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Old 07-14-2002, 08:26 AM
michael dunlea
Posts: n/a
Question 1989 260SE will not start also S420 1994 auto

I have a 1989 260SE that starts when cold and runs for five mins on high idle when returned to idle engine cuts out and will not start.I have replaced fuel distributor and controll unit still no start I have fuel pressure and fuel delevery to spec any help would be great.Car will restart the next day and do the same thing.

looking forward to your reply
Mick Dunlea

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Old 07-14-2002, 10:25 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Sounds like a huge vacuum leak.

Simple way to test. Get control of the throttle under the hood. Start the motor and keep it running with one hand. Now take the other hand and gently press down on the airflow plate. This is going to add fuel. Now start to release the throttle while increasing the airflow plate fuel addition (actually while using the plate to achieve the best running mixture).

If you have an airleak the fuel you are adding will give correction for the unmetered air coming from unknown source (when your finger gets it right). This will eventually leave you with the throttle closed and the airflow plate depressed a relatively exact amount and an engine running at the speed determined by all the air entering the motor.

Based upon the fact that the car dies I am guessing that with fuel corrected manually the engine will probably run over 2000 rpms in these conditions (if I'm right).

Remember two things. One engine speed is determined by the amount of air not fuel (fuel amount can only reduce speed if wrong) and two, the airflow plate adds fuel when going down and subtracts coming up. Manual correction in each direction can over ride normal system control and provide a huge diagnostic technique.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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