Hey guys,

Currently helping a friend with his 1991 300CE with the M104 and CIS-E (think M103 fuel system).

Currently we have no spark to the plugs. I have put a multimeter on everything and this is what I have found:

I get 6v at the coil. I get 6v at the end of the distributor wire connecting to the coil. I get 6v to the distributor button in the center of the distributor cap.

I do not get anything from any of the plug wires. No spark, no voltage, nothing.

I am thinking that the cap is fried. He had the distributor wire get sliced by the fan and I'm wondering if it arced off the engine somewhere and roasted the cap. The rotor showed some damage in the form of nicks on the head and melting on the plastic part itself.

We have replaced the rotor already, but the cap is specific to the M104.980. Before we order a cap, does anyone have any other suggestions on what to check or what might be the cause? We do not think it is the EZL since we have 6v to the cap.

Thanks,
Colin

mines a 99 but I have a coil fuse,they use to call them ignition fuses

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

99 is a completely different ignition system than the 91.

Colin:

It will be helpful if you could be more specific about which terminals on the ignition coil you are checking for voltage (there are three, two in the primary circuit, and one in the secondary), and the conditions of the checking, i.e., simply key on, or while cranking, etc. Both primary and secondary circuits have connections between the coil and the distributor! Edit: The pickup coil for the primary trigger is at the flywheel, rather than in the distributor, hence, no primary connection directly between coil and distributor.

What caused you to enter into this work? Was the car being driven when the engine stopped? Was some other work performed prior the the lack of sparks?

A couple of things.

Don't use a multi meter to check the spark plug wires while the key is on or when cranking the engine. Voltage here is upwards of 20 KV ( that is 20,000 Volts ) under the right conditions.

There is a gap between the rotor tip and distributor cap towers so you won't see continuity between these two. The cap won't be damaged by a cut coil to cap wire so the problem lies elseware.

You will need some sort of trouble shooting information from a manual. This system should be the same as the same year 300SL as the engines are the same.

I am testing the plug on the coil that the distributor cap plugs in to. This is a very early m104, with CIS-E like the M103. I'm not sure I follow where I would find three coils.

The car stalled a few times at red lights but would restart. Finally it stalled and hasn't restarted.

Recently we replaced the spark plugs and O2 sensor, but that doesn't seem relevant

We are not getting any power to the plug wires at all. This was tested by grounding a plug and by using a multimeter.

Today we replaced the distributor cap with no luck.

colin, I suspect a bad ICU that mounts on the left inner fender. If you can borrow a known good one and install it temporarily you will know immediately if that's the problem. MB dealers sell reconditioned ICU's for about $1,500. I had a similar experience with our 1992 300CE 2 years ago.

__________________
Fred Hoelzle

colin:

I think you misunderstood my reference; there are three terminals on the ignition coil, not three coils. The two small terminals are in the primary circuit, the larger central terminal is the secondary (high voltage) connection.

Ferdman is quite likely correct about the EZL (aka ICU [ignition control unit]). Before exchanging the EZL, perform this test: unplug the coaxial lead that comes from the flywheel pickup, and check that there is continuity of that circuit by placing one probe of your meter on the central pin of the coax cable, and the other probe on the ring. You should see a resistance of approx. 700-1200 ohms. If the resistance is either zero or infinity, you may have found the problem.

Borderline impossible to find a known good one for this engine. Already called MB and they are no longer available, and if they were it would be $2600.

We have found a place that rebuilds them though should this be the problem.

I did test this and did get between 700 and 1200 ohms.

This has the same system as my 91 300SL. One ignition coil behind the left headlight area and a distributor cap on one of the cams.

None of these would cause the problem you have.
Don't bother looking at the spark plug end of things yet, use the ignition wire from the coil to test for spark. ( the one that runs from the coil to distributor. ) Use a spark gap and don't hold onto any metal.

DO NOT USE A MULTI METER TO CHECK FOR SPARK WHILE CRANKING AT MINIMUM YOU WILL DAMAGE THE METER. THERE IS ALSO A RISK SEVERE INJURY / DEATH.

You can use the ohms function to check for a broken coil wire when both ends are removed and away from the car.

I{f you are not getting spark from the coil , everything past that isn't important at this time.

colin:

Re: EZLs
For testing purposes, any EZL that has the same pinout and the same connectors may be used. 4,6, or 8 cyl. types will work. The difference for varying cyl. counts is in the rate of advance (based on pulse frequency), and the TD output information. Plug in any known good EZL, and if the engine starts you may be fairly certain that the original one is the culprit. If the engine still does not start, a check of the continuity of all the primary wiring is in order, and a check of coil continuity and output.

If you have a very weak heart, possibly. There may be 25 KV at the spark plug but almost zero current.

The overhead cables on the trains here are at 25 KV but with immense current. Almost certain death there.

RayH

colin, have the dealer check availability of a reconditioned ICU for a 300SL. It is identical, and the MBUSA parts system seems to defer to that model. If there any MBCA members in your area one of them may loan you one from a running vehicle for test purposes. Our local indie told me years ago that it is critical to maintain all ignition system components of the 104 engines to prolong the ICU's life.

__________________
Fred Hoelzle

I am getting power from the coil to the end of the coil wire and in to the distributor. 6v, and I am certain of this. It is one of the things I mentioned in the first post.

Unfortunately we have already looked for both cars, reman and new, through MB and had no luck. The $500 reman option on ebay is the way to go it seems.

This is his only car, and sadly he nor I do not have the time to keep at it right now so he is having it towed to the shop on Monday.

I'll keep you all posted with what it ends up being.

Did you ever get this issue fixed? I'm going through the 90-92 300CE EZL NIGHTMARE right now. Trying to find one is like "hey mistering" for drugs on the street or something. Actually no, that would probably be simpler and less expensive. Smh.

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles