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In tank injection pumps,interesting (?) facts.
I have changed several in tank Bosch injection pumps this last year.Not
all Audis,but all from the same Bosch family.All showed similar
signs.First a noticeable noise,later,especially on turbo cars,a marked
deterioration in performance due to running weak.Fuel flow delivery tests
on the return from the metering head showed figures of about half that the
manufacturers recommended.(950 cc's in 30 seconds).
In all cases a new pump cured the noise and the misfiring under boost.I
had intended to cut an old pump apart,to see _why_ they failed,but until
today had no time.
So,in case anyone is curious as to what happens,here goes:-
I turned the commutator ends off 3 pumps,all had done over 90k miles,and
less than 110k miles, although hours operation would be a more meaningful
benchmark.In all 3 cases the brushes were worn,but not excessively.The
commutators in all 3 were worn down into an over 25 thou ridge (50 thou
reduction in diameter where brushes rub.This seemed a lot,but the
undercutting was still present.
I then removed the armature and magnets assembly,with the pump end
attached.No signs of wear in the spindle bushings.So I disassembled the
roller pump itself.In all three cases the problem was the same,and
obvious.From new the outer part of the pump seems to be coated with a blue
teflon coating.This had broken down / worn through,and the rollers had
eroded a perhaps 25% area of the outer circumference of the pump body.this
formed a step about 15 thou deep in all cases.The rollers themselves had
suffered damage,and showed signs of brinneling.
What's the point of all this? Nothing other than the interest element.If
Bosch made the pumps capable of disassembly without machining apart,the
pumps could no doubt be rebuilt cheaply,given the availability of pump
A number of questions are raised.Does the teflon coating suffer more with
unleaded fuel passing through it than with leaded with its associated
lubrication from the lead content?
What would a Bosch mechanical metering unit make of a drop of upper
cylinder lubricant in the fuel?Would this prolong the (expensive) pump
life without messing up the metering capabilities of the unit.(Bear in
mind the "slots" in the head are microns wide and laser cut).
BTW I have now got a source of correctly rebuilt and flow tested metering
units,and warm up regulators.Due to the (typical) pitiful performance of
Bosch in supplying genuine factory replacement metering units,I
investigated alternative sources,and we can now supply metering units at
around half the price of a Bosch unit,with reliable turn round times.
Anyone else find Bosch's UK service a joke?