuel water separator-no change but what was even stranger was when I went to unbolt the bleeder on the side of the housing to bleed the air, I was getting no fuel? Went to unhook the main feed line to the separator and no fuel? But this truck is running? Very strange, the primer button felt like it collapsed as well and had no pressure. I may end up putting compressed air into the lines to try and see if there is a blockage but was curious if someone has seen this before?
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M1083a1p2 No fuel flow through fuel water separator?
- Thread starter polk738
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Ronmar
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no fuel at the primary probably means it is sucking air instead of fuel.
1. check the primer is pulling suction. disconnect the input fuel line at the primer, put your finger over the inlet fitting to the primer to seal it. push in on the primer it should stay in as long as you hold a seal on the inlet with your finger tip.
if it does not stay in, remove the filter, disconnect the outlet line and unbolt the primer assembly from the side of the engine, and flip it upside down. there is a flapper type bypass valve that is probably not sealing which is usually why the primer cannot pull a vacuum.
If the primer seals and the bulb stays in with your finger over the inlet, and it won't lift fuel from the tank, the lift line probably has a pinhole in it somewhere sucking air instead of lifting fuel... It takes a surprisingly small air leak to jack this fuel system all up... Working primer and sealed line with no fuel init, you should be able to lift fuel from the tank to the primer(feel and hear fuel in the primer button) in 16 pumps. You can also pump primary fuel pressure up to ~10 PSI fairly easily with the primer once all the air is out of the system(bulb becomes more difficult to push as you get all the air out and start to force fuel hydraulically past the primary pressure regulator at the back end of the cylinder head)
I did a Youtube video showing the primer bypass flapper clean and inspect not long ago as this is not an uncommon issue. but the primer not lifting does not explain your running issue, a vacuum leak on the lift line somewhere could explain the running issue also... A pressure gauge looking at primary fuel pressure(output of HEUI lift pump/input to main fuel filter) would also show an air leak pretty clearly(I have a video on that also
...
On Youtube look for my user name Rronmar (2 R's in front) to see my vids on the LMTV. Mine is a 3116, but the fuel feed is basically the same between 3116/3126/C7 engines...
1. check the primer is pulling suction. disconnect the input fuel line at the primer, put your finger over the inlet fitting to the primer to seal it. push in on the primer it should stay in as long as you hold a seal on the inlet with your finger tip.
if it does not stay in, remove the filter, disconnect the outlet line and unbolt the primer assembly from the side of the engine, and flip it upside down. there is a flapper type bypass valve that is probably not sealing which is usually why the primer cannot pull a vacuum.
If the primer seals and the bulb stays in with your finger over the inlet, and it won't lift fuel from the tank, the lift line probably has a pinhole in it somewhere sucking air instead of lifting fuel... It takes a surprisingly small air leak to jack this fuel system all up... Working primer and sealed line with no fuel init, you should be able to lift fuel from the tank to the primer(feel and hear fuel in the primer button) in 16 pumps. You can also pump primary fuel pressure up to ~10 PSI fairly easily with the primer once all the air is out of the system(bulb becomes more difficult to push as you get all the air out and start to force fuel hydraulically past the primary pressure regulator at the back end of the cylinder head)
I did a Youtube video showing the primer bypass flapper clean and inspect not long ago as this is not an uncommon issue. but the primer not lifting does not explain your running issue, a vacuum leak on the lift line somewhere could explain the running issue also... A pressure gauge looking at primary fuel pressure(output of HEUI lift pump/input to main fuel filter) would also show an air leak pretty clearly(I have a video on that also
...On Youtube look for my user name Rronmar (2 R's in front) to see my vids on the LMTV. Mine is a 3116, but the fuel feed is basically the same between 3116/3126/C7 engines...
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no fuel at the primary probably means it is sucking air instead of fuel.
1. check the primer is pulling suction. disconnect the input fuel line at the primer, put your finger over the inlet fitting to the primer to seal it. push in on the primer it should stay in as long as you hold a seal on the inlet with your finger tip.
if it does not stay in, remove the filter, disconnect the outlet line and unbolt the primer assembly from the side of the engine, and flip it upside down. there is a flapper type bypass valve that is probably not sealing which is usually why the primer cannot pull a vacuum.
If the primer seals and the bulb stays in with your finger over the inlet, and it won't lift fuel from the tank, the lift line probably has a pinhole in it somewhere sucking air instead of lifting fuel... It takes a surprisingly small air leak to jack this fuel system all up... Working primer and sealed line with no fuel init, you should be able to lift fuel from the tank to the primer(feel and hear fuel in the primer button) in 16 pumps. You can also pump primary fuel pressure up to ~10 PSI fairly easily with the primer once all the air is out of the system(bulb becomes more difficult to push as you get all the air out and start to force fuel hydraulically past the primary pressure regulator at the back end of the cylinder head)
I did a Youtube video showing the primer bypass flapper clean and inspect not long ago as this is not an uncommon issue. but the primer not lifting does not explain your running issue, a vacuum leak on the lift line somewhere could explain the running issue also... A pressure gauge looking at primary fuel pressure(output of HEUI lift pump/input to main fuel filter) would also show an air leak pretty clearly(I have a video on that also
On Youtube look for my user name Rronmar (2 R's in front) to see my vids on the LMTV. Mine is a 3116, but the fuel feed is basically the same between 3116/3126/C7 engines...
Well I was able to test the primer and the button stays in while holding the inlet, so to me it looks like the primer seal is okay. I have a fuel pressure tester but I don't have a way to hook into these types of fuel lines on the LMTV. But even with that being said, if their was a leak it should be in the main feed line to the primer correct? If I'm not getting any fuel from that line while it is running. I have seen a few trucks where the line coming out of the primer into the HEUI pump was leaking pretty badly at the hose crimp, but I don't believe that is the case here. This is a C7 engine btw
quick update: Well I believe I found the leak, I was re-inspecting the lines at the primer and I noticed some moisture on the feed line, took my ZEP can and soaked it down (this stuff dries very quickly) cleaned it off and grabbed my light, sure enough I saw right below the crimp on the feed line it started to get damp while I attempted to prime the system, this was harder to see before because of all the residual fuel on the line from disconnecting it a few times. This makes sense I've seen a lot of these crimps on these fuel lines fail before, I'll order the new line, Ronmar thank you again for your help, nice to know I have good help in WA.
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Ronmar
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Correct! if the lift line from tank to primer is intact, the primer should suck fuel from the tank in ~16 pumps., just like in the video. if not, the lift line, crimps or fittings are not sealing properly and is allowing air in instead of lifting fuel, or there is a leak on the tank supply port fitting?
There should be a primary fuel pressure test port on the hard line from the lift pump to the secondary filter mounted on the side of the head. There may also be one on the outlet of that second filter hard line running back to the front of the cylinder head to feed the main gallery in the head...
There should be a primary fuel pressure test port on the hard line from the lift pump to the secondary filter mounted on the side of the head. There may also be one on the outlet of that second filter hard line running back to the front of the cylinder head to feed the main gallery in the head...
Dirtdiggler
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I had this happen after cleaning the separator. There is a small one way plastic valve the size of a pencil eraser. It allows the water to boil off. It had hardened and after cleaning it would no longer seal so no vacuum. That's my guess.