In tank injection pumps,interesting (?) facts.

[Chris Wilson <chris@maximum-bhp.u-net.com>]

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 
parts...
 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?


-- 
    Best Regards,
                 Chris Wilson
http://www.maximum-bhp.u-net.com
mailto:chris@maximum-bhp.u-net.com