Problem started before changing plugs, and that is why I changed them even though they had only been in about 10K miles. Order of plug wires is fine and have checked it several times.

As noted above, have already changed rotor and cap as well, with no improvement.

Tomorrow I am going to comb through all the vacuum hoses carefully. Still wondering about that coil too.

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

treiberg, check that the connections on the ignition wire from the coil to the distributor cap are tight. Also, check that the electrical connections on the coil are tight and no frayed wires.

Listen for buzzing from the OVP relay (typically located behind the battery). If so, it probably has a failed solder connection.

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Fred Hoelzle

Ferdman, I pulled the coil out yesterday and all connections are tight, and wires look good. On the OVP relay, keep in mind that I just replaced it with a brand new one.

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

Does it run well enough you can put a quality fuel system cleaner in it, and take it out and drive it highway speed for 50 miles or so? Then see if it helps your problem or not? Maybe you have already tried this? Have you ever checked the fuel pump relay too like tested it or has it been replaced?

I did already add injector cleaner and have driven it about 20 miles, but no difference yet.

However, a bit of a breakthrough on the diagnosis. Although I had already done this, I was probably in a bit of a hurry earlier and missed it. When I pull the boots on the plugs one by one, they all make a change in how the vehicle runs except for cyl 5 - I can hear no difference when I pull it off of the plug. I know the cylinder has good compression (thankfully), and I see a big fat spark as I am pulling that plug wire out of the socket, and have confirmed that the wire is firing with a timing gun too. So....my conclusion is that this injector on the cylinder is not working. Is this the correct conclusion? Could it be a fuel pump issue on that one cylinder, or is it pretty safe to conclude it is the injector? Aside from installing a new injector, what can I do? Should I remove it and try to clean it?

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

Hey treiberg,

I believe it was ferdman that mentioned the ignition coil, something I forgot. I recently replaced mine, it tested fine with over 200,000 miles on it, but the new one made a HUGE difference, it actually solved a problem with pinging that I had. I highly recommend shelling out the dough for a new one. Just be sure to get Bosch, I wouldn't trust anything else. And again, I highly recommend a bottle or two of Seafoam in your gas tank. It will clean carbon out of your top end, not just your fuel system. Really workedGREAT in my car.

Good Luck!

Also, if you're sure that cylinder is dead but has spark, im pretty sure it can only be an injector problem because the CIS system is not timed, all injectors just open and spray constantly (this is what I have read, somebody please correct me if I am wrong!!). Anyways, you can get new Bosch injectors for $23 at *********.com along with the necessary seals and the plastic holder.

Did you pull plug #5 then & compare it to one of the others? That should give you some good feed-back.

All plugs are brand new. The ones I pulled showed no difference for plug 5, but the condition just started happening, so wouldn't expect to see much of a difference.

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

Figured it out!! Injector number 5 was completely plugged!!

From one of my last posts above, you can see I isolated it to cyl #5 by pulling the plug wires on each cylinder. I knew it must be injector related because I had a good spark on that cylinder. I pulled the injector out (very easy) and threw it into my pop tester that I use with my diesels. The injector looked very nasty and dirty (nearly 20 years old, what do you expect?). After pressuring it to 100# it was barely dribbling. Finally at about 400# of pressure, it popped and blew out whatever was plugging it. After it was unplugged I got a decent (but not great) spray pattern at something less than 100#. I also pulled #6 injector and put it in the tester and it seemed OK, and then I swapped the two on re-installation, just in case the problem persisted, I wanted to see if it would move to the other cylinder. Fired the car back up and she is as smooth as ice!! That M103 is a smooth engine!!

So the new plugs, the coil, the O2 sensor, the wires, the OVP relay - none of these were it, although I learned a bunch in the process. I swear that after probably 3-4 hours of reading aricles on this forum and others, I never read anything about a completely plugged injector on a M103.

Thanks for all the input, and many of the ideas I got from others helped me to finally figure it out. StormyC88's idea to pull each wire to find the dead cylinder was a key diagnostic step that I passed over too easily early in the process. Also, being able to pressure up my injector with my pop tester (most folks probably don't have one) was another key.

Since these injectors seems to have poor spray patterns, and since they dribbled a bit even after they would pop, I am going to replace them all. Will cost less than $200 and I believe that it will make a pretty big difference in fuel economy to get those restored to new condition. And the installation is so easy.

Thanks again to everyone who gave me assistance.

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

For those that might be wondering about my pop tester, it is a hydraulic jack that is fitted with a fluid reservoir (typically diesel) that can pressure up an injector to see its spray pattern and to find its pop pressure, the pressure at which it releases its spray. Those of us that have diesels use it to work on our injectors - we use shims to adjust the pop pressure so that all cylinders are within about 10% of each other for a smoother running engine. You can buy them on eBay or from certain other "mercedes sources".

I just never really knew that I would someday find a use for it with my Mercedes gasser. Turns out the thread size is identical. Probably running that diesel through the injector while testing it also helped to clean it out.

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K

Glad you were able to find the fault. The injectors are something that should definitely be replaced on an older M103 especially if they are original. You will notice a big improvement in driveability and efficiency.

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1989 300CE

Congrat's on finding the problem there. I still believe a routine complete fuel system clean on those mechanicals is definitely a paying procedure. It kept my 240 diesel running from 90K to 170K(when I sold it) without a single fuel issue.

Did the clicking in the drivers door go away after cleaning the injector?

I wonder if you were hearing a "struggling injector" ?

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Hey Mike, if you read my first reply in the thread you'll see what I found. It was totally unrelated to the injector (window button was mashed down by not putting console paneling in correctly, so it was eternally trying to close an already closed window).

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Treiberg's Collection: 1981 240D, 1985 300SD, 1992 300E, 1997 E300D, 2005 C230K