Howell, Again

[Onebil2mny at aol.com]

OK boys and girls, this is where we have gotten. We installed the new 
computer and it fired up fine. A little hesitation at first, but that went 
away. I assume this is because the new computer had to learn. Anyway, the 
first 100 miles or so went fine, and I thought we had it licked. I thought 
wrong. Here are the symptoms, and what I have checked.

You may recall that this is an LT-4 Corvette motor installed in a 1956 
Chevrolet. The computer (18188021) and harness was purchased from Howell 
Engineering. The computer is set up as a speed density system, and uses the 
following sensors.

    MAP sensor
    MAT sensor
    Cam sensor (I assume) from the distributor
    (2) O2 sensors (4 wire)
    (2) Knock sensors (common wire)
    TPS sensor
    Coolant Temp. sensor

The problem is that sometimes, usually during "warm up" as the vehicle goes 
into closed loop, the computer will drive one bank so rich as to blow black 
smoke from that side of the exhaust. Although it hasn't acted up on the scan 
tool recently, the last time it did, the O2 readings were high, while the 
pulse width was wide, indicating that the computer was driving that bank 
rich. It recently acted up, and set a left side lean exhaust code (44) but I 
do not know which side was running rich at that time. 

I have checked for crossed O2 harnesses and they check out. I got a print out 
of the pin voltages, and did the requisite checks on the O2 sensors and 
everything checks OK, zero volts on the "low" side of the O2 sensor, etc. The 
low side does read around 1.5v on the harness side when the sensor is 
disconnected, but I see no specification for a disconnected sensor. While my 
next step is to start checking ECM grounds, I am hoping that someone else 
will have another idea. I am certain the ECM is grounded, and grounded well, 
but I am going to check just to be certain. 

Thanks for any input you can send me...  This thing is starting to... erm... 
well, I'm not real happy with it, that's for certain!

Shiny Side Up!
Bill K
----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org