jay_tibo

I'm currently working on tuning with MM (just started again after winter) turbo and car have been running fine. In my data logs were seeing the AFR go way lean over 6500rpm, like over 15 even 21 at the top, this is directly contradicting my wideband which consistently reads between 11 to 12 for the full pull. After seeing this I kept the car under 6000rpm all winter with no issues, and no I never experience detonation under any condition.

Short story on the build new motor at the same time a turbo install, about 4000km ago, relevant mods are BHR coils, AEM intake, and did the couple fixs suggested to the kit, I did not block the ports greddy suggest. For fuel I modded the housing and put a Walbro 255, this is something MM is suggesting may be the problem, after installing a pressure gauge I read 70psi up to approximately 6500rpm were it drops to about 65psi and holds steady.

So the question I have has anyone experience such discrepancies between gauges and data logging? Is the 5psi drop enough to drastically effect AFR? (70psi seems already high to me but what do I know) Would blocking the intake bottom portion (as greddy now does) help?

Cheers

RIWWP

iTrader: (2)

Do you have two different O2 sensors? I would assume so. Sounds like the stock O2 is bad.

jay_tibo

Yep I do and different harnesses, I had thought that could be it as well I'm pretty sure its the original O2 that has 130000km, the secondary O2 sensor wiring harness had to be repaired (thats what you get when asking your buddy to help pull the motor and he take the pulling part very literally lol) I soldered and heat srinked all the wires but I doubt this secondary sensor has any valuable impute, or maybe I'm wrong here too.

ShellDude

iTrader: (12)

What "secondary" sensor are you referring to specifically? The OE sensors are Narrow and Wideband... I'm unaware of a secondary sensor, except the secondary air sensor which is just the stupid air pump.

jay_tibo

I'm referring to the downstream narrow band sensor, as far as I know that purely emissions related.

ShellDude

iTrader: (12)

I wouldn't be so quick to dismiss the rear sensor as emissions only.

9krpmrx8

iTrader: (46)

Well, first of all, 70psi of fuel is too much. And I would replace your stock primary O2, it is very important. I can't believe MM has not suggested the same. What aftermarket O2 are you running and where is it located in the exhausts stream? Are you catless?

ShellDude

iTrader: (12)

Great point 9k.... We're calibrated for a static 60 psi with some +/- tweaks based on barometer.

I think the keyword here is static. Under no conditions does my fuel pressure deviate beyond 1 or so PSI.

Play it forward a little more.

Car runs fine at 70 psi ... trims likely kick in due to over fueling or Jeff has you tuned for it.

At 6000ish RPM fuel pressure drops 5 psi. That's a bit less fuel all of a sudden which suggests you really are leaning out.

Dyno tail pipe sensor would say for certain.

9krpmrx8

iTrader: (46)

Yep, I agree. My fuel pressure with the BHR pump assembly runs between 58-60psi and does not ever vary beyond that (or my alarm would sound).

jay_tibo

My aftermarket sensor is at the front of my mid-pipe it had a cat once but it's blown through(rx7.com), to be fair MM asked me to check fuel pressure I haven't had a chance to let him know what I'm seeing. As for the 70psi I followed the original mm solution seems it dosent always work out not sure what I could have done to screw it up.

9krpmrx8

iTrader: (46)

So your stock secondary O2 is where? You need to get the fuel system rectified ASAP. Just run a stock pump or do the 09+ RX-8 fuel pump swap. There are a few options but 70psi is no bueno.

jay_tibo

The secondary is in its stock location after we're the cat would be I added a bung right after the flange were you bolt the mid pipe to the header now turbo down pipe. I get the fuel pressure may be one of the issues, this still dosent explain the discrepancies, and it is a fix over stock.

9krpmrx8

iTrader: (46)

Oh okay you had another bung welded in, got it. Excessive fuel pressure explains a lot actually.

jay_tibo

I'm with you on that one, but I will double check the gauge as it is a electronic sender not mechanical. I did the Walbro install as per the instructions, has anyone experience high fuel pressure with this? As for the O2 sensor I had a hunch it could be an issue, now it is consistent at lower to mid RPM's but seems off in the high range could a bad sensor react like this?

ShellDude

iTrader: (12)

Did you mention which aftermarket Wideband O2 gauge you went with? Did you calibrate it to atmosphere prior to install?

I recalibrate my Innovate every 3 months.

jay_tibo

The gauge is fine and calibrated, and it is accurate and follows the data log up to approximately 6500rpms where the gauge stays fairly steady but the log goes way lean. Big question is can a O2 sensor only fail in higher RPM ranges.

jay_tibo

Well here's the conclusion to everyone that helped out. After speaking with MM he told me that bad O2 typically will start failing under increased stress as in higher RPM's, I replaced this with a NGK and sure enough my A/F ratios stay dead steady at 11.29 from the second I full throttle to when I pull off.

As for the fuel pressure the way my system is running is perfect and pretty much the same as MM runs his, as long as the pressure stays above 60PSI at all times it's great, the fluctuation between 65 to 71 isn't a problem at all.

O and the secondary O2 is just for emissions and completely disregarded when tuning and engine operations.

Cheers