MAC11 help needed

[Ben Swann]

Rick,

That sounds like a bad signal from the O2 sensor - your mixture is off.  Timing should
not be a problem unless pushing the envolope of performance - that is not happening at
low boost and RPM. Also I read you may not be using CIS for fueling and that may change
some things - big time!

With MAC-11 ignition - if the car starts and runs, then it will run until high RPM
unless bad rotor/cap/coil misfifre/bad wires, etc.  I'd be looking at the fuel side of
things right now unless the ECU is competely hosed.  If you have the engine started and
running through 2000 RPM the should continue to do alright to 6000+ RPM if ignition
essentials are in basically good working order, then  Don't get sidetracked by your
hypotheseis below - BTDT.  It is possible that the coil trigger signal to the EFI is
off, but not likely either.

BTW what is the fuel delivery to the EFI - I have been struggling for about 2 years to
get mine straigh - using Megasquirt, but expect same sort of operation, especially as
RPM increases.  The CIS pump/tank setup on my UrQ is not proper for an EFI setup -
cavitation problems due to lower fuel pressure setting with EFI than stock CIS.  I am
fairly certain of this after much trouble-shooting and analysis    I suspect 4000 Q is
similar. 

I believe my ultimate solution is an in-tank pump or pre-pump with surge tank to main
pump solution.  If someone knows differently - I'd sure like to know.  In fact am
looking for an interim solution for a pump that is designed to operate at between 35 and
60 PSI rather than above 60 PSI as for  CIS.

Suspect this will evolve into different thread - if so change the subject line please to
something like "Fuel delivery for CIS to  EFI conversion".

Ben

[Date: Sun, 31 Aug 2008 19:00:06 -0400
From: "Rick Houck" <rhouck at neo.rr.com>
Subject: MAC11 help needed
To: "Quattro List" <quattro at audifans.com>
Message-ID: <003101c90bbd$4f7d3560$6401a8c0 at rick>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

patient is coupe quattro conversion (dedicated track car) with 10v turbo 
(MC1 w/one knock sensor) motor. I can get the car started and running up to 
2000 to 2500 RPM before it starts backfiring. Can hardly get up to 3000 RPM 
even with throttle floored. The flywheel "0" mark, the cam mark, and the 
distributor mark all line up properly. If I move the distributor off the 
mark (advance) while running, it will rev like normal, but won't start after 
shutdown. I can move the distributor back to initial position and it starts 
right up.

I suspect that something is causing the timing to retard, but I have swapped 
out the ECU, complete distributor, the cap and rotor, plugs, wires, RPM and 
flywheel sensors. I plan to try another knock sensor, but can't figure 
anything else that would cause a properly running engine to start backfiring 
like this. BTW, after the problem, I took the opportunity to install my 
newly rebuilt engine, and the problems are the same, so I can rule out 
mechanical issues.

I have been using the 034 Motorsport EFI, and there is no sign that it is 
going lean or rich when this occurs. My fuel pressure (aftermarket FPR) 
rises slightly as revs come up as I would expect with the start of boost. 
Besides, the timing seems to be the thing that has changed, as evidenced by 
the regular running after advancing timing.

It acts as though the timing reference pin is in the wrong place, but it has 
been running fine for 8 years and the problem came on gradually during some 
rainy sessions at Watkins Glen in May. Thought something must have gotten 
wet, but after swapping everything I can think of, nothing has changed.

The pin is still on the front side of the flywheel, but it does not line up 
with the pickup when the crank is at "0" and the distributor and cam marks 
line up. Is this right?

Any help appreciated,
Rick
Pulling my (gray) hair out!