Troublesome ur-quattro

[quk@isham-research.demon.co.uk (Phil Payne)]

Spent another frustrating day up at John Robinson's, looking at his
ur-quattro.  It has me fooled, so here goes:

MB engine (think MC-1 with a couple of tweaks, no smog).  MAC12D ECU -
MAC11 with emission control removed.

Hybrid (i.e., non-stock) turbo - exact characteristics unknown.  K&N
filter, ported head.

Sypmtom - car goes like a train to 6000rpm in 1st gear, 5700 in second,
etc., 4500 in 5th.  The feeling is peculiar - it's like the throttle
cable starts to slip.  The engine doesn't cut or miss - it just stops
trying.  _VERY_ abruptly.

No other observable problems (but see last note).  No codes.  Hoses
perfect.  Chassis grounds perfect.  Fuel injection swapped (system
pressure, control pressure, frequency valve, metering head, air mass
sensor) for two other cars.  All ECU-attached sensors pass diagnostics.
All ECU diagnostics run.  ISV diagnostics passed.  Knock sensor (G61)
checked against 20V specifications (there are none for the MB).  ISV
current nominal 430ma at 800rpm.  Small hoses MityVacced, large hoses
water-tested.

Latest test is with a metering head custom built by KMI to deliver more
fuel at the top end.  Car runs slightly less lean and not so hot - still
has the cut-off.

Only inexplicable peculiarity - if you disconnect the fuel injection in
the approved manner, _very_ little fuel escapes.  Two or three minutes
later, the contents of the accumulator seem to erupt out of the supply
line like a fountain.

--
 Phil Payne
 Phone: 0385 302803   Fax: 01536 723021
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