RE ; MAC11 update

Rick Houck rhouck at
Tue Sep 9 19:37:39 PDT 2008


I have read through the suggestions on SJM's site, and feel that I have 
tested or eliminated things sufficiently, but since I have not yet found the 
problem, I am obviously missing something. Opening the ECU was one of the 
earliest things I did, since the problems started at a rainy track event. I 
found no evidence of moisture or water tracks, but dried it out in the sun 
just to be sure. After no improvement, I ordered a spare ECU and distributor 
from Force5.

I have at least two of each of the major ignition and mechanical components, 
and I have tried about every combination of ECUs,plugs, wires, dist caps and 
rotors, complete distributors, coils, flywheel RPM and TDC sensors, knock 
sensors, fuel filters, and COMPLETE ENGINES. Nothing so far changes the 
situation except turning the distributor counter clockwise.

It seems unlikely that I have two identically bad components, but maybe I 
do. It also seems unlikely that both engines have a sheered key on the cam 
or crank, but the relationship between the distributor rotor and the TDC 
trigger is good enough for starting but not for running at higher revs. The 
ECU is getting full voltage during the problems, and I also have confirmed 
ground (don't remember pin numbers now). As Ben says, ignition seems to be 
satisfied enough to start and run properly for the first 25% of the RPM 

Cody, I have some very loud exhaust backfires (3" from turbo back with no 
cat), but others come back into the intake system. I have been concerned 
that I may damage my turbo or intercooler plumbing. This indicates to me 
that the timing is getting confused at some RPM, or that the plug is firing 
at an improper time because of arching. When I changed plugs last week 
(again) the Bosch's had a dry carbon coating, but IMO nothing out of the 
ordinary for an engine running at low speeds. New plugs are NGK's, but 
results are the same.

about to give up

----- Original Message ----- 
From: "Louis-Alain Richard" <laraa at>
To: "'Rick Houck'" <rhouck at>; <cody at>; "'Ben Swann'" 
<benswann at>
Cc: <quattro at>; "'P Cole'" <pcolegrps at>; "'Ado 
Sigal'" <a.sigal at>
Sent: Monday, September 08, 2008 11:11 PM
Subject: RE ; MAC11 update

Well Rick, I have no answer to your turbo question, but before looking for a
mechanical failure, which is always possible but usually shows some
evidence, please complete the ignition route first.

If I remember well, you never mentioned any diagnostic at the MAC-11 ECU
itself, just that there was no codes ? I would open the ECU to see if
there's any water or corrosion in there. If not, I am sure there is a way to
test the boost pressure transducer in situ without an oscilloscope but with
a mighty-vac and an adjustable timing light, or something like that.

I once had to find a running problem on a friend's urQuattro, and an ECU
swap was the solution. But we arrived there after completing the whole
official diagnostic procedure, which is long and fastidious, and the ECU
replacement was the very last step.


> -----Message d'origine-----
> Guys,
> I think things are pointing to a wiring problem, but have a couple of
> questions first: Could a turbo that doesn't spin as easily as when it was
> new cause backfires?  My Garret GT2871 ball bearing turbo still spins up
> (as
> I can see when the cone filter is off), and I can hear it coast down after
> shutdown, but it is not quite as smooth as when it was new 3 years ago. I
> have not checked end play, but it certainly is not enough to cause any
> contact with the housing. I can't get enough RPM to get the boost up much,
> but it does get started up the dial before the backfires start.
> I don't have an o-scope, but I think it is time to find someone who does.
> Rick

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