How to change fuel distributor plunger seal?

[irieite]

My fuel distributor is leaking on my '91 190e 2.3. I can see the fuel leaking down inside the air flow meter when I press down on metering plate and look inside. My question is, after I take the distributor off, how do I replace this seal and where do I find a replacement? The only seal I see online is the one for the distributor to air flow meter seal.

[maheath]

I'll assume that your fuel distributor is similar to my M103 engine. First, you'll have to remove the fuel distributor from the engine. Should be a few torx or allen bolts on top of the distributor (and remove all of the fuel lines).

There's a 19mm nut in the center of the bottom of the fuel distributor. Remove that nut and you can pull the plunger out of the fuel distributor.

[maheath]

I forgot to add, Mercedes has a repair kit for the control plunger. If you can't find it listed online, call your favorite parts supplier, they'll be able to get it for you.

[irieite]

Thanks alot for the replies. I think I'll have to oder it from the dealer, because Fastlane does not have it listed and pretty much all the other sites use the same menu system.

Hopefully this will fix the leak. Will I have to recallibrate it once it's back on, that is will I have to reset the mixture?

[pmizell]

On a 103 engine, and assuming that this applies to your 1.6 which I'm almost certain it does.

The article reads:

"5. Check control plunger in fuel distributor for leaks. Briefly press air flow sensor plate (84) down fully and hold tight in this position; a a slight leak quantity is permissible when this is done."

SO, if this is what you're doing, then the small fuel you see coming out is OK!

Good luck

[irieite]

Interesting.. I wonder why a leak such as this would be permissible at all, unless it were by design for enrichment. Anyway, the fuel mileage is 19-21MPG City and 26-28 MPG HWY. If it were leaking enough to cause a problem, would my MPG figures be much lower? I figured the leak was to blame for my rough idle and sputtering hesitation while accelerating from a standstill (due to fuel loading up in the cylinders), as I've already changed all ignition components other than the coil. Injectors an fuel filter have been replaced and I've also changed the lambda sensor as well.

[pmizell]

When you say lambda sensor, do you mean the oxygen sensor?

Have you tried checking or adjusting your air/fuel mixture? Also known as lambda/on-off ratio.....

If you have a lower chamber pressure leak (in fuel distributor) then your lamda reading will fluctuate pretty wildly. You need a multimeter with duty cycle function to check this. Sears sells a good one for $30.

You can also check your fuel system pressure and make sure it is within specs. Do you have any warm start problems? Have you replaced your original overvoltage protection relay?

Good Luck and keep us up to date... we're here to help

[irieite]

Yes Paul, that was the oxygen sensor I was referring to. I replaced it because the check engine light was on. After reseting the computer (disconnecting the battery) the light stayed out afterward for about a week and now it's back on.

I'll consider picking up that cheap duty cycle tester at Sears and run some tests with it when I have time off in early May.

So, back to my previous question. Is it normal then, to have a bit of fuel leaking outside the fuel dist and into the air flow meter?

[pmizell]

According to the above referenced article, yes it is normal. I would imagine it is for full throttle enrichment as you mentioned. If your control plunger was leaking, your fuel economy would definitely suffer ... noticeably. You could also encounter fuel dripping from tail pipe.

Replacing the plunger seal is a very DIY job... I do not know if your need to recalibrate after replacing though ... I guess that depends on whether it was leaking or not.

You may try to adjust the lambda slightly in either direction without a DMM to see if your throttle response and idle clears up. 3mm hex key turned clockwise will richen mixture, counterclockwise will lean it.

Good Luck

[pmizell]

Irieite:

Just FYI, I have been informed (by someone who recently did this) that changing the plunger seal is a very delicate process. You MUST measure the static height of the plunger BEFORE disassembly or your basic setting will be off. Even if you do measure, there is no guarantee that setting will be accurate and you may need to remove it again to get it right.

Good Luck!

[irieite]

Thanks for the info Paul. I think I'll make darn sure it is indeed leaking before I take on that task then.

Just as a side note, because of the rough idle, the car shakes forward when in drive at a stop and I take my foot off the brake slightly, sort of like it's missing, after that, when I hit the gas it'll usually sputter a bit then take off and run and drive just fine. That's what lead me to believe that it may be fuel loading up from the leak, but then again, my mileage seems fine, especially for the way I drive it.

As I mentioned earlier I canged all ignition items, except for the coil. I wonder if it's a weak spark? How would I test the coil to see if it is in spec? BTW, the car has 166k on it.

[pmizell]

I don't know if there is a way to test the coil ... at least I don't know how to. I recently replaced mine thinking it was going bad, now I have a coil with 227k miles on it that works perfectly well.

You may have a clogged fuel distributor, or a bad fuel pressure regulator. Again, you'll need a fuel gauge to test. I recently ordered one from J.C. Whitney that has yet to arrive.. but when it does I'll be doing some testing to my system.

A couple of other things to consider: cylinder compression and built up carbon in compression chamber.

Good luck :p

[irieite]

When I first bought the car I had no MB experience and I thought I could easily fix this "minor" problem by throwing a few parts at it, since everything appeared to be original, and the car was in great shape overall, mechanically (ie no oil burn or leaks, firm shifting auto trans and solid suspension).

The other parts I've change since I bought it (and made no difference) include the fuel pressure regulator and the EHA valve, both new. I'm strongly suspecting the fuel dist at this point, but am feeling a little humbled (and light in the pockets) from my previous attempts to solve the rough idle.

I must also mention that the car has been to the dealer in order to get it to pass smog, which it now does. Again, this made no difference in the idle/off line hesitation/sputtering.

I think I'll start taking a more linear/logical approach to figuring out this problem by checking things such as EHA current and duty cycle that I've seen being discuss in this forum. I'll post the results as they are found.

[Rick Miley]

Have you considered the possibility of a vacuum leak?

[irieite]

Supposedly, when it was at the dealer get set to pass smog, they replaced all kinds of vacuum lines, fittings and plugs. Including one of the hoses for the idle air valve. So I don't *think* that's the problem.