From: ddoyle9570@aol.com
Date: Mon Jul 15 2002 - 07:29:16 PDT
In a message dated Sun, 14 Jul 2002 5:20:23 PM Eastern Standard Time, w7ls@blarg.net writes:
> Some cylinders have good pressure, and a
> couple are very weak, and the engine doesn't fire on those cylinders.
> There are two dead cylinders, #2 and #4, which are actually adjacent on
> the injection pump head. I'm wondering if I could have a blown gasket
> between those ports on the pump, but I'm not familiar with
> the pump, so
> it's a guess.
> Anyone ever fix their injection pumps themselves?
Jim,
I am sure you understand how the injection pump works, but others may not, so I will cover the operation, then get to the specific of your question.
The round part of the pump where the fuel delivery lines are attached is called the hydraulic head. (Which by the way is an easily replaceable part, and is often found on eBay).
Due to the extremely high pressures developed inside the injection system, there are essentially no gaskets (and very few o-rings) used. Extremely close tolerences are relied upon to keep it from leaking, and the head itself is a machined from a single piece of metal.
The 6 small allen head screws perpendicular to the outer surface of the head seal off the outer ends of the fuel passages. (a result of the machining operation)
These passages intersect passages bored down from the ports where the injector lines are attached.
Your foot, or other throttle, moves a lever on the outside of the pump. This slides a sleeve up (or down, when throttle is closed) inside the center of the head (big hex headed plug nestled amongst injector lines covers all this). The sleeve movement up or down covers and uncovers ports in the head which act as valves regulating the amount of fuel admitted. The higher the sleeve is raised, the more fuel is delivered. Inside that sleeve is a sort of dogbone shaped plunger. This plunger is the actual fuel pump, the sleeve is the metering device. In the pumping action described above, the fuel is being pumped on the top of the plunger. It flows from there under high pressure, past the fuel delivery valve (a glorified check valve, accessed through a plug screwed into the side of the head, sometimes the plug is hex shaped, but usually 16 pointed.) This valve is NOT replaceable. From there, it flows into the knecked down central part of the plunger. There is a slot machined in the plunger. The plunger is rotat
ed by a gear drive located in the large lower portion of the fuel injection pump. This slot is then aligned, by the rotation of the plunger, with the fuel delivery passages mentioned so many words ago (with the six allen screws blanking them off). The fuel then travels through the lines to the injector nozzles.
Jim, are you sure that the lines are in the right spot? I can say this without being disrespectful, 'cause a friend and I fought one of these for days before noticing three of the lines were swapped!
It is possible that the hydraulic head is cracked, but unlikely. Since all the pumping is done by a single plunger and check valve, the fuel delivery pressure should be the same on all cylinders. If there are leaks in the injector lines, this will affect the performance, as can defective nozzles.
Check the fuel line routing, and if it is good, swap injectors among others on your engine, and see if the miss follows the injectors.
Because of the high pressure, it is unlikely for a line to be clogged, but you can stop up a nozzle.
Hope this helps,
David Doyle
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