O2 sensor dillema, for 2 years

Ive been battling this problem for at least two years now, the o2 sensors are not doing their job. Between 1000-1500 rpms the car sputters and runs like crap under part throttle (anything above 1500 is fine, part throttle or wot) First of all, the car is a 96 gt supercharged with a saleen motor engine swap (01 s281) Around the time the swap was done, shortly afterwards, I installed a new h pipe and some bosh wideband o2s (i replaced them with brand new motorcrafts) Ever since putting in the new h pipe Ive had problems with the o2 sensors, though it was very shortly after the engine swap so that could have done it just as easy. According to the datalogs, the front o2s arent reading correctly, put in other words by my dyno tuner is they werrent heating up as they should. So Ive taken the wiring diagrams, done continuity tests from the front o2 sensor connectors to the pcm, I reflashed and reset my tune a dozen times, fixed the rear connectors so that they are plugged in and fine (though turned off in the tune) and of course I installed the brand new motorcraft sensors upfront. I even bought a spare pcm to try that out, with no results. I then turned to the grounds. First I rigged up my own ground right to the frame for the o2s as I read that someone tried this to fix a similar problem, but it didnt do anything. Found a disconnected engine ground strap, so I bought a new cable for that and installed it, surprisingly this did nothing... So she still sputters at low rpms, its sort of intermittent though. Such as, during really warm weather the car runs beautifuly, which makes sense I suppose as the sensors would heat up quicker in warm weather (with help of the exhaust of course). So here is what I need from you guys, ideas! This is the stupidest problem Ive had on this car, mainly because its such a simple circuit and it all checks out.. anyway, what other grounds should I check, and any bit of help would be awesome. I cant get the car retuned (successfuly) until those sensors work properly, but I might have to take a trip down there anyway. Thanks for the help guys!

bhuff30 said:

You said you bought new Bosch wideband O2 sensors? The key word here is wideband. That is a problem, because all wideband O2 sensors need a seperate controller. I don't really see how you would install a wideband sensor in the factory wiring though.

Ever tried installing different set of O2 sensors?

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yeah i returned those and bought motorcraft oem ones after i realized the mistake. as for intake leaks, ive checked and checked and checked. the problem seems to be the o2 sensor circuit both tuners said. they dont heat up and wont read properly until they heat up from the exhaust. im just wonder whats left to check that could effect the o2 circuit? again they are brand new motorcrafts, all wiring continuity checked out for the fronts, ill check the backs too, and the pcm is good, grounds are good. anybody got some ideas as to what else would cause them to not turn on?

Miles said:

Heat can be an issue for the O2's to reach the proper operating temperature, but back-pressure can also cause an issue.

On my car, with my long-tubes & prochamber, I couldn't get any voltage variation from the front O2's. After switching to a catted h-pipe, my O2's started to respond normally.

I searched for leaks for a year before I change the mid-pipe in order to pass emissions... turns out that helped with being to tune the car. So now I have to take back all the nasty things I said about doing emissions tests

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yeah thats the direction ive been heading for a while, seeing how everything else checks out. ive switched midpipes three times though. the one it came with was an o/r h pipe that i had 2 magnaflow cats welded into to pass inspection, i then installed another o/r h (idea was to swap in the catted one for inspection then swap out) and had a ton of issues with that one as far as leaking and fitting. I then sold that one and bought a mac catted h, which is what i have now. i remember when messing with the mac o/r h, i had a leak at the header to midpipe flange on the pass side, and that gave me the sputtering at part throttle until over 150 rpms (only a lot worse) however with the new pipe i have no leaks there that i know of. i suppose i can replace the gasket for that side, then tighten everything up again. thanks for the info guys, keep it comming.

***by the way, my current h pipe has highflow cats like I said, but also has two y pipes with elctric cutouts (sounds amazing when they are opened up!) they dont leak but could this possibly cause issues? the problem existed before i had those welded on, but who knows.

i have bbk shorties, but they are not heating up on their own said the tuner at the dyno. he had to warm it up on every pull...took for ever! i did check the fuses, all are good and i have 12v at both sensors with the key on ignition off. this weekend i will be replacing the midpipe to header gasket, if i can find a new one around here, and see what that does. any other ideas guys? im only putting down 333 rwhp because he couldnt tune it anymore, due to the sensors. i mean damn, i know he could get 450whp with what i got under the hood (vortech @ 15psi with my new inlet) just need those 02 sensors working! thanks guys

oh and as for a cel, none. in fact i havent had a cel since the engine swap which is why i tried a different pcm over winter. i couldnt get the sct tune onto the "replacement pcm" so i suppose that the pcm isnt ruled out yet. any takers on that theory?

urban96 said:

is the replacement ECU the same code as the OEM one? if not thats most likely why you cant load your tune onto the new one

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yeah that was the problem I ran into, you are 100% right. it was a pcm for the 96 gt, but different code. im going to try and find another with the same code, but its hard unless i buy new (400$!!).

what im looking for until then is the factory procedure for checking this circuit, i have a service cd but it doesnt have voltage drop specs or anything involving testing the cicuit (in other words its useless to me). anyone know where i can find the proper procedure for checking the o2 circuit? ive only done the continuity test, and checked for 12v with key on ignition off. i also need to check the grounds for continuity, i just replaced an engine ground strap (drivers side eng mount one) but that made no difference (it was completely disconnected before i replaced it though which may have hurt the pcm?) thanks for the feedback guys, keep it comming i really appreciate it.