MAC11 update

Rick Houck rhouck at
Thu Sep 11 18:49:44 PDT 2008


Great description for using the scope. I didn't think of using two channels 
at once, but that would be very useful. I will let everyone know what I find 
out, but it may be a couple of weeks before I can get it anywhere. 
Unfortunately, the driving season will soon start to wind down (at least for 
non-street legal track cars). Thanks.

Anybody else going to Waterford Hills this weekend for the Michigan Region 
ACNA event? I'll be in my black 20vt street coupe.

----- Original Message ----- 
From: "John Cody Forbes" <cody at>
To: "Rick Houck" <rhouck at>; <quattro at>
Sent: Thursday, September 11, 2008 8:51 AM
Subject: Re: MAC11 update

> There's no such thing as a dumb question, just dumb responces ;-). Using a 
> scope at all for the first time is a learning experiance with a steep 
> curve, but it sounds like you've already accomplished that one. We suspect 
> that the inputs are all ok, but it's worth checking anyways. How many 
> leads it has depend on how many channels the scope has. Many (maybe most) 
> scopes have 2 channels, meaning you can check 2 things at once and it will 
> display 2 signals on the screen. Each lead will have two wires and at the 
> end two clips, one for signal and one for ground as you suspected.
> With a 2 channel scope I would start with one channel on the flywheel 
> referance sensor (the one towards the rear of the car) and one channel on 
> the ignition coil inputs before the darlington transistor (back-probe the 
> 2 pin AMP connector that is just towards the passenger side of the car 
> from the coil). This way you can referance whats going in and whats 
> comming out at the same time. If all looks good then switch channel two to 
> the actual coil inputs which are two larger wires that plug directly into 
> the bottom of the coil (white and blue IIRC). The last part is watching 
> whats comming out of the coil and is harder. Most scopes don't come with 
> any sort of inductive pickup that you can use on an ignition wire. I think 
> the way you are going to have to handle that is either a spare spark plug 
> plugged into the end of one of the plug wires so you can view the spark 
> while it's running, or an inductive timing light.
> While you've got the scope you should go to the fuel side too. Check your 
> tach input to the 034 and all of the outputs.
> -Cody
> Rick Houck wrote:
>> I do have some dumb questions though about using a scope in an
>> automotive application. Should I start with the inputs at the ECU
>> connector, and the output at the coil? Also, do the scopes pretty
>> much have two leads (for ground and signal), or will we use a trigger
>> lead? Thanks.
>> Rick
>> ---- Original Message -----
>> From: "Ben Swann" <benswann at>
>> To: "'John Cody Forbes'" <cody at>; <quattro at>;
>> "'Rick Houck'" <rhouck at>
>> Cc: "'Ben Swann'" <benswann at>
>> Sent: Wednesday, September 10, 2008 3:34 PM
>> Subject: RE: MAC11 update
>>> 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!
>>> Ben
>>> -----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.
>>> -Cody
>>> 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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