Slight problem with 84 Olds 3.8 mixture control
#1
Supreme Member
Thread Starter
Join Date: Jan 2001
Location: Rock Hill, SC
Posts: 1,411
Likes: 0
Received 3 Likes
on
3 Posts
Car: 1999 Pontiac T/A Firehawk
Engine: ***'s Engine
Transmission: T56
Slight problem with 84 Olds 3.8 mixture control
I recently swapped my 2bbl intake for a 4bbl intake, and in the process changing from the original dualjet to an E4ME Qjet.
The motor doesn't really want to idle down, I'm sure I have a vacuum leak, but other than that it runs good at part and full throttle.
While watching the scanner, however, I noticed the the MC solenoid duty cycle is doing some WACKY stuff.
It'll sit at 5% at idle (probably cuase of the vac leak) for a little while, then it will suddenly jump up to 54% and sit there for a few seconds, and then jump right back down to 5%. You can hear the motor change idle speed and sound when it does this, so I have to think that it really is happening. The motor also wants to stall when it's at 54%.
Why the HELL is it doing this? the O2 sensor is still reading somewhat lean when it's sitting at 5%, so there should be no reason in the world why it should suddenly decide to pull fuel. When my Camaro was in a similar situation, it sat at 5% and eventually tossed a lean exhaust code, exactly how it should behave.
Also, the ECM does not throw a code when I disconnect the MC solenoid connector . It will throw one for EGR malfunction though .
I'm leaning towards it being something wrong with the ECM. I've never seen one of these cars randomly change the MC dwell like that without falling out of closed loop.
The motor doesn't really want to idle down, I'm sure I have a vacuum leak, but other than that it runs good at part and full throttle.
While watching the scanner, however, I noticed the the MC solenoid duty cycle is doing some WACKY stuff.
It'll sit at 5% at idle (probably cuase of the vac leak) for a little while, then it will suddenly jump up to 54% and sit there for a few seconds, and then jump right back down to 5%. You can hear the motor change idle speed and sound when it does this, so I have to think that it really is happening. The motor also wants to stall when it's at 54%.
Why the HELL is it doing this? the O2 sensor is still reading somewhat lean when it's sitting at 5%, so there should be no reason in the world why it should suddenly decide to pull fuel. When my Camaro was in a similar situation, it sat at 5% and eventually tossed a lean exhaust code, exactly how it should behave.
Also, the ECM does not throw a code when I disconnect the MC solenoid connector . It will throw one for EGR malfunction though .
I'm leaning towards it being something wrong with the ECM. I've never seen one of these cars randomly change the MC dwell like that without falling out of closed loop.
Thread
Thread Starter
Forum
Replies
Last Post
colton_carlson
Firebirds for Sale
7
03-08-2019 12:21 PM
db057
TBI
10
08-11-2015 10:11 PM