Hello folks!

I recently picked up a 94 E320 locally. The vehicle has about 150k miles on it but is in good shape and seemingly well maintained.

Within 2 months of purchase it threw a check engine light. I used the code check process of clicking the button under the hood to pull the codes. I pulled codes 2, 5, and 7. I replaced the o2 sensor to fix code 2. It did not fix the symptoms:
- Vehicle hesitates under load, especially at lower RPMs. Once it reaches higher RPMs the hesitation begins to minimize which causes a sudden surge of power. Seems to be misfire.
- Very rough idle, especially before it warms up, this causes a light bucking while in drive with the foot on the brake.
- Occassionaly there is what sounds to be a light backfire.

Other than that the vehicle drives well and recently went on a 300 mile trip where it maintains highway speeds just fine.

I'm guessing spark plugs or plug connectors? Suggestions on how to/what to parts to replace with each of those if you agree?

Thanks!

I would change the connectors under each coil and install F8DC4 plugs
Then go get codes from the other Engine management modules..

E320 16 PIN DTC Charts inc. pin 8, pin 14

I had a very similar problem with my 94 E320 (only 80k+ miles), I had Merc Dealer do the 90k mile service and it cleared right up. I think it was the plugs, make sure they the right ones...resistor plugs can mess up ignition modules on older Merc's. The overall reistance can be doubled if you have the factory correct resistor built-in wires and resistor plugs..not sure it would run in that case but you get my point.

One thing I have learned in owning several Merc's, BMW's, and VW's is that you should always check the obvious first, can save you hundreds of dollars everytime. German cars are the best engineered cars in the world, especially the Mercedes in my opinion, and these cars are built accordingly. Properly maintained and driven, these cars can easliy amount 300k before anything really major happens mechanically.

The first thing you should check is the engine wiring harness. Check around the connectors for cracking and/or exposed wires. If your car doesn't have a new one, it's now due. No point in diagnosing the car until it is replaced.
It's one of the 4 BIG issues your model and year Benz has.

I would not attempt to replace spark plugs on an old brittle wiring harness as any movement on brittle wires may make them fall apart.

Sorry,

-GH

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