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Re: fuel questions

-- [ From: Huw Powell * EMC.Ver #3.1a ] --

>I think we're (I'm) getting somewhere.  I managed to find a (less old)
control pressure regulator and frequency valve out of another MB today, and
put it in the car.

Nothing like a bad CPR to screw up a car.  I've used one from a Volvo with
success.  I hoard them now.  

>But it fixed the bulk of the problem.  Now I would like to establish a
definitive metric for my "old" and "new" valves - so that I can recognise
the condition again.

Measure the control pressure being sent back to the fuel distributor, from a
dead cold start.  It should be about 10 psi and then rise to about 50 psi if
it's working properly.  You'll need the Bosch tool for this.  handy
elsewhere in the fuel system, too.

>How can the duty cycle be adjusted?

Unless your car is really weird (and we know it is!) use a 3mm allen key in
the little hole between the fuel distributor and the rubber ribbed air
thingie.  You are adjusting the overall mixture by doing this.  CW = richer,
CCW = leaner.  I'm not sure if this is how yours will work, since in our US
cars this interacts with the OXS to maintain appropriate mixture.  The duty
cycle just represents the computers response to the system, and at idle is
usually set for about 50% which I presume gives it plenty of room to go
either way under load conditions.

One is actually supposed to set the mixture screw using a CO meter on the

BTW by changing the screw you are raising and lowering the pivot of the air
flow plate, which changes the amount of fuel flowing relative to the amount
of air passing the plate.  Then the duty cycle changes to compensate and
return the system to the correct mixture.

I think with the US system the only way to really change the mixture is to
mess with the OXS output to fool the computer.

Folks, feel free to correct all my errors....

Huw Powell
HUMAN Speakers

Sufficiently advanced magic is indistinguishable from science....