O2's Dropping.....need some advice

[99GST]

I am having a bit of an odd problem. When I hit about 5000 rpms at WOT my O2 readings start to drop rather quick down to the .65-.75v range. I am getting these reading from both a datalogger and my built in O2 sensor on my turbo timer.

In first and second gear, I dont have the problem (because it goes through the RPM band so quickly). Only in 3rd and 4th does it occur. My car does not buck when this happens, and my EGTs are not exceeding 810 degrees C.

I am currently running a Big T28 (17psi), 550cc, 255 lph pump, full ported exhaust system (3").....etc....etc....etc. SAFC is leaned out 20% across the board on high throttle.

I am thining it may be a bad front O2 sensor. The reason I say that is, when I am idling the O2 readings are below .10v. And when I am cruising, they are rather low as well (fluctuating between .18 to .40).

Any suggestions?
Please let me know.
Thanks,
Nathan

 

[awd4g63]

I'd replace the o2 sensor just to be safe. It sounds like that's what it is. You shouldn't have a problem running decent boost with your mods at all. Have you tried to richen the car up in the rpms you're losing o2s? -20% is a lot of correction.

 

[awd4g63]

btw - how is your knock?

 

[99GST]

Originally posted by awd4g63
I'd replace the o2 sensor just to be safe. It sounds like that's what it is. You shouldn't have a problem running decent boost with your mods at all. Have you tried to richen the car up in the rpms you're losing o2s? -20% is a lot of correction.

I haev tried to richen it up, however that doesnt seem to help. Actually, if I set the AFC to 0 across the board, the car bucks bad (too rich).

I cant read my knock count (being a 2g). However, my timing is rather low that moment, but that is because my timing belt is currently off my one tooth. I will be correcting that when I get my HKS cams in. But, that should be causing me the run lean above 5k, should it?

I am pretty sure it is the O2 sensor, considering what it is reading at idle. I just wanted to get more opinions.

I will lean it out a bit more tonight and make a couple of runs, just to double check.

Thanks for the reply.
Nathan

 

[awd4g63]

I haven't had any experience with timing being off one tooth, but I imagine that the timing you're reading on your datalogger is ignition timing, not valve timing. You might need to get that fixed, as I'm sure it's hindering your performance. Where did you get your O2 sensor? If you just bought one and it's dead, you may be able to just exchange it at your local parts store where you bought it.

 

[99GST]

Originally posted by awd4g63
I haven't had any experience with timing being off one tooth, but I imagine that the timing you're reading on your datalogger is ignition timing, not valve timing. You might need to get that fixed, as I'm sure it's hindering your performance. Where did you get your O2 sensor? If you just bought one and it's dead, you may be able to just exchange it at your local parts store where you bought it.

I havent replaced this one just yet. The one that is currently in there, I had installed about 35,000 miles ago. But, for the last couple of months, I have been running pig rich (different reasons). So, I am think that I burnt it out.

I will get my timing fixed as soon as my cams come in (I dont really want to have to do it twice

I will be ordering a new front O2 sensor this week. And I should be able to put it in this weekend.

Thanks,
Nathan

 

[awd4g63]

Cool, let me know if that works, if not, we can take it from there.