IP throttle rack jammed

[kanoa]

I recently had a problem with my OM617 injection pump (from a 300D turbo) that I was able to solve after many many many hours of reading through this forum (especially the "won't start for anything" thread) and pouring over the MB shop manual. I'll summarize it here because I didn't find anyone else posting about the problem and this was the second IP I have come across with the exact same problem. Also, I didn't find anyone who tried the solution that worked for me which might save someone else a little time and others may be able to add their expertise.

Problem: absolutely no fuel flow through any of the IP hard lines. Lift pump circulates fuel through the IP just fine, but nothing will come out any of the injector lines whatsoever even at full throttle.

Diagnosis: IP throttle rack jammed shut

Fix: purge the IP with solvent repeatedly until rack frees up

Contraindications: can also be caused by air in the IP or by a defective vacuum-driven shutoff valve, or mis-configured ignition switch holding the shutoff valve closed. A worn/broken IP bypass valve spring can cause a similar condition though in that case at least a little fuel will usually flow through the hard lines.

The IP rack controls the amount of fuel that the pump delivers to each injector, in the fully closed position no fuel is delivered at all. Normally the running engine is stopped by the shutoff valve or the throttle arm pulling the rack all the way closed. The rack is in the front half of the IP and is pushed and pulled by a rod that extends through the bulkhead and into the rear half of the IP. (the rear half is filled with crankcase oil and contains the governor, the front half is full of fuel and contains the pump pistons). In this situation the rack jammed in the closed position when the shutoff valve pulled the pushrod all the way back.

The reason this can be such a problem is that the throttle arm (the part connected to the foot pedal) only acts on the rack via the governor, which is to say via a system of springs. They are not directly connected. Therefore any significant resistance in the rack cannot be overcome by forcing the throttle arm because it will only compress or release the springs in the governor without actually forcing the rack to move.

I was able to confirm that the rack was jammed by removing the screws of the ALDA cover and rotating it slightly without removing the ALDA. In this position you can look down on the shaft of the rack in the rear compartment. There's a tab on the end where the shutoff valve (which _does_ directly connect to the rack) is clipped to it. Using a screwdriver I was able to force the rack arm back into the idle position (which is toward the front of the vehicle) and confirm that fuel flowed through the hard lines. However, the rack was still very sticky and the governor was still not able to move it.

I suspected contamination in the fuel side by a loose piece of polymerized veggie oil. For those who are not familiar with this, veggie oil forms a sticky plastic-like substance in contact with ferrous metals, the same stuff that makes the black coating on a cast-iron pan. Normally we only see this on the metal components of the fuel system before the filters but there's no reason it could not form after the filters too. I suspected this because I had seen this problem in two IPs, both from vehicles that ran on WVO and had excellent filtration (meaning a foreign object in the IP was unlikely). Clearing something like this would normally require removing the IP, disassembling it and soaking the components in a solvent like gasoline. To save all that work I thought I would first try soaking the internal parts with the IP still installed...

To do this I disconnected the fuel send and return lines and flushed the IP with gasoline using the manual primer pump. I used a screwdriver to manipulate the rack through the gap in the ALDA cover but it did not free right away so I let it sit and repeated after a couple days. After four flushes over the course of two weeks eventually a blob of brown colored fuel came out of the return line. I checked the rack and it was free. I checked the hard lines and they were pushing fuel. I purged the IP with diesel and bled the hard lines plenty to get rid of all the gasoline and the car is back on the road running perfectly.

A note of caution: I suspect that injecting gasoline into a running OM617 would permanently damage it. If you use this technique please do not skip the step of flushing the pump with fuel oil afterwards. A trace of gasoline in the fuel oil is no big deal but injecting straight gasoline would be a problem.

There are more common problems that could cause similar symptoms so to summarize the troubleshooting sequence for a lack of fuel at the injectors:

1. Visually confirm fuel supply by disconnecting the fuel return hose and pumping fuel into a container using the primer pump

2. Confirm lift pump operation by cranking engine and checking that fuel is still flowing into the container

3. Disconnect the vacuum lines to the shutoff valve to confirm it is not engaged.

4. Confirm there is no air in the IP by purging with the primer pump and bleeding the hard lines by cracking them at the injector and cranking the engine.

5. Check for normal movement of the throttle rack by visual inspection through the ALDA cover plate.

Good luck and thanks to all the many brilliant people who contribute to this forum without whom I would be so terribly lost!

Aloha,

-Kanoa

[kerry]

Good detective work there.

[Diesel911]

Originally Posted by kerry

Good detective work there.

X2

[Carpenterman]

Very concise and logically written! A welcome addition to our collective body of knowledge.

[1stbenznc]

Kanoa,

Thanks for this summary and diagnosis! I just bought a non-running 1987 300tdt with 143k. The guy/mechanic that sold it to me said that there IS fuel coming out of the lift pump (he replaced it), but nothing coming out of the injection lines to the injectors - just like yours and some others here. He didn't seem to know too much about diesels and was going to part out the car!! I hope I can get it running,..... and it does run, shift, brake etc

Attached is a picture from earlier this week when I got her home. It was a several hundred mile trip each way

I will be checking the return line for fuel first, bleeding air next, checking the banjo return bolt after that (not sure if mine is the serviceable one) to check the spring length. Not sure where the vacuum lines to the shutoff valve is???? pic of it??? Does my car have a primer bulb?

Worst case, I did find a good used IP for $200 that I bought the day before I bought the car. I hope I don't need it, but it is nice to have an extra.

[kerry]

Originally Posted by 1stbenznc

Kanoa,

Thanks for this summary and diagnosis! I just bought a non-running 1987 300tdt with 143k. The guy/mechanic that sold it to me said that there IS fuel coming out of the lift pump (he replaced it), but nothing coming out of the injection lines to the injectors - just like yours and some others here. He didn't seem to know too much about diesels and was going to part out the car!! I hope I can get it running,..... and it does run, shift, brake etc

Attached is a picture from earlier this week when I got her home. It was a several hundred mile trip each way

I will be checking the return line for fuel first, bleeding air next, checking the banjo return bolt after that (not sure if mine is the serviceable one) to check the spring length. Not sure where the vacuum lines to the shutoff valve is???? pic of it??? Does my car have a primer bulb?

Worst case, I did find a good used IP for $200 that I bought the day before I bought the car. I hope I don't need it, but it is nice to have an extra.

You need to start a separate thread on this so that everyone gets to drool.

[barry123400]

If your new aquisition was never on vegatable oil. There are many possible reasons for what is occuring. With the use of the archives or other help from this site it should be a walk in the park hopefully. Car looks very nice by the way.

Did the mechanic tell you how he verified there was fuel in the pump? The lift pump having output is no certainty there actually is. Now collecting overflow from the return line off the injection pump would while cranking. Always remember these older six cylinder engines in line type injection pumps are pretty reliable in general. Of course failure modes are not unknown. just not common.

[MTUpower]

Originally Posted by kanoa

I recently had a problem with my OM617 injection pump ...
Aloha,

-Kanoa

So to summarize, veg oil as fuel causes IP problems, don't use it unless you like problems and have time and $ to burn fixing them.

[1stbenznc]

Originally Posted by barry123400

If your new aquisition was never on vegatable oil. There are many possible reasons for what is occuring. With the use of the archives or other help from this site it should be a walk in the park hopefully. Car looks very nice by the way.

Did the mechanic tell you how he verified there was fuel in the pump? The lift pump having output is no certainty there actually is. Now collecting overflow from the return line off the injection pump would while cranking. Always remember these older six cylinder engines in line type injection pumps are pretty reliable in general. Of course failure modes are not unknown. just not common.

I'm going to do some diagnosis right now and let you know. Seeing gas pump out of the return line will be one of the first things to see and go from there. Thanks for the input. This forum is great!

[joeblack]

Excellent article timing. Sticking fuel rack is what I expect that my problem is.
Thank you for increasing my hope for this IP.

Problem.
1982 300TD. Car does not start. PO ran veggie through bad conversion. IP does not spray through any injector. IP does deliver fuel if injector is removed. Expected IP broken ,
Removed # 1 delivery valve and observed position of slot in plunger. It rotates a couple of degrees when I manually push the stop button on the IP. Fiddled with the alda cover and then sometimes it does spray through the # 1 and # 2 injector. May be fuel rack stays in shut off position.

How do you remove the alda cover and get access to the inside.
Are there pictures available on the forum from the inside.

Thank you, J

[1stbenznc]

I got it started! But it's not running well- HELP!

Not sure what I did or didn't do to get it started. I

Checked for return flow from IP - good

Check resistance to glow plugs - good....it think. I pulled the first one and tested it manually with jumper box.

I warmed the engine with the block heated for a couple hours as it is about 40 in the garage- I got it nice and warm.

Held the pedal to the floor and cranked. Within 20 seconds it started.

HOWEVER, it was choking and smoking a bit (which I expected - bluish gray) but it was idling with the pedal on the floor. Once I lifted the pedal it immediately died out. Something seemed to be restricted or its something I don't know about.

I do not have the trap oxidizer and I just checked the fitting in the intake that goes to the ALDA (it wasn't clean, but wasn't clogged)

I pulled the pressure test plug on the exhaust manifold and it allowed me to raise the pedal almost to the top then it still shuts off (very slightly better). It will not rev up at all!!!

ANY IDEAS???

I'm thinking maybe there is something really restricted in the exhaust somewhere. There are three different cat/resonators or mufflers on the exhaust still - I don't know where to look now?

Sorry I'm going to post this on another thread that I started too.

[kanoa]

Originally Posted by MTUpower

So to summarize, veg oil as fuel causes IP problems, don't use it unless you like problems and have time and $ to burn fixing them.

I would have to agree with this statement. However, running any car on any fuel will result in wear and eventually require service.

Choosing vegetable over petroleum oil will certainly require more frequent service but it may be worth it to some people.

The car I posted about has 320,000 miles on it and around 100,000 on 100% waste veg. oil so it's not like veggie oil destroys them on contact. Polymerization of the oil is one of the toughest long-term problems with veggie oil and I'm hoping someone will experiment and find a way prevent it from forming.

-K

[kanoa]

Originally Posted by joeblack

How do you remove the alda cover and get access to the inside.
Are there pictures available on the forum from the inside.

I looked into this but it sounds like a lot of work. You have to completely remove them ALDA and then release the connecting rod from the bottom of the cover plate. Putting it all back together sounds like difficult too. As I mentioned, you can rotate the plate to get access to the inside of the IP without removing or re-adjusting the ALDA. Taking the cover completely off would be great for servicing the IP in-place but it sounded like more work than it was worth.

-K

[kanoa]

Originally Posted by 1stbenznc

I got it started! But it's not running well- HELP!

Did you clean the injectors? The most common cause for limited injector delivery (when everything else checks out) is simply dirty injector nozzles. Diesels need them cleaned often and veggie oil diesels need them even more often. If someone bypasses a filter while running dirty veg. oil they can clog within a minute. It's not hard work, you just pull them, disassemble them, and soak them in our friend gasoline.

-K

[BoiseBenz]

Great thread, which may save a to-be-parted 340k 123 240D with only three years on a factory rebuild.

Originally Posted by kanoa

Polymerization of the oil is one of the toughest long-term problems with veggie oil and I'm hoping someone will experiment and find a way prevent it from forming.
-K

I was under the impression that that's what biodiesel is for?