Just discovered my 92Z with a 350 TPI has no O2 sensor in the exhaust..The car runs low 14's at almost 100 MPH, gets decent mileage, runs fine around town...Just took it on a hi-way trip, and was getting about 20 MPG..The car starts fine, and goes into Closed loop..A fellow worked on my exhaust, and I gave him a new O2 sensor to put in while he had it up on the rack..There is no bung in the pipe, nor can I find the pigtail to plug it in..It has Headman shorty's, and a really crappy home made Y pipe...What are some of the things the previous owner could have done to trick the computer..It does pop a O2 sensor code sometimes, but not always..Strange...Thanks for any help on this, Tom

 

Similar circumstance here.

 

A custom tune for full time open-loop mode would do it. I have done this to several vehicles, but not these specific ones mentioned here. I'm not the only one out there doing it though.

I don't trick the ECM to go closed-loop without the O2, but it is possible in many codes to do so with custom patches to the adaptive learning code.

If your car and EPROM are all stock, but with no O2, then I'm not sure what to tell you. It shouldn't be able to go closed-loop, and very unlikely to run well at part throttle.

 

Runs fine at any throttle, like i said, I never knew it did not have one....Thanks for the answers, this has really got me bugged..

 

how do you know its going into closed loop? you datalog it or try a scanner yet?

 

what is connected to the o2 wire? it should be on the drivers side down by the steering shaft.

 

I know where it should be, but I cant find it..I just replaced the one in my 89...It may be pulled up somewhere..I will have to look closer..Thanks

 

Well I say it goes into closed loop, the reason after about 5 minutes it idles down, and runs better just like my 89 does..Im not sure if that means it is tho, but it does get good mileage..Man, I don't know what to think...I have code scanned it, and it pops an O2 sensor code, but it only does it part of the time..Strange..

 

Idling down isn't a sign of going closed-loop. The idle speed is based on coolant temp, and time from start-up. That works no matter open or closed-loop. It sounds like you should hook up to a laptop for some data-logging to see what's going on there.

 

Not a bad idea, there may be 2 tenths of a second in chip burning, thing ran a 14.17 at almost 100 MPH several times, after being driven 50 miles or so...Will get it Data Logged ASAP....Have another set of headers, and crossover with bung, also much better complete 3 inch Eddy
exhaust....Thanks all...

 

If you look at the ECM, pull the cover and look at the chip, you may beable to tell if someone has put a custom chip in there or not.

Not 100% sure how this works, but I thought if the ECM didnt get an o2-ready signal, it would remain open loop. Factory Open Loop tunes are close enough to run right, even handle some mods. They have to be right since you are in open loop every time you start up and it stays like that for a few minutes if a cold start, or few seconds if a hot restart. I think your car is likely sticking in open loop

 

hello

i have orginal chip in ECM and i have O2 sensor in exhaust manifold but i dont have wire(s) for O2 sensor(pos. D6 & D7) in ECM and i dont get any error messages . what you think about this?? and it is true that you wont go closed loop without o2 sensor

 

Yeah, but in open loop you are getting gas like twice a day. It just wastes too much gas. Closed loop is the ticket IMO.