* Just finished replacing four cam follower/hyd elements on the left cyl head of this M119.985 ('97 W210.072). Also replaced all 8 oil tubes on the left head. The exact problems were one open oil tube and one ticking hydraulic element. Engine is now quiet but,
* Now there are misfires in cyls 2, 3, and 4 (you can feel it misfire and there are specific misfire codes). Replaced all 8 plugs, plug connectors and reset codes. Still the misfire. Again codes for cyls 2, 3, and 4. Reset codes again and swapped coil packs on cyls 2 and 3 with those on cyls 6 and 7. Still the misfire and again the codes for cyls 2, 3, and 4. So, unless I've missed something, that rules out coil packs and everything below them. If I'd reinstalled the left cams out of time, I don't believe that error would have triggered misfire codes.
* But it doesn't rule out an engine wiring problem. The wiring harness is(stiff and) original on this car. Comments lean toward frequent engine wiring problems through '95 E420s but infrequent after that.
* My question is this. How do I confirm a bad harness (hopefully without peeling insulation and hoping to find a problem) given the misfire codes and the above work? Any other ideas? Thanks.

Scanner have live data info? Smooth running to watch the misfires in those cylinders.
Possibly excessive backpressure on that side catalyst.
Have you performed a compression test?
The misfires are related to the RIGHT side of the engine.

The 1997 cars didn't have the bio-degradable wiring issues.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

* MB DOC, thanks for your input.
* Yes, do have live data (via PC Retriever). Reran live data this morning and have misfires on cyls 1-4 (not just 2, 3, and 4). So you're right that it's a right bank issue. Did have a couple of misfire blips on the left bank during a brief warm up period but no left bank misfire after a brief (not full) warm up.
* Did a compression test yesterday. With cold engine, cranked to highest reading. All eight cyls 185-200 psi. That falls at the upper end of 10-14 bar w/ a warm engine.
* Car ran without this miss when it came in. Just the ticking noise. Could a cat turn bad that fast? Thought that the plugged cat signs were more gradual. If I mistimed the cams, which I doubt that I did, could this cause right bank misfire codes? The timing pins and the 45deg BTDC starting point make that pretty straight forward. That's why I was wondering about the wiring.

Sounds like an exhaust backpressure test on the passenger side is the next step.

Simply make OR buy an adaptor that screws into the front O2 sensor hole & see if the backpressure at idle is at OR above 1 psi & also measure at 2500 in park, leas that 1.5psi

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

* Are we looking for too much back pressure or too little? Are you saying that up to 1 psi back pressure at idle is ok? If that's the case then running the engine with the front O2 sensor removed ought to smooth things out and not cause the misfires. I'm assuming that if the cat is plugging up, it's in the beginning stages of that problem.

1psi at idle is MAX psi, & 1.5 at 2500 is Max.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

* I'm trying to locate an exhaust back pressure tester (that I can afford) and will check the pressure asap. If the cat is the problem, I sure don't have any idea how to explain it to the customer, since he didn't come in for that. Any advice?
* Spot checked current pulse to #2 injector (with a noid light) and it looked fine (despite the misfire code on #2).
* An unrelated question came up. What does the coil fuse, #19 in the engine compartment fuse box, take care of? (The fuse is ok).

You can get a backpressure kit at NAPA & many other parts stores.

I made my own, lopped off an old O2 sensor & used 1/8" pipe tap & a 5/16 fitting that screwed into the old sensor. Then had an OLD fuel pressure gauge that read from 1-3psi & a piece of 5/16" fuel hose.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

* Thanks for all the info. Chkd on the Napa gauge. $214. Think I'll try to make one per your plans when I get a few minutes.
* Just took out the right front O2 sensor. Ran the engine briefly with live data connected. That maneuver should have relieved enough excess pressure, if there was any, to smooth out the engine. But still misfiring on right side. I think I've ruled out a plugging cat on the right side. Do I still need the gauge to be certain?
* I've spot chkd injector pulses on right side. Will pick up $30 tool later today to test for spark on the coil-above configuration (should have gotten these tools long ago).
* Now I'm beginning to doubt my work. Maybe the right cam(s) are out of time. Compression is good. Could a small timing error really cause such a misfire?

* Thought I would finish this thread in case anyone is waiting for the answer. The right exhaust cam skipped one tooth retarded and went unnoticed. The other three cams were spot on. Be sure to crank through a timing check AFTER reinstalling the chain tensioner.
* I reread the fine print for the misfire code P030X. It states that the misfire can be ignition, mechanical or injection. I can vouch for the fact that an exhaust cam one tooth retarded will set misfire codes on the whole bank.
* Five hours of extra work, and resetting codes and adaptations and this 420 is smooth and quiet again.