[urq] EFI + MAC-14 maxing ataround 5k RPM

Ben Swann benswann at verizon.net
Wed Oct 24 06:37:35 PDT 2007

More like the engine is "breaking up" and not a direct hard cut like you would get with
a fuel-pump relay cut.


Timing should not be an issue - it is digital setting and unlike the 5 window hall
sensor ignitions, the single window hall coupled with the 2 flywheel sensors is either
working or not.  There is no adjustment, only that the distributor is best set directly
in the middle of the hall window.  The ECU adjusts the timing according to RPM and load
and you can not vary the timing by moving the distributor - although you can stop the
car from running if you move it "out of window".


I know what you are saying about "distributor slop", but it is not happening.  With
distributor set dead middle of window, even if timing belt were flopping all over the
place, you would not get out of window.  I have seen where mis-adjustment causes a
random no-start condition.  In these cases, the timing belt was off a tooth or someone
retarded the cam sprocket and distributor skewed to edge of window.  Sometimes it did
not sync. with the flywheel sensors - usually when cold.  The fix was to properly adjust
timing belt and set distributor middle of window.  In one case is was because  someone
was trying to get more top-end by retarding the cam, but did not bother to reset the


We can be assured timing belt, cam and distributor are set right - checked and
double/triple checked.


I have contemplated installing a 5 window hall distributor and ecu from non-turbo car
just to check the ignition.  This would be a "last resort" if I don't find something
wrong with Megasquirt settings or injectors or some reason ignition is breaking down at





From: Mike Sylvester [mailto:mike at urq20v.com] 
Sent: Wednesday, October 24, 2007 8:28 AM
To: Ben Swann
Subject: RE: [urq] EFI + MAC-14 maxing ataround 5k RPM


I see there is a lot of action on this thread that I don't have time to read, so maybe
this was already mentioned...

When you say cut-out, I don't know if you mean a total shut down like an over boost
situation in a stock ECU or just gets flat at 5k.


If it just gets flat at 5k, it can be from incorrect timing.


I'm sure you know how the timing works with the two sensors on the flywheel and the hall
sensor in the dist.

The TDC pin must line up when the shutter wheel window lines up with the hall sensor in
the distributor for the card to start.  After the car starts you can actually un-plug
the hall sensor and the car will continue to run, however, I believe if the ECU doesn't
see the hall sensor signal with the TDC singal it will retard the timing above a certain


It is possible that the timing is such that on start up the TDC pin lines up in the
window but at speed there is enough play in the timing belt etc that it is outside the


www.urq20v.com <http://www.urq20v.com/> 


-------- Original Message --------
Subject: [urq] EFI + MAC-14 maxing ataround  5k RPM
From: "Ben Swann" <benswann at verizon.net>
Date: Tue, October 23, 2007 9:41 am
To: <urq at audifans.com>, <quattro at audifans.com>
Cc: 'Ben Swann' <benswann at verizon.net>

I think it is safe to rule out fuel delivery as a problem with my EFI'd engine now that
I have replaced fuel pump and assured getting good fuel delivery at all times. So back
to the problem. I think the ignition is dropping out at around 5000RPM, but at a loss
on how to verify it and how to fix it. To review, the engine is completely rebuilt MC-1
with NF head being fed by Megasuirt V2.2 fuel injection through 42 lb injectors - need
to verify as these are Lucas Bluetops, and might be 36#. 

For ignition I am using the MAC-14 with dual knock sensors. I have the car tuned fairly
well by now in the below 5000 RPM range, and the engine runs great and pulls hard until
it hits about 5000 RPM. It doesn't matter what load and engine can be free-revving and
still reaches about a maximum of 5000 RPM. If I gun the engine briefly, the tach will
hit 6K or so, but gradually increasing RPM it will go to about 5300 RPM and seem like it
is hitting a rev limiter. Holding the throttle open, the engine bounces - the RPM
oscillates between like 4800 and 5400. Occasionally I have seen 6000 RPM and holding,
but not able to maintain that result.

Things that can be automatically ruled out:
Fuel pump relay - this does not apply, as I am providing continuous power to the fuel
pump with a direct feed of #10 wire direct to the pump - relayed of course, but always
on with ignition. Once I get engine tuned, I'll enable cutout relay circuit - that can
actually be done through MS.

Fuel delivery - I have set at 45 PSI and it maintains good pressure with regulated flow.
There is a pressure port on the regulator that can vary fuel pressure about +/- 5 PSI
depending upon load/manifold pressure. I see not reason to suspect there is inadequate
fuel flow or pressure in the rail.

There are no codes from the MAC-14. Most of the fuel injection portion has been
disabled and only providing power to O2 Heater at this time. MAC-14 is being used
mainly for ignition only.

I swapped coils and it made no difference.

I pulled wires one by one and no one cylinder deviates differently from the others I
will check plugs and do compression test - again. When I installed the engine, I had
even compression on all cylinders - consistant with a new engine. Cap and Rotor are
new. Engine now has about 2000 miles on it and still running on the break-in oil.

It does not make sense that it is EFI since the cutout happens regardless of how the
engine is being driven or not - the cutout occurs at around 5000 RPM even just opening
the throttle without any engine load. If it were fuel, I'd think it would happen only
under load. Possibly the injectors are maxing out, but this does not make sense, as it
should not take much fuel to rev the engine without a load. I also don't notice any lean
condition when the problem occurs - seeing like a 12:1 on the O2 guage. Still I won't
rule out fuel injectors, but ..

I think there is some reason the ignition is dropping out - like not enough current to
the coil when the engine hits around 5000 RPM. There is of course the long run from the
battery located under the seat. I ran an additiona #6 wire to a jumper post located
near the coil and then runs down to the starter. Although the engine cranks faster when
starting, the RPM limit problem is still there. 

I'm wondering if the coil is not saturating, and not enough current is available at
higher RPMs. Why this would happen on this car and not on a 200? 

It doesn't make sense - this balanced engine should be good for well over 7000 RPM. I'm
going to post on some other forums - Megasuirt and MotorGeek, but this seems more like
an ignition problem where the MAC-14 is providing the ignition. Maybe installing a
capacitor or battery up front to test.I'm looking for ideas.


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