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6.9 K-jetronic rough and high idle cold start

Started by Jan S, 10 June 2021, 05:36 PM

Jan S

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

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

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. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1979 450sel 516 red/bamboo

Jan S

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

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

   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
Neglected ~ Rescued ~ 1977 450SEL 4.5L  U.S.A. ver.
Project of Compassion ~ Respect
Silver Green Metallic / Toast
Left Hand Drive
Sliding Roof

ptashek

Quote from: TNNBENZ on 26 October 2021, 10:36 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.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE

TNNBENZ

Quote from: Jan S on 24 October 2021, 01:19 PM
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

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

Jan S

NEW PROBLEM  >:(

All new/renovated parts have been assembled (radiator, hoses, thermostat, thermostat housing, etc.) and new coolant has been added (50-50 Comma antifreeze and demineralized water)

Engine started immediately (hasn't run since oct/nov 2021). Always a good sign ;D.

I let the car idle for 15 min. It seems the coolant doesn't reach the correct temperature. That means the aux air valve (AAV) doesn't fully close, which means idle is still too high (900 rpm).

The thermostat is new. What can be at play here?
1975-mod W116 450 SE with 6.9 engine

UTn_boy

Did you install an aftermarket thermostat or a genuine Mercedes thermostat?  Aftermarket thermostats are often bad out of the box.  Also, have you confirmed the engine temperature with an infrared thermometer to make sure your gauge and/or temperature sending unit isn't reading incorrectly? 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1979 450sel 516 red/bamboo

daantjie

Maybe you have some air bubbles stuck in the coolant path  however in my experience this usually leads to rapidly rising temp on gauge. 
Let it cool down then "burp" the coolant tank by opening the cap.  Also you can run the heater when you start it again to make sure the coolant is circulating through the heater core.  Might have to burp it a few times to get all the air out.
Daniel
1977 450 SEL 6.9 - Astralsilber

Jan S

Quote from: UTn_boy on 09 January 2022, 12:42 PM
Did you install an aftermarket thermostat or a genuine Mercedes thermostat?  Aftermarket thermostats are often bad out of the box.  Also, have you confirmed the engine temperature with an infrared thermometer to make sure your gauge and/or temperature sending unit isn't reading incorrectly?

Yes, I bought an aftermarket thermostat (Mahle). I will buy a Mercedes part next week to eliminate that uncertainty.

No, I haven't measured the temperature with a thermometer. I can touch the big radiator hose (from thermostat to radiator inlet), and it doesn't feel warm .... I would guess 60 deg C. This is very subjective.

Where should I measure? Thermostat housing cover, or the big hose?

I will also force-close the AAV by putting a plug in it (after the engine is warm), just to see what happens when the AAV is definitely closed.
1975-mod W116 450 SE with 6.9 engine

Jan S

Quote from: daantjie on 09 January 2022, 12:43 PM
Maybe you have some air bubbles stuck in the coolant path  however in my experience this usually leads to rapidly rising temp on gauge. 
Let it cool down then "burp" the coolant tank by opening the cap.  Also you can run the heater when you start it again to make sure the coolant is circulating through the heater core.  Might have to burp it a few times to get all the air out.

Yes, I had bubbles in the system before this job (the heater made gurgling-noises, very irritating). And yes, I forgot to turn on the heater today.
1975-mod W116 450 SE with 6.9 engine

goldacre

Hi JanS, was reading how the gubbins under the plenum which is in 2 parts can cause high idle if the rubber connectors are perished, they are out of sight out of mind so can cause vacuum leaks to affect idle but in my situation was isolated to cylinders 7 and 8 have a leak somewhere and idle was very rough, we worked this out by getting gas cylinder and unscrewing the connection to bbq so keeping the hose and regulator on cylinder then turning on the gas and gently poking the hose down into the plenum area, idle smoothed out in and around cylinders 7 and 8 so this caused the suspicion a vacuum leak (Propane is high octane around 110 I think ). Parts arrived from classic centre and included everything rubber for the Inlet system, and TJ450 donated new inlet manifold gadgets a while back, these parts presently on car are 43 years old...  :-\

while your at it check for vacuum at the hose on the right hand side of the engine as you face it, this is connected to the inlet and provides the vacuum for the positive crankcase ventilation, the 2mm venturi was blocked and when cleaned and refitted my idle screw had to be wound down quite a fair way. Will start this repair process soon and if can get pics on Org will do a thread on it  8)

Good luck!

G
12/1979 450 SEL 148K on clock (museum piece)
12/1986 Lotus Esprit Turbo 87K on clock 'Darling, look what Q has brought for us, isn't it nice' :)