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

Ben Swann benswann at verizon.net
Wed Oct 24 08:35:29 PDT 2007


I greatly appreciate all attempts at helping me solve the problem.  I do ask folks to
presume the original checks and underlying assumptions I mention up front are valid -
otherwise I end up repeating myself in email after email.  These questions were answered
up front with original post, yet folks keep asking me the same.  I know it is easy to
overlook something "obvious" but at some point we need to presume the person posting the
problem is supplying correct presumptions, especially in something this complex.

As indicated in original post:
There is no fuel pump relay or overboost/RPM or other cutoff that applies to this setup.
Folks for purposes of diagnosing the problem, consider that there is no fuel pump relay
and that the pump is wired on directly to the battery.

Assume Cam Timing and ignition are spot on and components new or in new condition.  Coil
may be questionable, but already swapped out with no change, so rule out for now.  Wires
and plugs - should be good, but slight possibility they could be culprit - rule out for

I should re-check plugs and compression, but rule out for now.

I'll rephrase and clarify so we are on track.  The system uses MAC-14 as ignition and
deviates from stock wiring in that it is relayed independant power supply relays and
pretty much overkill power feeds.  No stock fuse box or wiring is associated with this -
these are new power circuits added to the car.  The only stock wire used is the ignition
power on - current track 15, and that is used to toggle on the various system
components.  Megaquirt and MAC-14 are independent standalone control units and only
loosely coupled via ignition trigger wire. 

The ignition portion of MAC-14, fuel-portion and power-save all have independent power
supply relays - keyed on with ignition, except power-save which is wired hot all the

Megaquirt is fed by two relays - one for the injectors and one for the Control Unit.
Wiring for MS can be found:
http://www.rs-autosport.net/catalog/docs/RSA_v3-wiring_dist.gif  among other places.
Fuel pump is basically a direct relayed run to the battery and toggled on with ignition
- no other control is used.  

Wiring to the coil is basically direct to battery - there is of course a control relay,
toggled on with ignition.   

Megasquirt is not wired for ignition as MAC-14 is doing that.  
Megasquirt gets ignition trigger from coil 1 signal.

Narrow-band (OEM) oxygen sensor output to Megasquirt, MAC-14 and Digital Guage.

Manifold pressure control to Megaquirt, MAC-14, Guage and Fuel Pressure Control

Although I consider this the way it should be done, I welcome any suggestions for
improvement.  Ultimately I will install overboost/RPM and other protection, but
purposely wired without them as I get the system "tuned" at lower power levels.


Please note email changed to benswann at verizon.net
-----Original Message-----
From: Steve Eiche [mailto:seiche at shadetreesoftware.com] 
Sent: Wednesday, October 24, 2007 10:10 AM
To: Ben Swann; urq at audifans.com
Subject: RE: [urq] EFI + MAC-14 maxing ataround 5k RPM

Is the cutoff at 5k exactly?  What fuel pump relay are you using?  It is 
the one from a 200, correct?

Have you verified your cam timing?  If the cam is too far advanced, it 
will run OK at low RPM, but it will not want to rev.

How do the plugs look?


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