injector pump, vegetable oil conversion

You should get the injector pump checked for pressure and leaks, also the injectors opening at the correct pressure.

Veg oil does not have the lubricating properties of hydrocarbon based diesel and its an often reported problem of injection pumps that do not have their own lube oil resevoir.

Has this shop ever seen one of these cars before?

What does the compression test out to?

When was the last time the banjo bolt was cleaned out?

The stalling suggests the rack damper bolt is screwed in too far.

No, it is quite the opposite of what you said. Veg oil has MORE lubricating property than diesel.

I would agree with Richard on this matter but before you do any diagnostic... replace the fuel filter first. The reason is depending on how well the person filtered the WVO... if he didn't do a good job, then the filter will clog up pretty much within one tank.

Two ways to resolve this question:

Given the motor's 240K miles, have an independent M-B shop do a compression test on it. That will tell you the motor's internal condition and whether it has sufficient compression to run as it ought to or needs an overhaul. This will cost some $ but will give you a good estimate of the motor's remaining useful life.

Or you can nibble at the problem and hope to stumble on a solution - or ultimately discover that the motor needs an overhaul.

Nibbles (in approximate order of effort and cost):

1. Throttle linkage - with the engine shut down watch the throttle linkage while an assistant works the accelerator. When accelerator is floored the lever between the injection pump and the block - yes behind the IP - should reach its full throttle stop (limit). If it does then that's not the problem. Proceed.

1. At the very aft end of the motor's intake manifold - close to the firewall - is a "banjo fitting" attached to the intake manifold by a hollow bolt. Remove the bolt and clean it out with a wire; do the same to the banjo fitting. Reassemble and don't over tighten the bolt. Follow the plastic line attached to the "banjo" to ensure it's not broken or disconnected from its destination valve and then check it further, all the way to the injection pump. Examine the termination point - that's called the ALDA - a device to put added fuel into the motor during acceleration. Unfortunately it has an adjustment on its top center that dummies attack; some ruin the device. Does yours look like its been adjusted or opened? The motor's acceleration will be poor if it's ruined.

2. Look at the small clear fuel filter below the injection pump. Replace it if its color is very dark. You may as well replace the larger spin on metal can fuel filter that's aft of the power steering pump. You'll then have to purge the air from the fuel system - that's done by unscrewing the round knob and pumping the primer pump that's next to the small clear fuel filter until the air bubbles have left the clear plastic fuel lines.

1. There's an adjustment on the aft end of the injection pump whose function is to dampen the hot idle oscillations of the fuel rack and so ensure a relatively smooth idle. As was pointed out earlier this may be too tight and so cause stalling. But I doubt that's the problem here.

2. You say that the timing chain was replaced - by whom? If by an experienced mechanic at an M-B shop it's probably OK but if not, then the engine's valve and / or injection timing could be incorrect. Badly retarded injection will allow the motor to start but it will lack spirited acceleration (even on a diesel's relatively "spirited" basis). Were the motor's valves adjusted? A terrible valve (mis)adjustment will produce the exact symptoms you describe. A compression test will reveal it.

I suspect that your motor's problem is either a terrible valve adjustment (causes poor compression) or the valve and /or injection timing are badly off I but can't say so because I don't know the sequence of events. Was it running well prior to the timing chain etc. being done? Or is poor running why the chain was changed?

1. I've owned one of these for 26 years and never heard of having its "valves cleaned". Whose idea was that? Run if the same guy wants to rebuild its injection pump because that's pretty heavy $$ and IMHO he's just guessing what to do next - with your $$ funding his game.

A further idea on the "nibble" road:

This is something that you can easily check visually and will either raise another suspect or eliminate one.

The top of the injection pump has five pipe connections that appear to be held in place by steel yokes with a hold down nut in each. There's probably some yellow paint on each nut; it ought to be intact - as an unbroken seal - indicating the original setting is not been changed. If so that's good, if not this could be your motor's problem.

The hold down nut on each of these yokes is an adjustment of the fuel delivery to its nozzle in the motor. Each nozzle in the cylinder head has an "opening pressure" of about 2,000 psi; when the fuel is pumped there it opens briefly and sprays into the cylinder and closes. The yokes regulate the duration of that pressure and if some moron messed about with the yokes' adjustment the duration could be too short = insufficient fuel = poor performance.

If you suspect this is the case a Bosch Diesel Injection Service shop will be able to recalibrate the injection pump for you. They can also clean and recalibrate the injection nozzles - something to consider if the exhaust smokes more than you like. The nozzles can be done independently of the pump.

I hope these ideas help you restore the engine's "default" settings so you'll be on the road - happily.

I wrote this morning's post from memory and have a correction. The "yokes" that I mentioned are in fact hold down straps with TWO nuts - one at each end and these two nuts have small paint marks/seals. Its these paint seals that should be inspected.

Mr. Lambach,

Thanks very much for your thorough response, I've printed out what you said, and i'm going to hand the info to my mechanic. The poor acceleration and stalling were happening before the timing chain was replaced. It was something that the mechanic saw when inspecting the valves and strongly encouraged me to replace, as he said the tension on the chain was too loose. I've spend almost $2,000 in repairs so far and have not had an effect on the original problem...very frustrating. Well, again thank you, and i'll write again with any updates.

Tiger's right....veggie oil has much more lubricating ability and is also a better solvent. Thus, when converting to veggie oil you need to keep an extra set of filters on hand since the entire fuel supply system will undergo a good cleaning.

replying to dougcullen, InterociterOperator wrote: Doug - what ended up happening with this rig?