HARD KNOCK AFTER LIFT PUMP REPLACEMENT

Ian Rebmann

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Link to video above

lift pump went out on highway and she stalled. towed her home replaced to pump and she started right up but with a nasty knock. i know when these run out of fuel damage can occur to numerous parts (injectors ,pumps, rocker arms yata yata) if you have ran into this before or have a better idea than I, I would love some advice. I already cracked each injector to listen for a difference in idle and found none. i was thinking a purge next then move to replacing some injectors. then inspect head cover for valves and rockers then take off the IP. there is no smoke from the exhaust so i would assume an injector couldn't be stuck open?
 

genscripter

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Buy a 5 foot section of heater hose. Stick one end against your ear, and move the other end around your engine bay. It might help you narrow the location of the knock.

If you changed your lift pump and it's knocking, it might just be an accessory or other component tapping against a vibrating engine.
 

Clb

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Longshot here
Did you index the arm under the cam???
IIRC you can put the arm over the cam, hit the stickies.

+1 on stethescope and loose components.
 

genscripter

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Longshot here
Did you index the arm under the cam???
IIRC you can put the arm over the cam, hit the stickies.


I thought this too, but I wouldn't expect it to tick like his video shows.

Overall, I can't see how a lift pump replacement could produce a tick like that. Even if it were installed correctly or incorrectly. Also, if it was installed wrong, he wouldn't have any fuel pressure, and it would have been hard to purge the air from the fuel lines to the IP.

My thoughts are an unrelated accessory got the tick during the process of replacing the lift pump, something is loose from the installation process, or it's just a coincidence from an unrelated part.
 

Ian Rebmann

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I know when these IDIs run out of fuel some fuel system components can get damaged. Have you guys had to deal with that? That's what I'm thinking, when it started to stall(as the fuel pump died and it was not able to supply fuel) it started an increasing knock until she stalled completely. The current knock sounds like the same knock that occurredat the time of pump failure. I have lubro molly coming by Monday so I will purge before I start stripping and replacing things. Has any buddy had experience with this product? I have heard very positive things? Also can someone explain the injector knock? As of now my understanding is the injector would be cloged and the piston is basically slapping from lack of power in that cylinder? Clogged and not stuck open because she is running cool and no smoke from the exughst.
 

Macrobb

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Two thoughts:
1. If it's a lifter or some other valve train part, throw 2 quarts of MMO in there. It won't hurt anything.
2. It could be that you are finally getting fuel pressure to the IP. This will advance the timing a bit, so if you have an injector that's firing too soon(low pop pressure), it'll knock more than before.


I know when these IDIs run out of fuel some fuel system components can get damaged.
No, they don't. You have to worry about getting air out to get it to run again, but you won't ruin anything.
The IP uses fuel for lube, yes... but the housing(which contains the fuel used for lube) is on the return side of the pump; you will never be able to run that dry by simply running out of fuel.
IDI fuel systems are extremely hard to hurt, except with age or bad fuel(like WVO, WMO - mainly due to improper filtering).

Another thing to be aware of is that if the fuel supply side of the system is sealed(no air getting in, is primed), the IP will run with no lift pump at all. It contains a "lift pump" of it's own, and was designed to be able to run in a gravity-feed system; it just can't prime itself if there is air in the line, or if your lift pump breaks in a manner that allows air in.



Also, a 'stuck open' injector will not just pour fuel down the cylinder. There is no pressure in the injector line until the IP fires on that cylinder. What would happen is an extremely early injection, meaning very advanced timing. At idle, it won't inject much fuel no matter what, so you shouldn't get a large cloud of smoke -- usually, smoke at idle is due to retarded timing on all cylinders, so the IP injects a lot more fuel to maintain that idle RPM, most of which isn't burning correctly.
 
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BrianX128

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2. It could be that you are finally getting fuel pressure to the IP. This will advance the timing a bit, so if you have an injector that's firing too soon(low pop pressure), it'll knock more.

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This. My truck did the same sounding noise when I put new injectors and a pump. Was my own fault a hardline was slightly loose and leaking which barely changed its firing but fuel timing has to be perfect. Otherwise it can sound like someone hitting your truck with a wrench.
 

Ian Rebmann

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so id like to do this purge before i try the IP timing just because its good for the system regardless. in order to do so i need to re arrange the fuel hoses the goal is to create two cycles one of fuel filter to fuel tank and one of purge bottle to that same purge bottle. I dont know if you guys have re arranged your fuel hoses or have a different set up but mine has two separate returns one for the passenger side injectors that runs to the fuel filter housing and the second, driver side injectors run to the tank. the driver side has a t (injectors (driver side and passenger side) , tank and Injection pump) does any one know if the hose to the IP is an Input or and output?

Im going to re-run my whole fuel system (lift pump to the tank return line) so its not a ***** to work on. any useful tips? im thinking a bleed valve of the adapter for the fuel filter(i dont have one on the housing) im going to draw a diagram of it to help me ill up-load it as well.

Ive watched a few videos on the IP timing but im still a bit unclear and do not want to F*ck it up. Does anyone have a good manual they use maybe a free PDF download? or is there a section on this forum explaining repairs in depth that i missed?

I'm unsure about the flow direction of the injector to fuel filter and IP to the t after drawing it I would imagine they are both outs puts(direction flow toward the tank) in case of tomuch fuel flow?

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david85

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The only fuel entry point for the injector pump is at the rear, in the middle of the 8 fuel injector lines. The low pressure fuel return line from the injector pump is at the top housing (I believe this is the line you are asking about). Usually there will be a brass elbow fitting. Some have rubber hoses, while others like mine, have a hard metal pipe (copper, I think).
 

Ian Rebmann

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Yes it is, so that is just for pressure to be maintained right. extra fuel just flows back to the tank
 

Ian Rebmann

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Brian x so air was getting into your system? Another theory I have is the o rings on the injectors went bad from sucking in air? I know running out of fuel can dry them out? How exactly did you fix your knock
 

Ian Rebmann

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have another video that shows the knock while increasing the rpms if this could bring any more ideas.

Can anyone tell if this is a Fuel knock or a component tick? (rocker arm or valve)

this did not occur till the lift pump failed she ran very smooth before.

ANY IDEAS ARE APPRECIATED!!

thanks to the guys who already chimed in keep them coming!
 

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