Mercedes-Benz Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
I conducted a Duty Cycle test and these were my findings

Static Test -

DC engine off, ignition on
= (1-(3.5/11.9))*100 = 70.588 % Good result
DC Idle contact
= (1-(10.51/11.9))* = 11.681 % Good result
DC Full Load Contact
= (1-(9.3/11.9))*100 = 21.848 % Good Result

DC running tests

Warmup (.04v fluctations)
= (1-(6.48 to 6.50/13.2))*100 = 50.9 or 50.75 % Expected result of open cycle

1st 2500rpm test saw no change

Than sudden increase while idling (warmed up)

Volts at Idle when warmed up peaked and sat at 12.63 - 12.65 V

2nd RPM 2500 8.3-9.1 V
= (1-(8.3/13.2))*100 = 37.12 %
= (1-(9.1/13.2))*100 = 31.06 %

Indicating a Rich mixture, with an oscillating range of 4-6%

Returned to Idle, Volts at idle where 12.65

3rd RPM 2500 8.5-9.4 V
= (1-(8.5/13.2))*100 = 35.60 %
= (1-(9.4/13.2))*100 = 28.78 %

Indicating a Rich mixture, with an oscillating range of 4-6%

Idle DC % =
= (1-(12.63/13.2))*100 = 4.31 %

Indicative that the mixture is outside of the EHA? Leaning capabilities

Would a test of the EHA (which isn't leaking) reveal anything?
I loosened each injector and noticed an equal degradation to the idle smoothness across every injector, so no particular injector is severely out of whack
I have a spare fuel distributor that I can swap out which also has an EHA, however, the EHA was leaking (possibly at the two mating O-Rings so I replaced them)

Any other ideas that would cause such a rich mixture?
Spark seemed good although I am using a 2nd hand coil and will plan to replace it in the next year or two.
Plugs are new.
Plug leads are about 4 yrs old, and past a test a few months ago.
Rotor Cap is also about 4 yrs old.
The intake manifold has been effectively rebuilt.
I can't see a Vac leak causing such a rich mixture.
 

·
Outstanding Contributor
Joined
·
1,383 Posts
I‘m currently actually not participating in threads here at Benzworld … but you present your information so nicely & clearly that I want to compliment you for that. (y)

Although it is not very relevant in this case, the only information that I miss is what car you are talking about and what your location is. … Before this forum was severely downgraded / damaged on August 20, that information was directly displayed below the member‘s label.

Re your duty cycle results:

The first thing
I suggest to do is check for proper movability of the AFM (air flow meter) and the fuel distributor‘s CP (control piston). I described in detail how to do that in this thread (IIRC): https://www.benzworld.org/threads/no-start-after-filter-replacement-fuel-distributor.2992371/#post17451853

If that is good, I recommend to do a fuel volume flow test at the fuel return line of the fuel pressure regulator. The amount of fuel that comes out of the pressure regulator in 40 seconds should be at least 1 liter, respectively (if you prefer horse-and-buggy units ;)) 0.26 US gallon.

If that is good, I recommend to use a really good injection system cleaning additive for a few hundred miles and check the duty cycle (especially at 2500 rpm) again.

If that does not bring any change, it‘s time to open the FD (fuel distributor) and check its metering slits for cleanness ... or to try that spare FD you mention.

Based on your duty cycle readings your Lambda adjustment screw (commonly & misleadingly called “mixture adjustment screw“) seems to have been tampered with !

BTW, thank you for having posted your test results in this (separate) thread instead of in my Lambda control tutorial thread. :)

H.D.

P.S.: Since last week I have not received email notifications from Benzworld anymore, despite the fact that many replies were posted in another 126-forum thread that I posted in before. If you are interested in further advice of mine, you can send me a PM with your private email. :)
 

·
Registered
Joined
·
3 Posts
Discussion Starter #3
The vehicle is a W126 560SEL 10/1986, Is the CP the plunger poking out the bottom of the FD?, I am in the process of reading that thread and figuring out how to do the first test, I don't understand how you can track that the CP is following the AFM plate on the way up at a quick release when you can't see it, or am I missing something.

I can do the second test quite easily, I know that last time (about 6 mths ago) I did a fuel pressure test going into the FD and had ~6 bar at idle and it dropped to 3bar while running if I recall, Ill do that test again though I may do these tests after I drive home (500km away) where ill put some injector cleaning additive into the fuel, however, I suspect there are minimal issues with the injectors as they were tested a while ago and were all good, though I am planning to test them after I have ruled out every cheap alternative test.

I'll be swapping out the FD after this trip so as to not risk demobilizing the vehicle 1 wk away.
 

·
Registered
Joined
·
77 Posts
That 3 bar does not sound like any of the pressures KE-jetronic could have. At the stickies there is a link to some workshop manuals. There are instructions for fuel pressure measurements.
Also on YouTube Pierre Hedary and MMWA are showing how they measure pressure difference between upper and lower cambers. Do you know what has been played with and what is in original adjustment? If the fuel distributor is not leaking and it delivers same amount to all ports it is doing its job and with the original parts adjustment of lamda screw could be avoided if not already adjusted.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #6
In all honesty, the 3 bar is me pulling that out of my arse because I can't recall the pressure that I measured, I plan to do that test again soon, however as mentioned before I don't want to risk breaking my car before this trip.

Thank you greatly for that document, ill dive into it straight away.

Idle at first start is about 650-700 no more, it will drop down once I engage the transmission to 550-600 and will return to about 600-650 if I disengage the transmission, so the Idle is alright.

Of the things that have/haven't been adjusted, basically everything is stock, except the ICV, I had two ICV, one that was full of gunk but had good bearings, and one that was good but had terrible bearings so much so it couldn't hold a steady Idle rpm, so I adjusted the gunked one after I cleaned it to match the average setting of the bad ICV, which in turn was roughly about right expected.

I do need to clean the ICV again though, hopefully, the heat of it being in a running engine has softened shit up.

Neither FD has been adjusted and to my knowledge neither leak, however that needs to be tested, ill test both outside of the fuel pot when I go to swap them to see if there is any fuel leaking into the lines.
 

·
Outstanding Contributor
Joined
·
1,383 Posts
... Is the CP the plunger poking out the bottom of the FD? ...
Yes.

... I don't understand how you can track that the CP is following the AFM plate on the way up at a quick release when you can't see it, or am I missing something. ...
Yes, you are (missing something). … Please click on the link in post 26 of the thread I mentioned in post 2. You‘ll see in post 22 of that thread that I said:
Push the AFM plate completely down again and this time let it slowly move back to it’s base position and feel if the CP follows the AFM plate (stays in contact with it) along its whole path, which it should.“

This “feeling“ works best if you let your hand jitter a little up & down while you let the AFM plate slowly move back.

Also check for correct rest position and play of the AFM as I described in that thread !

And don‘t touch the Lambda adjustment screw, at least by far not yet … also not if the play of the AFM plate is not correct !

... I can do the second test quite easily, I know that last time (about 6 mths ago) I did a fuel pressure test going into the FD ...
I did not say “fuel pressure test“, I said “fuel volume flow test“ … (at the fuel return line of the fuel pressure regulator).

... ill put some injector cleaning additive into the fuel, however, I suspect there are minimal issues with the injectors ...
I did not say “injector cleaning additive“, I said “injection system cleaning additive“ … (mainly to clean the FD‘s metering slits and other parts inside the FD).

... I'll be swapping out the FD after this trip so as to not risk demobilizing the vehicle 1 wk away.
I recommend to do the things I mentioned in post 2 in the order as mentioned there.

Besides what I said at the end of post 2, I‘m currently quite busy with other things and hope that other forum members can assist you up from this point.

H.D.
 
1 - 7 of 7 Posts
Top