Author Topic: 6.9 K-jetronic rough and high idle cold start  (Read 1134 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