I need to find the cause of a slightly rough-running engine. It's
a 300SD with 220,000 mi. and a recent valve adjustment which I hoped would cure the problem. Didn't find any excessively tight valves, so I don't think there is a burnt valve. Funny thing, though is the fuel mileage seems to have gotten better with the advent of the "skip." I do not have any means of checking the compression, but have an infrared heat gun I'm going to try. The car is a Calif. model, and I can hardly see the exhaust manifold to find the cold cylinder. Another idea I guess would be to try cracking the nuts loose on the injector pump one at a time to try and find the culprit.
What I am wondering is if I get a replacement injector, what gasket, gaskets, seals, etc am I likely to need to replace?
The car needs other work, (exhaust and brakes) but I want to get the engine problem resolved before going on to those issues.
Thanks.

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Mike.

Truly you aren't supposed to replace just one injector because if one is bad so are all the rest generally, also they are supposed to be within 5bar of each other.

There are only two things that should be replaced then, the leak line hoses going from injector to injector and the injector heatshield beneath it. The heatshield can be had as cheap as $.25/ea upto $3ea, hose costs about $3/m but retails $12/m.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

$5.25 *each* at the stealership.

MSKULICK,

NEVER loosen the nuts at the injection pump to check for a misfiring or knocking cylinder. Loosen the nut on the injectors instead.

Not true about "if one injector is bad, all are". One can fail and all the others can be perfectly OK. Another case of "If it ain't broke, don't fix it".

If you find a suspect injector, switch it with one you think is good. The missing or knocking should move with the suspect injector. If it doesn't, the problem is something else than the injector..

P E H

Jeeze, the stealership is really living up to its name!

I said generally. I would think it is much more probable for all injectors to be equally worn with lower POP pressures and nozzle wear than having four nearly new nozzles with perfect POP pressures and one bad injector. POP pressures are supposed to be within 5 bar and a new injector is 2ksi with the service limit of 1.75ksi which is about 17bar difference.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

If it runs good enough don't mess with it. I'm having a similar problem. I opened up a bigger can of worms trying to put "new" injectors in my 300D. I'm putting mine back the way it was.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

Hello......BoostnBenz.....So, there is no actual gasket, per se, just the heat shield? I have one of the $12 service manuals somewhere. I haven't seen it since we moved up here from Maryland a couple years ago.(It would be nice to be able to look at a picture)...........lietuviai....... I wish it were running good enough not to mess with, but I'm not comfortable with the idea of selling it to someone without knowing for sure...... PEH, you bring up a very good point. If I'm not mistaken, an overly-tight injection line nut (at the pump) runs the risk of moving the delivery valve holder when cracking the line loose. Thus putting the pump out of calibration and necessitating the r&r of the I.P. and sending it out to the diesel-injection shop for repair. I have done the "nut-cracking" routine quite a bit in the past, but must admit putting a pump out of calibration once and then having to send it out to be recalibrated.
Is this the reason you say not to loosen the lines at the pump?
I work on trucks, mostly electronic these days, but now and then have to replace an injector on a mechanical engine. Generally, it's a lot easier to remove all the lines as a unit from both the I.P. and the injectors. Usually there are a bunch of clamps and brackets holding them together, just takes less time to do it that way.
Excellent point about moving the "problem" injector to see if the problem moves with it!!!
I guess what I had better do is get some of those heat shields and return fuel line so I can see if I really need an injector.
I have been trying to sell this car as is, and getting a lot of interest, but the prospect of fixing it scares 'em all away. So it
looks like I've got to do the work. Not much time, I work two jobs and we recently bought "this old house"
Thank you all!

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Mike.

The heatshield doubles as the seal, it is a machined piece of metal designed to seal the compression and help absorb the heat from going into the injector.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

mskulic,

Yes as to releasing the injection pipes at the injector instead of at the IP to prevent the possibility of damaging the IP.

I can't ever remember an injector causing a misfire in an engine. The ones that failed on my engines, just made the engine knock on one cylinder. I had other used injectors so I just replaced the bad one with one of the used ones.

I did have an IP that caused a missfire in one cylinder. It just stopped pumping fuel to that cylinder. I replaced the IP with another used one I had and that fixed the misfire.

If it isn't an injector, you might try a compression test.

P E H

Mskulick2, you might just try and get another used injector to replace the one you are suspicious of. Just make sure you get one for a turbo diesel of the same type. These injectors say 135 bar on the side of them. The non turbos use a different type of injector and they won't work in your car. Then just try to get what you can for your car. It may not be worth dumping more money into the car and not get it back when you sold it. Get your best offer and then see what it would take to get it running a good as you want to. More than likely, you'll be ahead taking the offer for the car running as it is.
That's what I plan on doing.

__________________
DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012