I have a 1985 300TD with 290k miles. It is in generally excellent shape.

About 700 miles ago I started to experience a pretty rough idle. Hard to cold start with lots of smoke, then an intermittent rough idle when warm.

Sometimes i'll pull up to a stop light or take my foot of the accelerator and everything will be smooth, but 60% of the time the idle is quite rough. As I say, this is a new symptom.

To track this down, I've replaced the glow plugs, confirmed the glow plug relay is working right, replaced the fuel injectors, done a valve service, and tighten up the rack damper bolt.

She runs great on the road, but still has an intermittent rough idle and hard cold start.

My mechanic feels it is the fuel injector pump... and I have to admit I can't think of any thing else it could be.

So, I'm looking for a fuel injector pump rebuild.

Anyone have a good experience with a mechanical fuel injector pump rebuilder lately?

Thanks,

Bill

I would google Bosch shop nearby and give them a call. Hopefully they won't tell you too old.

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Jim

Do not jump to soon, cold weather starting, pump has a start mode, a fuel enrichment
setting, push down on throttle let off, do not touch throttle again, crank engine. problem
if oil is too thick pump will not go into this start mode, cranking on and not starting floods
engine. Thick oil slows engine cranking, worn starter same, weak battery same.
Low fuel pressure can cause hard starting, poor fuel same. I would check every thing.

People frequently suspect the fuel injection pump because it is the item they least understand.

Who did the valve adjustment for you and what did they find when they checked the valves before the adjustment?

Also look at the fuel emission sticker and see what the proper idle speed is. Make sure the idle speed is within the proper range. An old engine may need to be up at the higher end of the idle speed to idle smoothly.

Your fuel supply system can cause the issues you mentioned. That would be from the fuel tank forward through that tank scree, filters and the fuel supply lift pump and out of the fuel pressure relief/overflow valve.

Concerning tightens up the rack damper bolt. I am not sure what was done there.

To adjust it the rack damper blot is backed out a way and you adjust your idle speed with the actual idle speed adjustment.

With the rack damper bolt, you slowly turn it in until you can get rid of a bit of shaking and in theory it should not change your idles speed. And in my experience, it won't remove much shaking. And use the lock nut to hold it in place.

When I replaced my rack damper bolt, I found the spring much weaker than the new one and the plunger was worn on the end. If it has not already happened the rack damper bolt could be one of those parts that will be or is no longer available.

When I had intermittent shaking at idle it turned out my fuel hoses were hard and when the plastic fuel filter got hot it was warping the plastic and allowing air in. So, I got that asking when the everything was hot.

So, the issue is that something like changing the hose is cheap as long as you do that yourself.

Troubleshooting the issue is cheap as long as you do it yourself.

If you have the old-style hand primer with the shiny aluminum body and the hard plastic knob that eventually becomes a source of an air leak.

If you have the type of fuel pressure relief/overflow valve that can be taken apart there a ball bearing that is the valve and a spring inside. That spring can be stretched till you have a free length of 27mm and re-assembled. If you can't do that you are stuck buying a new one.

Besides the spring if the ball bearing has pitted spots on it that can cause a pressure loss. However, I know of no one who has replaced the ball bearing.

I bought a new fuel pressure relief/overflow valve, and it changed nothing, so I guess my old one was still doing the job.

There is a 5mm O-ring inside of the fuel supply/lift pump that gets rock hard. The whole pump can be rebuilt but this more than most common mechanics can do. Too costly to pay a mechanic to do it.

Some when they are done with all of the other stuff and that shaking is still going on have found changing the delivery valves inside of the Fuel Injection pump has worked. However, that is very invasive and takes some reading up on. Not an area where you want to loosen the wrong thing or screw something up.

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84 300D, 82 Volvo 244Gl Diesel

I type slow ,will get timed out so second part Rough running, I have removed delivery
valves cleaned lapped new seals, done several times, engine idles good for two weeks
than starts rough running again some times, did clear some, my thoughts, do a injection
pump purge, mine was very dirty inside, have not done this yet, but I feel it would help.
Why rough idle just some times? Is it possible that small particles float around delivery
valve area only after hot?

I don't know your mechanic nor his skill level nor if he can troubleshoot your problems accurately.

Some mechanics are what I call parts replacers. They convince you that part X is the issue, and they collect their labor chare for the removal and re-installation of part X and maybe get 10-20 percent of the cost of the part. If the replaced part does not fix the issue, they are going to convince you that it was old and needed to be replaced and replacing it, had you dodging the bullet on that.

Next, they are going to suggest replacing part X2. And that can repeat itself over and over again till you have spent a lot of money on your car.

In part that is because the mechanic just does not know how to troubleshoot proper and impart because of making money off of you.

What I am saying here is the removal and re-installation and timing of the fuel injection pump is going to have a high dollar labor cost. And that is assuming the person knows how to do that.

If the Bosch shop tears the pump apart and rebuilds the fuel injection pump that is like a $1200-$1500 adventure here in the Los Angeles area.

If you don't do what you can yourself, you will be at the mercy of the mechanics skills and or abilities.

I was a diesel mechanic for 18 years and worked in a fuel injection shop for 5 years. I would love to have had a customer drive his vehicle in and say remove my fuel injection pump, rebuild my fuel injection pump, rebuild it and re-install and time it. That would be like an approximate in today's money a $2000 job.

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84 300D, 82 Volvo 244Gl Diesel

If you really want a rebuilt pump and are t willing to try to be sure that's the issue first, you can get a rebuilt m pump with 6mm elements from Benz injection for 1500$ and it will be capable of a lot more power. You can keep it detuned if you don't want to change other things. It still may not be your issue though.

https://www.benzinjection.com/product-page/performance-om617-m-injection-pump-dieselmeken



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WARNING!!! VINTAGE MERCEDES MAY MULTIPLY UNCONTROLABLY!!! I have tons of Sl/Slc parts w108 w111 w126 and more. E-mail me with needs
BirchsgarageMB@gmail.com

People spend years chasing hot idle shakes (myself included) firing the parts and procedure canon at every shadow along the way.

Yes, these pumps are esoteric and catch a lot of flak for it. Rare it’s deserved, but rare is not never.

If you/your mechanic have been thorough and rigorous, eg, changing fuel hoses on general principle before bothering to rebuild injectors, its possible you have an issue with the governor, namely the spring.

Yup, I chased my shakes during the pandemic. All kinds of adjustments. New hoses. New nozzles and pop testing. Timing. Finally I traced it to low compression on a cylinder.

Whenever I’m at the JY I notice a lot of pumps on the cars. It may be a lot cheaper to pull one and mount it up on your car and see what happens.

The fact you see dirt in your pump is a bad sign.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

Maddening isn’t it…

Curious about your compression numbers.
Guess things respond differently/tolerances change with heat soak, but I could never isolate components in a meaningful way. I remember running the garden hose over the IP, no tangible difference… I had a theory at one point that the engine mounts softened at a certain temperature exacerbating lateral wobble (never tested this one). The idle would always calm down 5-10 mins after a highway run/city driving which made things difficult to test. Was also worse in the summer, etc, etc…

I posted them up years ago. It’s here buried someplace. It was pretty bad. Most of my cylinders were in the 300s but one was in the 200s. (On the SD).

The good news is I got rid of a lot of the shakes using a catch can for a few years. My intake was full of oil and I’ve really reduced the amount I inadvertently pour into the engine. I think this has cleaned up the engine after driving a lot. It took a year of driving around but it idles acceptably smooth. That was the big change.

Oh yeah in the shakes thread I recall doing some aggressive cleaning on the cylinders by directly pouring harsh solvents down the injector holes. Do this at your own risk.

Ok, dug up the original thread. It was a lot worse than that. So I thought the engine was done and I concluded that throwing Berryman’s Chem Tool down the cylinder bores wouldn’t make a difference at that point. I recall looking for replacement engines at the time and it was a Hail Mary. This happened deep in the pandemic and I had way too much time on my hands to obsess about my car.

Dang these were bad numbers. No wonder I didn’t mind pouring harsh solvent directly into the cylinders. It’s amazing my car runs so well now.

https://www.peachparts.com/shopforum/diesel-discussion/407898-tested-compression-my-300sd.html

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles

I remember that thread!

It's actually what motivated me to remove the exhaust manifold for cleaning and then install a catch can.

I've about a 25psi spread across cylinders (from about 365-390), just under the 10% threshold. Might be the reason, but still suspect something else. One thing I've never done is a leak down test. One of these days...

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1981 240D 4sp manual. Ivory White.