Bought a 95 XJ6 about six months ago. I really love this car. Bought it with < 130K miles. Fixed a few minor things since purchasing (coolant hose, rear shocks, interior tidbits).

Anyway, car has been running great until just recently. Starts up w/out issue and drives normally until fully warmed up. Then, I have to give it barely any throttle and keep the RPMs below 2000. If I give it too much throttle, it really hesitates, bucks, and just won't accelerate unless I release pedal and gingerly give it barely any gas. Driving it home on the interstate, I gave a little too much throttle and it stalled...CEL and Transmission Light came on. My code reader / scanner said P0727 (Transmission not receiving speed signal, or vice versa). Pulled over to side of interstate, waited a few mins, and it started right up, without the Transmission light on...just the CEL. Cleared codes. No lights have returned. Drove it home on back roads.

I just took it down to the store. It started and drove great (shifted gears, etc) until it fully warmed up and, then, same problem...won't rev past 2000 RPMs.

We had a gas shortage here just before the problem surfaced, when I was unable to purchase premium fuel. Twice, I was trying to fill up with mid-grade and only got $.30 and $.27 before tank went dry. So, was forced to put regular unleaded. Car still seemed to drive without issues, but then this suddenly started. Thought maybe it was bad gas so, when tank was almost empty, I put in a bottle of HEET gas treatment and filled up with Premium. Was hoping maybe it just needed to cycle some bad gas through, but I'm now down to about 1/2 tank and no improvement.

I don't really want to start throwing parts at it. I've replaced fuel filter, tested Crankshaft Position Sensor (w/ multimeter), pulled EGR (seems fine), and cleaned all connectors with electronic cleaner.

Tested vacuum at intake manifold and it held steady at 19. No fluctuation. When I increased throttle, the vacuum gauge dropped sharply down to about 0, before releasing throttle and it bounced back slightly above 19. Then, steadied out at 19 again.

Any help or guidance on what to check/test would be greatly appreciated. Wondering if this sounds like a clogged Cat and, if so, if it could've happened that quickly from running Regular or getting the dregs of the underground tanks?

Thanks for taking the time to help out a new member to the Jag community.

If any add'l info would be useful to help diagnose, like LTFT, STFT, etc., please let me know.

Thanks again,
Keith

 

I'm also not a fan of throwing parts at a problem but with these symptoms I would throw a CPS at it first.

You cannot really test the CPS with a multimeter. A bad reading will confirm you have a bad one but a good reading doesn't confirm you have a good one.

You can test the signal with a scope if you have access to one but other than that I would replace it. If it doesn't need one now it's only a matter of time before it does so it will not be wasted investment.

 

The fact that it's okay cold when it's on open loop, where fuel mixture is determined by info stored in the ECU, and won't run when warm on closed loop when the oxygen sensors get involved might indicate a sensor problem.

The 95's don't communicate through the OBD port very well and you usually can't measure the LTFT, but you should be able to read the STFT. Also, use your reader to check the temperature, that sensor may have a problem. Lastly, does the outside air temp read correctly on the climate control panel?

You may have to take it to a Jag specialist to sort this out.

Please visit the new member area and introduce yourself when you have time. Link below.

New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum

 

Thanks for the quick replies. Well, the CPS was my first inclination but, when I realized it didn't start acting up until car was fully warm, I started to question whether the CPS would be temperature dependent. So, then I began to question O2 Sensors or clogged Cat, but haven't really got a clue at this pt.?

Using scanner to check temp, the IAT and ECT temps appear normal. I'll check the temp display on the climate control panel.

Thanks for the tips.

 

Also check the short term and long term fuel trims as I mentioned in my post. I've never had a problem with my XJ6, so I think we need one of the more experienced members to consider this case.

 

"Well, the CPS was my first inclination but, when I realized it didn't start acting up until car was fully warm, I started to question whether the CPS would be temperature dependent."


Yes the CPS can be temperature dependent. Read this thread.

https://www.jaguarforums.com/forum/x...p-guys-160411/