I have posted before--this is a new thread for what I believe to be a new problem. Previously had egr fault, also had pin 8 code 13, and pin 14 code 11. Replaced MAF with new unit, checked egr valve, cleared egr tube, replaced vacuum line that runs across front of engine, checked for other vacuum leaks. Kept getting pin 8 code 13. Replaced engine wiring harness. (painless except for cost of part-1.5 hours, easy job) Car runs better, smooth idle and smooth cruise. no fault codes after 3 days of driving. Problem now is that engine has intermittant miss at idle and under medium and heavy acceleration. Feels like ignition or spark problem. Have read threads about coil to plug connectors--could this be the problem? Does this problem reveal itself with a fault code? Any suggestions?

Thanks, this site has been very helpful.

J. M. van Swaay

I have '96 E320 (W210) which has the same engine I believe. Replacing the spark plug boots solved my similar problem. No fault code was present due to that condition. Good luck.

Yes same engine.

The spark plug resistors or plug ends have a history of that exact symptom.
When doing the harness you may have disrupted one of them.
Usually you can pull them off and see visible signs of damage or burn streaks down the length of the plug resistor, but not always. That is an easy thing to check as well as replace. plugs/wires

Thanks. I'll replace them and post the results.

J. M. van Swaay

replaced plug connectors on cylinders 2, 4, 6. Still have miss problem. Should I replace plug wires on 1, 3 and 5? (Wires are original, 178,000 miles)
Is there a way to test igniton coils?

Thanks.

J. M. van swaay

Hopes this helps someone else. Replaced plug wires--no fix. Replaced ignition coils--engine now purs like a kitten. Here's a question for those more knowledgable than I. Can bad plug connectors, and or plug wires lead to premature failure of the ignition coils. (I think I may have read something about this somewhere on this board) The reason I ask is that the iginiton coils I replaced had about 50k miles on them. The car has 178k miles. The plug connectors and wires were original

There were some bad coils .. they are the blue ones.
If you have a led tool and go to pin 8 , usually bad coils will show misfire codes 21,22,and 23 One code for each coil pak/circuit..

Thanks for the reply. I checked for fault codes 5 or 6 times during the period I was experiencing the engine miss. (both pin 8 and pin 14) No codes were revealed. Is it possible that a marginal coil could work well enough to not trip a code, but not well enough to prevent occasional miss during idle and acceleration? Also, the miss seemed to be more prevalent during periods of high humidity and after the engine had warmed up. Is this consistant with the "marginal coil" theory?

Thanks

Just did a C280 this week where the open circuited coil resistor had driven coil output to the point where the spark was arcing from the output to the other cylinder to ground. The terminal was eroded totally and the bottom of the hole had fallen totally off.

One should remember that the coil fires two plugs on each firing. One plug is at the end of the exhaust stroke and the other at the end of the compression stroke. only one plug firing is of any use, but the circuit isn't complete without the other spark firing.

I would be extremely surprized to see a misfire code on a 94 "E" car

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

The best way is to scope the ignition, but the resistor connectors are so problematic on 104 Waste Spark ignition systems that one just changes them with a plug change, just to save a lot of time. Along with using Bosch F8DC4 plugs... they don't like plats and don't need resstor plugs cuz the resistance is already in the connectors.. as SB states , each coil has to fire 2 plugs , in series.. even though the wasted spark [non compression stroke] requires less coil output demand . there is still a large gap for the coil to cross with the series circuit.
I have seen misfires codes on 104 HFMs , but the codes I referred to [21.22.23]
are actually coil output test codes , rather than actual Mis-fire... as stated , the early blue coils were known for low output and have been upgraded.

I'm in the middle of this same issue, today I went in to look and found the insulation of my wiring harness had been so cooked it was flaking off from between the wraps.

Should I replace the harness (ugh!) or take it back to good wire and solder in new wire to plugs??

Any thoughts here?

There won't be any good wire.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician