Hi All

​​​​i have a 2010 V6 XF Petrol.
Have a rather strange situation where I replaced the MAF air sensor months ago, all seemed of for a short time, then the orange check engine light would come on and off at different times.
I filled up with premium unleaded from BP one afternoon and noticed as I went through the tank that the light came on less and less.
Eventually I refilled on BP and now check engine light doesn't come on at all. When it did come on previously, diagnostic computer reported it was running a bit lean.

Is it possible that my engine only likes BP??? Or could this be indicative of a part of sensor having issues?

Thanks, I understand BP is a higher quality fuel but seems odd that I get an engine light if I choose Caltex or something different one day
Cheers

 

Without checking the codes it's all a guess?
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Sure, attaching a screenshot from my cheap wireless fault reader, don't have the proper equipment. Lots of different things came up, I'm assuming this is what mechanic saw months ago
Thank you kindly for any insights offered.

 

It's probably something like a problem which affects fuelling but is (on the premium fuel) not quite bad enough to flag the codes.

Watch the live data fuel trims, especially at idle (hot engine, parked). Then rev to 2500 or so and see if they change markedly.

#1 likely outcome of the above will be bad trims at idle which drop - if so, an air leak.

 

Thank you very much.

About 15 months ago my mechanic did a proper smoke test and didn't find any air leaks.

The mention about fueling was interesting. I don't understand all the inner workings but if I had a slight problem with the part delivering fuel to the engine, could it be that the BP ignites ok but the poorer quality fuel just falls short causing it to register as running lean? If so, what fuel delivery components could be the cause?

I'm wondering if it may not be related to air but more to fuel

Thanks again, appreciated

 

Not igniting... maybe. Would likely be lack of spark but you normally get (other) codes (such as for coils). Or poor ignition which could be spark plugs in dire need of a change (or wrong kind).

Watching the trims is easy and has to be worth doing. You can even do it wearing a suit!

Your engine is near enough like https://web.archive.org/web/20220409...com/page02.htm
and the PCM (aka ECM) software is rapidly going round a loop reading the sensors and controlling the actuators.

 

Thank you kindly. By the way, my cheap fault reader
​​​​... My Jag really really doesn't like it when it's plugged in and more importantly, it doesn't start or operate properly when engine is on, only when engine is off.

So you recommend any cheaper devices that play ball with jags onboard computer nicely?
Thanks

 

Hi mdroc1,

Are you using the correct octane rated petrol? Does it contain ethanol?

Cheers,

Don

 

Probably an elm327 will work.

 

hi Don B
Thanks for your response. Yes - I am using correct octane rating.
I'm in Australia and I can say now that if I fill up using Premium Unleaded 98 Octane from Caltex, Mobil or (a local service station brand), the engine light will be on around 90% of the time.
I'm now on my second straight tank of BP 98 Octane Premium Unleaded and have not seen the engine light in a week, despite a bit of driving, including giving the engine a bit of a workout.
I have been made aware in the past that mechanics regard BP as "a higher quality fuel" but that would make my car or its sensors very very sensitive to fuel quality if that's the real reason I have issues.

It wouldn't surprise me if the Caltex or Mobile is not quite the quality of BP, but if it says 98 octane premium on the pump, I would not expect it to the throw up lean running warnings.

I am rather interested in putting in the middle "95 Octane" petrol from BP. It isn't the recommended ideal petrol and I would expect it not to run as beautifully, but I was curious as to whether this would trigger the check engine light. I assume it would.
Suppose I could just accept that I only can put BP in, but somehow it seems like something about the fuel delivery system might be off by (eg) 5% and that's enough for the engine to 'split the difference' between BP and Caltex.

Any further thoughts welcome

 

Just use OBD live data and get actual data instead of guessing!

 

Yes unfortunately my fault reader doesn't produce great info all the time and I certainly can't drive with it plugged in. Car computer goes bizarre with it plugged in with strange dashboard errors like park brake failure, gearbox fault.

Though my mechanic with a full proper Jag diagnostic computer only came back in the past reporting lean running. In this case , seems like a touch of thinking is involved.

 

elm327 about $5

 

I don't think we've asked you how many miles the engine has done and when was the last time your mechanic gave it a good tune-up. You told us you replaced the MAFS, but when have you replaced the spark plugs with the correct OE parts, cleaned the spark plug holes of any baked-on oil residue, replaced the air filter, put a bottle of Techron Concentrate Plus or Wynn's fuel injector cleaner in the fuel tank per the instructions, cleaned both ends of the engine ground strap and other engine-compartment grounds, etc.? Over time, components drift out of spec and can cause difficult-to-diagnose symptoms. And you mentioned that the last smoke test was 15 months ago. That's plenty of time for more small air leaks to develop in the air intake and crankcase breathing systems.

Cheers,

Don