Author Topic: K-Jetronic and WUR problems  (Read 760 times)

raueda1

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K-Jetronic and WUR problems
« on: 26 May 2018, 09:57 AM »
This problem is my final barrier between a dark present and a bright world of total 6.9 motoring nirvana.  I had several threads on the M100 board last summer, did some work but couldn't fix it and moved on.  Now I'm back at it.  Here's a recap and list of the stuff I did.

The basic problem:  For whatever unknown reason the WUR doesn't work properly.  It can be described thus:

[control pressure] = [(primary system pressure) - (~0.3 bar)] regardless of the system pressure.

When system pressure is set as low as possible (no shims in the pressure regulator) the car runs pretty well. A casual passenger might not notice anything amiss but it's most definitely not optimized.   Idle is pretty rough and it's very hard to start below, say, 50-55 deg F, and impossible to start when colder than that.

Efforts to fix:


>  Rebuilt fuel distributor block in rear and cleaned out gas tank (needed that anyway).  Fuel pressure is fine, filters are all good, pressure accumulator is good, fuel dampers are clear and open.  No effect (except no more fuel starvation at 1/2 full tank of gas).

>  Blew out fuel return line and replaced hose stub from return line to tank. It's now 100% clear, the hose stub was partially occluded.  I also bypassed the fuel return line entirely with a parallel line from the injector head back to the fuel tank.  No effect.

>  Blew out tank vent, which seemed to be clear.  No effect.

>  Triple checked that all lines to/from WUR are clear. They are.

>  Tried another WUR (rebuilt unit).  No effect.

>  As a further test I installed just the top half of a WUR so that the button on the diaphragm was exposed and could be pushed manually.  Pushing on the button had no effect on the control pressure.

By the way, the WUR is an early version with vacuum enrichment.  It's mounted differently than WURs I've seen in other engine pix (see below). 

So what to do next?  I want to avoid going to a real mechanic if possible.  My fear with obscure problems is that they play the dart-board repair game:  replacing stuff till they finally hit on the problem rather than diagnose and then fix.  Hopefully we've got some K-Jet geniuses out there. 
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: K-Jetronic and WUR problems
« Reply #1 on: 26 May 2018, 10:28 AM »
More history, maybe it helps.  The car was this way when I got it last summer.  I didn't really notice till weather got colder and I noticed the hard-to-start issue.  It seems that somebody managed to identify the problem of no control pressure regulation and couldn't fix the root cause.  Instead they messed with the system pressure regulator to get system pressure in the range of what the control pressure should be, more or less, and left it at that.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: K-Jetronic and WUR problems
« Reply #2 on: 26 May 2018, 04:51 PM »
Dave I've heard Larry Fletcher at CIS Flowtech is the man. If you've hit the wall probably best to send both the WUR and FD to him.
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: K-Jetronic and WUR problems
« Reply #3 on: 26 May 2018, 05:15 PM »
dont forget your idle air valve -  the round thing to the left of your WUR.  is the plastic idle screw on it turned all the way in?  if so it isnt working.  Does the engine start at a higher rpm and then after about 4-5 minutes slow down to idle speed?  That is what it is suppose to do. 

search and  you will find fairly easy way to fix and test. They can be taken apart and cleaned to get back to where they open and close properly based on temp.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

djenka018

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Re: K-Jetronic and WUR problems
« Reply #4 on: 23 January 2019, 04:52 AM »
More history, maybe it helps.  The car was this way when I got it last summer.  I didn't really notice till weather got colder and I noticed the hard-to-start issue.  It seems that somebody managed to identify the problem of no control pressure regulation and couldn't fix the root cause.  Instead they messed with the system pressure regulator to get system pressure in the range of what the control pressure should be, more or less, and left it at that.

I hope that 9 months later the issue is resolved and the epilogue is available for sharing...
Vitamin C for SL... the SLC

raueda1

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Re: K-Jetronic and WUR problems
« Reply #5 on: 23 January 2019, 06:10 PM »
More history, maybe it helps.  The car was this way when I got it last summer.  I didn't really notice till weather got colder and I noticed the hard-to-start issue.  It seems that somebody managed to identify the problem of no control pressure regulation and couldn't fix the root cause.  Instead they messed with the system pressure regulator to get system pressure in the range of what the control pressure should be, more or less, and left it at that.

I hope that 9 months later the issue is resolved and the epilogue is available for sharing...
Yeah, there is a kind of epilogue.  I ended up getting a rebuilt and recalibrated WUR from the kind folks at CIS Flowtech and then fixed the primary pressure to where it should have been in the first place.  Car runs well.  It's now winter here but I did take the car out on a nice day a couple weeks back.  It started instantly at about 2°C after sitting for a couple months.  Cold idle is still a bit lumpy but I've experienced much worse idles!  After a couple minutes it smoothed out.

The car runs very nicely.  I have great confidence in it, would drive anyplace in it without hesitation.  But.... it still isn't completely sorted out, it's just not quite as powerful as it ought to be.  When spring arrives I'm going to get the fuel distributor rebuilt and replace injectors on principle.  Will also test the cold start injector (though I assume it's doing something or it would be a much harder start).   Also, despite my lengthy thread on distributor cleanup I'm not 10% persuaded that the timing is entirely correct.

My neighbor always shouts over the fence, "David, you're always working on that car!"  And I always shout back, "It's not a car, it's a hobby!"
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: K-Jetronic and WUR problems
« Reply #6 on: 24 January 2019, 07:41 AM »
Have you been able to get the timing set correctly? When I got my 6.9 it was sluggish and setting the timing correct really made it jump. search here and you can find info on specs and issues setting correctly.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: K-Jetronic and WUR problems
« Reply #7 on: 24 January 2019, 08:18 AM »
Have you been able to get the timing set correctly? When I got my 6.9 it was sluggish and setting the timing correct really made it jump. search here and you can find info on specs and issues setting correctly.
Yeah, I've done the search, found the specs (thanks largely to you!).  I'm sure it's not a coincidence that Mike Morris, who i met at Lodefest, echoed your experience with the timing https://www.morrismotorsusa.com/?fbclid=IwAR3hHE_oix-U7SNJcHYNqGBWaoJFC9dG-MEZJHFbUgcNvoZhXaQ5L9dEcpE

Best I can say is that is that I've played around with it.  I'm not confident that it's spot on though.  In fact, I'm confident that it isn't spot on.  One issue is that I don't have a good tachometer. I'll get one by the time spring rolls around and then return to it.  Stay tuned...
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: K-Jetronic and WUR problems
« Reply #8 on: 24 January 2019, 10:28 AM »
Is it truly possible to dial in  40+ year old setup completely to spec?  Just playing devil's advocate here and in no means trying to discount the work that has been done of course.  I guess if one has enough time and money anything is possible, and maybe my standards are just lower 8)
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: K-Jetronic and WUR problems
« Reply #9 on: 24 January 2019, 11:59 AM »
Is it truly possible to dial in  40+ year old setup completely to spec?  Just playing devil's advocate here and in no means trying to discount the work that has been done of course.  I guess if one has enough time and money anything is possible, and maybe my standards are just lower 8)
Danielle, you make a good point.  To be clear, I'm not going to go totally nuts on this.  That said, I didn't look very hard at the timing after the distributor cleaning project.  Prior to the distributor rebuild I know that the vac retard/advance wasn't right.  The lever on the diaphragm was jammed so all I was getting was centrifugal advance.  I'm surprised it ran as well as it did.  Last fall I kind of got it in the ballpark but I recall it still wasn't right, though now I can't remember details.  I did make another observation at the time - at no point in messing with timing could I get the engine to ping or knock at all.   I tried the advance-till-it-knocks-and-back-off and it never knocked, which seems odd.  I'm not sure I'm doing any of it right.  I'll therefore be returning to it come spring and start fresh - review the procedures, my timing light, crank readings etc etc.

As for the fuel distributor, it just seems prudent to have it checked and rebuilt if need be.  I'm not confident that it hasn't been messed with in the past.  The original WUR and fuel pressure regulator had both been screwed around with.  CIS flowtech will bench test for a small fee.  The injectors are relatively simple and cheap, so I figure "why not?"  Time is something I have plenty of, money not so much.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: K-Jetronic and WUR problems
« Reply #10 on: 24 January 2019, 01:53 PM »
Well yes, there are a lot of parts in play to run the best they can.  Fuel and ignition. Having your  FD checks is probably a good idea.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550