Rough running 300CE
 

Hello,
I am a newbie to the forum. I have enjoyed reading the posts and how everyone helps out each other.
Well, it's my turn to ask for help.
I have a 1993 300 CE. About two weeks ago I got a wild hair and decided to change the fuel filter. I had guy come over and replace it. Then He changed the plugs for me. Started right up and ran great.
The next day I went to pick up my son and about 7 miles into my trek I stopped at a light and the car ran really rough. I made it back home but the car was slow taking off but once it got going it ran good.
I have so far changed the injectors. I started the car and it ran great for a few seconds then it once again idled rough. Changed the plugs and the wires with no positive results. I'm getting ready to order three coil packs but I'm hesitant to do that. I feel that the problem is a simple one but I can't put my finger on it. I asked my local parts store guy about the gap for the plugs. he told me .028. is that correct? I checked the old plugs and they were at .038/
I need help!
I appreciate any and all help.
Thanks for your time

Replaced Injectors?!?!?!? Yikes!
 

Welcome to the forum. Others more knowledgeable will chime in here, but one of the first things you must do is to replace most or all of the rubber bits in the vacuum system. I guarantee you there is at least one leak someplace. The ECU in the HFM-SFI system can compensate for some vac leaks up to a point, but it only goes so far. At this age, all those vacuum parts are as hard as a rock. Buy a couple feet of vacuum tubing and start replacing all the short pieces of tubing in the engine compartment. There are a couple down low, down near the trans. Then replace the two approx 1/2" diameter pre-formed hoses on the botttom of the intake manifold. You also need to replace the pre-formed elbows and tees in the system that connect to the EGR and the other sub-systems. Just start replacing the vacuum parts one by one in a logical manner.

You need the car to be placed on an ignition scope to verify if coils are bad (as far as I know).

How is the condition of your engine wiring harness? You do know that your car may be one of the ones with the disintegrating harness? DO a search on here and you will find out how to determine if your harness is going bye-bye. A degrading harness causes all manner of intermittent driveability problems.

New injectors?!?!? How dd you verify your old ones were no good?

Check the plug type (non-resistor only they say) and replace the three plug connectors directly under the coils. Common problem with this engine. Mark

Thanks for the replies. I did say I changed the injectors. I only changed the number 3 because like all people who know squat about cars like myself, I listened to a guy that said he checked them all and the number 3 was bad. Mind you I was not there when he made his diagnosis. So I didn't see him actually check anything. The one thing he did check twice was that the amount of the check I wrote him was correct. He was a friend of a friend.
OK, so I will start replacing hoses systematically.
In response to the other advice : I did change the three connectors under the coils. I also replaced the spark plugs with the Bosch Super Plus plugs gapped at .028.
I did notice a hose missing under and by the manifold. Hmmmmm. I will go check that now.
I will report in.

Right on. Do you want me to give you the part numbers for the vacuum parts? I am going through this very effort right now on my own '93 300E with M104 motor. I have the PN's for 95% of the hoses and fittings in the vacuum system. I used the parts diagram in the StarTek parts manual along with a knowledgeable MB parts guy to get the stuff. There are one or two I haven't tracked down yet though.

Yes Please. I refuse to take my car to the dealership and pay out the nose. So It would be very much appreciated to have part numbers and whatever else you can throw my way.
Oh , I was wrong about a hose by the manifold missing. I think the only thing missing here is my sanity in this matter. LOL

Right on. The alternative to the dealer is an independent MB mechanic. They vary in quality so ask around other MB owners in your area to see who they use.

I will dig up the PN's and post them up here in the morning. I hear ya on the lost sanity bit :-P

I thank you very much.

Aren't Bosch Super Plus resistor plugs?

OK here you go. This is not all of it but this is 90% of it. There are one or two more I haven't sussed out yet, like the one on the canister purge valve.

104-094-35-82 Hose between bottom of intake manifold and A/C mounting bracket (this is a crankcase vent hose). Cost $4.95

104-094-36-82 Hose between bottom of intake manifold and top of throttle body. Cost $13.54

007-997-61-82 Vacuum hose, thick-walled, for all the small short pieces of vacuum hose scattered here and there around the motor. Cut to length as needed. This is the good stuff that fits correctly, not the El Cheapo krap they sell at AutoZone. 3.5mm ID x 9.0 mm OD. Cost $3.40 per meter.

117-078-04-81 U-shaped hose connector on top of the black plastic intake manifold. Cost about $3.50.

601-078-02-45 Branch-off fitting (wye fitting) located on metal part (the lower part) of the intake manifold immediately forward of the throttle body. Cost about $3.50.

117-078-01-45 Branch-off fitting (wye fitting) located at the EGR SOV. You have to remove the black plastic decorative cowl cover on the front of the motor, the one with the MB star on it, to get at this one.

Another very important one is the short piece of vac tubing at the EGR valve located near the back of the exhaust manifold. That is the special red high-temperature vacuum tubing. Don't use the black hose for this one or it will die a quick death. Ask me how I know :-) I don't have the PN for that one yet.

Warning, some of these are pretty tough to get to, for example, the hose between the manifold and the throttle body casting. You may have to remove a bunch of parts to get at that one. I think you can access this one if you remove all of the air intake ductwork and the large rubber connector tube that connects the inlet air duct to the throttle body (the one on top of the throttle body). In doing this you may wack that big connector tube so be prepared to buy another one; they are aobut $25. You also may have to cut off the old ones because they have hardened. All this was easy in my case because my motor was all torn apart.

Do you have a factory service manual? If not you need to get one. They are on CD, about $65, and available from 1-800-FOR-MERCEDES. When you get that there is an index you need to download that makes navigation of the manuals MUCH faster.

Hope this helps!

Hey Elsinore, you did a lot of research to help a fellow enthusiast out, and I know that'll be appreciated. But it's generally regarded as bad form to recommend a competitor on a forum sponsored by another online parts vendor, as this one is. Many of us here have dealt with Fastlane Phil and can attest to his marque knowledge, competence and reasonable prices. For your future consideration. Woody, why not click on the "Buy Parts" button at the top of this page and give Phil a try? That's one way of showing you value access to this great forum.

Cal - Post has been edited accordingly. Thanks for the counsel and the correction. I had completely forgotten this was a sponsored forum. Sometimes I'm not the sharpest tool in the shed :D Thanks!!

Cal,
Thanks for the advice. Like I said in my first post I am a newbie and I'm still learning how to navigate through this informative forum. I will take advantage of all the information that's offered.

Elsinore,
Thank you for all your help. I'm going to start by purchasing the manual. Hopefully I can get the old girl running like she should in a couple of weeks. Thanks God my son has a car and no job. LOL

No, there are 2 variations of Super Plus. One is copper core w/o resistor and the other has yttrium.