MAC11 update

Ben Swann benswann at
Wed Sep 10 12:34:06 PDT 2008

Second that remark - signaling to the coil might be correct, but that amplifier does
require a good ground as does the coil.  I invariably put them all into one common point
that tie together in a standoff post on firewall with at least #6 wire running back to
the battery post - even if the car is a giant ground strap itself.

You will also want to examine the positive feed to ECU - I noted some of the "stock"
wiring to be seemingly marginal to support a load of a coil, yet seems all goes through
the ECU - with possible exception of the coil positive feed itself  - I forget how that
is, but may be something to check.   However, typical coil feed breakdown would occur at
more like 7000 RPM, not at 2K I'd think.

Still I believe it to be something else than ignition.  I swore up and down I had
ignition problem on my Megasquirted UrQ with MAC-14 ignition and pretty much went
through the same things as Rick.  It really turned out to be EFI pulse width was too
high - injector duty cycle longer than the engine rev.  In addition I had and still have
a serious fuel delivery problem that is not easy to diagnose or resolve.  

On the fuel delivery issue, I believe - an educated belief with lots of trial and error
- that the tank and pump are not designed to support the type of fuel flow and pressure
an EFI system requires.  Basically with the lower pressure of the EFI Rail, the fuel is
pulled into the pump faster than the tank can deliver ultimtely resulting in cavitation.
Originally the problem reared its head at around 5-6k, but once thing get warmed up, the
car will sometimes barely get out of its way - sucking - starving - bucking.  Changing
pumps and lines have helped to a degree, but it seems I either need to find a pump that
delivers a lower flow, a surge tank setup, or get a completely different tank with
submersible pump.  If Rick has not experienced this yet with his setup, I suspect he
will as the 4000Q tank/pump are nearly identical to the UrQ.  And it feels like a
ignition problem, but not!


-----Original Message-----
From: John Cody Forbes [mailto:cody at] 
Sent: Wednesday, September 10, 2008 3:14 PM
To: Ben Swann; quattro at; Rick Houck
Subject: Re: MAC11 update

DING DING DING Ben just found a possibility that I haven't seen suggseted nor checked
yet. Check the engine's ground strap for cleanliness and tightness. Then check it again.
Maybe, just maybe, the ground is not good enough to allow the ammount of current flow
required at higer-than-idle RPM's.


Ben Swann wrote:
> Cody,
> That is a good clarification - what this also means is that in order 
> for the primary signal to be generated, both flywheel sensors need to 
> be present and signaling and they must sync. up with the Hall sensor 
> in the distributor cap.  This also triggers the fuel pump.  From then 
> on out, the primary goes through the Darlington Transistor/signal 
> amplifier mounted on the coil then through the coil, cap and rotor and 
> out through the wires and plugs to ground.  So the only things that 
> could be breaking down are coil, cap, wires or ground.
> Once again, unlike the earlier cars that used only hall signal to 
> generate primary( five window hall distributor), there is no ignition 
> timing adjustment - distributor must be in a set position, which is 
> preferably dead middle of the hall window.  The ECU does the rest of 
> the timing.
> One possibility that breaks this above "rule" down is that the timing 
> belt has slack and/or window is just on edge so that the ignition 
> slips out of window.  Usually this reveals itself in a no-start 
> condition that is temperature related.
> So - you might have a breakdown in the spark output side, but I think 
> you have covered thost bases well.
> Ben
> -----Original Message-----
> From: John Cody Forbes [mailto:cody at]
> Sent: Wednesday, September 10, 2008 1:08 PM
> To: Ben Swann; 'Rick Houck'; 'Louis-Alain Richard'
> Cc: quattro at; 'P Cole'; 'Ado Sigal'
> Subject: Re: RE ; MAC11 update
> What Ben means to say is that all is well with primary ignition 
> (signal output to the coil), but the ECU knows nothing about whats 
> going on in the secondary ignition (everything between the coil and 
> plugs inclusively) and won't store codes for these areas. Thats where 
> the scope comes in. Get ahold of that scope, your problem will be 
> diagnosed for sure.
> -Cody
> Ben Swann wrote:
>> Again - what do the MAC-11 codes say.  If 4 4 4 4 then all is well 
>> with ignition.

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