MEP-803A Injection Pump sticking

I have a 1999 MEP-803a with 2300 hrs. One of the injection pumps (#4 cylinder, furthest from the engine fan) is sticking. The piston in the pump if very difficult to move up and down or rotate. The spring is not strong enough to pull the piston down to the bottom of the stroke. I've taken it apart and I don't see any obvious damage. Both the piston and the bore of the pump are clean, no residue. I don't know how this unit got 2700 hrs on it with one cylinder not firing. Any ideas on how to fix the injection pump or what could be the cause of the problem?

-Jason

First off, I don't have any experience with this pump. The first thing I would try would be using spray carb cleaner or lacquer cleaner or acetone to clean the bore and piston. Saturate a rag and clean thoroughly and see if that helps. If not the next thing would be is using some silicone carbide sand paper of 2000 to 3000 grit and polishing the piston. If that doesn't do it you might have to bite the bullet and get a different injection pump for that cylinder. Maybe someone else will chime in and recommend something else.

You may want to switch it with another cylinder. Also how are you checking that its not fireing? Temp gun on exhaust? Cracking the fuel line at the injector?

The pumps are very simplistic and I've had several apart to clean them. Try carb cleaner as mentioned above and then spray with wd40. If they continue to be hard to move then they are not put back together correctly. Take it back apart and reassemble.
How do you know the piston is not going to the bottom of the stroke? The large spring on the bottom of the pump holds the piston down and when that spring is comprised by the cam is when it sends the piston upwards, which pressurizes the fuel and sends it to the injectors.

Thanks for the responses. The piston is so tight in the cylinder that the spring is not strong enough to pull it down. It's basically stuck in the up position. I will try cleaning all parts then polishing the piston until it moves. It appears to be in good condition. I wonder if this pump is a defect and has been stuck in the up position for 2700 hours. I don't see how it could get harder to move as it wears. Doesn't look like there's any varnish in the cylinder. The piston is perfectly clean, no scratches or defects.

Be careful with polishing this stuff. The tolerances are very very small.

You may be better off sending it off to a shop that can fix it if disassembling and cleaning doesn't correct the problem.

When you reassemble the pump, how do you ensure the locking collar is in the correct position to limit the piston control arm correctly?

jamawieb said:

The pumps are very simplistic and I've had several apart to clean them. Try carb cleaner as mentioned above and then spray with wd40. If they continue to be hard to move then they are not put back together correctly. Take it back apart and reassemble.
How do you know the piston is not going to the bottom of the stroke? The large spring on the bottom of the pump holds the piston down and when that spring is comprised by the cam is when it sends the piston upwards, which pressurizes the fuel and sends it to the injectors.

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When you reassemble the pump, how do you ensure the locking collar is in the correct position to limit the piston control arm correctly?

Fixed it! Turns out the top of the piston was mushroomed out about .0005" more than the rest of the shaft. Polished it down and it works great!

Wonder how it mushroomed out? When you get it up and running take exhaust temperature readings to make sure its putting enough fuel into that cylinder. Also keep a close eye on your oil level since you polished the piston down because it could leak fuel into the crank case. Just things to keep in the back of your mind.

You can also hook up a water manometer IAW the -24 TM and compare the values in the TM to what you get.

jamawieb said:

Wonder how it mushroomed out? When you get it up and running take exhaust temperature readings to make sure its putting enough fuel into that cylinder. Also keep a close eye on your oil level since you polished the piston down because it could leak fuel into the crank case. Just things to keep in the back of your mind.

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Thanks for the advice. Only the top 1/8" of the piston was polished, so hopefully it won't affect the overall sealing capability of the pump.

Guyfang said:

You can also hook up a water manometer IAW the -24 TM and compare the values in the TM to what you get.

Click to expand...

What pressure are you suggesting I measure? The output pressure of the injection pump is around 3000 psi. That's a big water manometer!

Look in the TM. You use a water manometer to check crank case vacume. Your set would show less then normal vacume, or, in worst case, positive pressure if you had leakage.

Guyfang said:

Look in the TM. You use a water manometer to check crank case vacume. Your set would show less then normal vacume, or, in worst case, positive pressure if you had leakage.

Click to expand...

That makes sense. Thanks for the tip. I'll look it up in the TM.

If you do not have a manometer, there are instructions on how to make a simple one in the -24 engine manual. It's even more simple then a tinker toy car.

Two years ago, I got a good deal on an 803 that did some time in the sand. After I got it home I changed all of the fluids & filters, added fresh fuel and a pair of batteries, replaced the dead primary fuel pump, and spent some time cleaning the sand out of the switches on the control panel. Once all of that was done, it fired right up and purred nicely. I ran it for a a couple hours with varying loads and verified that it was making steady power, then put it away in the back of my garage with a float charger to keep the batteries up.

Fast forward 2 years. Last weekend the weather was nice so I did some spring cleaning and rolled it out into the light. While priming it and checking things over, I discovered that the return fuel line was leaking in several places near the injectors. I had some 3.5 mm yellow stripe fuel/vacuum hose on hand, so I replaced the return lines and let it prime again until I could hear fuel making it back to the tank. Unfortunately, I have not been able to get the engine to fire.


When I crank it over, I don't see any smoke. Not white, not black, just none, which makes me think it's not getting fuel. I've verified that there is decent fuel flow past the injector metering pumps. The fuel cutoff solenoid moves as expected. I drained the fuel out of the tank, and added a few gallons of fresh diesel. Changed fuel filters again. Primed, primed and re-primed. I can hear fuel making it back to the tank via the freshly replaced return line. Still no luck.

I'm assuming it's not getting fuel, so to test that out, I cracked the hard lines at the top of the injector metering pumps one at a time to see if any fuel is coming out. What I found is that on pumps 1 and 4, there is a small amount of fuel coming out. Each stroke raises the level a little under 1/16", so it took a handful of strokes before a drip was able to run over the top of the threads where the hard line attaches. The middle 2 metering pumps did not show any fuel movement. So... where to from here? I'm not sure if the middle 2 metering pumps have failed or are just seized/gummed up from 2 year old fuel. Do I need to remove them to inspect and clean, or is there something else I can/should do first? I'm also kind of surprised that it wasn't trying to fire on 1 and 4. Maybe I need to pull those injectors and take a closer look.

I likely won't have time to try much until this weekend, but wanted to reach out for advice and formulate a logical plan of attack. Thanks for any help!

Sounds like there's a good chance that one of the metering pumps has a stuck lever and that is keeping your fuel rack stuck in or close to the off position.
The slight amount of fuel coming out of #1 and #4 could be that they are slightly out of adjustment or possibly the rack is not quite all the way in the off position.
I'd start by removing pumps 2 and 3, check that they are moving freely. Both the lever and the plunger. Also check that the fuel rack is moving freely when you pull the shut off solenoid out of the way.
Refer to the TM if you need guidance removing the pumps. They say not to remove all 4 at once because it makes it more difficult to get them back in.
Also when testing the rack motion you need to have any pumps that are still in the motor tightened down with the hold-down, otherwise the lever arm will hit the underside of the block casting and give you the false impression that the rack is not moving correctly.
If you find the rack isn't moving but pumps 2 and 3 are good, you will need to remove the other pumps 1 at a time to determine which one is causing the rack to hang up.

First thing that comes to mind is that it is bad for diesel engines to sit for 2 years without being routinely run at least every 90 days, or more often based on climate, to get unit up to temperature and fluids circulating. Most if not all of today's diesel contains biodiesel which is hydroscopic and if enough water is absorbed over time due to tank breathing/condensation it can become corrosive as well as gumming up the works in close tolerance parts when left stagnant.

Secondly, it might be best to start your own thread with a good relevant title to attract better assistance. While it could be related to the OP's original issue it might not be.

Thanks Ray70,

This is also helpful for me, too. Still trying to figure out what the heck the fuel rack is...