320E (My first Gas MB) Misses and sometimes smokes - PeachParts Mercedes-Benz Forum

777funk · #1 03-01-2010, 07:30 AM

UPDATE: 3/9/10

Changed the plugs to F8DC4 Bosch copper non resistor and the springs under the coils. Here's what I notice now. Turn the key to on for a second, start, runs smooth for 3 or 4 seconds then resumes missing. It does this every time I repeat the procedure.

I just bought my first Gasoline powered Mercedes (94 E320). I got it for $200 thinking that if it's trash (has 200k on the clock) I can use the W124 parts for something eventually. Heck, my climate control unit is needing to be changed on the 87 and that alone would cost me half of that used.

Anyways, before I go gutting anything, this 320E is a nice car. I did a little bit of a search and I don't think I came to any conclusions. It seems like plugs, wires, coils, and harness are the main mis-fire culprits.

Here are my symptoms.

Rough lopey idle (obviously missing)
Unburnt Gasoline smell until the cat warms up. Then MAJOR rotten egg smell
Some white smoke (not sure if it is the unburnt gas hitting the cat or a bad head gasket)

Here is what I found so far:

Autolite Spark Plugs (obviously someone has given this a 'tune up' a year or maybe couple years ago)
Here's the weird part, I couldn't even see the spark plug in cylinder 3 and 4 they were so covered in carbon. It almost looked like the soot and semi burnt fuel had gotten past the spark plug.

So here's what I did:

Cleaned the spark plug well out and cranked the engine over a little to blow out the soot (thick grainy soot and lots of it. Enough that initially I couldn't even get to the hex on the spark plug with my 16mm socket).
Cleaned the connections up

Then I started the car and it ran smooth as a top. UNTIL... I put it in reverse for my test drive and then the miss came back. I figured, oh a little soot or something so I gave it a good incline Italian tuneup. Still missing. Put it in park and still missing.

I've done this twice and same result... good wire and plug clean up and runs smooth then misses.

Could it be that as soon as I put it in gear that it's not getting enough fuel or could being in gear effect something electrically with my spark? Or something else???

EDIT 03/03/10: Update, OVP Relay had a bad fuse. Changed it and the ABS light went off and check engine light came on. Codes read and posted later in this thread. Still misses regularly. Every so often it will smooth out but mostly missing. Codes cleared and we'll see which ones pop back up.

Ferdman · #2 03-01-2010, 08:10 AM

Recommend replacing the spark plugs with Bosch F8DC4 plugs, gapped properly. I suspect the middle coil pack has failed, and the spark plug connector may need replacing also. If possible, swap a known good coil pack into the middle position and see if the engine runs smoother. From what I've seen online it's a better value to buy a complete ignition wire set (which includes 3 spark plug connectors) than buying the spark plug connectors separately.

White exhaust is usually due to coolant ... a bad head gasket.

777funk · #3 03-01-2010, 09:01 AM

Quote:

Originally Posted by Ferdman

Recommend replacing the spark plugs with Bosch F8DC4 plugs, gapped properly. I suspect the middle coil pack has failed, and the spark plug connector may need replacing also. If possible, swap a known good coil pack into the middle position and see if the engine runs smoother. From what I've seen online it's a better value to buy a complete ignition wire set (which includes 3 spark plug connectors) than buying the spark plug connectors separately.

White exhaust is usually due to coolant ... a bad head gasket.

I'm new to Gas MBs but is it common for the coil pack to fail? I saw a post by a frequent poster on the Tech Help forum and it seemed like what he was saying is that the spring underneath is a common weak point. I wish I had another coil pack to check with before throwing $70 out on one. Is there any way to test the coil pack? I suppose I could pull one of the other two and swap. But I don't know if I'd be able to tell which cylinders are missing to track if the coil pack is a problem. It seems to be an intermittent thing (usually misses but fires occasionally and ran perfectly smooth after disassembly/reassembly twice now but always returns to a miss).

Ferdman · #4 03-01-2010, 10:22 AM

Nick, one of the coil packs failed on my 1995 E320 that's why I mentioned it to you. Suggest you thoroughly clean the spark plug recesses, connectors and ignition wiring when you replace the spark plugs. Then see how the engine runs.

Ask the seller why he/she sold the 1994 E320 for $200. It's likely that a costly repair quote prompted a quick sale. Actually, a local charity would probably have paid $400 or $500 for it.

babymog · #5 03-01-2010, 10:42 AM

If the coil pack fails, the computer is designed to sense no fire in the cylinders, and cut injection / fuel to those cylinders. It does it, I've experienced such, and that is to save the cat plus emissions.

First thing to do is to build / borrow the Arthur Dalton design code reader (around $10 in parts) and read/reset/read the codes. Might be in limp-home mode already and have some issues.

Also, pull the vacuum line from the fuel pressure regulator (driver's side of the head, front of the fuel rail) and see if a ruptured FPR diaphragm is pumping fuel directly into the vacuum line, sounds likely.

777funk · #6 03-01-2010, 11:58 AM

Quote:

Originally Posted by babymog

If the coil pack fails, the computer is designed to sense no fire in the cylinders, and cut injection / fuel to those cylinders. It does it, I've experienced such, and that is to save the cat plus emissions.

First thing to do is to build / borrow the Arthur Dalton design code reader (around $10 in parts) and read/reset/read the codes. Might be in limp-home mode already and have some issues.

Also, pull the vacuum line from the fuel pressure regulator (driver's side of the head, front of the fuel rail) and see if a ruptured FPR diaphragm is pumping fuel directly into the vacuum line, sounds likely.

Thanks for the reply. The Check Engine light isn't on. I'm assuming that means no codes or that the bulb is burned out. I'll have to turn the key and see if it lights up.

So fuel into the vacuum line... what indicates this is a possibility?

samiam44 · #7 03-01-2010, 12:09 PM

Hold the phone and back up a set.

THE FIRST CHECK needs to be a compression test. Make sure the motor meets before proceeding into coil packs, wiring harness, or fuel system problems.

Michael

d.delano · #8 03-01-2010, 12:52 PM

w124 for $200 what a bargain!

777funk · #9 03-01-2010, 01:20 PM

Quote:

Originally Posted by d.delano

w124 for $200 what a bargain!

It's in good from 20 feet away condition too and I love the color (charcoal almost black metallic). There are some defects but you have to look for them. It's a sharp car. I like the look of the later W124s more than the earlier ones like my 87.

But of course, possible bad headgasket and other issues. But still... for $200!

babymog · #10 03-01-2010, 01:24 PM

Quote:

Originally Posted by 777funk

Thanks for the reply. The Check Engine light isn't on. I'm assuming that means no codes or that the bulb is burned out. I'll have to turn the key and see if it lights up.

So fuel into the vacuum line... what indicates this is a possibility?

Might mean the CEL iis burned out, does it come on with the key on before starting?

Fuel in the vacuum line will go directly to the intake, very rich at idle.

The coil pack and plug connectors are certainly another big possibility, and very common. Original blue-stickered Bosch coil packs were especially problematic from what I've read.

Next possibility is the engine wire harness, check it over, do a search here for wire harness issues on the M104 (as well as other early '90s Mercedes).

Compression is unlikely a problem IMO, a highly unusual failure in the M103/M104 engines.

777funk · #11 03-01-2010, 03:51 PM

Sure enough, Check Engine Bulb is not working.

I have the push button and LED in my car. But seems like that's not working either. I hold the button for a few seconds and nothing.

I'll have to build the Arthur Dalton reader when I get a few minutes. I'll probably go build it now and trouble check later.

I think I read that I can check coil packs by moving it around and watching for different codes (coil pack codes). I'll try that.

babymog · #12 03-01-2010, 04:11 PM

Does the ABS light work? If not, I'm wondering if there's an issue with power to the control modules behind the battery, someone pulled the bulbs. The LED on the connector doesn't burn out, ... something's not getting power (or is toast). What else doesn't work?

777funk · #13 03-01-2010, 05:01 PM

Quote:

Originally Posted by babymog

Does the ABS light work? If not, I'm wondering if there's an issue with power to the control modules behind the battery, someone pulled the bulbs. The LED on the connector doesn't burn out, ... something's not getting power (or is toast). What else doesn't work?

The ABS light is on as is the brake pad sensor (brakes seem to work really well).

I haven't pulled the cluster out yet.

777funk · #14 03-01-2010, 06:47 PM

I just did the test on pin 14 to pin 16 and also tried pin 8 to pin 16. I used a small 12 volt bulb instead of the led. It lights up on 1 to 16 when the test is initiated but no blinking at all.

babymog · #15 03-01-2010, 10:13 PM

I'm wondering if the OVP is bad. Perhaps other things, but check the OVP.