Hi Nick,

Unless the supercharged engines use a different thermostat, 80C/176F definitely seems to be on the low side. If I'm not mistaken, the OE thermostat has an opening temperature of 88C/190F. This means the engine will often run at temperatures over 94C/200F, especially while stopped and idling.

80C/176F rings a bell - is it possible that was the thermostat temp for certain earlier Jaguar engines? Is it possible that in the past a parts store sold you the wrong temperature thermostat?

Cheers,

Don

 

Thoroughly clean or even replace the ECT ( EV - 1 type ) connector as a dirty or corroded connector socket is a higher resistance reading which in turn the ECU sees as a lower temp reading ( biasing the fuel trim rich ?) . I don't have the experience of the different temp settings of the different thermostats . But have to keep in mind 2 different things . One being the actual fluid temp ( correct or incorrect ) and the other is what the ECU sees as a sensor circuit ( correct or incorrect ) .

M'Lady P. had a ECT code as I received her and after cleaning the connector ( all of the engines connectors as a whole ) the ECT code is gone .

Not saying the ECT is the area to focus on but at least do a good cleaning of the connector

Connector condition is one of those foundation items to stay clean and protected .

 

Sorry I'm late to the party, Ive had them all, as crazy at it seems, does your car have a GLOVE BOX?
Yes early cars with no glove box.
Early XJR6 1995 had a load up issue with carbon due to the h/p and CAMS.
Early on they used BG oil additive and recommended bringing the car up to 3,000 rpm to clean the valves.
If so loaded up they REMOVED THE HEAD AND DID A VALVE JOB!
In 1996 the cams were changed, they still had the issue but a lot less.
I had both years, GO BACK TO THE K+N FILTER
Why because I used it FOR JAG back then it let in more air! less carbon build up.
Its all in the head, trust me. but again its 20 years old.
If the throttle body has been changed , youll notice the back of the butterfly really black.
That's why they used the k+n filter back in the day.
My standard xj3001995 I used the k+n , we pulled the head after 150,000 miles it was brand new.
Again that issue leads to fouled sensors and everything else, but the valves are it!
Easy trick, try a full bottle of CHEVRON TECHRON INJECTOR CLEANER, High test petrol run it flat out with a set of STANDARD stock plugs, you will see garbage coming out the rear, last but not least does your idle stumble?
GOOD LUCK
GTJOEY
Try what I said its well worth it!
I put 50,000 miles in one year on my 1996 xjr!

 

Keep in mind the 2 different temp sensors on the AJ16 engine . The single wire sensor runs the instrument gauge and the 2 wire thermistor sensor runs the ECU ( this is what the ELM327 sees through the serial data bus ) and a replacement connector is the same used in the trunk white dome lights that will most likely be in a better condition based on the environments they reside it .

 

Hi Lady P and GTJoey,

Lady P thanks for the connector advice. I have ordered a new thermostat and will clean the connectors as you have advised. Hopefully this weekend it will be sorted!

GTJoey to answer your questions.
1. My car has glove box - it was manufactured December 1996.
2. Throttle body has been cleaned and was hideously dirty (black)
3. Yes! My idle stumbles.

I will check out the Techron cleaner.

Cheers to all! It always feels better when you have a plan ;o)

Nick

 

Nick, I feel for you, having been through all this when I first got my XJR 3 yrs ago.
I am not an expert, and my mechanic did most of the work for me.

I would agree, a new thermostat may help. If it doesn’t properly get up to temp, the ECU will think the car is cold and stay in open loop, running rich. When hot, it goes into closed loop and runs off the numbers it’s receiving from O2 sensors, throttle position sensor, MAF etc.
( I find the terms ‘closed and open loop’ counter-intuitive, so I hope I’ve got them the right way around)

You may also need a new throttle position sensor - I think correct name is TCV but I can’t remember. And it’s installtion is adjustable so important.
you may possibly need two new oxygen sensors in the exhaust downpipes, and once they’re installed, someone with the right gear needs to do a lambda orientation for the new sensors. The genuine Jag sensors cost an arm and a leg but there is a Japanese brand which I have on my car for a fraction of the price that are perfectly good.

All this advice is ‘hit and miss’, and as Graham says above, throwing new parts at it is expensive and rarely solves the problem. However all these parts are probably 20 yrs old and close to replacement anyway.
Diagnostics are critical, and you may have to bite the bullet and use a Jag mechanic - look for an older guy who worked on X300s when they were new! I am lucky that my mechanic in small town New Zealand did just that, working for a large Jag dealer in London in the 90s.

I went through all this and the car would run well, but never got quite the fuel economy it should have. I finally needed a replacement ECU as it never went from open to closed loop. The old ECU was just faulty. Once replaced, it sorted it (I have Andy’s reprogrammed EPROMs and these can be carefully swapped from one ECU to another )

Out of curiosity, what MAF meter did you buy? A Worldcarparts one? Or secondhand genuine Jag part?
(My latest issue seems to be loose electrical connections where the MAF plugs in. I have solved the problem by gently twisting the three parallel prongs on the MAF so the plug is a tighter fist. It is a hamfisted solution, but I did it very minimally and gently with long nosed pliers. My new MAF from world car parts should arrive in a few days,)

Good luck!

 

If that's all that ELM327 can provide then its pretty basic and probably not enough info to properly diagnose it. If I can suggest something it might be a good idea to get one of these cheapo D900 readers(search on eBay, they are ~$20 and well worth it. They don't need any extra software etc, everything is shown on a small screen). Other than a lack of some basic info like oxygen sensor mode(closed or open, which would tell us whether your oxygen sensor work or not) as some people already mentioned, thermostat reading is a bit low, but changing it wont improve your idle and its possible that the temp would go up after some further driving anyway or maybe even the temp sensor itself is faulty(cheap to replace if needed)? To test it, does your temp reading on dashboard show up right in the centre after driving for 10 minutes? If it does, then chances are the coolant temp sensor might be faulty, as someone else mentioned its best to clean up the connectors first too, but the coolant temp should be around 88C after some driving, 80 is a bit on the low side.

Your short trim reading is definitely too high, although you'd need to confirm whether it was just a temporary reading or whether it stayed in that area (above 15%) while driving. If its stays at above 15% most of the time then you will need to look further at oxygen sensors operation(no idea whether elm327 can read these(?) but D900 certainly can).
The MAF reading is also too low, I don't think I saw any x300 reading 0.1g at idle, mine usually shows 0.2g-0.3g at idle and should easily go up to lets say ~0.7g while driving(Jag OBD only shows MAF within 0-1g), you shouldnt have to drive it 30 minutes for the MAF to register ~0.4g. Faulty MAF may indeed cause idle issues and lack of power so its probably a good idea to at least clean it up(use electronic contact cleaner) or swap it.
You also have, what appears to be a faulty intake air temperature sensor - LHE1602AA. I'm guessing that 'intake' reading within that obd interface is that, maybe someone familiar with that interface and this software could confirm this?
Mine was also faulty and showing very similar reading and it should show up a reading slightly higher than outside temperature.

Hope this helps!

 

ELM327 can read everything the ECU sees and calculates including O2 sensors , it even makes up stuff so you have to be aware of the gimmick . But there is a learning curve to reconfigure it

 

Hi All,

AL NZ, thanks for your comments, I agree at some point soon I may need to bite the bullet and pay an expert, but I would like to try and cure this myself if I can, for now. To answer your question I bought the worldcarparts MAF; replacing it did not resolve my problem, but did not make it worse (marginally better) so I don't think it was a bad purchase.

Katar83, thanks for your extensive tips and looking at the ODB data I provided. I have been playing with this some more and as Lady P says it seems all ECU data is available, the app I have used allows you to add all manner of widgets and displays covering many elements, so if there is some data I need to grab please let me know. This evening I checked the closed/open loop mode and the car starts on open loop, warms up and then goes to closed loop as I believe is expected.

Regarding the coolant sensor, the dial on the dash does not go completely up to N (normal) if there are four notches to N, it gets to 3 out of four and stays there. The ODB data shows it stays at 80C and this evening I watched it climb from 6C when the car was cold to exactly 80C and stay there so I think the sensor is OK?

The short trim osciliates around +15 all the time including when driving the car very well warmed up. Again if there is any data re O2 sensors I need to look at I would greatly appreciate being nudged in the right direction.

Thanks for pointing out the intake air temperature sensor issue - you are correct in your interpretation of what this means - I can't believe such a crazy reading was staring me in the face! I added a "graph" to the Torque app to track this and found the reading goes bang from -40C to +215C and later down again... Something is wrong there so will clean / replace that sensor. Could this be a root cause of my car's problems? How did your caar behave when this sensor failed?

As always everyone's help is much appreciated!

Cheers,
Nick

 

Your welcome and good luck but if your butterfly was that bad, Its going to end up as the valves are carbed up, they wont close properly.
GTJOEY1314
Good luck hopefully any of the above from everyone works out, its still 20 years old......

 

Nick, the temperature sender (single wire connector) is what powers the dash gauge, the temperature SENSOR (two pin connector) is what the ecu reads to regulate the fuel supply.
If this has failed then the engine is effectively running on choke, hence the black plugs.

 

Both my X300s (XJR and 3.2 N/A) sit with the dash temperature gauge needle just on the low edge of “N”. They both creep up to that warmed-up point in tiny increments probably less than 1mm, about 12 or more little jumps when warming up. Every photo of an X300 dash I have seen is the same (eg: adverts for cars for sale), so if yours sits a bit low, then thermostat may be an issue. I can’t remember if you said you’ve changed it or not.

Will post a photo of what I think is “Normal” ... found an old one from when my xjr rolled over the 100,000 mark..

 

That's a good news then. One question though, does your interface actually show up each o2 sensor operation mode separately or all together as closed/open mode? They should be all marked separately so make sure that all oxygen sensor are in closed loop mode when the temp goes up to 80C.
I'm not sure whether your car has two or four sensors but look at the sensors operation within the OBD, check whether both banks(front three cylinders and rear three cylinders) work in a similar way, they should both kinda flicker between 0-5V(or 0-1.6V depending on the software). If you have 4x o2 sensors(upstream and downstream?) compare both banks and sides. Its possible that the engine overcompensate for the slightly too low temperature and air intake faulty sensor but its also possible that you have an air leak somewhere. Its also possible that the sensors might be mixed up and plugged in incorrectly, my early x300 had that and although its easy to check with two o2 sensors, its not that easy with four. A lot of possibilities here but lets start with the thermostat, intake air temp sensor and then the updated oxygen sensor readings.

Sounds right, if it sits on '3' then its most likely a slowly failing thermostat. It should indeed sit just below N(sometimes a bit more than that, 1-2mm below the pictured reading from the post above)

The fuelling is definitely off. As mentioned above, let us know whether all the sensors are working in closed loop mode, how many o2 sensors you have and how they operate. One more thing I'd like to know is what spark plug gap did you set? My car will happily overfuel and not run right on a factory gap which I think is 0.95mm but will run perfectly fine on 0.85mm so I'd look into this as well, especially since its very easy and quick to check. While checking it, run the car and unplug each coil for a few seconds, make sure that there is a difference in how the car runs on unplugged vs plugged in coil, I know you mentioned that the coils are new but I've seen to many of them failing and its usually the second thing after OBD I'd check myself. Just had to change coil no5 on mine couple of weeks ago. Although it ran ok, there was a very slight misfire at idle which really annoyed me.
Also as another test to check the spark side of things, you can lower the spark plug gap temporarily to 0.7mm(after checking the 0.85mm and if no results). It should run rich but the idle should improve. If it doesn't I'd look elsewhere.


No problem, easy to miss these things if you're unfamiliar with them I'm pretty sure the sensor is shot and you will need a new one(luckily cheap).
I find these sensors(or other ones) to be very model/version specific in how they affect running of the car. My very early x300 would happily run without this sensor, with MAF unplugged and air box removed and my late x300 didn't run ok with this sensor faulty(or will stall with MAF unplugged) although I've replaced faulty coils at the same time so cant be sure how it actually affected the car and how it runs now. Since your sensor is definitely shot, replace and report, hopefully there will be an improvement

I'd also check the MAF again, see how it shows up in OBD, your first readings were definitely too low, I know you mentioned its new, but it might be worth checking how it shows on the old MAF if you still have it.

Check for air leaks too. Any hissing noise anywhere? Check all the intake rubbers, etc.

 

Post updated: Nevermind, just noticed the K&N filter was already replaced with standard airbox

 

Hi All,

Thanks to all for your feedback, I will be working on the car over the coming weekend and report back to everyone. I am also planning to plug my ODBII scanner into my friend's XJR6 to compare readings.

Robman25, thanks, I plan to replace both the thermostat and the temperature sensor as they are inexpensive items.

AL NZ my temperature gauge does not go up as high as in your picture. I hope renewing the thermostat and sensor will resolve the cold running issue. I will also replace the faulty air intake sensor.

Katar83, thanks again for the extensive feedback, I don't know if I can get reading from each O2 sensor separately to ascertain whether each one goes onto closed loop, but I will look into that at the weekend. I *think* the car has two O2 sensors but I'm not certain.

Regarding spark plug gaps they were set to .035 in
Regarding the MAF, the old one moved even less (upwards) from 0.1. I will fit the thermostat and the two sensors and see what happens.

I will report back soon, thanks for all the advice. Very much appreciated!

Nick

 

Just realised you're based in UK so you will most likely have 2 oxygen sensors and I assume you didn't mix up the plugs since you bought the car? Both should be visible separately under OBD, hopefully you can figure it out.

.035 will be 0.9mm, try lowering this down to 0.80mm - 0.85mm, my car wont run well at 0.9mm gap so its definitely something to try if all else fails

 

To verify the O2 sensors are not crossed the group of 4 wires on the car side of the connector have the same colors with the exception of 1 . This 1 wire determains it's position as well as visually following the sensor side pigtail into the pipes .

Upstream sensor Bank 1 / green

Upstream sensor Bank 2 / brown

Downstream sensor Bank 1 / blue

Downstream sensor Bank 2 / red

The wire color on the receptical side as bank 1 always includes cylinder 1 which is the fwd cylinder on the AJ16 engine different then the AJ6 engine

Look for corrosion in the connectors .

May have to remove the sensors and soak them in gasoline overnight flushing though the vent holes to clear the inside area of interest from clouding over soot .

Yes on your observation of the engine inlet air temp sensor . Mine was clouded over with crankcase breather oil residue that would bias the signal but yours is fluctuating . Inspect and clean the connector

Personally , I would focus on the MAF since that number is low . Some in the tank product may help with the suspected valve buildup like a injector cleaner .

 

Nick , I agree with most but for 10 dollars you can cure a lot of the symptoms
put a half tank of fresh gas.
Add one full bottle of chevron techron, warm up to speed.
Go to open highway and get it above 3,000 rpm .
Run it there, local stop and start only makes things worse, drive a good 20/30 miles .
I bet you MANY things will happen, p.s your idle will get worse for a bit cleaning out the crap, then presto an even idle.
Just try that first, then the thermos and all the rest.
Its 20 years old. No ethanol back then as well........
gtjoey1314

 

just minor detail from the vehicle service manual:
so Jaguar has take in account gasoline containing ethanol and in US the ethanol started to be in fuel quite early and started to grow from 1970 onward if I am not completely mistaken

 

Ethanol was non factor overall back then, farmers were getting subsidies for corn but not till the late 1990s till it was in big cities.
Now basically manditory.
Also don't forget it was 5% then 10% and they wanted to push it to 15%
Fear was the filler or ethanol would kill older cars.
Remember LEAD petrol or gasoline was in the states till about 1983. Its like comparing E85 today, Id say 1% to zero use it. Make sense?
GTJOEY1314