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Old 07-31-2004, 12:16 AM
Registered User
Join Date: Feb 2001
Location: grand rapids mi
Posts: 5
Idle problems and stalling 450SEL

I'm having trouble finding the source of poor/no idle and stalling of my 1980 450SEL. Unfortunately I have been guessing and replacing components without a logical diagnostic plan. My first question is what type of CIS do I have? Some sources state that the K-Jet and the K-Jet w/ Lambda have a cast iron fuel distributor painted black where as a KE has an unpainted aluminum fuel distributor. Mine is aluminum and have a frequency valve mounted on the left and a O2 sensor on the exhaust manifold (one). Evidently MB stopped making the electronically-controlled CIS in 1976 why would it be called a KE? Could some one direct me on a sane diagnostic pathway? I have replaced injectors,plugs,wires, distributor cap,rotor, intake manifold gaskets and intake sleeves and throttle body gasket sleeve,fuel filter,checked and replaced vacuume connections. Fuel pump output volume and pressure are within normal limits. Hard start,poor idle and stalling persists. Any comments or suggestions would help. Thanks Spencer S.

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Old 07-31-2004, 03:59 AM
afmcorp's Avatar
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Join Date: Jan 2002
Location: NW Indiana LaPorte
Posts: 571
i don't like beating a dead horse cause i know some may not agree with me but start looking at your ignition's primary wiring. your car is going on 25 years old. check all the connections replace wire where it is corroded or the fittings look corroded. the external resistors too. get all the juice you can to the distributor which will give you a stronger secondary spark.

with all that you've already replaced that ought to do it. i discovered this problem on my 72 350sl [450 eng]. that was all that was wrong.

another thought might be to check the charging system to be sure you're getting the 13.6 volts from the altenator.

good luck
Thanks Much!

1972 350sl Red/Blk 117k
1988 420sel charcoal/Blk 140k
1987 420sel gold/tan 128k
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Pound it to fit then Paint it to match!

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Old 07-31-2004, 11:32 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Well I'll need more info to come to any conclusions for repair. It is of little use to know what you replaced. What is more important are symptoms and test values.

What I can tell you about is what you are working on. You are working on a K-jet w/lambda car. The first and only year it was used on 450s. The previous system that started in 1976 was a plain K-jet with no electronic controls all hydraulic.

K-jet w/lambda was used on V8s from 1980 till 1986 when KE was started. All replacement fuel distributors for all these versions are currently aluminum and only early K-jets used the black cast iron units.

Most important to your car is the frequency of the frequency valve. It can be measured and used to adjust the idle mixture by monitoring pin #3 of the diagnsotic socket on the left fender well. Timing is also still adjustable and very important on that model. I'd bump it 5deg over factory setting.

Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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