Possible O2 sensor problem...Gurus inside!!

My SS ran a best of 13.3 @ 109.7 a week and a half ago. I ran the car last night, in almost identical conditions and only trapped 105.9. A buddy of mine ran his car on the same night I trapped 109.7 and ran it last night as well, and trapped nearly identical so it wasn't the conditions. This is with same driver, tires, etc....nothing has changed since the LTs were installed.

The car has felt sluggish for the past week or so...pretty much after the trip to the track where I trapped 109. I figured it was a psychological thing and the car was running just as strong.

Here are my mods: Whisper lid, Jet-hot LTs and dual cutouts 12-14" after the O2 sensors.

The car had also been idling rough (which it wasn't doing a couple weeks ago) so I hooked it up to my friend's laptop and drove around a little.

Here's what I have found out so far:

O2 voltage is normal at idle and part throttle (fluctuating between ~200 and 900 mv.).

O2 voltage does not stabalize at WOT. I made a few WOT pulls and the voltage was fluctuating the whole time.

No misfires.

4* of knock retard at one point, but y-pipe is hitting on floorboard pretty good.

Here's what I'm thinking so far:

Possibly running with both cut-outs open (being 12-14" from the O2s) could have 'fouled' the O2 sensors. I've read a little about this online and have seen a few people have problems with this.

Possible bad or dirty TPS sensor - if the TPS wouldn't read WOT, it wouldn't put the PCM in open loop mode...hence the fluctuating O2 readings at WOT.

Clutch is not in the greatest shape (slips occasionally)...could be slipping just enough to cause the drop in MPH (however....keep in mind I ran 4 MPH faster a week prior). A Spec stage 4 is in the mail.

A bad tank of gas...?

Bad fuel filter?

The fact that the car doesn't appear to be entering open loop worries me. What all could cause the car not to enter open loop at WOT?

Any help is greatly appreciated.

:)

The fact that the car doesn't appear to be entering open loop worries me. What all could cause the car not to enter open loop at WOT?

:)

The car won't enter open loop at WOT. It goes into some mode, but its not open loop. So like it wouldn't change from closed to open then back to closed on any system that your scanning with.

The car won't enter open loop at WOT. It goes into some mode, but its not open loop. So like it wouldn't change from closed to open then back to closed on any system that your scanning with.

Next please.

If you had a scanner on it, what did it read for TPP (throttle position percent) at WOT? If it was 100%, you don't have a problem with the TPS. Additionally, power enrichment (PE) mode - what the above post was trying to point you to, not open loop - is enabled at less than WOT, depending on the engine RPM. It doesn't take much TTP % to enable PE mode at 4,000rpm.

Is it possible that over the period of 1.5 weeks, the LT's have losened up and developed a leak at the head flanges?

If you had a scanner on it, what did it read for TPP (throttle position percent) at WOT? If it was 100%, you don't have a problem with the TPS. Additionally, power enrichment (PE) mode - what the above post was trying to point you to, not open loop - is enabled at less than WOT, depending on the engine RPM. It doesn't take much TTP % to enable PE mode at 4,000rpm.

Is it possible that over the period of 1.5 weeks, the LT's have losened up and developed a leak at the head flanges?

We observed the TPS values, but didn't really pay attention to the % at the time. We were more concerned with the O2 readings, knock retard, etc.

There are no exhaust leaks at the head, or anywhere else.

Also checked the fuel pressure - holds 60 PSI up to 6200 RPM.

Injuneer - what else could cause the O2s to not stabalize at WOT?

Thanks for the reply. :)

Bad O2's could cause the indications, as well as an air leak. I know my exhaust manifold->y pipe connection on the driver side leaks, and my O2 voltages dance around alot.

Another thing, about Power enrichment mode, is that depending on your tune, your a/f ratio does not stay the same throughout the rpm band, therefore, as your rpms change, your o2 voltages will change as the computer adjusts target a/f ratios with rpm and load.

Jonota

Thanks for the replies.

Jonota, I know they O2 readings will fluctuate a little at WOT, but they should be fairly flat. They were still cycling from .2v-.9v at WOT. I replaced the O2s and the car seems to be running better.

A little late but here goes.

My first check for a bad o2 is to turn the key on but leave the engine off. You should have .450 v. (this eliminates toasted wires with more than normal resistance.)

Its ok for them to flucutate a little at WOT but if its more than .050 V than its likely to be an ignition missfire. If its consistantly lower than what you think its probally an exhaust leak.

A bad O2 can be either lazy or completely off. I had a set of o2s on my personal vehicle recently read 800mv when my on board wideband was reading 16:1.

A little late but here goes.

My first check for a bad o2 is to turn the key on but leave the engine off. You should have .450 v. (this eliminates toasted wires with more than normal resistance.)

Its ok for them to flucutate a little at WOT but if its more than .050 V than its likely to be an ignition missfire. If its consistantly lower than what you think its probally an exhaust leak.

A bad O2 can be either lazy or completely off. I had a set of o2s on my personal vehicle recently read 800mv when my on board wideband was reading 16:1.

OK. Could a bad O2 cause the O2 readings to cycle from .2-.9v at WOT? At WOT, they acted the same as they did at part throttle/cruising. I don't have access to my buddy's scanner, so I can't check anything else until this weekend.

Like I said, the new O2s seemed to have fixed the problem but I can't tell if the O2s are stabalizing at WOT until I get a scanner on the car.

I don't think i've seen one fail that way. But I have seen the wiring harness burnt up to where it woudl fall off big time like that.

Get a datamaster datalog and let us look at it.

When you have the scanner on the car let the car idle cold or engine off for that matter and jiggle the wiring down at the o2 sensor. I see them burn up on the inner side of the passenger wheel well all the time.

I don't think i've seen one fail that way. But I have seen the wiring harness burnt up to where it woudl fall off big time like that.

Get a datamaster datalog and let us look at it.

When you have the scanner on the car let the car idle cold or engine off for that matter and jiggle the wiring down at the o2 sensor. I see them burn up on the inner side of the passenger wheel well all the time.

I guess I could also check continuity of the wires as well.

The strange thing is, both banks were cycling at WOT...not just one O2. This leads me to think it may be something else...possible TPS sensor. This is all too coincidental given that I just put LTs and dual cutouts on the car and a week after running a new best, I trap 4 mph slower with zero cylinder misfires. However, stranger things have happened.

How fast is the cycleing?

Check to make sure the INT's lock at 128 to make sure the car is in PE.

How are you sure its not misfiring? That would give a indicated lean, especially being spurratic like that.

How fast is the cycleing?

Check to make sure the INT's lock at 128 to make sure the car is in PE.

How are you sure its not misfiring? That would give a indicated lean, especially being spurratic like that.

The O2s were cycling pretty quickly. They cycled just as quick as they did at part throttle/cruising.

I watched the cylinder misfire counts for 4 or 5 WOT runs through 2 or 3 gears and didn't get one misfire on any cylinder.

When I loaded a mail-order tune to my car, the o2 sensors would still fluctuate at WOT like it wasn't at WOT.

Going back to the stock (richer) tune, stopped that problem and the o2 readings went back to going solid at WOT.