My 1996 XJ6 loses power after about an hour of driving. From a complete stop, it struggles to accelerate and if given too much throttle it “chugs” to the point where it almost stalls. Similar chugging occurs at any speed if too much throttle is applied. Give it a 10-15 minute break and acceleration will come back at lower speeds and some acceleration returns at higher speeds for a short period of time. I have replaced bank 1, sensor 2 O2 sensor. Check engine light is on after being reset following the replacement of the O2 sensor. New code is P1138/P1158. I have cleaned the MAF with MAF cleaner. I understand the O2 sensor may be the culprit but was curious if other things come to mind. Also, my fuel pump is whining and will be replaced once I get it in the mail along with the filter. I am no mechanic but am able to follow guides/videos to get things done. The most confusing things to me are when the symptoms occur (after an hour or so) and how it “resets” for a short period of time after a break. Any input would be appreciated.

Thanks

 

I would start with the fuel filter. As the pump is whining it’s in tank filter may also be getting clogged and turning off for a few minutes allows the crap to sink to the bottom of the tank, till the cycle starts all over again.

 

Plus heaps to what has already been mentioned.

Back to basics,

Filter 1st, maybe pump, tank flush 2nd, then see what happens.

The X300 OBD is pretty basic and not that good.

 

Thank you for the responses. A new fuel pump and new filter should be arriving soon. Is there a “best” or “easy” way to flush the tank. My intention is to replace the fuel pump from the top by cutting an access panel in the decking behind the back seat (I know it’s a shame to cut up a beautiful car).

 

Hi BluuJaag,

What codes were present prior to your replacement of one of the O2 sensors, and which sensor did you replace?

I am attaching the Diagnostic Trouble Code Summaries for your car, which give Jaguar's definitions and possible causes of each DTC, which are often different from the generic definitions. Here's what the manual has to say about your current codes:





Since the O2 sensor connectors are identical, a common problem is connecting the Bank 1 sensor to the Bank 2 sensor harness, and vice versa. You might try reversing the connectors for the two downstream O2 sensors, clear the DTCs and see if they recur.

Your whining fuel pump certainly sounds like a good suspect and an obstructed fuel filter can cause premature pump failure. I heartily heap dittos on Cafcpete's and Grant's recommendations.

Other possible causes of your symptoms that come to mind are a failing Crankshaft Position Sensor (CKPS), which is known to have heat-related failure modes, and a failing Engine Coolant Temperature Sensor (ECTS), which could be telling the Engine Control Module (ECM) that the engine is cold even once it reaches full operating temperature, prompting the ECM to continue to apply cold-start fuel enrichment even when the engine is hot, leading to over-rich running. Sometimes other components can exacerbate the problem, such as an obstructed air filter, stuck-open coolant thermostat, etc.

Cheers,

Don

 

Only good way to flush that tank is OUT of the car.

One of mine had a plug, dead centre, bottom, facing the spare wheel, the other 2 did not. That one was easy, the others, tank out, not that bad really.

Make sure you have, or fit, a hose clap on the fuel pump supply hose, they did not all have a clamp, and that hose blows off. There was a Service Action about it, but none of mine had a clamp.

 

So I replaced the fuel filter; just for fun I guess as it made zero impact to performance. I did discover that the fuel lines looked dirty when looking inside of them. Also, the sluggish performance seems to worsen when the car is lower on fuel. Leads me to believe, as others mentioned, the tank is dirty and the gunk is more concentrated at lower fuel levels. Have decided to replace the fuel pump the right way by dropping the tank so I will be able to clean it thoroughly. I am a little apprehensive to do it as it seems like it could be a challenge to disconnect some of the fuel lines. I have only run through two full tanks of gas on the car so it is still pretty new to me. Just received new front shocks which feels like a more manageable job at the moment. Thanks again for the responses.

I do think the CO2 sensor that was replaced could be loose. My father helps on the car and was the one to do that job. It seemed he had a hard time getting the sensor to thread back in. Saw somewhere maybe tack welding a solution? Not at that point yet.

 

The O2 sensor should thread into the exhaust as easily as a spark plug threads into a cylinder head. If he had trouble getting it to thread in, perhaps it is cross-threaded and leaking, or perhaps the threads in the exhaust are corroded. Unless access to a particular sensor port is very difficult, I always clean the threads in the port with a battery terminal brush and apply anti-seize compound to the threads of the new O2S if compound was not pre-applied at the factory. Tack-welding should not be required!

You may be able to hear an exhaust leak at the new O2S. If you can't hear it with the "naked ear," a 3-foot section of rubber tubing can be used as a stethoscope to hear exhaust gasses leaking around the sensor.

Cheers,

Don