Author Topic: 6.9 K-jetronic rough and high idle cold start  (Read 1443 times)

Jan S

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #15 on: 24 September 2021, 01:27 PM »
Yes, I have opened the file and started reading  :D

I will go step by step. The story will continue ......
1975-mod W116 450 SE with 6.9 engine

Jan S

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #16 on: 03 October 2021, 09:52 AM »
Yesterday I visited a local K-/KE-jet specialist, as part of a local MB enthusiast club event.

He did some quick tests of the CO-level on several cars, including mine (US 1977 6.9). No time nor the event for more extensive tests.

The idle screw was at its end point. Still the idle was approx 900 rpm warm. This is too high -- 700-750 rpm is probably more correct. I suspect the cooling water thermostat is shot, and I need to check/clean the aux air valve.

The engine was running way too rich (CO = 4.14 and Lambda = 0.89). He adjusted the CO and we stopped at CO = 2.17 which is probably still a bit too rich. Anyhow, I will leave it there for now and do a new reading after I have replaced the thermostat and checked the aux air valve (and done the other K-jet tests).

Any comments on the BEFORE and AFTER test results?

Before / After:
CO 4.14 / 2.17 %vol
CO2 11.99 / 12.91 %vol
HC 429 / 359 ppmvol
O2 0.62 / 1.43 %vol
Lambda 0.89 / 0.98

1975-mod W116 450 SE with 6.9 engine

UTn_boy

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #17 on: 03 October 2021, 01:07 PM »
Did the expert think to ask of your intake upper to lower intake manifold plenums had been resealed or not?  This will also cause a high idle and possible a run rich condition if the system tries to compensate for a lean (too much air) condition. 
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Jan S

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #18 on: 04 October 2021, 02:45 PM »
A crowded event, hence not much time for one-to-one discussions. He mentioned vacuum leaks in general.

I will start with the AAV and the termostat, and take it from there.
1975-mod W116 450 SE with 6.9 engine

Jan S

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #19 on: 24 October 2021, 11:19 AM »
Yesterday I replaced all 8 injectors inclusive the rubber seatings.

They had to go - old and rubber seatings were stone hard.

I tested them with a borrowed tester - both new and old. Spray patterns were fairly ok, but half of them leaked and had a tendency to squirt instead of a "fine shower". New injectors were fine.

Unfortunately the tester had a diesel gauge 0-3000 psi - impossible to check release pressure in the range 3.5-4.5 bar. Good enough for now.

Car started immediately. But rough idle cold is still there. Cleaning cooling system and replacing thermostat this week. Then the newly inspected, tested and cleaned AVV will work as it's supposed to.

1975-mod W116 450 SE with 6.9 engine

TNNBENZ

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #20 on: 26 October 2021, 08:36 AM »
   Is the idle lean or rich. Do you smell gas, any smoke or gas smell from exhaust pipe ?  At this very moment I am watching a video on the k-jet system.   Pierre Hedary on youtube.
He is not as good as uncle Kenny but he tries... :P ha
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ptashek

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #21 on: 26 October 2021, 10:01 AM »
He is not as good as uncle Kenny but he tries... :P ha

His presentation skills are mediocre, but I'd rather watch Pierre making sense in a weird way, than Kent waffling about to sell more of his stuff.
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TNNBENZ

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #22 on: 26 October 2021, 10:10 AM »
Yesterday I replaced all 8 injectors inclusive the rubber seatings.

They had to go - old and rubber seatings were stone hard.

I tested them with a borrowed tester - both new and old. Spray patterns were fairly ok, but half of them leaked and had a tendency to squirt instead of a "fine shower". New injectors were fine.

Unfortunately the tester had a diesel gauge 0-3000 psi - impossible to check release pressure in the range 3.5-4.5 bar. Good enough for now.

Car started immediately. But rough idle cold is still there. Cleaning cooling system and replacing thermostat this week. Then the newly inspected, tested and cleaned AVV will work as it's supposed to.
Fuel return line maybe blocked ???
Neglected ~ Rescued ~ 1977 450SEL 4.5L  U.S.A. ver.
Project of Compassion ~ Respect
Silver Green Metallic / Toast
Left Hand Drive
Sliding Roof

Jan S

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Re: 6.9 K-jetronic rough and high idle cold start
« Reply #23 on: 28 October 2021, 03:53 PM »
I measured the CO before I replaced the injectors. Idle varm 2.18%vol. So I would say a bit rich?

Next on my list:
-- to clean the cooling system and replace the thermostat. That will result in a fully closed aux air valve when warm (the valve has been cleaned and tested. Fully closed at 80 deg C). That job will be done 1-2 weeks from now.

-- adjust idle to 700-750 1/min (warm), if possible

-- a new CO test and adjustment

-- do the tests described in the k-jet manual, including searching for vacuum leaks.
1975-mod W116 450 SE with 6.9 engine