Suspect O2 sensor - but no CEL when removed

ultreos · Postby **ultreos** » Sat Feb 22, 2014 8:39 pm

93_Clubman wrote:you may not have had a chance to baseline service it & therefore have not checked the ignition timing

Coincidentally, I recently picked up a timing gun for that purpose. The Fuelmiser I picked up seems to have been a bad choice, from a financial perspective anyway. It's dearer than the Bosch sensors, even the ones listed by SCA for the MX5. Thanks for the extra references as well. I've got a lot of extra reading ahead of me.

Mr Morlock wrote:I agree with 93- it could be a number of things and its often quicker and cheaper to take it to a pro.

I'd much rather find the number of things myself then take it to a mechanic - regardless of how much time or money I'll save. The thrill of DIY is more attractive to me than a car that runs perfectly that someone else fixed.

JBT · Postby **JBT** » Sat Feb 22, 2014 9:09 pm

hks_kansei wrote:
JBT wrote:If another O2 sensor doesn't fix it, check the crankshaft pulley key way - yes, it can and has happened to BP engines.

But unplugging the o2 sensor fixes the issue.

Wouldn't a keyway issue show up at all times?

Ah yes, missed that - too early in the day. :roll:

Gladiator · Postby **Gladiator** » Thu Mar 27, 2014 12:08 pm

Any update? Was it the o2 sensor?

ultreos · Postby **ultreos** » Sun Apr 06, 2014 12:10 pm

Gladiator wrote:Any update? Was it the o2 sensor?

No. Replaced the Repco O2 sensor with a Bosch LS05 yesterday (took a long time to arrive). It still exhibits the exact same symptoms. At this point, it's looking like a wiring issue or the ECU is shot.

Curiously enough, I removed the ECU out of curiosity and stuck to it was a handwritten label that said "Only fires on 2/3". Hopefully there is a way to find the pins on the ECU that connect to the O2 sensor, and somehow pull a voltage reading off it to see if what it is measuring is accurate. If it is, a replacement ECU may be in order.

93_Clubman · Postby **93_Clubman** » Mon Apr 07, 2014 12:53 am

ultreos wrote:Curiously enough, I removed the ECU out of curiosity and stuck to it was a handwritten label that said "Only fires on 2/3".

One coil in the coilpack fires 1&4 while the coil other fires 2&3. Coilpacks are usually more reliable in NA8 than the NA6 & NB8A, but NA8 ECUs do occasionally cause issues.

sailaholic · Postby **sailaholic** » Mon Apr 07, 2014 10:14 am

I've got ecu pin outs kicking around for early na8 if required.

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93_Clubman · Postby **93_Clubman** » Mon Apr 07, 2014 10:59 am

ultreos wrote:Hopefully there is a way to find the pins on the ECU that connect to the O2 sensor...

Third column in following should be ok for ADM 1993-1995 NA8 ECU:
viewtopic.php?f=76&t=38367

Adaptronic in Aust also have a pinout map, which a few of us will have.

ultreos · Postby **ultreos** » Fri Apr 18, 2014 10:43 pm

Excellent responses - much appreciated, especially the link to the ECU pin schematic.

Currently the O2 sensor has dropped priority as I'm in the middle of changing the clutch and it's my first time removing a transmission in a car as well so I'm taking it nice and slow.

I will post a resolution or any other findings I have regarding this issue - hopefully soon.