Author Topic: Next mystery - Plug keeps fouling out  (Read 21764 times)

twistedtree

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Re: Next mystery - Plug keeps fouling out
« Reply #25 on: April 07, 2012, 21:07:51 »
OK, I'm back and I think I finally got this one figured out.  To make a long story short, it turns out the condenser was not making good ground contact with the distributor body.  The result was flakey spark, fouling plugs, and fouling points.  After a lot of cleaning and buffing of the distributor housing and the condenser mounting band/bracket everything appears to finally be working correctly.  Once it finally occurred to me that this might be the problem, a screw driver between the condenser body and distributor body yielded a spark which confirmed the problem.
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi

Benz Dr.

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Re: Next mystery - Plug keeps fouling out
« Reply #26 on: April 08, 2012, 21:33:57 »
That small bracket that holds the condensor on is available and I'm starting to include it for most of my rebuilds.

 Looking carefully at the spark plug electrodes would tell me what I need to know. Weak voltage will present as a dark but dry fouled plug. Closer inspection will reveal that just the very tips of the plug are clean where the current was jumping across.
Unlike oil fouled plugs that are usually coated with hard brown deposits, or fuel soaked glugs that are shiny and wet, these plugs appeared to be dry which started to lead me down the path of fauty ignition.



 I was standing in the pits at a race track one day watching a small group of men discussing the particulars of a set of used park plugs. One of them had a flash light and a magnifying glass. After looking at this one plug like an oricle inspecting the entrails of an owl, he pronounced that the spark plug from the problem cylinder had low voltage. Someone brought over a tool to test for such things and that's what it was.
 
Later, I asked him how he knew about the fouled spark plug. All he said was that the plug told him what was wrong. Being young and not accustomed to those who gaurd their secrets, I pushed on and asked what he meant by what he had just told me. He must have been a patient man because he pulled out a book with coloured pictures of used spark plugs.
 '' Find the one that looks like this one. '' He instructed me. He had kept the used plug and pulled it out of his pocket. Placing it in my hand hand he asked, '' Are you always so curious? ''
'' Yes, sir.'' I answered.
I looked through about 20 pictures but nothing looked exactly like the plug in my hand. Not wanting to fail his test, I pointed out two pictures that looked similar but also pointed out that they didn't really match and that they were only close to the one in my hand.
'' Can't find it, eh? ''
'' No sir. ''
'' Well, that's because it's not in that book.'' He asked me for the spark plug and continued with his lecture. '' See, this plug is firing but it's not producing a good kernal.''
I wasn't sure what corn had to do with spark plugs so all I could say was, '' OK? ''

He knew that this was over my head so he detailed the things that would prevent good cumbustion.
'' The kernal is the actual spark the plug makes which starts the fuel burning,'' he explained. '' This plug isn't getting enough voltage so the flame front, or spark kernal, isn't hot enough to burn all of the fuel. The plug looks dark because the unburned fuel is leaving carbon deposits on the electrodes.'' He held the plug up to he light and continued. '' See how only the very ends of the tips are are clean? '' I nodded that I could see what he was pointing out. '' The voltage will jump across and only keep that area clean but the rest of the plug will be sooty. Only weak voltage will do that.''
'' Oh...... thanks.'' Was all I could say.

 I was only about 15 or 16 at the time but I never forgot what that kind man taught me. I was just another nosey kid hanging around getting in the way but he took the time to show me one of his many secrects. That man was my brillant uncle, long passed away but never forgotten.
   
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

twistedtree

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Re: Next mystery - Plug keeps fouling out
« Reply #27 on: April 09, 2012, 01:07:30 »
And the real kicker to finally getting this car running right was the mixture which it turns out was very lean.  I think I originally read about this here somewhere, but it bears repeating....

I think it's pretty commonly known that adjusting the shims under the barometric compensator alters mixture across all speed ranges.  Rather than removing the BC and changing shims each time you want to adjust the mixture, you can loosen the BC, then wedge a short piece of hose between it and the WRD.  All the hose does is create a little friction so the BC stays in whatever position you rotate it to.  Then, to play with mixture all you need to do is pull over, rotate the BC a bit, then continue your test drive.  It's way easier and faster that shutting down and swapping shims.

I marked a point on the BC at 6 o'clock so I could keep track of exactly how much I rotated it and in which direction.  The threads on the BC are 1.5mm pitch, so a full turn is equal to 1.5mm worth of shims, with partial turns being proportionally less.  If you rotate 2/3 of a turn to get proper mixture, then you know you need to add (or remove) 1mm worth of shims.  Then you just shim it up when you are done and be sure the BC tightens up at the proper position and you are all ready to go.  It's also WAY easier than adjusting the main rack screw which typically requires removal of the solenoid to access the screw.
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi

Brian Davidson

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Re: Next mystery - Plug keeps fouling out
« Reply #28 on: April 09, 2012, 08:32:23 »
Thats a pretty smart hose trick. I like it. Many thanks.

stickandrudderman

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Re: Next mystery - Plug keeps fouling out
« Reply #29 on: April 09, 2012, 08:41:51 »
Nice story Dan.
When I was a kid my sister married an aircraft engineer and he was very instrumental in my learning about engines. He wasn't at your uncle's level though!

twistedtree

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Re: Next mystery - Plug keeps fouling out
« Reply #30 on: April 14, 2012, 11:01:12 »
This has been one of the more maddening problems I've encountered.  With an adjustment to the BC the car suddenly came to life and was running great.  Problem solved, right?  Wrong.  I started it the next day and it was right back to crap.  #2 wasn't firing again, and perhaps #4  too.  So, off came the FIP and injectors and in the mail they went to the FIP spa.

Hans called yesterday to report 2 sticking pump pistons, 2 injectors that were dribbling rather than spraying, and shot bearings.  I shoulda just pulled it earlier.  Oh well.  I'm now going to round up every injector off every car, plus my spares, and send them for testing so I know what's good and what's not.
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi

Jonny B

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Re: Next mystery - Plug keeps fouling out
« Reply #31 on: April 14, 2012, 16:07:07 »
If you purchase new injectors, be sure to test those too. I bought a set last year, and one of them had to be returned as it was not spraying properly.
Jonny B
1967 250 SL Auto, DB 568
1970 280 SL Auto, DB 904
1966 Morris Mini Minor

twistedtree

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Re: Next mystery - Plug keeps fouling out
« Reply #32 on: April 14, 2012, 22:13:29 »
Happily I have 14 injectors in my spares collection, so I'm sending them off to H&R for testing to sort out which ones are good.  Hopefully I'll end up with the replacements I need plus plenty of additional spares.
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi

Benz Dr.

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Re: Next mystery - Plug keeps fouling out
« Reply #33 on: April 15, 2012, 03:16:59 »
This has been one of the more maddening problems I've encountered.  With an adjustment to the BC the car suddenly came to life and was running great.  Problem solved, right?  Wrong.  I started it the next day and it was right back to crap.  #2 wasn't firing again, and perhaps #4  too.  So, off came the FIP and injectors and in the mail they went to the FIP spa.

Hans called yesterday to report 2 sticking pump pistons, 2 injectors that were dribbling rather than spraying, and shot bearings.  I shoulda just pulled it earlier.  Oh well.  I'm now going to round up every injector off every car, plus my spares, and send them for testing so I know what's good and what's not.

I've been where you are a lot of times. At some point you start to question your questions. This was a case of having several things wrong rather than just one, but fixing each problem still didn't result in a real fix. Been there too......

I have a series of tests that I make. Once I've gone through all of those things then I start to question the pump because everything else affects how the engine runs. If it's not plugs, points, wires, rotor, coil, fuel pressure, fuel volume, fuel return, leaking CSV and a number of other things; then it's likely the pump. Since I like to be sure, I make sure.

During any engine rebuild I do, the pump goes out for a calibration test or rebuild. A full engine rebuild is a waste of money if your pump is not working right. You can destroy a good engine with a leaking pump or CSV. Get your injectors cleaned as well.

I know it's some money to spend but it's one of those investments that is worth a lot more than new bumpers or some other cosmetic item that really doesn't make your car run any better - looks nice though.   
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

twistedtree

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Re: Next mystery - Plug keeps fouling out
« Reply #34 on: April 15, 2012, 10:55:29 »
Dan, that about sums it up.  Yes, there were layers of problems here, and you just need to find and fix them one at a time.  One of the complicating factors here is working on a car that was recently put back together (mostly) after an unknown amount of rebuild, so there is no baseline of probably-good parts.  I think in general people jump to indite FIPs and injectors too quickly.  It's the influence of the Random-Part-Replacement method of car repair used by way too many shops.   But unlike typical cases where I'd consider a FIP innocent until proven guilty, the previous owner's "calibration" work on the FIP on another car should have been more of a hint.  I now consider any pump he's touched to be guilty until proven innocent.
Peter Hayden
1964 MB 230SL
1970 MB 280SL
2011 BMW 550xi