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Another 6.9 that wont raise (diagnostic tips)

Started by secondslc, 17 May 2020, 12:00 PM

secondslc

I need to get a bulb in that spot as its burnt out, but I should probably let the light tell me if im reaching pressure...
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

secondslc

Put a used pump in. The old one was wet on the back... assuming it was leaking into the block ugh.

-Primed it as per suggestions in the forum
-Hooked it all up
-Started it
-The pressure selector finally started clicking.
-The rear end lifted up as if magic
-The front end lifted up as if magic

After 20 years, it drove around the block on its own.  :D

Next up I get to tune the engine as it's low on power.
But first:
-Change the plugs
-Change the oil
-replace the hydraulic oil filter
-Oh, and celebrate :-D
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

Good news.

Check your timing, that should help with power.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

daantjie

Changing out transmission fluid and filter should be high on the list too.
Daniel
1977 450 SEL 6.9 - Astralsilber

secondslc

Timing... any leads to a procedure?

Trans was empty as the cooler lines were shot. Replaced all the lines and put new fluid in. It shifts ok but itll get flushed once its road legal
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

raueda1

Quote from: secondslc on 01 June 2020, 05:23 PM
Timing... any leads to a procedure?

Trans was empty as the cooler lines were shot. Replaced all the lines and put new fluid in. It shifts ok but itll get flushed once its road legal
MB manuals are on this site.  Here's the link:  https://img.w116.org/tech/Manual_100-985_Combustion_02_83.pdf
Drill down to the section on timing.  Specs are there.  Before doing so, however, make sure the elements of the distributor can move freely and aren't gummed up (quite likely if the car has been sitting for years).  And if so, you'll never get the timing right. Good luck!
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

secondslc

Thank you for this! I have a hard time finding the tech articles for the 6.9 specifically.

The distributor moves, it was loose when I got the car  :o

1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

raueda1

Quote from: secondslc on 01 June 2020, 06:24 PM
Thank you for this! I have a hard time finding the tech articles for the 6.9 specifically.

The distributor moves, it was loose when I got the car  :o
My grandmotherly and forgetful neighbor repeatedly calls over to me as she trims her roses, "David, you're always working on that car!"  And my reply is always the same.  "Glenda, this isn't a car.  It's a hobby and way of life!"  A week later this will be repeated verbatim.

Anyway, the tech page https://www.w116.org/tech/.  The 100.985 manuals are the ones you want.  The quality is not great and photos are near useless, but they're there. A lifesaver.  Thanks to whoever put them up in the first place!
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

revilla

Quote from: secondslc on 01 June 2020, 06:24 PM
The distributor moves, it was loose when I got the car  :o

Hi secondslc.  I think Dave was referring to the guts (elements, weights, sliders, springs, etc) inside the bottom of the distributor housing.  If they are not clean free of grime they have difficulty responding to the centrifugal forces to advance the timing which will have an impact on power.

He documented the procedure in a post here with details and pictures, etc.  When I did mine following his guideline the improvement was quite noticeable!     


secondslc

ohhh, i am a little intimidated taking that apart, but I suppose it will make sense when i get into it. I'll report back once I get going.
1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

secondslc

Alright,

Had a friend over who has worked on cars from Ferraris to VWs with CIS. He helped set the timing, and we tried getting the fueling right... but I still need help with fueling

-Found TDC and set the distributor to line up with it.
-We made sure it was at 0 degrees without vacuum at 800 rpm.
-Vacuum advance brings it to 9-16 degrees advance as you bring rpms to ~1500.

So then we gave fueling a shot.
-No matter what we do, it will lean backfire as revs go past 1500 into the 2k range, even if its running extremely rich at idle (you can smell it)
-The two adjustments we were trying to dial in are the idle air screw and the fuel enrichment 3mm screw.
-Unplugging the cold start injector didn't change anything
-It simply hates revving past 3k rpm
-The exhaust system was getting hot enough to smoke the entire underside, even sending smoke into the cabin.

I'm not one to want to mess with marginal parts, and am OK spending money on new fueling parts, but here are my questions.
-Would you shot gun it and replace the WUR. idle valve, and cold start injector (once I verify the signals are reaching the devices?
-Would you start with one at a time?
-Would any of these devices be dumping fuel at idle and then leaning out too much when applying throttle?

The last thing
-Can the cats be clogged? To me, that would explain the issues with it not wanting to rev, and if its super rich, I may have burned them up already. I plan on Taking the car to an exhaust shop and having the cats dropped with test pipes installed, and adding a Wideband so we can adjust the levels and tune the CIS

1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

daantjie

#42
You will need a fuel pressure gauge plumbed in to see what's potting, no other way to get KJET to run right.  Also if you do not need to pass smog I would yank all the anti-smog crap they put on these cars, like the smog pump, cats etc.
Daniel
1977 450 SEL 6.9 - Astralsilber

secondslc

I want to yank the cats, but how much smog stuff can I remove? I don't have to pass emissions. I just want to know if I can just yank the air pump and egr to no ill effects?

Fuel pressure, wouldn't it be ok with a new pump, accumulator, regulator, and all the lines showing no signs of leakage? Are there pressure adjustments I'm missing?

Or are you saying the WUR could be finicky and a fuel pressure test will tell me?

1979 6.9
1983 urQuattro
1991 200 20V Avant
1993 Corrado SLC
1996 SL600
2009 Super V8

daantjie

I can only speak for what I did and I pulled absolutely all the smog crap off and blanked off all the open ports, no ill effects, in fact it idles smoother and for sure breathes better IMHO.  If nothing else, think of it as weight reduction ;D

There are specific fuel pressure ranges and set points you have to meet and they should be in the service manual (check out the Library section).  From memory there is cold pressure (at cold engine start), then fully warmed up of course, and there is also a "stabilization period" from memory.  So to really make sure you need to plumb in a test gauge between the fuel distibutor and the WUR, this is where you take the readings.

As many folks here on the forum know, my approach is one of "base line", so I like to replace all old parts at once with new to try and eliminate cultprits.  I know this apporach is frowned upon by some but it works for me.  For sure if you think the accumulator, pressure  regulator (at the fuel distributor) are original, I would just go ahead and replace these along with obvious things such as fuel pump, filter etc.  These parts are not unique to the 6.9 and are not too dear, so I would just go ahead and replace them, but that is just me ;D
Daniel
1977 450 SEL 6.9 - Astralsilber