Hello all, and thank you for reading and offering any advice.

I recently purchased a 1996 4.0 VDP. I am now the 3rd owner and the car came with extensive maintenance history, including every fill up. The car moved about 900 miles in the past 3 years, and had a total 81,250 miles on the dash.

After purchasing the car and trying to drive it home, (2 hour drive), I noticed it never reached normal operating temperature on the dash and the needle moved about a quarter to normal. It started jerking and bucking about 20 minutes in shortly after getting on the highway which I now think was limp mode. It would lose power like it was stalling and then regain power. I started to smell a burnt smell in the cabin and pulled over at the next available exit which was 2-3 more miles. It lost complete power on the exit ramp and I was able to pull it into the gas station. I had it towed home the rest of the way.

I immediately replaced the thermostat, car now reaches normal temperature, drained and filled radiator, new Champion spark plugs, crank position sensor, fuel filter, and oil change.

The car now consistently stalls. If I start the car and let it idle in park, it will stall after 15 minutes and throw a P1775 code. If I drive the car around the neighborhood, the transmission seems to shift fine, but the car will stall 5-10 minutes later, the transmission light will illuminate, and will throw P0727 and P1775. The car will always restart after either situation, but will stall again after 10-15 seconds. It now has 81,295 miles.

Again, thank you for reading and offering your advice. The car is in such beautiful condition and deserves to be out on the road.

-Carter

 

Please let me know where the car idles, in park, either cold or warmed up.

Immediately I want to tell you that these cars are notoriously stingy with helpful codes. The two you have shared are of the less useful type.

I would recommend, because its free, to check and clean the EGR valve.

I would also recommend, because its cheap, and the car had a cooling issue, to replace the $20 coolant temperature sensor. It will take you 5 minutes and you might loose a pint of coolant.

Lastly, you should have a tool that will read the OBD2. Not just the codes, but also the LTFTs, coolant temps, etc. A simple ELM27 dongle, with a smartphone app would be valuable. iPhones only work with WiFi dongles, while Android phones can use bluetooth types.

 

This is a "long shot " but is the tank venting OK? If the tank builds up a vacuum the fuel pump struggles to supply fuel to the engine
I currently drive an X300 but a previous XJ40 I had gave me similar problems which I traced down to a venting problem
Try running it with the fuel cap off and see what happens.

 

Vee, thank you for replying.

The car idles at 1100 RPM upon cold start, lowers to 800 a few seconds later, and idles steady at 750 when warmed up in park.

I wish I had more useful codes/info to share. I have a more advanced scan tool on the way and will share more information when available.

I checked and cleaned the EGR valve. The valve will stick open when pushed very hard but seems to operate freely when depressed gently. The car has the same symptoms.

Just to be sure, the coolant temp sensor is the one with the single red/orange wire on/near the thermostat housing?

Again, thank you for taking the time to reply.
-Carter

 

Bill, thank you for the tip.

I tested running the car with the fuel cap off but that didn't seem to change anything.

Thank you,
-Carter

 

The ELM - 327 device will give live data which will be helpful other then no codes flagging

The coolant temp sensor to the dash is the single wire connector and not he most accurate

The coolant sensor to the ECU and engine regulation is the 2 wire connector and the close loop mode is reached at 88 C

There is 1 speed sensor in the transmission ( other then the CKPS ) that passes through the transmission body connector to the transmission ECU and on to the engine ECU as they talk to each other as they regulate during there dance together

Stalling moments out of the park detent is the behavior from reading of a dirty transmission connector

The connector must first be pulled aft about 1 / 8 inch and then twisted , note the use of tie wraps to grip on twisting

With the ELM - 237 your EGR _ Error PID is target value 0.0 %

Short term fuel trim is also 0.0 %

See page 51 for your AJ16 engine with codes on page 111

801S TITLE (jagrepair.com)

ELM - 327 also comes in USB cable for laptop













Pics coming

 

I think Parker7 meant to indicate that the LTFT goal is zero. The STFT should be changing all the time.

Nevertheless, the ability to see what the ECU sees is quite valuable to solving problems here. Take advantage of this feature!

If we can cross off the EGR (for now) then that is good. I had similar issues when I first bought my car. One day that darned thing shut off on me on the highway! I was able to safely make it to a shoulder, but the power steering was gone (since the car was off) and the power assist to the brakes were also deactivated! The car did finally manage to deliver the failed EGR code and a replacement resolved that problem forever.

Next up, try the coolant sensor. It's cheap and easy. I have attached a picture of the AJ16 indicating which sensor is which. (You want #17)

I can be wrong here, but for the XJS, a warmed up car idles at 700rpm. The fact that your car is idling higher may indicate a vacuum leak. Please check hose connections between the MAF and the intake manifold. Make sure none of the rubbery hoses have a hole in it. Sometime they can be difficult to spot, so it may help to remove these assemblies for close inspection.

The next item would be cleaning out the throttle body. There's a small coolant hose that connects to it from underneath. A golf tee will clog it up nicely once removed. After that it's just four 10mm bolts without any gaskets at the manifold. Be ready with a full can of carb cleaner.

We're going to have to go step by step here, but the ELM27 with the phone app would be most helpful.

 

The fuel trims from reading other the best is + or - 3.0 % in practice

Do not remove or adjust the throttle position sensor on the throttle body just yet

The IAC valve bolts can snap off if not applied heat to the inside of the TB , locktited , there should be a gasket on the IAC valve that can be missing

There is no gasket between the TB and the intake manifold.

The coolant temp sensor fror the ECU is the 2 wire attached to the thermostat housing

Your idle speed can be found on page 90 and your vacuum hose map is on page 60 of the Jaguar 801s doc

Your idle speed settling down after a few seconds would indicate ...................................

Your cruise control vacuum lines are independent of the intake manifold vacuum lines , it has it's own electric vacuum pump

You will have 2 hot coolant lines to keep the throttle body from icing up and they will enter for and exit aft under the throttle body

I had a vacuum line missing on the EVAP valve under the engine air filter box . you can get the EVAP valve to click with a 9 volt battery

You can jumper the fuel pump relay between socket 30 and 87 to be powered at all times , this will drain your battery with keys in your pocket

Best to use blade type terminals on the heavy gauge jumper wire and not just stuff a wire in there for better connection to run the pump properly

 

Parker 7,

I bought the BlueDriver bluetooth diagnostic tool.

I replaced the coolant temp sensor that talks to the dash gauge and it now says that I am overheating.

The coolant temp sensor to the ECU I ordered does not fit the wiring harness connector as advertised on RA.

Here are my live data logs after running the car in the driveway after 9 minutes.

 

Vee,

I posted a snapshot of live data above responding to Parker 7s post. As mentioned above, the dash now says I am overheating after replacing the single wire sensor. I am returning the coolant sensor to the ECU and ordering a replacement.

I still intend to record live RPMs, clean the throttle body, and check my transmission speed sensor.

Thank you all for your time and input. This was not a car I intended to have to work on, I do apologize for the delay in response.

 

The single wire temp sensor on the thermostat housing is the instrument gause and is not accurate as is a dummy gauge

The 2 wire sensor next to the sigle wire is the one transmitting temp to the ECU for close loop regulation

Age of the Fuel ?

The X300 thermostat does not have a rubber o - ring even if it comes with one , cracks the thermostat housing casting

You will not be using the O2 sensors until the coolant reaches 88 Celcius on the 2 wire sensor

There is a EGR_Error value on the ELM - 327 as you learn to change the PIDs , learning curve thing

 

1. Let’s get that coolant sensor fixed. It will prevent sending your car into closed loop, where sensors operate your car.

2. That being said, I’m rather surprised that the engine isn’t running better with the car running off preprogrammed maps.

3. Your short term trims should be swinging more, it’s practically a flat line! I’m wondering if that’s due to the fact that the car stays on open loop. You should have a PID that allows you to see whether it’s in open or closed loop? On my app, it’s called “Fuel System Status”, and I get a 1.0 value if it’s in open loop. 2.0 or 4.0 if it’s in closed loop.

I’m hesitant to throw out another guess until that sensor has been corrected. Yes, it really is that important. I believe it’s part number LHE1600AA.

 

By thermostat I'm meaning the coolant flow device and not the sensor

2 wire sensor should be changed

No O - ring if you change the thermostat flow device

 

I see new oxygen sensors in your future. The sustained "valleys" in your O2 voltage readings just look too long.

But first, the coolant temperature sensor.

In the meantime, I might pull the ECU harnesses off and inspect the pins. Maybe some corrosion? It's free and shouldn't take too much time.