Timing is controlled by ESC module and computer. Middle 80's, GM started using knock sensors to detect engine detonation. So the ESC watches that and stator (pickup coil) signals for ignition timing and injector pulse rates.[8D]

 

Actually, when you open the throttle, engine vacuum drops until you reach a consistant rpm. And the knock sensor detects detonation via a quartz material inside it that vibrates and creates a miniscule voltage that the ESC module watches. If it generates the proper voltage, then the ESC retards the timing a couple of degrees to try and eliminate detonation. Sorry, just a little theory there.

 

you might also look into getting a heated O2 sensor. some people have problems with the engine getting into closed loop with long tubes sense the sensor has trouble getting hot (needs to be something like 500F before the it can go into closed loop)

 

Quick question----if it stays in open loop, what are the results? Running rich? Running lean? No power? etc?

 

Open loop is in a richer mode because the computer is looking for certain criteria, coolant temp, O2 voltage, MAT sesnor temp, in other words it still thinks it is a cold engine because it has not seen all the criteria met for closed loop operation. [8D]

 

Thanx to all for the input.

Has anyone converted to the 3-wire O2 sensor? If you have, what part # did you use? How did it work out for you??

I understand that all you need is a switched +12V source, ground, and the lead back to the computer. The more I read about O2 sensors, the more I think that mine isn't going into closed loop---so I'm looking to convert to a 3-wire unit.

 

does your vette with long tube headers pass emmisions tests?

 

3 wire sensors require a 12v source and ground for the heating element. The source has to be controlled on time in order not to burn up element, thus has to be controlled by ECM based on exhaust temp and coolant temp. Can't leave it on all the time or you are just wasting your money.

 

MECH259??? Will you marry me???

 

thespannerboys: Haven't attempted to take it thru emissions. Bought the car about a month ago as a project and just working on it to get it running right. The engine doesn't seem to have the punch I would expect out of this car. It bogs down when the gas is punched. Plus the fact that, once it warms up, the SES comes on and it kicks out a code 13. The O2 sensor is new and, from following the trouble shooting chart, it doesn't seem to be going into a closed loop condition. That's why I'm looking at the 3-wire option.

mech259: in everything I've found on 3-wire sensors, nothing has mentioned the 12v having to be controlled by time. Do you happen to know where I can pick up a "time controlled" 12v source?