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

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

raueda1

Starting a new thread, I progressed (???) on the previous one and it was getting stale anyway.  Here's where I am:

While trying get my system pressure right, the fuel pump started making whining and gurgling noises.  I took this to mean that it was dead or dying, so I replaced it.  Replaced fuel filter too, cause why not?  Fuel flow seems fine and the return seems to be ok.

Now, when testing primary pressure, the pressure gradually rises to about 4 bar.  But it rises quite slowly.  My recollection is that it was originally pretty quick, maybe 10 seconds.  Then there's a faint click and pressure drops to ~3 bar almost instantaneously and then climbs back to 4 in about a second or so.  This repeats.  It's like the pressure is trying to get where it should be, but then the regulator pops open.  There's a pressure drop but then it climbs again and cycle repeats.  I tried 3 different valve bodies, 2 different springs and 2 different cylinders.  All with the same result.  Is it possible that pressure needs to be set MUCH higher with more shuims?  That is, more cylinder pressure is needed to get smooth regulator action?  And on top of that the new fuel pump started making the same noises!  The system pressure does hold up well though.

Does this suggest that the problem isn't the pressure regulator valve but something else?  But what?  Logic has failed me, I'm stumped and it's getting frustrating.  Any suggestions would be very welcome at this point.  Thanks and cheers,
 
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

s class

It's quite common for fuel accumulators to fail.  Only occasionally though I've seen them fail so badly that the leak back to the tank so fast that the pump can't keep up.  Have you checked your accumulator


[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

Are you sure it's the correct pump (nominal 6 bar, stall 8 bar) and not the unit intended for 124/126 twin pump setups (3 bar nominal, 4 bar stall)


[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

Sorry for the split up messages, I'm typing from my mobile

Other thing to check is if the pump is getting adequate voltage AND current. Try giving it a good earth and a nice thick temporary power wire direct from the battery


[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

As to the primary pressure regulator in the FD, I think it's highly unlikely that it would have suddenly go so far wrong.

BTW where are you measuring this pressure - at the line between fd and WUR? With your measurement valve closed ie system pressure?


[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

Dave have you traced all the hard lines front to back?  Probably a long shot but maybe a pin hole leak somewhere?
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Thanks for the suggestions.  I made big progress today, but still a ways to go.  The fuel accumulator seems fine - it holds pressure for over 30 minutes.  I can't find any other leaks anywhere.  But I did discover a couple other things.
 
First, I replaced fuel pump whether it needed it or not (looks like maybe it did).  New OE pump from Classic Center.  Then, it turns out that I DID mix up the cylinders in the pressure regulator in the course of monkeying around.  I read on a Porsche forum that they're mated to the FD, same as the metering cylinder.  That was new to me.  I stupidly fell into the traps of doing too much at the same time, no pictures and bad labeling of parts.  ???  When I finally put in the original cylinder into the FD (trial and error) the pressure cycling stopped but system pressure was still low.
   
Second, I discovered that the regulator plug/spring assemblies are NOT all the same.  I have several.  The only one that works correctly right is the one that originally came with FD.  The length is slightly different from the "same part" out of a parts car and another from eBay.  Something else to be aware of.
 
Third:  After the new pump, new filter and the right parts in the pressure regulator,  the system pressure was still low, only 4.5 bar, and control pressure was the same.   Looks like the WUR had suddenly gone crazy.  (??)  After swapping it for another WUR in my parts box, pressures were now pretty spot on:
  • System pressure: 5.5 bar
  • Cold control: ~1.8 bar (test done at 30C or so)
  • Hot Control: ~4 bar (maybe on the high side, but not crazy)

Wunderbar!  Now the car starts and is drivable again.  But a problem remains.  Under heavy throttle not much happens and the engine kind of bogs down.  Going up a hill there was a kind of burp from the air flow sensor.  Time to get seriously systematic.  The CIS manual Problem Diagnosis chart recommends as follows:

Symptom                           Test 
Stumble on acceleration:    3, 5, 9, 10, 11
Engine miss:                       3, 5, 11, 12, 13
Lack of power:                    1, 3, 7, 9, 10, 11, 13
High speed break up:          3, 4, 2

Here's the list of tests and what I seem to know at this point.  I don't find the diagnosis chart very helpful since there's so much overlap.  In the end you just need to do almost everything anyway.  This is another case of systematically starting at the beginning step-by-step.  Which I (and others) seem to ignore, again and again.  ::)  Anyway, results thus far:

Test                                                  Result
1    Check throttle linkage`              OK, on inspection seems fine
2    pump delivery volume              OK, excellent, well over spec
3    primary system pressure           OK, 5.5 bar
4    static pressure test                     OK, tests accumulator
5    injection nozzle leak                  OK
6    cold start valve                          Didn't test, but no cold start problem
7    cold control pressure                 OK, 1.8 bar at 30C deg ambient.
8    auxiliary air valve                       Didn't test but no apparent problems here
9    warm control pressure                OK?  4 bar.  Spec is  3.4-3.8 bar, so a bit high.
                                                           But probably not so much to cause a profound lack of power. 
                                                           I should correct spec for engine vacuum.  I think mine is on
                                                           the low side (high altitude?) but not sure where to measure.
10   full load vacuum enrichment     Looks like a problem!  Taking vacuum off the
                                                          WUR drops control pressure from 4 bar down to 2.5 bar,
                                                          That's a whole 1.5 bar.   Spec is dropping from 3.4-3.8 down
                                                          to 3.0-3.4 or just 0.4 bar!   So, under heavy throttle I'm running
                                                          super-rich?  I'm not sure what to make of this.
11   idle speed and CO adjustment   I set mixture screw as best I could and adjusted idle accordingly.
                                                           Idle is actually very smooth and stable.  It drops a little when A/C
                                                           is on.  It didn't used to do this.  Maybe suggests a small vacuum leak
                                                           someplace?
12   fuel injector test                         Didn't test but doesn't seem likely.  (??)

13   test fuel distributor                     Didn't test but doesn't seem likely.  (?)


What's next???  First, I'd greatly appreciate any comments on all this.  I tried to go back and systematically describe it all by using the logic of the manual.  At this point it all seems to point to a vacuum enrichment problem, so I'm going to follow that.  But I'm really not sure how. 
  • Something faulty in the WUR or maybe wrong WUR?  Maybe I ought to refurbish the original WUR.  FWIW, it's a rare high altitude version.
  • Some kind of wrong connection of WUR (I'm not sure how that's possible)
  • Some other underlying vacuuum problem?
Finally, this is all rather long and tedious.  Would it be better to start a new thread on vacuum enrichment?

As always, thanks for the ideas and continued support.  Happy motoring and cheers,

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

rumb

Perhaps start considering sending the WUR and FD to CIS Flowtech for testing and calibration?
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

raueda1

Quote from: rumb on 31 July 2022, 01:40 PMPerhaps start considering sending the WUR and FD to CIS Flowtech for testing and calibration?
LOL, ironically it IS a WUR that CIS rebuilt but never used.  The reason was that I installed a high altitude WUR from that parts car.  And it worked fine till now.  I've got a box of WURs.   I'm gonna test and tag them all.

While we're At it, do you know where to measure vacuum for purposes of setting control pressure?  The vacuum that the WUR sees from its tubes seems lower thanthereal enginevacuim.  The manual isn't clear on whether real manifold vacuum or the vavuum that the WUR sees from its tubes.  Hope I'm making sense....
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Lance

Control pressure too high will cause a lean condition, which could cause stumbling. Get pressures spot on before you look at anything else.

Randys01

It seems you are nearly there in terms of the correct values for everything except hot control pressure. You have to get that down. At 4000+ feet SLC has slightly less than the ave air pressure but at times it seems it is only by a gnat's whisker. Frankly, I feel as tho it is  a red herring.

There's a million cars a year go to 6000 feet in the Victorian snow fields and no one is in crisis. Indeed my own 6.9 travelled from sea level  up to the mountain top every day for 10 years with a standard WUR.
So forget Hi altitude WUR's .
You have to get the control pressure down to 3.6 then let's see.

raueda1

Quote from: Randys01 on 01 August 2022, 03:57 AMIt seems you are nearly there in terms of the correct values for everything except hot control pressure. You have to get that down. At 4000+ feet SLC has slightly less than the ave air pressure but at times it seems it is only by a gnat's whisker. Frankly, I feel as tho it is  a red herring.

There's a million cars a year go to 6000 feet in the Victorian snow fields and no one is in crisis. Indeed my own 6.9 travelled from sea level  up to the mountain top every day for 10 years with a standard WUR.
So forget Hi altitude WUR's .
You have to get the control pressure down to 3.6 then let's see.
Thanks much!!  Got some progress to report.  First, the system pressure is now exactly 5.5 bar and stable.  I played around with a few WURs and seemed to find a good one.  Hot control pressure is 3.5 bar.  Cold pressure is a bit low, ~0.9 bar at 30C ambient.  Should be more like 1.8 bar at that temp, but never mind for the moment.  The car starts instantly and idles very smoothly.  It revs freely and is drivable, kind of. 

So far so good.  But problems remain.  It still bogs down under heavy throttle.  Basically, anything beyond about 1/3 throttle doesn't have any effect.  There are a couple further issues:
  • Static pressure - The system holds static pressure OK for a few minutes, but gradually creeps down.  There don't seem to  hot start problems, though I haven't tried a hot restart after sitting 10 minutes.  So, there's a leak someplace.  For the time being I'll assume it isn't the fuel pump non-return valve since it's new.  Regardless, the leak doesn't seem severe enough to cause lack of power.  Or is that a bad assumption?
  • Fuel pump sucking air - there's a variable hissing noise emanating from the fuel delivery cluster.  It sounds as if air is getting sucked in somehow.  Can that mess things up?  Probably it can, but the power loss was present from the start, so seems unlikely.
  • Full load vac enrichment - Manual indicates that malfunction causes stumble on acceleration and/or lack of power.  Disconnecting the vac hose drops control pressure from 3.5 down to 2.5 bar.  The spec is a drop of only about 0.4 bar as I understand it.  But I tested 2 WURs and both did the same thing.  When the vac hose is disconnected at idle the engine speeds up.Maybe a candidate?

Next steps:
Check fuel accumulator for a leak
Check cold start valve for leak
Confirm air leak and eliminate
How to really check vac enrichment?

That's where I'm at.  Any ideas or suggestions would be wonderful.  This is killing me.  Thanks again,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

s class

Dave,in any complex problem it pays to fix the known problems first before looking for more problems.  I think you need to get that acceleration control pressure sorted first.  I recondition warmup regulators and then set up the system on the car.  In my experience you really want no less than 2.9 bar at acceleration.   Warm control pressure with vac is a little bit more forgiving. All the good condition unmolested wurs I've seen seem to have been 3.5 bar from the factory, but anything up to 3.8 bar should be fine.  As you point out the differential between readings with and without vac is crucial.  Aim for 0.5 to 0.6 bar.  Then set the exhaust gas CO correctly with vac applied.  As I'm sure you realize, CO is set with vac applied, which means that if the differential between control pressures with and without vac is too great,you will be going too rich under acceleration.


[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

Next try to confirm and resolve the air ingress at the fuel pump package.  I've only seen this once before, and the culprit was the hose from the tank to the damper which had gone slightly porous.  The result was pinging under acceleration due to being too lean.

As you then chase down your acceleration issues,you need to be sure the ignition system is good,and that timing is correct with proper advance characteristics.

You loss of static fuel pressure is highly unlikely to be the cause of your troubles, it's just not fast enough.


[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 06 August 2022, 02:06 PMDave,in any complex problem it pays to fix the known problems first before looking for more problems.  I think you need to get that acceleration control pressure sorted first.  I recondition warmup regulators and then set up the system on the car.  In my experience you really want no less than 2.9 bar at acceleration.  Warm control pressure with vac is a little bit more forgiving. All the good condition unmolested wurs I've seen seem to have been 3.5 bar from the factory, but anything up to 3.8 bar should be fine.  As you point out the differential between readings with and without vac is crucial.  Aim for 0.5 to 0.6 bar.  Then set the exhaust gas CO correctly with vac applied.  As I'm sure you realize, CO is set with vac applied, which means that if the differential between control pressures with and without vac is too great,you will be going too rich under acceleration.
Thanks muchly!  Very helpful.  It really does seem like the vac is having an extreme effect.  But why? Unfortunately the manual isn't very helpful.  All it says is "replace warm-up/full load enrichment compensator."  It's not clear whether this means replacing the whole WUR or just the internal diaphragm or other parts?  It's also suspect that 2 WURs seem to be doing the same thing.  I'm going to recheck that. And nowhere have i found even a shred of info on adjusting the full-load control pressure.  All I can imagine is a bad diaphragm (which would presumably not change control pressure at all) or the wrong spring pressure.

This all seems to relate to the whole WUR/vacuum interaction and the warm-up process.  I can find almost nothing on either this or more specifics on the Full-load enrichment.  On my car the Small WUR tube is not open to the atmosphere, it goes to the big tube behind the aux air valve.  The larger vac tube connects to the curved rubber hose before the auxiliary air valve.  It's worth noting that as the AAV closes during warm-up it effects where the WUR is drawing vacuum - before of after the AAV.  Moreover, the respective vac ports on the WUR have opposite effect on control pressure.  Maybe my tubes are switched?  Yet I never changed them!  And their size if different.  None of the Bosch literature I've seem shows or describes this configuration though it seems to be very common.

Anyway, this is going on too long here, so I'll start another thread devoted to the WUR/vacuum/warm-up system. I've already made a few discoveries that I've never seen discussed and might be useful for others.  My plan is methodically characterize what happens with vacuum during the warm-up process.  That way I'll have a clearer idea what I'm talking about.  In the meantime, if anybody knows how to alter the range of the full-load enrichment control pressure I'd love to hear it.  Thanks again and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0