94 E320 Starts Smooth---3 seconds---Misses like Crazy. Repeats everytime.
 

I've been working on a newly acquired E320 and so far it's taken quite a bit of time to diagnose a mis-fire condition. Here's where I'm at now and I'll give the history of what I've done in a second...

Ok:

• Turn key on... hear fuel pump pressure (pitch changes a little bit as it sits key on... not sure if that means anything)

• Start Car (starts easy)

• Car runs smooth for 3 seconds or so then begins mis-firing consistently.

So Far:

• OVP Relay had a bad fuse. Changed it drove it and read the codes. Got:

1. Code 4
2. Code 13 (Lambda Rich Limit)
3. Code 23 (Coil for 3 and 4 mis-firing)

Changed:

• 6 New Bosch F8DC4 Spark plugs (non resistor copper)
• 3 New under coil spring boots

Still misses. I really wonder if it's an electronic problem because it runs smooth for 3-4 seconds EVERY TIME and like clockwork resumes the miss.

I sort of thought fuel filter but it performs under high load (up hill floored). I wouldn't think that'd be possible if it wasn't supplying enough fuel to idle right.

So far I'm pretty stumped. I'll cut the wire harness wrap in a few spots just for a visual. But I don't know what else to check. I don't think a bad coil would let it run for 3 seconds and then cut out Every Time.

But of course... I don't know anything other than basic gasoline operation. I don't know squat about the Lamba system or how this engine runs (computer control) etc.

I think what you may be seeing the ECU detecting a misfire on cylinder 3/4 and shutting down fuel to those cylinders, leaving you with a 4 cylinder 6 cylinder.

Try this easy test. Swap the cylinder 3/4 coil with one of the other ones. Clear all the codes. Start the car and see what happens. Check codes.

If a coil is bad you will get a misfire code for the cylinders now served by the bad coil. Cylinder 3/4 should be OK, so code 23 should not reappear.

If you still get code 23, then it's time to chase cylinder specific causes. Off the top, I would probably get new plug wires, then look into the engine wiring harness.

Have you checked the part number on your OVP? Early OVPs were bad and were replaced with a new part number. You should be able to find the old & new part numbers using search on the site.

Where's Arthur Dalton when you need him!

He's already helped me quite a bit here and there with various problems. And I've read a ton of his Ignition troubleshooting posts. Great info.

I didn't see anything like what I'm experiencing (smooth for 3 seconds after startup then misses) in my search. The exhaust has a pretty bad rotten eggs catalytic smell to it as well if that means anything... Hard to say though with it running the way it is.

Nick, with a bad coil pack the engine will run rough and shake at idle. At least that was the symptom with our 1995 E320.

on your M104 the ECU will shut down a cylinder pair if it detects a misfire on one/both of the cylinders. There is a possibility the 3 second wait is the time required for the ECU to perform the detection. The rough running is after the cylinders are deactivated. Shutting down a cylinder pair is setting the code 23.

Swap the coil packs around and see if the fault moves to a different cylinder pair. If so, you almost certainly have a bad coil. If the fault does not move, look elsewhere.

The exhaust smell is likely from dumping a bunch of raw gasoline into the exhaust from the misfiring cylinder(s) before they get shut off.

All the symptoms hang together and point toward a single bad coil.

Ok, I just bought 3 coils on ebay. Hopefully they'll work.

I swapped coils a bit and am not getting codes period. But the coils now in the car say Germany on the bottom and Srylanka or something like that on the top. They're probably originals.

We'll see if the 3 coils fix the problem. $88 probably not totally wasted if not the problem.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=120539286347

Any word on the quality of the Ebay coils listed above?