Hi everyone,
I have a 1995 XJS Coupe with the 4.0 6-cylinder AJ16 engine and automatic transmission. Last Thursday, on my way to work (I'm apparently an essential worker two days a week and inessential working from home the other three), my XJS stalled out. Fortunately, it was in the parking lot at my office, so it was pretty safe. I tried re-starting a few times and it eventually fired back up. The gas gauge read ~1/4 tank. Low, but well above empty. I thought maybe the gauge was wrong and I was out of gas. I got the car to the first spot I could find and went about my day. Leaving work, I decided to go immediately to the nearest gas station. It started up, but stalled out on a hill going up to a traffic light. Again, I was able to re-start it after a minute or two and made it to a gas station, where it stalled just as I was turning into the station. Fortunately, I was able to coast to one of the pumps and fill the tank. It took 16.8 gallons, which indicates to me that there had been ~4 gallons remaining in the tank. Leaving the gas station, it took a few tries to start the car and the check engine & check transmission lights came on. I made it home, and the car stalled out again in my driveway, thus maintaining its record of never leaving me stranded. I checked the codes with an OBDII scanner and got P0727 and P1775.

Looking up the codes, it seems as though they just indicate that the car stalled and don't offer any real diagnostic help. Reading through various threads here, I have a few ideas as to the problem. Please let me know if I'm missing anything and which avenues are the most likely. I'd particularly like to know what I can diagnose in my driveway, because I'm scared of breaking down now. Thank you!

1. Gas. Either the bottom ~4 gallons of gas are bad/dirty or the fuel pump pickup doesn't reach them very well. This isn't totally convincing because the car stalled out after I filled up the tank. I suppose it's possible that there was some crud in the bottom of the tank and that got sucked into the fuel lines, clogging either the lines or the filter.
2. Transmission fluid. I read that low transmission fluid can cause stalling. I checked the fluid level and it was fine and the color was bright red and clear.
3. Idle Air Control Valve or Exhaust Gas Recirculation Valve. I had just cleaned out & lubricated the throttle body before this happened, so it's possible that I damaged or gummed up the IACV or EGR.
4. Spark plugs. I replaced them less than a year and 1,000 miles ago.
5. Ignition coils. I don't know how old mine are. At >$100 each for the good, made in Japan ones, I'd rather not just throw new parts on. How can I diagnose these?
6. Crankshaft Position Sensor. I replaced this within the last five years, but it could have gone bad since. Again, how do I diagnose it?

 

Hi EastRando

I've got a similar Car to yours and when I replaced the Fuel Pump, 5 gallons of Petrol was only just enough to reach the Pick up Filter on the Fuel Pump, so don't discount the possibility that there may not be enough petrol in the Tank

 

Start by testing the fuel pressure. It could be a failing pump. If that is Ok, then it is some sort of electrical fault.

 

There's no easy way to test fuel pressure on this engine. There's no test port! You can check the tiny hose that hooks into the fuel regulator. If it smells of fuel, its toast. But that's just the regulator. You'll likely have to take it to a shop that can check fuel pressure at the rail. It could certainly be the fuel pump, but that's an expensive job. It can be DIYed, but its tough.

It can be the coils, something else that can't really be diagnosed well. They can test well, but in reality, fail. If they're originals, they've given you all they had.

While we're on that train, the TPS, can also be behind this. Also, a part that can bench test well, but be bad.

Let's start with the LTFT readings. Please tell me you have a reader that can get this information from the OBD2 port. If not, you should buy one. An ELM27 wireless from eBay or Amazon will do nicely, and cheaply, then download an appropriate app on your Android or iPhone. iPhone will require a WiFi ELM27, whereas the Android can use the Bluetooth ELM27.

In the meantime, while you wait for the mailman, you can clean out your throttle body and check the EGR. Perhaps disconnecting it when you drive? (You will...errr....uhhh.....should get a code, but you can ignore that) You should also check your spark plug cylinders for oil. If the gaskets leak, you can flood the cylinder, although I would imagine it would give you a misfire code.

As for the codes you do have, you are correct. This OBD2 is so cheap with the codes. It really hates to dole them out. Hopefully you will be able to get it to flash another code that will get you to the right spot.

 

Thank you, Orange, Greg, and Vee.

I have an OBDII reader - what should I look for in the LTFT readings? I've read about them before but never got a sense of what a "good" range versus a "bad" range would be.

Throttle body is clean. I can check the EGR. Spark plug gaskets were changed last year, but I can check them easily enough.

Vee, I saw a thread in which you were trying to build an adapter to check fuel pressure. I take it you were not successful?

 

No...I was not. Too many fittings to adapt. Ultimately you could just cut the runner fuel line and insert the right barbed tee with a port, but I was nervous about doing that. I tried to do it using only threaded connections so should something go wrong (it did) I could put it back the way it was. (I did)

Anyways, perfect LTFT is 0. Anything between -3 and 3 isn’t terrible. After that, we have some work to do.

On top of that, you’ll have two banks to read. They should read the same. If they don’t, that will give us some work to do as well.

 

I checked the LTFT and STFT values using a WiFi OBDII reader and got the values below. The short-term fuel trim graphs show me revving the engine a few times, hence the variation, while the long-term fuel trim numbers appeared to be static.

Does an LTFT -93.75% make any sort of sense?

The car didn't stall at any point while I was testing, so I'm getting a little more hopeful that it just couldn't pick up the last four gallons of gas.

 

Are you sure the OBDII can read the fuel trim on a 1995? It will not read it on my 1995 6.0 coupe. The cars were required to be OBDII compliant for 1996 and I've read that the V-12s could not be made OBDII compliant and that is why there were none sold as 1996 models. If anyone knows the serial number of the 1st compliant car it would help to determine if your car is.

 

I had a 1995 XJR as a daily driver for many years and pulled my hair out with fuel trim readings ….and drivability issues in general. Great car, but it became known to me as "The Tormentor"

Anyhow.....

Very often (but not always) I got LTFT and STFT readings that made no sense and, if I understand correctly, shouldn't even happen.....such as +/- readings of 70-80-90% as you mention. This on top of other readings that made no sense, phantom DTCs, reluctance of the system to record misfires, and so forth.

I never did come to a firm conclusion as to why I had so much OBDII weirdness but I wasn't alone, and there was fairly broad consensus that A) the system simply wasn't 'fully developed' on the 1995 MY cars and B) non-propriety scan tools were not playing nicely with the system

Sorry I can't offer anything actually useful.

Cheers
DD

 

That brings up a very good question.

It might well be a case of OBDII capability existing on 1995MY cars, to some degree or another, but it wasn't actually compliant...and perhaps Jaguar never intended it to be compliant?

Sort of a "trial run" to develop the system?

Cheers
DD

 

Hi East Rando

5 Gallons of Gas in a 1995 XJS 4.0L hardly wets the bottom of the Tank or makes it past the Pump Fuel Inlet Strainer, which has to be fully Covered and that's on nice level Surface, so once again don't discount 'not enough fuel in the Tank'

Try 10 gallons and then see if you still get problems

 

East Rando,

I have a 96, but it's a convertible. I'm still trying to hunt down the cause of an inaccurate fuel gauge. I drive until the Trip Computer shows me I've burned off 16 gallons, ALL THE TIME. Almost everytime. That will not be the cause of your problem.

The OBD is a bit wonky on your car. The LTFTs are practically useless, except for the fact that Banks 1 and 2 match, which is good.

When I first got the car (the first time, but that's another post), I did experience a similar issue. I couldn't figure it out. No CEL, no clue as to why it was shutting down. Then one day it did it on the highway! Yeah, freaky. Luckily, I was able to take it on to the shoulder. Even luckier, I was finally awarded with a CEL! I pulled the code and it was showing an EGR fault. I bought a new one, and never had an issue again.

I suspect had it been one (or more) of your coils, which is also a distinct possibility, you would have seen some kind of CEL. It's way more generous with those problems, however, checking the wells for oil might be a good idea. You might have a failing spark plug gasket allowing fluid to enter the cylinder, and shorting out the coil. QYL coils from eBay have gotten very positive reviews here, and at $80/full set, it might be something to consider.

Unfortunately a new EGR is closer to $200, so you may not want to throw all your money around just yet. People have recorded success with cleaning it, I was not able. I bit the bullet, bought a new one and haven't had THAT problem since.

 

Thanks, everyone.

I think I'm going to check the spark plug wells for oil, because that's pretty easy, and otherwise just be careful while driving for a while to see if it happens again and hope it throws a useful code.

 

Good information from Vee. I had a similar problem with my 96 4.0 and a new EGR has solved the problem.

 

Did you replace the fuel filter?
Before you install the new one you might want to run the fuel pump into a bucket to see if that is an issue.

 

Update:
I pulled all of the spark plugs and 6 had a significant amount of oil, 5 had a little, and 4 may have had a little or it may have just been transferred from the socket. Either way, it seems that Vee's suggestion of the spark plug gasket failing is probably correct.

I had them replaced last August, so they're still under warranty, but they seem pretty easy and none-too-expensive to replace, so I'm leaning towards doing it myself. It'd save me a trip to the mechanic whilst hoping my car didn't stall during a pandemic.

Unfortunately, when I was putting everything back together, nearly all of the bolts holding down the coils stripped their holes. I was able to get all of them finger-tight, but couldn't get to the 7 nm torque spec. I'm thinking I should helicoil them while the valve cover is off.

Questions:

• Is there any reason I shouldn't do the helicoil work myself? I've seen a few YouTube tutorials and it seems pretty straightforward.
• Are the Champion RC12YC plugs an acceptable replacement for the RC12YCC? They're listed as being for lawnmowers and such, but the RC12YCCs have been discontinued and being "double-copper" seems to be the only difference. How about the NGK BKR6ES-11?
• All of my coils are Lucas-branded, presumably original to the car & made in Japan. Vee suggested the QYL coils, at about $82 for 6, and a few threads have indicated they work well. Anyone have issues with them?
• Should I go with Jaguar OEM valve cover gasket + spark plug gaskets + bolt seals? I'm seeing on Ebay a Eurospares kit including everything for $80 and that sounds pretty good. I'll probably use Permatex gasket dressing, as recommended by Vee in another thread.

Thank you!

 

1. You don’t need the gasket dressing. I was really high on the stuff, but that was because I was trying to shoehorn the Eurospare camcover gasket, which is too big. Use the (unfortunately much more expensive) OEM gasket for the camcover, the after markets just don’t work. The aftermarket spark plug gaskets are a different story. URO makes a decent aftermarket part for just the 6 plugs, they don’t make a camcover gasket. Lastly, buy the 13 bolt seals from RockAuto. Much cheaper. I can’t believe what OEM prices are for those bits.

2. If the coils are original, I’d consider investing $82. Keep the original ones.

3. The double copper Champions no longer exist. The equivalent NGK number is 5. Every auto catalog quotes a 6, but those are equivalent to the originally specified RC9YCC Champion plugs. I have used NGK BKR5e plugs without any issues. No need for anything fancy. It seems people who spend extra on iridium or platinum plugs tend to have problems, not always, but why chance it? Changing plugs will take you less than 20 minutes.

4. I have done helicoils, and since all the holes are easily accessible, with the tricky ones being closest to the windshield, I would do it myself. You will have several to do, so just remember to take your time. It isn’t difficult, but when you have so many, you start to get cocky. I would consider Timeserts, only because I think it’s a better concept. Either one will work well because the torque needed isn’t much at all.

 

Quick update: the new coils arrived and I thought they were going to come with gaskets but did not. My car has never had gaskets on the coils. How necessary are they?

 

The gaskets just keep dirt and moisture out. I just got a set on line for about $27.00. Probably good to have them to keep the dirt out so none falls into the spark plug holes when replacing the plugs.

 

I use them when I have them, don’t when I don’t.

For $27, I’d rather buy a sheet of rubber from the hardware store and make my own....they would probably work better too!