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Sensitivity to brands of petrol - BP Ultimate versus Shell V-Power


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I am wondering whether my  2004 x-type 2.1 v6 is particularly sensitive to BP Ultimate in its new formulation and whether I should stick to Shell V-Power.  

As I mentioned previously my Jaguar is an LPG conversion.  Originally, just after buying it I filled it with a bit of supermarket 95 octane petrol and gave it a full tank of LPG. It ran OK at first but then the engine appeared to misfire slightly, then the engine management light came on and stayed on. I filled the tank to the brim with Shell V-Power petrol - the premium petrol and continued running on this. The misfiring greatly lessened. My garage reset the engine management light and all seemed well - for a bit. 

I then found that there was a Valve Saver tank under the bonnet which was empty. So I stopped running the car on LPG while I obtained some JLM Valve Saver Fluid and refilled the car with BP 97 octane Ultimate petrol. The JLM Valve Saver Fluid arrived and I refilled the Valve Saver tank. All appeared to be well - at first. I also bought my own code reader so that I could reset error codes without going back to the garage.

Then when driving around on LPG the engine appeared to misfire and the engine management light came on. Using the code reader I reset it. I ran the car for a bit on petrol alone and all seemed to be OK ... until there was a slight misfire and the engine management light came on again. I reset it and ran it back home. On a 50 mile return journey on petrol alone the engine management light did not reappear. But the engine when running on 97 octane BP Ultimate petrol does not sound as smooth as it does when running on 98 octane Shell V-Power petrol.

Now what I am wondering is whether the Jaguar X-Type has a learning ECU which adapts the engine to use higher octane fuel. The other potential issue is that BP Ultimate now contains a "new engine-cleaning additive pack" Those with long memories will recall the launch of Formula Shell as similar designer fuel in 1986. In a small number of cases the fuel was implicated in the burning out of inlet valves on car engines and Shell withdrew it in the same year. BP claims to have tested its new Ultimate in a wide variety of applications, including older engines and says it is safe for all including the new generation of small-capacity turbocharged petrol engines as well as supercharged, Miller cycle and Atkinson cycle engines.  But frankly, I don't trust BP.

Thoughts? Honest John in the Telegraph when asked about Shell V-Power and Tesco Momentum said "Put it this way, I use nothing else apart from Shell V-Power Nitro plus petrol or diesel and get the best possible performance from my engines, best possible fuel economy and no fuel system problems like the problems readers get when they run their cars on the cheapest fuels."


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Ive seen a program where they tested various fuels and grades from different fuel stations and when tested them they could not tell the difference

they also dyno run the cars and there was only 1 hp difference between the lot

though I use bp ultimate in my jaguar, not for performance, but i think its cleaner and helps the fuel system and injectors

I just wonder if you dropped on a bad batch of fuel, I know years ago a local tesco to me had a few problems with cars, where there fuel damaged lambda sensors, due to a bad batch of fuel



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Thanks. What I think has happened is that the EPC in the Jaguar is making a series of measurements and calculations based upon other sensors including a knock sensor. Controlling fuel delivery and the ignition timing are high on the microprocessor's priority list. The microprocessor dictates the opening and closing cycle (pulse) of the fuel injectors, effectively regulating the air/fuel mixture ratio when making minute timing adjustments thousands of times a second. Using LPG which has a RON equivalent of over 100 has meant that I need to have petrol which is between RON 98 to RON 100 to keep the EPG within its parameters. BP Ultimate is only RON 97 but it used to be RON 98 prior to its reformulation.

The entry in Wikipedia regarding Shell V-Power suggests that I may well be onto something:




Edited by AliKelman
Correct and insertion of a Wikipedia link
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I don't think its air/fuel mixture ratio

Modern cars are microprocessor controlled as you say, its constantly try's to reach stoichiometric, A/F ratio is 14.7:1, as it does this many thousand times a second, 

if fuel alters or you get a air  leak it compensates for it instantly,for a air leak you have fuel trims, short term fuel trims and long term fuel trims, but if they usually reach 25% you get a engine management fault

can't see fuel grade effecting it, unless there's another under lying fault

here a video describing fuel trims to attain stoichiometric its interesting https://www.youtube.com/watch?v=5WnM_NsOtd8&t=51s



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Thanks. Part 2 of the video establishes that it should not be a fuel pump fault because a V6 has two stoichiometric codes, one for each bank of cylinders. Since I was only getting a single code fault this would indicate that it was not a fuel pump fault. 

I'm going to top it up with Shell V-Power this afternoon - I used about four gallons of petrol yesterday. Let's see if it runs any better. 


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