Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Low dwell problem (ECM, PROM M/C solenoid) what to do next?

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Peer81:
I think OBD 0.5 is a good discription of what this system is!  ;D :o
On the L81 corvette forum people are also pointing at the wide band as it could be the problem. No the original oxygen sensor is not in there it's the wide band (Bosch LSU 4.2 sensor) and the Fast module sends a simulated narrowband output to the ECM. I also changed the original oxygen sensor in the past to a heated sensor (widebands are also heated) so no more in and out of closed loop at idle cooldown. But I'll first switch back to the original oxygen sensor and only use the wideband to monitor on the passengers side. Maybe the ECM gets an overload on oxygen sensor input so it just goes into full rich mode. Only one way to find out :)
I'll let you know!

Greetings Peter

jjr:

 Peter I own and admin a automotive resto site that deals
with the Pontiac 301 and 301Turbo engines.

 Lots of '81 owners have CCC headaches, and I have done a good deal
of research on the 81 CCC. I also have a lot of 81 CCC materials posted
there.

 You "might" need the original O2 sensor back in there as the 81 ECM is not
too tolerant. Also,I would highly suggest the use of an original Delco sensor
as I have found the Bosch replacements to NOT be very consistent.
 Some are great from day one, others die a few days after installation.

 What is ironic is that Bosch pioneered the tech for the thing.

 But to be sure, a 1981 CCC system CAN be made to work just as the
general intended, even on a Vette... just kidding... <grin>

 Joe
 

Peer81:
Hello Joe,

Great to hear other people also dig deep into the first ecm systems. I also have the OEM 2 wire oxygen sensor laying around so I'll reconnect that tomorrow.
The first question. The OEM oxygen sensor is a two wire system. First goes to the high ref? oxygen sensor input on the ecm.
Second goes to the low ref? oxygen sensor input on the ecm, it appears to also be connected to ground. So what does the low ref input do as it is connected to ground? Or am I reading the wiring diagram in the wrong way?
I'll also check the low ref to ground connection tomorrow.

Greetings Peter

ejowrench:
As far as I know, the ground or reference low, simply completes the circuit. Some o2 sensors are grounded through the exhaust [one wire], grounded by the ECM, or some other ground source [engine , chassis]. Think of the sensor as a small battery, generating voltage to the ECM.

You mentioned you had hedders, and they can be a problem for o2 sensors, as you probably know. Placement of the o2 sensor is critical on some applications. Just because the hedder manufacturer put the o2 sensor bung in this spot doesn't mean it is the right spot.

Where's the best spot for the sensor? In the factory exhaust manifold! Sorry, I know you didn't want to hear that. I think if you locate it as close to the engine as possible, with the pigtail up, you can get it to work.

One more thing, some o2 sensors use reference ambient air through the sensor wiring, and some through the sensor itself. So splicing some harnesses can be a problem.

Peer81:
Thanks for the tip but no the exhaust manifolds are still stock and the O2 sensor is still at the original place. There is no splicing going around in the signal wiring so that isn't a problem. And I also think connecting the low ref wire to isolated ground or body ground shouldn't make a difference if the ground signal is good and strong. I'll let you know tomorrow what I found out :)

Groeten Peter

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