1973 450 SEL injectors not clicking - PeachParts Mercedes-Benz Forum

#1 08-26-2002, 11:55 AM

Hey all~

Yesterday, I removed the Bosch Platinum plugs and when examining them, I found that they showed signs of cylinders running too hot. I replaced the plugs with Bosch Copper core plugs.

I drove 2 miles and suddenly I get this loping feel. So bad that it sounds like maybe more than one cylinder is misfiring! I could barely make it up a hill, I pulled over, revved it: *poof* loud bang and a plume of black smoke out my exhaust, then it ran okay and I drove it one more block when it started again and I parked it.

I remove the plugs. They are covered with black soot. Some plugs are slightly moist. I start the car and it lopes like a misfire. I check all the cylinders and make sure the are getting a spark from the distributor, I re-gap the points, and I check the wires with a dwell meter to make sure there's voltage in the wire. Everytime the engine loped the voltage would drop off (probably fom the lope). I also checked the vacuum advance and it works fine. Othr vacuum hoses seem to maintain proper pressure. I put a stethoscope to the injectors. Sure enough 3 of my 8 cylinders injectors aren't clicking. I messed with the Emmisions Control Unit (ECU) earlier to make the misture a wee bit richer or leaner because the MB tech told me it may be running hot from a lean mixture. 1-800-222-0100 option 7 and asked to speak to a tech.

This has happened before to me but this has been the worst case. Before I simply drove out of it but now its time to fix it. I wonder what is causing this? I still have to try attaching a noid light to the connectors. Is my ECU bad? Is there a vacuum leak I wasn't aware of? Is there a broken wire or controller? A sensor?

Funny enough, I backed it out of my driveway feeling hopeless and sure enough it was running fine again. 2 hours of hell and now it ran okay! I didn't want to chance it though so I parked it, ran to my computer and here we are.

Ideas on this or my overheating problem? 1973 450 SEL running hot at high speed

Thanks for any input!

mbdoc · #2 08-26-2002, 12:28 PM

On this system there are "trigger" points in the distributor that send dwell signals to the EFI computer & it will pulse 2 injectors at every stroke.
Cylinders 1 & 5 are on one set. The other pars of cylinders are 4/8, 2/7, & 3/6. IF you are losing any pair then the trigger points could be the problem. Many times oil will push thru the distributor and cause this problem.

hill · #3 08-26-2002, 09:30 PM

Pull the distributor then clean and check the trigger points. If there are no clear plastic covers over the points buy new ones at Fastlane/Partsshop. Use the search function there are lots of references to trigger points. I have purchased a couple of DJET cars that were tuned up by non Mercedes mechanics and still ran badly because they did not know that the points even existed. This might take care of your overheating problem to.

barndoor · #4 08-26-2002, 10:21 PM

I had the same problem with my old '73 450 se.
the trigger points would get oil/grease on them and it would run bad (misfire)
after cleaning (which is quite easy) it would run fine.
but because the car was running too hot (another problem) the points would "grease up" again.
there is a plate that goes into the bottom of the distributor,remove it and clean two sets of points,install and thats it!
keep that 116 running!

joe p · #5 08-27-2002, 01:48 PM

Damn,

I dont feel old now! More people who know what TRIGGER POINTS are!!!!

LOL

Check that D-sensor for a rupured diaphram as well if it's still rich after getting the trigger points right.

I never will forget that old type 3 VW that I opened the injection harness on and found allthe wires were white with these tiny little numbers on them.

Joe

#6 08-28-2002, 04:08 PM

Thanks so much for all the input. I will certainly check out what you all suggested.

So back the the main question as far as the injectors are concerned, the problem is related to the points? Even though I was getting a spark in all the cylinders?

This is odd because the sparkplugs were firing. If yes, then this is my problem, if not, then maybe the injectors are getting messed up by something else? I understand the two are related but....

Cheers,

joe p · #7 08-28-2002, 04:16 PM

The trigger points only run the injectors. Seperatly from the ign.

Joe

mbdoc · #8 08-28-2002, 05:08 PM

IF you re-read this you will see that the "trigger" points for the injectors are not the ones under the distributor cap. BUT they are in the distributor BELOW the ignition points mounting plate. AND there are 4 seperare points that "dwell" 2 injectors each. This comes only as a complete unit.

#9 08-29-2002, 01:12 AM

Quote:

Originally posted by M.B.DOC
IF you re-read this you will see that the "trigger" points for the injectors are not the ones under the distributor cap. BUT they are in the distributor BELOW the ignition points mounting plate. AND there are 4 seperare points that "dwell" 2 injectors each. This comes only as a complete unit.

Thanks for the clarification....

#10 09-03-2002, 11:00 AM

Hi!

Hello all. This monring I got into the car and started it. It ran great. No injectors clicking or anything. It started to miss injectors on my way home. But I came home from work and a took off the distributor and checked out the trigger points. They look good and I took them apart and cleaned them off. Now the car is running with 4 injectors not clicking! I left it over night, turned the key the next morning and it runs great again.

If the trigger points were bad, wouldn't the problem be more consistent?

stevebfl · #11 09-03-2002, 11:11 AM

Trigger point problems are usually intermittant. The problem can also be in the harness connection. Next time it happens identify the cylinders involved and watch that they are the same each time.

One problem that isn't exactly electrical is that due to constant pressure from one side (due to the ignbition points) the distributor shaft wears in one direction. The movement can reduce the amount certain of the trigger points get moved. A good reason to install an optical triggered ignition.

#12 09-03-2002, 04:18 PM

Those are some really good ideas on the problem and I as well have traveled that way. I actually went ahead and was able to replicate the problem by unhooking some of the grounding wires.

Cylinders 1/5 always run strong. 2/6, 3/7 are particularly consistent in missing and 4/8 do it sometime.

I made my own grounding wire, bolted it on top of the current wires attached to the throttle linakge on the w116 and attached it to the fire wall. No problems for 2 days now. If that is not the problem, I will be replacing the distibutor and the trigger points as one unit and then I will seek a new harness.

Thanks for all your help, I'll keep you updated.