My first post here. Hope you experienced pros can give me some advice. Thanks for your help.

2004 XJ8 N.A.

Local shop replaced a bad fuel injector. Then they had an additional problem they couldn't understand. After replacing fuel pressure sensor and regulator, they threw up their hands and gave the car back to me. Here are the symptoms:
Cold starts fine. Runs and idles perfectly. But on a warm restart acts over-rich. I need to hold throttle pedal half down, it fires after a few seconds of cranking, runs rough a few seconds, then clears itself and idles and runs fine. After a few of these warm starts, throws codes P1072 & 1075, too rich bank 1 & 2.
My thought went to Engine Coolant Temp sensor, but temp gauge reading normal, and does not appear to run rich other than during a warm restart.

 

Again, this from Copilot AI:


🔍 Sensor Location

• The coolant temperature sensor is located on the coolant rail, on the top right side of the engine, about two-thirds of the way toward the rear.
• It’s typically the sensor behind the one with the single green wire (which is the temperature transmitter).
• On some models, it may appear as a grey connector on top of the engine.

🧪 How to Test It

You’ll need a digital multimeter for this.

1. Visual Inspection

• Check the sensor and wiring for corrosion, cracks, or loose connections.
• Make sure the connector is clean and seated properly.

2. Cold Engine Resistance Test

• Disconnect the sensor.
• Set your multimeter to ohms (Ω).
• Measure resistance across the sensor terminals.
• At room temperature (~70°F or 21°C), it should read around 2,000–3,000 ohms.
• If the reading is far off (e.g., open circuit or very low resistance), the sensor may be faulty.

3. Warm Engine Resistance Test

• Reconnect the sensor and warm up the engine.
• Turn off the engine and disconnect the sensor again.
• Measure resistance—it should now be lower, typically 200–300 ohms when hot.
• A sensor that doesn’t change resistance with temperature is likely bad.

4. Voltage Test (Optional)

• With the sensor connected and ignition on (engine off), back-probe the signal wire.
• You should see a voltage between 0.5V (hot) and 4.5V (cold).
• If voltage doesn’t change as the engine warms up, the sensor or wiring may be faulty.

🛠️ Tips

• Always test with the engine off and cool unless otherwise noted.
• If you’re getting a check engine light, a scan tool can confirm if the sensor is sending erratic or implausible data.

 

I you can buy a SDD, you could start the value logger there.
You can see, if bank1 and bank2 are symmetric and within normal range.

How did the shop find out, that a fuel injector had to be replaced ?

 

Hi @JayChicago
There are at least several threads discussing the issue with the early x350s having issues after a short drive/hot starts. This is typically caused by using fuel blends, i.e. fuels with increased RVP for easier winter starts. The ethanol/butane will vaporize from the heat, creating gas pockets (vapor lock) in the fuel line causing hard starts and a temporary rough idle. This may not be the problem in your case, but it may be. There is a TSB for this problem.

-j

 

check your purge lines at the valve and see if it’s being pulled under vacuum. if the purge valve is stuck open when not commanded and the canister is saturated your trims will trend dumpster rich and it will be bitch to start. when the canister is clear it acts like a large vac leak and trims go lean

 

That was a previous problem. Distinctive miss, P0203 injector misfire. Ohmeter on the injector showed it bad. New injector solved that. But during that work, this current problem showed up, was not a problem before the work on the injector.

 

Then I should have a drivability problem due to the lean condition, right? Once started, drives and idles perfectly.

 

you need to check trims. the car will run ok with maxed out trims or in open loop fault

 

Coming back to your statement regarding the normal reading of the temperature gauge, please be aware that once it reaches the normal reading, it will not show the real water temperature.

Most cars today have a circuit that keeps the reading of the temperature gauge constant and eleiminates fluctuations once the engine is warm as long as the real water temperature remains with certain limits. Only if these limits are exceeded, the needle will start showing the real situation, be it too low, or too high.
The reason for this "compensation" is that people started panicking about overheating as soon as the temperature gauge showed values slightly above the normal values.

So, if you want to see the real water temperature, you will need an external gauge, or a code reader/SDD that can show the real values.

Best regards,

Thomas

 

Further to my post above:

Are you sure about the falutcodes P1072 & 1075? I tried to find them in the DTC catalogue for the X350, but without success.

What I found instead are P0172 and P0175:


Best regards,

Thomas

 

You are correct. It was P0172 & 0175. I made a typo, transposed numbers. My apologies. I'm asking for help here, the least I can do is post correct info so I don't waste your time. So sorry.

 

Thanks for that. That explanation seems consistent with my symptoms. Where can I find the purge valve on this car? (2004 XJ8 sedan)

 

driver’s wheel well

 

No problem, it can happen.
I had posted the excerpt from the Jaguar DTC catalogue for the correct codes in any case. Xalty's reference to the purge canistes seems worth looking at, as there is a reference to it in the DTCs, as well.

Good luck!

Best regards,

Thomas

 

Just pulled the plastic inner wheel well from the dirver's REAR wheel well. Nothing there but brake and wheel sensor lines. Nothing that looks like a purge valve or a canister. Please bear with me, I'm not a pro. I still need to locate the purge valve.

 

Maybe this can help...




Best regards,

Thomas

 

Thomas
Perfect! Just what I need. Step by step, with pictures. Thank you.
Jay

 

I'm back for more help.

Replaced the purge valve. No change; still acts rich on a warm re-start. The old valve did not appear to be standing open, as I could pull a vacuum on either side of the valve with my mouth.

Here is something interesting: The replacement purge valve measured 3.6 ohm. The valve removed measured 0.3 ohm. That's practically a dead short! When I bench tested it, wires started melting.
Looked for a blown fuse. Owner's manual shows purge valve (among other things) as engine compartment fuse 14. That fuse did not blow. Is there a relay somewhere controlling the purge valve that maybe got burned open due to the over-current in the valve?

Or should I be looking elsewhere to explain my rich on warm re-start?

 

Make sure you actually have 12 volts on F14, to ensure you haven't got a bad EMS relay upstream.
Check you have 12V supply right through to evap canister purge valve (no rat chewed wire somewhere), if so, then you might have a failed FET in the ECM due to it driving into a shorted original purge coil.

Note: For NAS vehicles the 2004 V8 schematic also refers to a "evap canister close valve" also supplied via F14 but driven from a separate control line from the ECM (Reference Fig. 3.3 in the 2004 schematic)
You might want to check that this is operating properly as well.

 

valve unplugged means no purge flow period end of story. if that doesn’t help it’s not your problem

slave relay r9 powers a bunch of stuff and then the valve is pulsed to ground directly by the ecm. if the low side driver is shorted it’ll light a hot test light all the time with the key on