XJ8 4.0 1998/9, hadn’t been used for about a year. Came out of storage seemingly good. Then, I got a MIL on the way to the testing station and a mis-fire. Car failed on emissions, as expected running on 7. Came home and read the codes. P0356 and P1646. Changed the #6 coil (P0356) but decided to ignore the P1646. Car no longer mis-firing, no EML, no codes. Failed emissions again. Lambda reading 1.039 against a max value of 1.03, other readings ok.

Came home, found the P1646 had re-appeared in pending codes. So fitted a new upstream sensor on A bank. The old sensor had a high resistance across its heater wires (50k ohm). New one read 1.5 ohm. I bought a sensor for B bank as well but decided not to fit it until a later date since the existing one isn’t coding and looks bloody hard to fit...

Road tested; all well and no codes stored or pending. Then a pending P1797 started intermittently appearing; I decided it was because I had been running with my (VGate) scanner plugged in and opted to leave it since it shouldn’t be emissions critical. This has since disappeared.

OK… so I took it back to be re-tested today and it failed again! The lambda has dropped to about 0.86 (too low) and the other readings are now well out as well. A gaggle of mechanics formed around the car while they tested it three different ways and kept checking they’d selected the right vehicle model. They don’t know what I’ve done wrong and neither do I. I need to get a ticket for this car asap because I’ve lost my off-road parking for it. Apart from meaning I’m parking illegally, it also makes it tough to work on the car - and I have to go to work during the day of course.

Any expert thoughts would be gratefully received. Could I have done something wrong fitting the sensor? I tried not to over-tighten it so is it possible I didn’t tighten it enough and there’s a leak round it? Could all the WD40 I had to spray to free up the old sensor have somehow got into the cat or something? Can you contaminate a lambda sensor while you’re fitting it? According to my relatively crude reader, the bank B upstream sensor (the original one) is wobbling between about 0 and -0.1 mA. The A sensor (the new one) is wobbling between about -4 and -7 mA. Reading taken at a 700rpm ish idle. If the new sensor is working, bank A is running rich, yes? This was all I could learn before a neighbour took issue with me and I had to move the car.

For what it’s worth, in my ownership this is the 5th MOT it’s been to. Emissions have always been on the money in previous tests, the last one being a few months before it was laid up. However, it’s done 107,000 miles and a lot of the innards are still originals.

Justin

 

So... it's possible you've fitted the wrong sensor... but I doubt it (if you tried to find an appropriate one).

You could try a few things... like
1. hard reset (disconnect battery for a while) because it will clear the learned values and that will make it relearn the new sensor - worth doing
2. watch fuel trims - but give it a chance to relearn if you do #1
(look with hot engine,parked, at idle then rev to about 2500 - you're looking for LTFTs and hoping they're always fairly near 0)

You're in a tough place but don't panic (apart from grief caused by officialdom) as the cars are basically sound.

 

Here's an older thread regarding the P1646....https://www.jaguarforums.com/forum/x...-57005/....its well worth the read for you to help evaluate your issue. Even though its for an R, they list links for troubleshooting.

Dug around on another site (Jaguarforum.com, sorry for cussin' y'all ) and found this for reference:

1 + Heated oxygen sensor + To VIN (M45254) + green + front XR86938 1
+ From VIN (M45255) To VIN (M69499) C2C8441

+ From VIN (M69500) To VIN (N41471) C2C12588

+ From VIN (N41472) To VIN (N52047) C2C29250

+ From VIN (N5204 To VIN (N79163) C2C22681

+ From VIN (N79164) C2P8810

 

Thanks for your replies.

I think the sensor is correct. It was bought on line from a seller that confirmed the part number (and for what its worth it was pre-wired to a correct grey connector).

I disconnected the battery while fitting the sensor, so I assumed it would be reset. Of course, the car hasn't been able to do any mileage since then (apart from the 3 mile trip to the MOT centre).

I will dig deeper into my scanner ( a VGate) tonight and report back on fuel trim readings.

Justin

 

It will relearn idle trims if you let it idle (I know, statement of the ....) but I'm not sure how long it takes. 10 mins and see if it's settled? And idlling is OK as you don't need an MoT

 

Funnily enough I was just trying that very thing - sitting at idle letting the scanner show me the fuel trims. What I noticed was that the short term trim on the bank with the replaced sensor was much higher than on the other bank. I expected the long term trim to change to correct that fairly qucikly, but it didn't.

I had to give up though. I'm becoming convinced my VGate scanner is screwing up the car. Whenever I have it connected I get weird stuff going on and this evening, sitting there for 10 minutes, all hell broke loose. One after another I got ASC/Traction control fault, then the engine warning light, then restricted performance, then gearbox fault (and the shifter locked into park), then brake fault. I shut down, disconnected the scanner, took a breath and restarted and everything went back to normal and I drove it to the end of the road and back to be sure.

I'm not going to go through that again. Tomorrow I'll have my shiny new bluetooth interface which cost a fortune and I'll start again with that.

I did manage, just before the balloon went up, to observe that the fuel trim figures were starting to move...

I am also wondering about the battery. Before storage, it was a new-ish battery but it was allowed to go flat (because my 'friend' was using it to jump other vehicles). When I got the car back I took the battery out and put it on an 'intelligent' charger - it took about two days before the green OK light came on - and since then the car has always started immediately from cold. Nevertheless...

 

When you store your vehicle or don't drive it for more than 2-3 weeks, I highly recommend a battery tender device. I also recommend your friend be a friend and make sure your battery stays charged, especially after borrowing it.
What kind of Bluetooth device did you get? The most expensive one I've seen cost about $50 (US), but they usually run about $20 (US) for the better ones. I have seen a couple at $99 (US), but I don't see what they do any better than the others than cost more.
Back to the battery, be sure you don't have any corrosion of any type on the cables/terminals. If you do, it will be down in the cable and you can't get that out, you'll need to replace it. That corrosion will cause interrupted power loss and you'll be chasing ghosts.

 

Highhorse, I bought the most stupidly expensive adapter in the world, for which I will be forever in repentance.

it's the Kiwi 3 Bluetooth interface and costs £99. This is the latest low-power Bluetooth 4 device, 50mW in standby, faster than previous versions, and of course pretty lights.

The software I've chosen (which cost a lot less) is OBD Auto Doctor, one of relatively few such products which works on a Mac.

I won't go into the circumstances of the car's storage because it gets my blood pressure up. The battery is the least of the thing; if I'd known, I would have pushed the car off a cliff rather than have to see what was done to it.

 

That's the same App I use on my Windows phone, works well for me, I think it was all of $2. As for the Kiwi Bluetooth, I saw your other thread shortly after I posted what I did. Man, that's a lot for one of those.
Sorry to hear about the storage issues. I had a vehicle being watched by a so-called friend while I was overseas. I came back and he had these excuses the vehicle was broken into by a bum and the lies continued. Funny how a bum actually took the time to nicely pop the wing window open without breaking it on the Ford Bronco and even relocked the door after taking all my knives that were hidden. Yeah, 25 yrs later and I still hold a grudge on that. Some friends we have..., right?!

 

I had a quick go with the new scanner setup - more just seeing how it worked than doing any real analysis.

I did capture this (attached), which shows lambda of 1.079 on bank A and 1.03 on bank B. Total fuel trim on bank A is 10.2%, bank B 5.4%. The engine has only just got warm however. Could it be that the ECM is still getting used to the new sensor? These figures are better than what I was seeing yesterday so maybe I should risk a test drive tomorrow to see if things improve further.

 

A test drive is never a bad thing, especially when its a Jag. Give it a go, put on about 10-20 miles and retest.

 

Using the new software I could see that the more I ran the engine, the better the figures seemed to get.

So, despite breaking the law (since the car isn't taxed) I went for a 50 mile round trip involving some country roads and a stretch of the M23.

When I got back, the results looked like this: (attached).

Without an appointment and brandishing a hard copy of that I went round the MOT place. After scratching their chins for a few moments they let me back the car up to the machine - and it passed. The machine read

CO 0%
HC 38ppm
Lambda 1.00

Couldn't ask for more, really. What a relief. Moral of the story: it takes a lot more than you think for the ECM to 're-learn' after component changes and a battery removal.

Justin

 

Excellent, glad to hear it....for the ECM, you have to take into account all driving ranges. From the in town stop and go, to the country constant roll out on the roads. Many folks think its just a turn it on and its set scenario, when in fact it does learn.

 

Thanks. Here in the UK it raises an interesting legal point. My car had been on SORN (that means declared as 'off-road'). It cannot be used or parked on a public highway.

A pre-requisite of applying for road tax is a valid MOT. In other words, I haven't been entitled to buy road tax and so just parking it on the road is illegal. If I drive the car, my insurance is not valid so I am driving without insurance.

Having repaired the fault that caused it to fail its MOT I was obliged to break the law in order to complete the repair. The law says I can drive the car "to or from a place of repair" but it's a big stretch to say a long run up and down the motorway counts. Not to mention the fact that I'd have been arrested if I was involved in an accident.

Ever since electronic registration of tax and MOT came in and police cars started having numberplate recognition linked to the DVLA database I have thought that stopping you from taxing a car because the MOT has expired is pointless. I was ready to pay my £260 to DVLA weeks ago, which would have meant my car was legally parked outside my house.

 

Government intervention sucks, cubicle queens that think they need to come up with something to keep there jobs or are trying to be hero's. Some of the regulation makes sense initially, but then they keep adding to them and then they get way off course and create catch 22's.

 

Phew! A pass!

It probably didn't actually need that drive. You may well need a new battery as it relies on it for short pulses of high current (for things like coils) and getting a relearn with a lowish battery is hardly ideal.

Strictly, as I expect you know, you need an already-booked MoT to be driving to/from. I think the UK gov just don't care at all about DIYers as MPs mostly (I hesitate to say all) don't DIY cars and of course hardly any have much science or technological knowledge.