Scarecrow

That Datascan app looks really neat! Unfortunately I’m on Apple only, doesn’t look like they do an iOS version ):

Thanks Jeff, I thought just getting an adaptor cable seemed too easy. I have seen claims of OBD compatibility but without Canbus I assume it’s only limited data and maybe on US cars only. Back to grovelling in the footwell then! :)

I have (courtesy of Father Christmas) an OBD II scanner which happily lets me perform limited brain surgery on the more “normal” cars in the household. In theory I should also be able to use it on the Z as she’s a 1996 Series 4, and it would be a lot less pain than digging around in the footwell and tripping the ECU into diagnostic mode, but I’m confused about how to do this or even if it can be done! I can find online adapters to convert the Conzult plug to an OBD II, but will that actually work? Great if so, but I’m a little suspicious it could be that easy. I also found online posts that suggested there is a second, OBD II port on 1996+ cars, but can’t find anything about where it should be and I suspect that may be a US market thing only. Anybody out there managed to get a generic OBD II scanner working, or is it just a no-go like my old Discovery, which has an OBD II port but speaks in a LR-specific protocol? Thanks for any help!

Just did the PayPal thing myself, subs should be with you now :)

After a week of driving with the lambda sensors disconnected I went for an emissions test again today. CO was around 0.12 or less, HC was almost non existent, but lambda was zero. Zero. It only appeared at all on the overrun, when it briefly went to 1.12, then back to zero. My initial thought was the tester was duff, but I queried and mine wasn’t the first MOT that day so unless it had failed that minute it seems unlikely. Is zero lambda even possible?!?! So I’ve reconnected the LH sensor, which read out OK, and disconnected the battery to reset the ECU and will go for a long drive tonight. Last chance test tomorrow when the MOT actually runs out, after which whatever the result I think it’s time for a visit to Uncle Jimmer!

Thanks Chris, I know a place where I can get that done. If it doesn’t get through I can then try it with the AIV solenoid hose disconnected, that definitely cut down the CO last time

Sensors disconnected this morning, battery off for an hour or two, reconnected and running smoothly. Will go for a couple of long runs and get booked back in for another test. Fingers crossed!

Thanks Alic, I hadn’t considered it might have memory. I hate that my car is probably smarter than me.

Even on a cat test? Worth a try anyway, thanks. I spoke to Jimmer and he suggested unplugging too so it must be good advice!

OK, I THINK I might have found it! After changing the air filter and checking the TPS and coolant temperature sensor I ran the Mode II diagnostics. The LH lambda sensor reads fine, but the RH one does not - it stayed stuck on Rich most of the time, occasionally flipping to Lean. That would (I think) explain the test results, which had good CO until the lambda sensors kicked in, then the CO went sky high. Obvious answer is to replace the RH sensor and see if that does the trick. Question for the panel though - what happens when a lambda sensor is disconnected? Will it default to lean, rich, or something random? Just wondering if in the short term it would be worth pulling the plug on the RH sensor and getting it tested, or would I be wasting my time?

Got tomorrow afternoon off to play with my multimeter and see if I can track down the problem. Thanks for all the tips. Well, maybe not the one about the wheels... ;)

Thanks for the tipper! Just looked up the correct readings for that, and at least that’s an easy one to reach and test.

Good point Chris. I’ll get the new air filter on and check the lambda sensor codes, then get another test done when it’s nice and warm. If (when?) it fails that I’ll be sure to get a printout then get on the phone to Jimmer to book her in!

So I *might* be able to get through elsewhere if they don’t think too hard about the registration date, but looking at the results from last year’s gas test the CO was 0.2. This year it was 3.9, which would fail even a pre-cat test, until I started pulling hoses. It does seem like something has gone out of whack. Hopefully a duff sensor or blocked filter rather than ruined cats!

Thanks Jeff. Jim has previously had the car on Conzult several times and it’s been fine so it probably is time for another trip to Avonmouth! Just looking for quick diagnostics in case a round trip wasn’t necessary. You make a good point about the fail being logged, I just checked on DVLA!

First of Feb 1996

What I have found is last years printout which confirms it was a non-cat test! That time the HC was 96ppm, and the CO 0.2. The car was definitely warm this time, I’d just done a long blast. I’ve never needed to do that before, but it was always a non cat test!

Sorry I didn’t get a printout, I was just watching the data on the screen. The CO and Lambda were the ones that were going red at times, the third number (which I guess was HC?) was ok all the time

Hi all, my S4 TT has just failed MOT on emissions (which have never been a problem before). Before the test I went for a 60 mile blat up the motorway so she was nice and warm, but the CO reading was 3.9 - yes that decimal point is in the right place, the allowable limit is 0.2! Having a search through previous posts I tried disconnecting the two hoses by the balance tube, one at a time, and that dropped the reading to 2.0 but still 10x the limit. Sadly my car is just new enough that it has to have a post-Cat test not Basic Emissions. Just looking for suggestions on what to try next. I’ve got a new air filter arriving tomorrow and have found the instructions on how to check the ECU for lambda sensor error codes. The idle when warmed up is rock solid at about 900 with air con off in current temperatures, and the lambda reading on the MOT was borderline but ok. It has crossed my mind that previous testers may have assumed it had no cat, so the “try another garage” option is already on the table! Thanks for any ideas Chris

Parked near the harbour on Friday 11th August. Either white or pearl, hard to tell in the drizzle!

Finally had time to take a look today. Looks like the patch loom is in there but it's going to take removal of several dashboard/column panels to get it out. However I got enough wiring out to just unplug the timer box, and after removing that everything works as normal so the loom obviously connects the box in parallel with the ignition wiring rather than in series. So just unplugging 2 connectors and tidying the wiring away has sorted it! Thanks for your help everyone!

So if it's got the harness in do I just need to disconnect the 4-pin plug that goes to the box, or remove all the patch cables too?

Finally got home and have had a squint under the dash. It appears to be a Greddy box. There is a plate on the side with a label on saying GTT2 24817. Not sure how many cables going into the back they're hidden in a shroud. Does that help?

That's kind of what I'm hoping for, thanks. I'd like to get rid of the thing so there's one less thing for the insurance companies to charge extra for! I'm away now till next weekend but will get under the dash as soon as I get back.

Good question! I'm away at the mo but will take a look when I get back. I don't recall a model number on it but if there isn't one I'll post a photo.