Missing/Rough Running M104 AFTER a coil replacement
 

A few weeks ago I mentioned that while returning from a long trip and on the last 400-500 miles I had an intermittent miss that developed while getting off the interstate to get fuel. After refueling, it still had the miss but it was a Saturday night about 11:00 and just north of Knoxville with virtually no choice but see if it would smooth out once upon the interstate again. Long story short: it did smooth out after maybe 10-20 miles and all was good the rest of the trip. Weird, I thought, but hey the ol' gal had over 150K miles at the time and was pretty certain the coils had never been changed so...

I started out on a SEARCH of the forum to see if I could nail down the exact problem. I came across THIS THREAD and a couple others but I thought Arthor Dalton did a great service for the forum (and Jim Villers) helping us understand what to look for with these missing issues so I kinda followed that particular thread over the other threads I ran across.

I decided to order just two new BOSCH coils from Pelican and not the under-the-coil connectors since I knew that I had changed those along with new BOSCH F8DC4 plugs back a couple years ago (a realtime check of my spreadsheet records told a slightly different story!). In reality, I have 37K on the plugs and one of the connectors while ~25K on the other two connectors. Earlier this week I ran a code check to see what might pop up and this is what I found:

Factory Diagnostic LED -

• 2 "Heated oxygen sensor faulty"
• 4 "Air injection system faulty hot film mass air flow sensor with hot wire"
• 5 "Exhaust gas recirculation faulty"
• 6 " Idle speed control faulty"
• 7 "Ignition system faulty"
• 26 "Upshift delay faulty"

PIN #8 -

• 9 "O2S (before TWC) - voltage too high, circuit open or voltage implausible"
• 21 "Ignition output 3 or ignition coil for cylinder 1 and 6"

PIN14 -

• 6 "Starter lockout/backup lamp switch"
• 14 "Closed throttle position contact switch"

Given the code #21 and #7 I thought I'd simply go ahead and try replacing the cyl 6 coil and see if that fixes it. I also thought that since the car had the original 'blue labled' coils, it was time to start replacing them. I installed the one coil last evening, started it, sure seemed to run smoother, then took it out for a spin. Wow! It seemed to be 'HEALED'! Pulled back into the garage for the evening and shut off the lights. Got up this morning to go on a ~50 mile one way trip and not 3 miles from home it started running really rough! Considerably rougher than the previous encounters. Returned immediately to the garage, took another car on the trip and now I'm home trying to figure this out!

Ran another code check: (Cleared after previous check)

Factory Diagnostics LED -

• 6 "Idle speed control faulty"
• 7 "Ignition system faulty"
• 26 "Upshift delay faulty"

PIN #8 -

• 9 "O2S (before TWC) - voltage too high, circuit open or voltage implausible"
• 21 "Ignition output 3 or ignition coil for cylinder 1 and 6"

PIN #14 -

• 6 "Starter lockout/backup lamp switch"

Where should I be going from here? Your help will be greatly appreciated :)

Triple check the spark plug boots. I just fixed an intermittent miss on my M104. It ran smooth until I accelerated somewhat hard, then would throw a CEL on a cylinder 1 misfire and miss like crazy until the car was shut off and restarted. Finally noticed a spot of white dielectric grease on the outside of the boot. Looking closer you could see a tiny hole and it had blown grease out the hole. Swapped the boot with cylinder #3 and the code followed. Replacing the wire/boot on #1 resolved the problem.

Thanks Jay for the suggestion. I will try moving the boot to another cylinder and see if the code follows. Funny thing is I'm not getting a CEL. I checked continuity on the coils but for whatever reason didn't on one of the boots. As I said in the original post, I thought I'd forego getting new connectors because 1. I thought I had replaced them "not too long ago" and 2. Didn't realize the sensitive nature of them! Well it may be that it's time to pony up for new boots.

I year you. I didn't change mine at first because they looked relatively new. It wasn't until I'd swapped coils around and changed the fuel filter that I just happened to notice the white spot on the bad boot. Just dumb luck on my part.

If your ignition electrics seem OK, consider the MAF. I assume you already have a replacement engine harness?

check if cranksensor is plugged in good.They can be knocked loose,by road debris.

Hirnbeiss, yes the harness was completed a couple years ago.

Where is this sensor located?
EDIT: NM, I found it.

Well, perhaps I've found a big part of the problem. There is no continuity through the #6 coil connector to the plug. So, I'll wait to pick up one (maybe all three) from the dealer tomorrow and get it put back together...stay tuned :-)

:::UPDATE:::
 

This just in: a half-fast auto mechanic wannabe has just completed installing three new dealer acquired cable connectors on the coil packs. The car was taken on a short test drive following said surgery but it did not go without a hiccup. At an intersection stop sign while waiting to get the all clear to go, the patient suddenly began idling rough and was given a 'goose' on the the old go-pedal to 3-4000 rpm and it seemed to clear the the rough idle once started rolling again....

I pulled into a gas station and turned off the car and when restarted it ran smoothly the rest of the way back home. Did I mention it's running really smooth? :cool: I read the codes and got:

OBD factory LED button -

• #7 Ignition Faulty
• #26 Upshift delay faulty

PIN #8 -

• #21 Ignition coil #3 for cyl 1 & 6

PIN #14 - Nothing

I have cleared codes and will be watching it for a while but I have a new set of BOSCH wires expected delivery on Thursday that I will install directly as I suspect the #21 fault code is a bad wire. We'll see - as they say in the looking glass factory :P

Wifey and daughter had to go ~20 miles this morning for a 4H dog training session and she texted me to tell me it did fine on the interstate but when she got off it she had to put it in neutral at traffic light and every stop. She also said it's shifting "weird"...not wanting to shift and "jerking" when it does. Then nothing (I guess she means 'not acting up')

Sounds like a vac problem now - with the hard shift thing?

the ignition switches in these cars can cause problems,and the k40 relay.I had to replace both.My k40 is behind the fuses under the hood,you remove cover.Your crank sensor should be above the starter near bell housing. I would replace any way,buy a hella not a bosch.Oh yeah open the coffin shape box under the hood near passenger firewall,and check to see if ATF has wicked up in there.If so clean ATF out,and replace electrical connector in transmission.I forgot exact number for relay maybe k38,its the starter lock out relay.Being a E class,it could be behind glove box,or drivers side transmission tunnel near gas pedal.

Ignition switch was replaced a couple years ago. I'm still holding out that the miss is due to a plug wire malfunction since I'm STILL getting the #21 fault code for the #3 coil for cyl's 1 & 6. New ones come tomorrow...

I'll update..

Well guys, I believe the new plug wires did the trick! From the get-go I was pulling a code #21 indicating a coil or wire for cyl 6 & 1 and sure enough, I did an ohm test and it revealed no continuity no matter how hard I tried. The other two wires showed continuity. Took the car for a nice long drive of mixed type driving and it hummed along near flawlessly. I'm a happy camper at the moment :D

Thanks for all the replies and suggestions toward a resolution :)