Mystery solved... Engine Running Problem

[kampala]

Over the holidays I had a small window of time to work on the pagoda as I was back in California.  As I had mentioned a couple of months back, the car was suddenly not running well.

In brief, the symptoms:

Difficult start at times
Not a good idle
Back-firing
Very rough running at low rpm (below 2000)
At times ran good but then symptoms would appear again.  
Not fun



What was checked a couple of months ago:

Since the car had been run with very low fuel, I suspected a dirty tank.  Checked fuel flow … it was okay but decided to check the tank.  Emptied the tank and the good news was that tank and tank screen were exceptionally clean.

Replaced the main fuel filter in engine bay … old filter was not too bad … however car ran very good just after this so I thought the problem was solved. Turned out to be a coincidence. The symptoms returned after a short drive. Checked Fuel flow again and it was well above what our tech manual says should be minimum.  

Heard a vacuum leak near the air intake…  fixed that and again the symptoms went away … another coincidence as this leak would mess with the idle but should not really cause the other problems.   A forum member advised that the problem sounded likely to be ignition related.

Took the car to a specialist as I just wanted it to run right and really didn’t have time as my trip was short.  Of course the car ran good the entire two hours at his shop!!  We checked plugs, linkage, cap, rotor, points, HT leads etc etc.  Really found nothing wrong.  Even spark plug color looked quite good.  

It was thought that I had an intermittent distributor issue.  Drove the car home from his shop and as expected the symptoms returned 30 miles later.   I was out of time, parked the car and headed back to France.

I thought the best solution would be to put a Pertronix or Hot Spark and read quite a bit about it … but then … kept thinking I just wanted the problem resolved and so many on our Forum have had so many problems go away by installing a 123!  This has to be the holy grail of ignition solutions.   I decided to go whole-hog and ordered a 123 ignition.


Cut to:

Christmas Holidays back in California – all I want for Christmas  ... is a 123.

As always ... I had very little time during the holidays to work on the Pagoda … family time.   I installed the 123 … lined up cylinder #1 to TDC as the instructions advised, pulled the 051 Dizzy and installed the 123, set the program to #8 per the instructions, replaced the coil with the recommended one by the supplier of the 123 and started the car.  It started, but ran badly with lots of black smoke and died before I could get the timing adjusted.  Could not get it to start again.  Pulled the plugs and they were completely coated in dry black soot after only a few minutes running.  Plugs were fine prior to this.  

Checked the spark, the spark was present but was yellow/orange … I believe it should be blue.   Could not figure out what was wrong.  Cleaned the plugs, adjusted static timing a little and started it again.  It started, got black smoke and died before I could get timing adjusted. Plugs were full of black soot again.

Cleaned the plugs and put them back in.

Naj, from our forum, reminded me that I made a basic home mechanic 101 error by replacing coil and dizzy at the same time and that it would be a good idea to start again by reinstalling the original coil, and the original 051 and try and find the fault.  So that’s what I did. Pulled the 123.

A discovery --- upon re-connecting the wire to the coil  (from the Dizzy), I pulled the rubber boot back and checked the wire connector … the wire was frayed and only 1 strand was still attached to the connector … all hidden under the protective little boot.  Installed a new connector.

Tried starting the car with the original coil and original 051 dizzy … after adjusting the dizzy a bit, the car started.  Adjusted the timing at idle after warm up and adjusted the timing at 3000 rpm.  Started the car several times ... clean easy start each time.  Took the car on a several hour run.  The car ran excellent.   It started very easy, drove great at low revs, great at cruise speed and great at high revs.  Gave the car a real workout.   It had more power than I have noticed since my 15 months ownership.  Drove fantastic.


Well …  it was a simple frayed wire hidden under the protective boot.    The moral of the story is pretty obvious … check the SIMPLE BASIC STUFF FIRST.  

Very nice to have it running so strong … put a grin on my face and I have a brand new 123 spare to install at some future time if I need it.   Hmmm … wonder what I should ask for next xmas.


A couple of not–so-exciting photos … but at least the sun was shinning at high noon while I drove through some orange groves.  

[Flyair]

Kampala,

Your experience demonstrates that, although our cars are still the mechanic cars, i.e. they have components that can be manipulated in your own garage, the are, nevertheless, very complex and interwoven structures, where one banal element can have a decisive impact on the general outcome. 

This is a very educative story, which I read with high interest as I also found in my car most of the symptoms you described, maybe only not as acute as in your case. For the moment, I leave the fine-tuning till early March, just before the start of the new season. The lesson and the advice is well taken.

Many thanks for taking time to produce such an exhaustive story.

[114015]

 

Dear Oz,

What a great story. Thanks a lot for letting us participate your experience you made here.
Quite astonishing how often only the simple(st) things result in a large effect.

I personally learnt my lession again from your story. 

Again, thanks a lot.

All best,
Achim

[ja17]

Congratulations. The experience and results are well worth the effort. At least you did not get the injection all scrambled up, trying to fix the problem!

[mdsalemi]

Kampala: regarding your runnability issues, the fact that you live in France (some of the time) and at least one of the problems was a frayed wire, reminds me of something I discovered in an old, comical but true British service manual:

Carburetor is a French word meaning, "It's the electrical system, stupid!" 

(the author was emphasizing the point that many shade tree mechanics loved to blame the fuel system when indeed, particularly on British cars, the problems were almost certainly electrical.)

[kampala]

I am quite pleased that it turned out to be something so simple … even though the journey was circuitous  … clearly got to know the car.  

And yes, I am very glad I did not start taking apart WRD, TTS, CSV and a hundred other acronyms and really put the running into a tailspin.  I know where to "begin" looking the next time I have a “carburetor” problem.  

Appreciate the words of encouragement and really appreciate all the help I receive from the generous folks within this forum … those that provide technical guidance, moral support and those that created this site and keep it working so well to allow us to collaborate.  

[jameshoward]

Kampala: regarding your runnability issues, the fact that you live in France (some of the time) and at least one of the problems was a frayed wire, reminds me of something I discovered in an old, comical but true British service manual:

Carburetor is a French word meaning, "It's the electrical system, stupid!" 

(the author was emphasizing the point that many shade tree mechanics loved to blame the fuel system when indeed, particularly on British cars, the problems were almost certainly electrical.)

One day, Michael, when you're away on holiday, I'm going to replace your electrics with a Lucas loom, coil and distributor.

Sleep with one eye open, ye denigrator of British automotive wizzardry and dark arts...






 

[JamesL]

emphasis on the "dark"

[mdsalemi]

One day, Michael, when you're away on holiday, I'm going to replace your electrics with a Lucas loom, coil and distributor.

Sleep with one eye open, ye denigrator of British automotive wizzardry and dark arts… 

I grew up, so to speak, fixing, restoring, and learning about cars with a succession of Brits, starting with an MG Midget, moving on to a series of Austins (the 1200, a/k/a the America) and an MG 1100, and the piece de resistance, a '66 Austin Mini Cooper S with a SCCR gearbox, wide tires, forged rockers, a 42DCOE Weber, Minilites, Paddy Hopkirk accelerator and more. The worst offender of anything was the leaky Weber, which nearly conflagrated the car until we got smart and put in a set of 1.5" SU carbs ex-MGB, pre-emission '67. I had no issues with Lucas electrics, was just reciting the book...

[Wulff]

I have question....at the end of your story you mentioned repairing a frayed wire in the protective boot?  I'm in the US...have 1971 280SL, and am wondering where is the location of protective boot you are referring to?  My car is doing same thing as you described your car was doing, and thought I'd check the simple fix first?

Thank you!  JW

[Jonny B]

I believe it was the two small rubber caps that are on the coil. One of the small wires was frayed and hanging on for dear life.

Had a similar issue with my 280 SL. There is a lead added from the transistor box under the battery to assist with setting dwell. The connector used has a small piece of hose to protect the bare end, but the wire going into the piece of hose was frayed. We suspect it was making contact and it just stopped the car.

[Wulff]

  Thank you for your help!!  I'll go out and look under the hood ASAP...   I'm grateful for your guidance.... In the meantime, I enjoyed seeing photos of your beautiful Mercedes! 

[kampala]

Yes --- as Jonny stated, the frayed wire for me was one of the thin wires attached to the coil and hidden under one of the small protective boots that cover the connections to the coil. 

Good luck.