My 1993 300e 176,000 miles has started to run rough. I don't know where to really start with fixing it. Installed recently new wiring harness, MAF and fuel filter. Should I just start with the obvious? Plugs, wires and connectors? Perhaps a coil is going weak? Which one? I don't dare take it to Sunflower motors in Topeka, last time they charged me $488 to replace a coil and put in connectors on 2,4,6. What a rip off. I built a code reader and get the following codes (if it really makes any difference) I took the coil cover off just to check things out and now only 3 of the 6 bolts will tighten-up! Its almost like the threads in the head have gotten lower or something. How weird.

Pin #6 3,6,8,9
Pin #7 1
Pin #8 1
Pin #10 No lights
Pin #14 14,5,11

Any advice would be appreciated.
Rick Potter
Potters Barber shop
Osage City, Kansas

You're on the right track to read the codes but I think you'd better do it again. It needs to be done very precisely or the output is giberish. Also you need to read pin 3, the DM, very important. There is no pin 10, at least for fault codes. And pin 14 does not have a code 14 so there's something wrong there. If you have ignition problems they should show up on pin 8. Then look up the fault codes (link below) and post the description, not just the number. The good news is you can heli-coil the 3 bolts but the even better news you don't really need to bother - it's just a dust cover, doesn't need to be tight, people run their cars just fine with the cover missing.

http://www.geocities.com/MotorCity/Downs/1039/mercedes/cs1000_mb.pdf

http://www.emhart.com/products/helicoil.asp

Error codes read with code reader - 1993 300e 2.8 fuel injection

Pin 6
3 - Driver Air Bag
6 - Front passenger seat belt buckle switch
8 - Voltage supply interrupted
9 - SRS warning Lamp

Pin 8
4 - Load sensor in EAL/AKR control module faulty

Pin 14
5 - Stop lamp switch
11 - Fuel safety shut-off to LH-SFI control module

Nothing to plug into for Pin #3 - Empty

Other than wires, connectors and Bosch F8DC4 plugs is there anything else I need to get this car running correctly?

Comments appreciated - barbershop@mchsi.com
Rick Potter

Can you describe in more detail what you mean by "runs rough?" Is it at idle, cruise, accelerating? Engine warm vs. cold? Air temperature? With or withou a/c engaged?

How old are the plugs, wires, connectors, coils?

- JimY

Sounds and feels like a plug wire is pulled. Seems to idle ok, but during acceleration it has a "chug" "chug" feel. Used AC today and it had no real effect on performance. Seems to run better during cooler weather. Plugs and wires may be original. #2 coil and boots for 2,4,6 replaced 3 years ago. Ordered a new wire set and plugs today. Hope it solves the problem as I'm not to thrilled at paying $500 again for something simple. I pulled #2 plug last night and it was a light tan color and looked ok. Wiring harness replaced 5 years ago.

Comments appreciated.

Code 4 on pin 8 is "hot film mass air flow sensor" (page 31 of Baum) which is a real clue. In any case next step should be to erase all the codes and see what comes back. It doesn't sound to me like an ignition problem - you're not getting any ignition faults.

If you don't know the plugs are OK, definately change them. This engine calls for plugs at 30K mile intervals. It's also a bit particular about plugs, so be sure to use recommended plugs. It doesn't like platinum plugs.

I'll second erasing codes and seeing what comes back. Shouldn't have that code 4 on pin 8 with a new MAF.

- JimY

When I say new I mean about 2 years ago. Anyway to test a MAF? Perhaps a coil is weak or going bad? How do I test a coil? Cleared codes and ran car, codes clear now. Socket #8 returns a "No fault found"

Replaced wires, plugs and boots. NO luck, still ran rough. Read codes again and got #22 on Socket 8 which is the coil for cylinders 2 and 5. New coil from Ebay $40 delivered and every thing is great now. Thanks to everyone who helped. I now sell code readers on Ebay for $32. Been making them for a couple years and everyone seems to like them, especially the cheap price and fast shipping I offer.