My VW Scirocco has a Bosch fuel injection system. A warm-up mixture control device is bolted to the side of the cylinder block. Although there appears to be little to wear out or go wrong with this unit, it does drift off optimum setting with time. Whilst to some extent this can be offset by adjusting the mixture control on the main injector control unit, a point is eventually reached where starting becomes difficult or impossible.
Replacing the warm-up mixture control unit solves the problem but these are relatively expensive and becoming increasingly difficult to find. Is there any way these units can be "Tweaked" to restore correct function?
Regards,
Tony Lee.
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Tony
Warm-up fuel-pressure regulators are almost totally reliable and have nothing to do with starting. How are you testing this "drift" and how far out of spec are the pressures.
Once properly set up; a K-Jetronic should almost never need touching.
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Screwloose,
The history behind this goes back several years. From the beginning I was impressed by the instant starting and the ability to just drive off even on the coldest mornings. The first incling of change was a note on an MOT test report of a very low CO level indicating too lean a mixture. Tweaking the mixture screw cured this for a while but the problem returned, cured by more tweaking until the point was reached where starting became difficult. From cold the engine would fire and then stop after a few seconds, presumably after the auxiliary starting injector cut out. After consultation with my friendly garage mechanic and an RAC engineer I decided to fit a new warm up mixture control device. Result - instant cure.
That was a few years ago. Recently, probably as a result of change of usage, I found that if after a run the car was left to stand for half an hour or so i.e. the engine had cooled but was not cold, the engine would not start. Tweaking the mixture control half a turn rich enabled a restart and I then backed off the mixture to drive home. Fitting a new warm up mixture control device again provided an instant cure to these starting problems.
As stated in my original enquiry, there appears to be little to go wrong with these devices, but obviously the balance is critical for correct operation. The drift with age is towards a leaner mixture. I wonder if the judicious placemnt of a washer could restore correct functionality. The question is, should this washer be placed under the bimetallic strip to reduce pressure on the diaphragm or under the spring to increase this pressure, and how thick should this washer be?
Any insights would be helpful.
Regards,
Tony Lee.
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Tony
You've created your own problem. If it was running lean; then it needed the cause finding, not covering up by adjusting the arm screw.
You've now gone so far adrift on the setting that it's put the whole system out of kilter and weirdness has ensued. The warm-up regulator only adjusts the control pressure a little; it may not be able to compensate for massive maladjustment as it ages.
Instead of adjusting; on these systems you work systematically through the pressure and flow readings to find any abberations.
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they can be messed around with
i think the 16v wur fits the 8v, the 16v unit can have the anti tamper cap on the rear drilled out and the warm pressure ajusted via hex key
cold pressure can be ajusted via drifting part of the internals one way or the other
id suggest you search www.clubgti.com for "wur mod" and you will need a suitable pressure gauge and co meter
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