It seems that I will need to replace my 02 sensors again. This is the third time in 6 months. Just read a thread were a link between bad 02 sensors and Hooker Longtubes was mentioned. Has anybody else heard or considered this???? Just wondering.

Also, I know that a overly rich condition can cause 02 sensors to go out. I was wondering if a sensor ruined this fashion will "go lazy." By this I mean the readings from my 02s are really slow. In fact, I get an error that basically says "low/high resolution failure" or something like that. When the PCM goest into closed loop, my longterm and short-term BLMs fall through the floor (108 long-term and 80s for short-term). I thought that bad 02s caused a false lean condition resulting in a puke rich fuel mixture. In my case, a false rich condition exist resulting in a really lean fuel mixture. I have verified this by looking at my injector pulse widths. The quickly fall from around 3.8 to 1.5 ms when closed loop is enabled.

Thanks for listening

 

First off, use AC Delco O2 sensors in these cars. I've heard of many Bosch sensors getting fouled, even when not running longtubes. Not sure what you're using.

There is a possibility that longtube headers do not retain enough heat to keep the O2 sensors at operating temp. If you are running non-coated headers and unheated sensors I could see this but it's much less likely with coating and the heated sensors that '94+ cars use.

Rich conditions will foul the O2 sensors, resulting in "lazy" O2 sensor response. Many times a fouled sensor can be revived by "cleaning" it with a torch. The most likely cause of running rich, especially with headers, is an exhaust leak. Make absolutely sure that you are running with good, stable, BLM's that are not bottoming or topping out. This can also kill the catalytic converters if you are running them. Check the slip fit on the primary tube for the hookers and be sure that all gaskets are sealing as they should. Might also want to check to make sure that any wiring is not getting cooked by the headers.

 

Well I cant say the LT's killed my O2 sensors but they've never worked right since I installed the headers.

First I had to replace one beacause it constantly read rich so the ECM pulled out waaaay too much fuel on that bank. I replaced the sensor and all was ok for a few weeks untill they both appeared to crap out and again the ECM started pulling fuel like crazy. It got to the point were the BLM's would bottom out at 108/108 within a minute of entering closed loop. This effect was more prominant at lower RPM/MAP cells vs. higher ones. So now I have 3 O2 sensors and none of them seem to read correctly, I tried the torch trick to no avail... (these are all heated AC Delco sensors BTW)


Eventually I said "f*** it" and I went open loop 24/7 and the car ran 10x better. I have a DIY wideband kit on the way for tuning purposes. Goodbye evil closed loop!

I would order another set of sensors and closed loop again but I cant justify spending $65+shipping on another set just to see them go bad again for no apparent reason. (Yes I realize the WB O2 is even more expensive but at least I can use it to tune at WOT as well).

 

Soma07, have you converted to heated O2 sensors? The '93 sensors are not heated and may definately have problems with longtubes.

 

sounds like you have some kinda exhaust leak that is ruining your O2 sensors.

i think i have a similar problem right now. one of my O2 sensors only reads 300-400 most of the time and is giving me a rough idle and split BLMs. i think my problem originated from a bad plug and/or exhaust leak. good luck.

 

Yes, as mentioned in my previous post they are heated. AC Delco p/n AFS-75. They are the stock 4 wire sensor for 94+ F-bodies.

Actually I think I started the whole heated O2 conversion thing about a year ago as I was the first to try it (AFAIK). The stock non-heated sensors didnt do any better but at least they were cheap...

 

I was thinking the same but these guys are saying that the BLM's dive down to 108 A leak or ignition problem will look as a lean condition on the O2's and result in a rich mixture, they're having the opposite problem.

 

Possibly, but the ECM would interpret an exhaust leak as an artifical lean condition and it would raise the BLM's accordingly which is exactly the opposite of whats going on with my car.

 

oh my bad i thought he was pegged on 160

wonder if his MAF is wearing out. or his fuel pressure is too high.

 

This is very interesting! On a side note, I know that coolant will fry an O2, but that doesn't seem to be the case here. Are there any lights on the dash (MIL)?

 

I must be the only 93 running LT's w/out problems using non heated 02's. Somao7 how did you go about running open loop 24/7? I'm curious as I may want to try that just for giggles too.

 

Its easy if you have Tunercat, there is a parameter called "Min coolant temp for closed loop". Basically the ECM looks at this setting to see how warm the coolant needs to before it can go into closed loop.

If you want to run open loop 24/7 you just take that setting and max it out to like 250°C. Since the engine would probably burst into flames before the coolant got that hot the ECM never goes into closed loop.

 

I'm a victim of this problem! I've got Hooker LTs and heated O2s in my 95Z. A week after installing my Hooker LTs the O2s started going downhill. I replaced them and the new ones lasted a bit longer but still degraded....started getting more and more sluggish and the BLMs started dropping like Soma07 indicated. Idle was the worst.

Figuring the O2s were the symptom and not the problem, I started looking elsewhere. I disconnected my MAF and the car ran better so I figured my MAF was bad. Bought a known good used MAF element and installed it. Things were better for a while but the O2s were still somewhat goofy and started getting worse again.

Thinking that maybe I am burning a little coolant or oil, I pulled the heads this past weekend. Looks to me like #7 may have been burning something a little "different" but things didn't look real bad. I've got the car almost all the way back together, with new O2s, so we'll see how it goes. BTW, from inspecting the gaskets, my headers had NO leaks but as mentioned earlier, an exhaust leak should cause higher BLMs anyway, not what I'm seeing.

Rob
95Z28

 

Mine are good also.

 

But have you guys actually verified the BLM's are ok using a scan tool or logging software? When mine started to do it I attibuted the roughness to a burnt plug wire or something else. It wasnt till I put a scanner to it that I realized what the real problem was.