Voltage readings @ the c3i Harness , KOEO ?

[Lockman]

Can't find any tables on the pinout , particularly the white wire ' A ' ? Mine is showing .145 Volts , KOEO ?
Thanks, Gents......

 

[pacecarta]

ign module A white wire is EST goes to B4 at ecm ,
ecm voltage diagram shows it should be .08V key on , 1.10 engine running

if that wire is open the ecm goes into bypass mode

 

[Lockman]

Thanks for the reply & info. That's where I'm having troubles ........ been stuck in bypass mode. I had found the charts in my TSM, but it helps a lot to have those #'s that you quoted.
Thanks , again.

 

[pacecarta]

heres a little better view of whats going on

 

[pacecarta]

gnttype's link to description of code 42

Malfunction Codes Reference

ECM Trouble Codes and Diagnostics for Buick 3.8l SFI Turbo V6

www.gnttype.org

 

[TurboBob]

The pic in the service manual (and pasted above) is incorrect on several points.

A is the spark timing output, it sits very close to 0v most of the time. To fire a spark it switches to ~5v for a few mSec, then back to 0. The spark fires at the end of that pulse.

B is the Bypass control. Engine off it stays at 0, the ignition module is in bypass mode, and the coils are controlled by the module alone. Sparks are fired at 10 degrees BTDC

After the engine starts, the ECM looks to see if there are pulses on A, there should be none because the ignition module shorts A to ground in Bypass mode. If pulses are detected it presumes the timing signal wire is open circuit, and triggers a 42.

If this is ok, the ECM activates Bypass, the module ungrounds the timing signal and switches to run mode. The ECM then expects to detect pulses on A, if it doesn't it triggers a 42 and switches Bypass back off. (puts the system back in bypass mode) This is how it detects an open or shorted Bypass wire.

Complex diagnostic, but effective to diagnose the 2 wires.

Bob

 

[Lockman]

Thanks , Bob....... Then, what do you think would be the cause of the .145 Volts, KO, at the B4 / White wire ?

 

[TurboBob]

thats essentially 0, so I would say its a normal reading

 

[Lockman]

I was able to buy the last OEM, NOS , ICM out there . Some of my TSM diagnosis has pointed toward replacement. I have been trying to R & R with my ' Old Stock ' .......... But they are , of course , 40 year old solid state pieces ?
I'll be installing that today, & I'll follow up on my findings when I finally defeat this.

BTW, I did the ' EGR Delete ' & after talking to Eric, whose going to turn off the SES light warning in my chip, I had posted this question in another Forum yesterday :
..... I believe that I isolated a Short to ground in the EGR harness circuit ? After the mechanical removal , should I remove the ECM gray wire feed for this , at the ECM ????

Thank you so much , Bob, for your tutoring & encouraging knowledge. I much needed these for my confidence in solving this tough electrical issue....... Especially for this Locksmith that is doing the repair