Missing: Cylinders #1,2,3 & 4
 

Hello all,

As some of you may have read in a post from a few days ago, my 94 E420 was having its airpump tested with a "Baum" diagnostic device, when suddenly the engine died. (as if someone had turned off the ignition)

Today I was told that the first 4 cylinders (all the ones on one side of the engine) were not firing.

Does anybody have a clue as to what the heck is going on? My mechanic is thinking that it may need an ignition module, and is tossing some high dollar figures around. Naturally this has me freaked. (freaked? ok, fine... panicking)

Any ideas?

Personally, I am still wondering about the wiring harness, in other words, if a faulty one of those, could do what is happening.

thanks for any help!

-Larry

Thank you for the reply :)

My mechanic is more of a BMW specialist than Mercedes. He did tell me that he will be looking at the coil tomorrow, as well as looking into replacing the cap and rotor. (it is probably time for those anyway). The next thing he suspects (like I mentioned) is the module. I hope its just the coil.

Naturally any further suggestions are appreciated.

In the meantime, I will hope for the best.

-Larry

The car has two coils . one for each bank.. The right bank[ 1 thru 4] one is T1.
You may also have him check the crank position sensor...

The thing that has me puzzled, is that it quit right there in front of my very own eyes. What are the odds of a coil going bad, while it is being eyeballed? Not only that, but then to have it go bad at such a tender young age of 88 or 89k miles? What are the odds? I still think there is some other gremlin* at work. Especially since we were fiddling around (for lack of a better term at the moment) with the diagnostic tool, which was activating the airpump - to make sure it was working ok.

-Larry


* not the AMC kind of Gremlin. ;)

I woud also check fuse # 6 in fuse box for looseness/bad connection..

give it a spin...

Update on missing cyls. #1,2,4,7 (I think)
 

Hello,


So far, it has been determined that both coils are good, and that both rotors and caps are good too.
My mechanic, again, wants to point to the ignition module.

Does anybody concur, or are there other things to check out first?

thanks for you help

-Larry

How is your primary voltage doing? If you connect oscilloscope to the ignition coils primary contacts the voltage should be 12v with ignition on, during starting the signal should be rectangular. If you can see this then your ignition module is fine.
If i understand correctly you have a conventional ignition system ( you have a coil and high-voltage distributor).

Even if you will not get the rectangular signal, first of all the voltage supply of ignition module and the signal from engine speed sensor should be checked.
I think you should replace the ignition coils on trial basis(but you have to use the brand new ones).
I had a similar problem with 4.2 Sklasse. engine would not start.
I cleaned the spark plugs with gas burner and the engine would start immideately and i advice you to do the same thing. After cleaning of the spark plugs engine worked fine for couple of days and then the problem started again. Problem was solved by replacing the ignition coils. So try to either clean or replace the spak plugs and let me know the result.

I agree with tkamiya, but also want to add that the coils may be allright by resistance but the insulation is bad. this results in a weak secondary voltage- this leads to a weak spark- and this leads to dirty plugs which do not allow the engine to start. Of course the insulation may be bad on the wires, and i would definately advice to change them too.

The ignition system doesn't fire one side or the other. If you look closely you will see that 2 cylinders on the left side go to 1 coil(cap) & 2 to the other side. IF one side of the engine is misfiring then check compression OR exhaust back-pressure on that side.

M.B.DOC,

Thank you for your reply.
You are correct, it is 2 cycls, on each side that are out.
They are numbers 1,4,6,7.
Oddly enough, the check engine light is not on. I would think that if there was ever a time for it to come on, it would be when its only running on 4 out of 8.
Rumor has is that it is not very unusual for the ign. module to need replacing on these engines. What is your opinion?

Thanks!

-Larry

That WOULD'nt be an ignition problem! You need to check the compression & exhaust back-pressure

When the ignition module does fail every other cylinder in the firing order goes dead.

Firing order is 1-5-4-8-6-3-7-2

M.B.DOC

It is every other cylinder. ( #1, #4, #6, #7)

When I initially started this thread, I thought my mechanic said it was it was numbers 1,2,3,4. Sorry about that.

So, since it is every other cylinder, I can conclude that it is definitely the ignition module?

Thank you for your help :)

-Larry

PS: I want to mention, that before this happened, the car was running great, with the only thing worth mentioning was a slight hesitation on occasion.

Larry, sounds bad! That is exactly what happens when the ignition module fails! Replace that coil as well as most likely it caused the ignition module to fail.

Have seen that problem at dealer at least 10-15 times!

Could it be a wiring harness problem?

Good Question!
I was wondering myself, if a bad wiring harness could have caused the module to go bad. But so far, no one has said that it could be the cause, ...only the coil has been fingered for its early demise.

-Larry