I currently have a non-flashing orange check engine light. I also saw a quick flash of 'Restricted Performance' but it goes right away. The car does exhibit reduced power. The engine is also running rough.

I had Pep Boys do a complimentary code reading today. It showed 11 codes:
P0300
P0305
P0305P
P1316
P1316P
P2097
P2097P
P0456P
P0355
P0355P
P1000P

My first question: Several codes appear to be the same, the difference being the 'P' at the end of the code - e.g. P0305 and P0305P. Is there a difference between the two or is it the same code?

This whole problem started the day before the Florida storm. I went to get gas at Sunoco, my usual station. But they were out of the usual grade that I put on - Grade 3, 91 octane. So I put in Grade 2 - which would obviously be a bit less than 91 octane. My suspicion is that this couldn't have started the problem, but I thought I'd mention it. I'm also torn between where I should bring the car - the dealership, or my local tech, who I have a lot of faith in. But he's more of a European car specialist, as opposed to a Jag specialist.

Thanks in advance...

 

Extra P may be "pending". Fix the others and they'll probably be fixed as well.

You probably have a marginal/failing/dead coil on cyl #5, though it could be wiring or perhaps the plug.

Take coil out and check for oil/water/etc in plug well.

Swap coil with another if you like and see if the fault moves.

P1316 is bad news as it means damage to the cat. Don't let this happen for long...

I'm doubtful it's the fuel though maybe it tipped it over the edge.
---
You should not have P1000 - it should be P1111 - so worry about how that happened, but fix the cyl 5-related issue urgently.

 

Never heard of fuel being referred to a Grade 3, 2 etc, but the octane rating of fuel has no relationship to misfires. Old myth.

I'd delete the codes an see which one(s) immediately come back. Start there.

 

Just meant that there are 4 gas choices at the Sunoco, with 4 being the highest oct. (93 I think).

 

MediaBob

"This whole problem started the day before the Florida storm. I went to get gas at Sunoco, my usual station. But they were out of the usual grade that I put on - Grade 3, 91 octane. So I put in Grade 2 - which would obviously be a bit less than 91 octane. My suspicion is that this couldn't have started the problem, but I thought I'd mention it. I'm also torn between where I should bring the car - the dealership, or my local tech, who I have a lot of faith in. But he's more of a European car specialist, as opposed to a Jag specialist."

Your 4.2 (unless it's S/C'd) engine is spec'd to operate in a range of 10.25 to 11.25 compression and that requires 93 or higher octane for maximum performance. Lower octane fuels without the addition of what used to be called "antiknock" compounds back in the dark ages of the 60's will, in a high compression engine pre-ignite or knock. Yes the engines are equipped with sensors to retard the timing to minimize that but they will still knock and you will have a drop in performance. There's a lot more detail and over 100 years of research and development that supports all this as well as real world experience to back this up so there are no rumors or myths involved.

The effects are almost immediate so your right to suspect that your choice of a lower grade fuel is most likely the proximate cause. This is especially true given that prior to that you weren't having these problems.

My '99 XK had a similar problem a couple of weeks ago with what I suspect was a bad load of 93 Octane Standard Oil that made an already troubled engine much worse. I ran about 1/2 a tank before I switched to a different station and brand (Shell 93 octane) and within a matter of 15-20 miles most of the troubles went away. I'm still working on a couple of longer term fueling problems but there's no doubt in my mind that they were made worse due to a load of bad or tainted fuel.

It's a real problem with cut rate stations, off brand fuels, and older in ground tanks with water contamination problems. Florida also suffers from a high rate of sulphur in it's fuels and has for decades with the lower tier suppliers and west coast suppliers

 

False. The owners manual clearly states 91AKI fuel for all versions of the 4.2 engine. Test have proven that running higher octane achieves zero.

Again, false. The 4.2 engine has been around since 1993. Not one person including myself has noted any negative effect when running on lower octane fuel (as low as 87) either short or long term. Even if low octane were to induce detonation in these engines, it would not be detected as a misfire as a requirement of detonation events are preceded by the normal initiation of combustion.

Let's not keep repeating old myths and misunderstandings.


Contaminated fuel has nothing to do with octane levels. Since almost all fuels come fro one or two refineries in a given area and only the additives (may) vary, how do only off brand stations get high sulfur fuel (which wouldn't cause the OP's prblem anyway?)

 

To add to this, don't forget that more recently, alcohol was added to fuel, at least part of the year. Alcohol LOVES water, so old assumptions about water in fuel don't necessarily hold any longer.

From a personal experience, I went through a bout of detonation recently. I was running 93 octane pretty consistently (tried 91 once). Symptoms were "popping up" going uphill at low rpm. I was surprised the knock sensors did not jump in and adjust the timing. I ended up finding high fuel trims in the teens (not enough for a code). The cure was to go around the heads and replace all o-rings, including PCV valve and dip stick. VVT seals, too. Also replaced the air flow meter with an appropriate DENSO unit as I was not terribly happy with the air temp. After all of that (mostly a bit of time, very low $), the trims are back in the low single digits, and the uphill/low rpm is now quiet again.

I suppose I am saying that even if codes only trigger for high trims (25+), having mid trims is not a good place to be, and you can feel it once you manage to bring them down: engine more responsive, and able to handle more torque without downshifting.

Best of luck, keep us posted.

 

Much of North America has had E10 for 20-30 years. Nothing new, other than regulations in the Lower US which states that there must be a sticker on the pump.

 

+1 that having mid-teens trims already points to problems

I check trims more often than I change oil - and would not dream of leaving oil in past the jag schedule.

 

[QUOTE=Mikey;1761142]False. The owners manual clearly states 91AKI fuel for all versions of the 4.2 engine. Test have proven that running higher octane achieves zero.



I've been driving everything from tractors to Formula Fords and a wide variety of street cars including 12 cylinder Ferrari's and 4 cylinder Fiats for 60 of my 70 years and while a couple of your statements may have some germ of truth to them for the most part they're wide of the mark.

Lower octane fuels in high compression engines inevitably lead to knock and loss of performance one way or another.

There are anywhere from 8-12 varying octane ratings around the world and in the U.S. there are generally only 3 available at most stations (Sunoco has offered a variety of dial your own blends for decades but I haven't used them in 40+ years so I don't know their current set-up) with those being 87, 89, 93 in our area.

As for higher octanes being of no advantage you should ask folks who drove air cooled low compression engines like the original VW Beetles and other such cars when they started to have engine run-on after they turned off the ignition that was caused by hot carbon deposits on the plugs continuing to fire the remaining fuel vapors.

For those who have an interest in finding out the reality instead of half-truths and B/S here's a link to an in depth paper on fuel octanes......or you could spend time with people who build and race cars for a living.

https://en.wikipedia.org/wiki/Octane...28R.2BM.29.2F2

"An octane rating, or octane number, is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance gasoline engines that require higher compression ratios. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines, because diesel engines (also referred to as compression-ignition engines) do not compress the fuel, but rather compress only air and then inject fuel into the air which was heated by compression. Gasoline engines rely on ignition of air and fuel compressed together as a mixture, which is ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters mainly for gasoline engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking.[1] "


In the mean time you can argue with the engineers who design these engines about the intelligence of burning lower octane then is spec'd in our engines since they've only spent 100+ years learning their craft in the real world.

 

[QUOTE=fmertz;1761192]To add to this, don't forget that more recently, alcohol was added to fuel, at least part of the year. Alcohol LOVES water, so old assumptions about water in fuel don't necessarily hold any longer.



fmertz...I need some clarification. Are you saying that the use of alcohol in current fuels RULES OUT the possibility of water contaminating fuel? Since alcohol and water have a love hate relationship it would follow, I believe, that water would in fact be attracted to fuel more readily. Of course in reality alcohol just allows the water to more easily mix with gasoline instead of floating on top so that any water that would get into a gas stations tanks would more thoroughly mix and get pumped into your car instead of floating on top of the gasoline and only getting pumped out as the tanks get closer to empty. All things being equal of course.

And by the way (for those on the sidelines) water and other fuel contaminants do reduce octane levels absent any other off setting measures.

As an aside hangovers are caused by the alcohol you drink combining with the water in your body and being drained at every visit to the can. That cause dehydration and the constriction of blood vessels which really effect the ones in your head the worst. Next time you go on a bender <G>) drink lots of water every time chance you get and the after effects will be a lot less.. And owning a Jag can sure cause a person to go on a bender now and then.

 

That's run-on induced by pre-ignition, nothing to do with detonation. If you don't know the difference between pre-ignition and detonation, then the wikipedia article you quote offers the following


In a normal spark-ignition engine, the air-fuel mixture is heated due to being compressed and is then triggered to burn rapidly by the spark plug. During the combustion process, if the unburnt portion of the fuel in the combustion chamber is heated (or compressed) too much, pockets of unburnt fuel may self-ignite (detonate) before the main flame front reaches them. Shockwaves produced by detonation can cause much higher pressures than engine components are designed for, and can cause a "knocking" or "pinging" sound. Knocking can cause major engine damage if severe.
The most typically used engine management systems found in automobiles today have a knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level.


Note the final sentence about knock sensors.

 

This might help clear up more myths

Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

 

My (superficial) understanding is that alcohol in the fuel will tend to carry any residual water with it to the engine over time. Here in the mid-atlantic, I believe gas is supposed to contain alcohol only during the winter months. So I assume this water consumption is out the rest of the year. I am talking about the normal process of running a car. As the fuel is consumed, air is allowed back in the tank. That air contains moisture that can condensate in the tank if it is colder. I believe (with no data, really) that this additional water can be handled by the alcohol in the fuel, over time. Now, I am a lot less confident this would work at the level of an entire gas station so contaminated fuel is still possible. But from the perspective of water in the fuel distribution, having alcohol helps.

 

[QUOTE=Mikey;1761582]That's run-on induced by pre-ignition, nothing to do with detonation. If you don't know the difference between pre-ignition and detonation, then the wikipedia article you quote offers the following.

Mikey, oh Mikey, I was suffering from pre-ignition woes probably before you were born as my mid 60's bugs, which like most low compression air cooled engines running on gasoline engines burning tetraethyl led compounds to reduce knock tended to do from time to time. The plugs would get fouled with carbon deposits that could be reduced or burned off by running a tank of high test as higher octane fuels run cooler. You'd notice the difference within 10-20 miles. we didn't run it for anti-knock we ran it to minimize or eliminate for awhile the tendency towards pre-ignition. I posted as just one of many reasons for using higher octane rated fuels which you appear to believe are a waste of money....much like those who believe that childhood inoculations cause more illness than they prevent.

As for knock sensors reducing knock to an "acceptable level" I have stated as much in previous posts with the caveat that by doing so you also sacrifice not only the horsepower your engine was engineered to develop but all the performance that goes with that. As general rule every
1 point drop in compression, for whatever reason, lessens an engines output by 20 horsepower. If your fine with that and the long term negative effects of running hotter burning lower octanes then go ahead as it's your car and your money.


Just don't try to make the case that people should run lower octane fuels and expect to have the same level of performance both in the short or long term as those who run the proper octane fuels.

 

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I suppose there's some truth to your belief about it helping get water 'burned' but here in Florida with our generally low lying coastal areas and high ground water levels contaminated fuels from older inground tanks have always been a problem that's best addressed with water separators in some areas. We also used to suffer from lower grades of gasoline that had high sulfur content, especially Tampa. That may be less of a problem now but if the gasoline or diesel is refined from poor Venezuelan crude there will be high sulfur in it as there oil is low grade stuff even though we have been cutting back on Venezuelan crude over the past few years.

About the only positive thing I'm willing to give alcohol credit for is that it does help cool the fuel charge as it burns less rapidly than gasoline but gives less energy in the process. Some 20% less if I recall correctly. It's also quite a bit more corrosive than gasoline so it's effects in high concentrations can be a real problem in engines and fuel systems not specifically designed to deal with it.

 

You're still not reading or comprehending. I did not suggest that the OP SHOULD run low octane gas, just that it's not the source of his problem. There's plenty of proof available if you take the time to read up.

BTW- all gasoline burns at the same temp (and speed) irrespective of octane rating. Again, please stop repeating myths.

I spent 31 years in engineering and support at a major engine OEM and would have been fired on day 2 had I repeated some of stuff above. Luckily I already knew better.

Hopefully the OP has not been scared off by this and will report how things are going.

 

If you weren't in Florida or Houston before, during, and directly afterwards you'd be largely unaware of not only the immense traffic jams (took me 3 hours to drive 15 miles to home) as people evacuated S. Florida in the days before Irma hit. I live 400 miles NORTH of the Keys and on the western side of the state and traffic during the day was often backed up for 15-20 miles heading north. Police had to man the intersections and guard the gas stations which were all overwhelmed with people desperate for gas.

The problems start when the stations tanks start running dry as all the garbage accumulated at the bottom of those tanks starts finding it's way through the various filters into peoples tanks and with the almost microscopic injector holes in most of today's fuel injected cars there's bound to be problems with lean burning cylinders, misfires, etc.

Add to that the contaminated and sub-standard fuels that second and third tier stations have supplied to them (and the occasional 'gypsy' tanker load that gets bought on the cheap) and you're likely to get just the kind of problems that MediaBobNy had to start this thread.

In other words it isn't always the cars fault<G>

 

The 4.0 and 4.2 V8's in modern Jags are designed as high compression engines and their production variances allow a deviations of 1/2 of a point in compression so that they can have a ratio anywhere from 10.25 to 11.25 from a spec'd rate on 10.75. At either point they require, for maximum performance, a fuel with an octane rating of 91. Since the majority of pumps in Florida, and I suspect most of the states, offer one of 3 grades of gasoline marked 87, 89, and 93 respectively it would be difficult to regularly fill up with 91 octane. In fact it would be damn near impossible although Sunoco with there 'blend their own' pumps may have it.

So what happens if you have to use, for whatever reason, a lower than spec'd octane fuel? The engine will knock as the lower octane ignites due to the increased compression BEFORE the spark plug fires. Of course our engines, like all engines today, are equipped with knock sensors that work to reduce knock to acceptable levels. Since the computers can't raise the octane level they have to reduce compression through changes in timing that change the valve overlap of intake and exhaust valves through their variable valve timing.

A lowering of the compression level always results in a loss of horsepower (as a general rule of thumb every 1 point drop in compression results in a loss of 20 HP) and depending on how much lower the octane is that loss in HP could be greater. Modern engines generally do well with the following octanes at the following compressions. (not absolutes but probably safe enough for most of us.)

87 Octane is good up to about 9.5 to 1,

91 octane is good up to about 10.5 to 1,

and 93 can go up to about 11.5 to 1

So, in order to drop knock to "acceptable levels" it's probable that our Jags lose something on the order of 1-1.25 points of compression and the loss of the relative amount of horsepower.

Also at 93 octane, which is two points above the required minimum our Jags are good to something on the order of 11.5 compression which is over the highest production variance of 11.25.

What else might contribute to a loss of octane? Well, anything that would dilute the fuel in sufficient amount to mess with the blended compounds. Historically water has been the most prevalent contaminant and that is especially true in Florida and other low lying areas with high water tables.

While Mikey contends that no one on the forum has every experienced or stated that they've had a problem with tainted or sub standard fuels I can state that he's wrong as I personally have gotten at least two bad fuel loads in the past 3 years with my XK8 and over 70 years of motoring all over the country I've had several more.

Whether that was or is the case with MediaBobNy, it is a possibility since in his own post he wrote:

"This whole problem started the day before the Florida storm. I went to get gas at Sunoco, my usual station. But they were out of the usual grade that I put on - Grade 3, 91 octane. So I put in Grade 2..." (most likely 89)

And to me I wouldn't toss fouled fuel as being the proximate cause as we're too often firm believers that every code means a failure of the car when all it is giving us is a hint at what it MIGHT be because of a certain result.

 

I should have said that when the computer detects knock it adjusts the timing of the ignition sequence so that the plugs fire BEFORE the compression level reaches the point at which the knocking starts. That reduces compression in every cylinder and reduces both horsepower and torque as well. Yes our engines have variable valve trains but that's not the way to lower compression.

If your satisfied with an engine that operates at 9.5 to 1 or even lower and the loss of 20,30, or more horsepower then by all means continue using lower than spec'd grades of fuel. After all its your car and your money.