3SGTE: Need a 91 JDM downstream O2 sensor replacement recomendation

[MrDuce]

Ok to make a long story short... I have a 91 N/A that I swapped a 91 JDM 3S-GTE with ECU. Modified the head and installed a fully functional US Emissions system. No Codes and drove like a rock. Got it smogged and it almost passed. So I was going to change the cat. But had a fatal engine miss-hap (all my fault). So two shops, 5 mechanics, about $12,000 and a year with no car, I finally got it back. During this long rebuild process I had the Cat. changed. Well it passed smog with flying colors, both visually and emission readings. But now, it boost like crap. A rock solid no higher than 7psi. will not go faster than 105 mph and takes for ever getting there. But still no codes. Trouble shot everything. the only difference that I can come up with is:

1. The JDM cat. has a 2 wire downstream O2 sensor. The only Cat I could find was a USDM Cat with no downstream hole. After running it with no downstream O2 sensor, and no codes, I figured that it was not needed. But after not being able to get boost, I am starting to think differently. So has anyone replaced there 91 JDM Downstream O2 sensor with no performance problems? If so what part and or part number did you use? I am planing on drilling and tapping for a downstream sensor. The spot is castted in the cat housing but there is no hole.

2. Now this is just a shot in the dark, but I think the first shop(shaddy) during there overheating trouble shooting process, removed the thermostat. Now it takes forever to get to operational temp, and if I am driving downhill in neutral, the engine water temp will go below 60 degrees C and take a while to get back to operational temp once back in gear. So maybe if the ECU is sensing a cold engine it will not fully boost boost. The only flaw in this thought is that at operational temp, I still have no boost. But I will be installing a new thermostat anyway.

Any an all other suggestions welcome... Thanx guys!!!

[mr2magic]

I can't imagine it being the thermostat. Even if it's permanently open the collant will at some point reach operating temp. I can send you a new one (not denso though) for $111 + shipping. I assume the sensor is the same as a USDM 91T.

[MrDuce]

Originally Posted by mr2magic

I can't imagine it being the thermostat. Even if it's permanently open the collant will at some point reach operating temp. I can send you a new one (not denso though) for $111 + shipping. I assume the sensor is the same as a USDM 91T.

yea, I don't think its the thermostat either, but I do remember reading something about a cold engine and low boost in the BGB. but yes it does get to temp and no boost.

on the O2 Sensor, I don't think its the same as the USDM sensor. I do not think any USDM MR2 has a downstream sensor. Moreover; the upstream sensor I believe is a single wire sensor. My JDM downstream sensor had 2 wires.

[mr2magic]

That is correct - Engine not in operating temp spec = low boost.

I don't think it makes a big difference, because the output is the same I can also offer you a two wire downstream from a european 3S-GE for about $15 more:

http://www.UNI-FIT.de/Artikel_DOX-0101.html