Date:         Sat, 30 Mar 2002 07:10:07 -0600
Reply-To:     Larry Alofs <lalofs@ENTERACT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Larry Alofs <lalofs@ENTERACT.COM>
Subject:      Re: highway Dyno
Comments: To: Jack Pronovost <jackpron@AWESOMENET.NET>
Content-Type: text/plain; charset=us-ascii

Jack Pronovost wrote:
>
> Hi
>     Forgot to mention on previous post how I made my diagnostic, and since this might usefull to others, here it is. I needed to see what the ECU was doing when it would temporarily fail on the highway. I spliced two wires onto the two injector supply wires at the outlet of the ECU, The heavy white and heavy red and white. The signal is a series of square wave pulses with varying pulse width (duty cycle) to match engine fuel requirement. I hooked an analog DC meter with a scale of 0-10 volts. The meter averages the pulses to read an average DC value. At full duty cycle the meter reading is 10 volts and half duty cycle is 5 volts and so on. This becomes a fuel delivery meter expressed in % of full delivery such as 5 volts is %50, 2.5 volts %25 etc. At 50 to 60 Mph, the meter reads %30 to %40. However When the problem would occur I would get spikes of %70 or %80 on the meter with the usual bucking sputtering, and then the meter would return to normal for a while. Replacing the AFM
> had no effect and left me with no other choice then to replace the ECU. Problem solved.   Jack

Jack,

Good idea.
 But I thought the injectors were activated when the ECU grounded one of
the leads and the other connection was to positive battery voltage thru
the same relay that supplies the fuel pump.  This would mean a reading
close to 12 or 13V for no fuel (coasting?) and a low voltage reading on
your duty cycle meter under high fuel demand.
  This would be logical if your sputtering corresponded to high
percentage spikes (less fuel than normal).  It seems unlikely that
increases in the fuel /air ratio would cause serious bucking at highway
speeds.

Larry A.