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K-jet troubles - totally stumped, K-jet expert needed!

Started by raueda1, 29 July 2022, 10:24 PM

s class

It sounds like your vac connections are correct.  Is it the correct wur though what is the bosch end number... '056, '057 and '010 should all serve.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

If the diaphragm was torn, then vac would have no influence.  I'll reveal some of the dark secrets of kjet now.  There are three adjustable posts on the wur.   The fuel cell that the two fuel lines attach to can be driven up or down.  Yours needs to come outwards about 0.3mm to warm reduce control pressure from 3.8 to 3.5.  You can screw an m10x1 bolt into the inlet port and couple a slide hammer to it to pull the cell upwards.  Use a vernier to monitor your progress


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

Once the warm control pressure is on 3.5 bar, you can adjust the enrichment pressure.  This is set by the plug on the underside.  You need to drive yours in deeper to raise the enrichment pressure to 3.0.  DONT overdo it, or you will have to strip the unit ruining the diaphragm in the process to get the plug back out.  Use a vernier and go 0.1mm at a time


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

One warm and enrichment control pressures are correct you an turn to the cold control pressure.  That's the post next to the electrical connector.  Deeper in (knocking it in) lowers the cold control pressure, higher up (drill and tap it for m6x1) raises it


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

daantjie

Here is a doc I found online, may or may not help with your WUR shenanigans:

WUR Tips.pdf

 
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 08 August 2022, 03:51 PMAnd another:

WUR Tips II.pdf
Daniel, THANK YOU, this is great!  Exactly what I've been looking for.  So much more specific than the other WUR rebuild stuff out there.  Everybody should have this.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

Quote from: s class on 08 August 2022, 02:39 PMOnce the warm control pressure is on 3.5 bar, you can adjust the enrichment pressure.  This is set by the plug on the underside.  You need to drive yours in deeper to raise the enrichment pressure to 3.0.  DONT overdo it, or you will have to strip the unit ruining the diaphragm in the process to get the plug back out.  Use a vernier and go 0.1mm at a time
Thank you, thank you!  I got the system pressure and cold/warm control pressures spot on with one WUR.  It seems to just be the vac enrichment pressure (if I can call it that) that's off.  So his is exactly what I've been missing.  In reasoning through it all, it seems like there would have to be some way of adjusting the small spring pressure acting on the diaphragm.  So this is it.  I'm a bit puzzled though by why this piece of info seems to be so broadly overlooked.  I've been looking at the various Porsche, Volvo and Audi sites and never came across it.  Well, no matter, I'm going to get on it.

My next step is to methodically measure all the WURs in my small collection.  It's still a bit puzzling why the vac enrichment pressure would change rather abruptly, if it even did.  The car was running great for several years and I didn't change anything.  Presumably it couldn't run well with Vac enrichment pressure so far out.  But then power kind of fell off a cliff all of a sudden and we find that the vac pressure is totally wrong.  ??? ??. Anyway, I'll post my findings in due course.  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

Quote from: s class on 08 August 2022, 02:39 PMOnce the warm control pressure is on 3.5 bar, you can adjust the enrichment pressure.  This is set by the plug on the underside.  You need to drive yours in deeper to raise the enrichment pressure to 3.0.  DONT overdo it, or you will have to strip the unit ruining the diaphragm in the process to get the plug back out.  Use a vernier and go 0.1mm at a time
"When the going gets weird, the weird turn Pro."  -Hunter S. Thompson

Very wise.  It seems I'm becoming VERY pro.  All that said, some minor progress to report.

I went about very systematically checking 4 WURs in every way.  There was something wrong with all of them, all different.  One was sacrificed by experimentation on how hard to tap the adjustment elements.  Well, not destroyed, but now maladjusted.  I had never actually done that before.  At the end I decided to focus on the unit with the excessive full load enrichment.  FWIW, this was a unit rebuilt by CIS.  I never used it when I got it several years ago.  It didn't work right at the time, so I threw on a high altitude WUR that I had on hand.  The latter worked perfectly and was on the car until my problems started.

So, to recap:  the CIS WUR is perfectly to spec apart from full load enrichment pressure.  System pressure is a perfect 5.5 bar.  Hot control pressure is 3.5.  Perhaps a tiny bit on the low side, but within spec, 3.4-3.8 bar (especially since I'm at 1200m elevation).  The problem is vacuum controlled enrichment.  Pressure drops to 2.5 bar, as noted elsewhere.  Spec is 3.0-3.4 bar.  The specified pressure drop is pretty damn small!  Regardless, my pressure drop is easily 2X the spec.  So that's a problem and I reproduced it again today.

First, it did turn out that I had an air leak before the fuel pump.  I fixed that.  Next, per S class' info above, I tried to adjust the vac enrichment post and tapped it in ~0.5mm  That was the least I could manage (how anybody manages 0.1mm increments is beyond me). This had NO EFFECT.  Maybe that's OK, cause it was so far out of range that much more is needed?  I did note that the adjustment post was oringally farther out than those on all the other WURs.  So, what to make of this?  Just keep tapping?  Or should this absolutely have had some effect? Obviously I don't want to ruin the WUR by overshooting.  It occured to me to take a test drive anyway, but I couldn't cause car is elevated.  The idea behind that is to remove the vacuum enrichment and see how it drives.  Sure, it wouldn't optimum.  But if it's a significant improvement then it would point to excessive enrichment - maybe? ???

Again, comments, ideas and prayers welcome.  Thanks and cheers,

-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

s class

The way the enrichment works is when you remove vacuum, the diaphragm drops down internally against the lower end stop in the base layer of the WUR. If the plug is way low, then the diaphragm is resting on the base layer itself, and not the lower plug.  You may need to drive it up a bit more before it is internally standing proud of the aluminum of the base layer itself and actually effective.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

On my test bench the WUR is mounted on a steel base, in which I've drilled and tapped for a bolt which I can turn from underneath to press the plug upward in an easily controlled manner


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class



[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

raueda1

OK, thanks, maybe some progress to report.  Or at least some things that are now known NOT to be the problem.

I rebuilt and set up an entirely different WUR. Good results:
   1. system pressure 5.7 bar - OK
   2. Hot pressure 3.5 bar - OK.  Low end of range perhaps, but OK.
   3. Enrichment vac pressure drop: 3.5 (control) => 3.0 bar. OK.

Other things that are also OK:
   1. new fuel pump
   2. new fuel filter
   3.  Checked ignition timing and function:  OK

Control pressure could be hair higher but still within spec.  Yet the original problem still exists: The car drives fine at low speed but bogs and stumbles under heavy throttle.   The engine revs freely when parked (no load).  Again, I'm at a loss.  What else is there to check?  I'm starting to panic a little.  Cheers  :'( ,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

s class

Whilst it doesn't solve your problems, I'll reassure you that 3.5bar is good.  The published spec is 3.4 to 3.8, but all the unmolested units I've come across had been factory set to 3.5bar,so that's what I usually target.


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

raueda1

Quote from: s class on 11 August 2022, 03:58 PMWhilst it doesn't solve your problems, I'll reassure you that 3.5bar is good.  The published spec is 3.4 to 3.8, but all the unmolested units I've come across had been factory set to 3.5bar,so that's what I usually target.
Well that's something anyway.  But I wracking my brain on how it can all fall apart under load when all that stuff seems to be as OK as it can get.  Inexplicable exhaust back-pressure?  Simultaneous failure of all the injectors?  Tachyon beam entanglement?  What's left?
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0