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

Ben Swann benswann at verizon.net
Tue Oct 23 15:14:35 PDT 2007

Sensors are either new or clean.  This is basically a brand new engine and all
components either new or rehabbed.


I’d buy the cylinder pressure hypothesis except this happens even without any boost, or
I guess that is that what you are saying.  This is strictly RPM related.  This is
basically using the distributor from a 200Q20V, and that I know from experience gets an
easy 7k RPM..


Would be nice to have an oscilloscope, but I seriously doubt it is the sensor – it would
have thrown a code.  Flywheel is like new.


I’m wondering if the pulse width setting on the injection system is not right and the
injectors are simply maxing out at RPM.  That seems like another possibility than
ignition.  I need to check this in my MS settings.  I did some math:


I have a Max pulsewidth of 11.9 msec that I see in the log.  


5500 rev/min|min/60sec|sec/1000ms|=.0917rev/ms  -> 10.9ms/rev @ 5500 RPM or roughly


Roughly @6000RPM is 10ms/rev


So if my max pw is 11.9 but if a rev. happens in only 11 ms then the injector pw > rev,
so injector is open 100%.  


So I don’t know if some setting can be changed to compensate or I need bigger injectors.
I’m still on the megasquirt learning curve.


Or is it ignition?





From: mike schowengerdt [mailto:urdrquattro at yahoo.com] 
Sent: Tuesday, October 23, 2007 5:11 PM
To: Ben Swann
Cc: urq at audifans.com; quattro at audifans.com
Subject: Re: [urq] EFI + MAC-14 maxing ataround 5k RPM


my thoughts.........not ign coil, that's mostly likely a problem under cylinder
pressure/spark load.......

possible ignition rotor, i've heard of problems due to the wider contact on the outer
end of the standard replacement part..........experience and gut feeling says to pull
the RPM sensor from the bell housing and check for small metal debris that can mask the
signal @ higher RPMs, especially if the starter teeth are worn.

if that looks OK, try a different sensor while you already have it out,BTDT...adefinate



----- Original Message ----
From: Ben Swann <benswann at verizon.net>
To: urq at audifans.com; quattro at audifans.com
Cc: Ben Swann <benswann at verizon.net>
Sent: Tuesday, October 23, 2007 8:41:43 AM
Subject: [urq] EFI + MAC-14 maxing ataround 5k RPM

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.

I swapped coils and it made no difference.

>>>.  Cap and Rotor are
new.  Engine now has about 2000 miles on it and still running on the break-in oil.

>>> – the cutout occurs at around 5000 RPM even just opening
the throttle without any engine load.  

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?  



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