1972 280 Se 4.5 V8 - PeachParts Mercedes-Benz Forum

benjira · #1 09-05-2007, 12:57 PM

Ok

#8 Cylinder not firing : Changed injector, Cleaned trigger points, Took #8 injector wire and put on 7, AOK,Put #7 wire on 8, Nothing. Got spark at distrib,got spark at plug .Still not firing on 8. Only thing I haven't done is check compression. Any help would be awesome. I am getting frustrated.

BB

nhdoc · #2 09-05-2007, 01:39 PM

Are the wires you switched ignition or injector wires?

listen for the click of the injector to see if it is firing. You can hold a piece of vacuum hose up to them and stick the other end into your ear and you will hear them fire...if #8 is not clicking you will know why you are getting a miss in that cylinder. If it is clicking then I would say check compression next.

Have you checked valve clearances yet? Could be that a valve is not opening or closing too...but a compression test would lead you that way.

Tomguy · #3 09-05-2007, 05:32 PM

You haven't checked compression, have you checked the valve?

Your valves are probably "Too tight" - not closing. These are mechanical adjusters and, ideally, should be tuned every 15k but often go neglected.

benjira · #4 09-05-2007, 08:48 PM

Ok Guys

I thought I had it, I traced to a bad injector that I swapped earlier. Fired it up and she sounded like she was running on all 8. She was idled high from when I had adjusted the timing running on 7 cylinders.Then she started undulating up and down so I retarded the timing a bit. She sounded good for a minute and then I noticed a huge sucking noise coming from near the flapper valve .I have not isolated the sucking as it is getting dark. And she seems to be running back on 7 cylinders again. Does this sound familiar to anyone? At least I got the injectors firing again. God this is fun.

BB

GaryF · #5 09-06-2007, 04:03 AM

"Flapper valve"?

The Auxiliary air valve probably closed as the engine warmed up and you could hear the air flow being restricted which is normal?
Have you got the equipment to set the timing and dwell properly ? The idle mixture could also be wrongly set up too.

nhdoc · #6 09-06-2007, 07:07 AM

Yeah, we probably need to know what you are referring to as the "flapper valve" in order to help out.

Tomguy · #7 09-06-2007, 09:15 PM

There is no flapper valve but you probably mean the throttle plate (inside the throttle body) and, if you have the air cleaner off, hearing a loud sucking noise is 100% normal. It's where the air is going into the aux air circuit (above the throttle plate, the hole there - again, normal!)