The 4.0 is different than the V12 as far as engine management (running) is concerned. Much more so with the AJ16 4.0.
You should use Tier 4 grade gasoline and of the octane listed in the owners manual. You will never hear the engine pings, knocks and rattles equipped with a knock sensor. Unless you go far down in fuel to bad gas or kerosene.
The engine management will retard the spark reducing performance, but you will never hear the knock.
Geoff
Thanks for a great question and great replies.
I have a '92 4.0L and if I don’t put in premium
fuel it runs bad.
Is this just my imagination or do I have other issues? I
get ‘‘throttle hesitations’’.
what I’'m doing to the engine, buring
regular unleaded???
Probably waisting money causing the spark to be retarded reducing fuel milage.
In reply to a message from Rile sent Sat 3 May 2008:
Reading from an extra manual I have laying around, JJM 18 02 06/52
may be for '94 or '95, not sure. Page 35 says ‘‘Use only unleaded
gasoline with an octane rating of at least 95 RON…ie Premium
Fuel.’’ Further on under Unleaded Fuel it reads ‘‘Unleaded gasoline
is available in two grades: Regular labeled at the pump as 87 AKI
(91 RON) and Premium labeled at the pump as 91 AKI (95 RON).’’
For myself there’s no real difference between 3.79 for regular and
3.95 (or the 4.05 I saw at one station) for premium. I can still
remember Chevron Custom Supreme 104 octane at 36 cents a gallon,
and filling the gas tank of for 5 bucks and change which seemed
like a lot back then. I get sticker shock every time I fill the
tank and have since 1974. But if it does get to the point that 20
or 30 cents a gallon makes a difference, I’ll sell the car, or if
nobody will buy it, drain the fluids and put it up on blocks. But
for the 2-3k I drive it a year it’s probably not an issue.
Lee Murray–
The original message included these comments:
I’ve got a 96 XJS convertible with the 4.0L engine. Automatic
tranny. Now!!! The sign ON the gas cap says premium. However
the prior owner says, ‘‘don’t have to. I burn regular unleaded’’ So
I did, and have been since first part of April. But I’m wondering,
what I’'m doing to the engine, buring regular unleaded???
I’d appreciate the comments from those ‘‘in the know’’/??? Thanks.
In reply to a message from 345 DeSoto sent Sat 3 May 2008:
DeSoto,
For what it’s worth, my wife’s daily driver is a 97 STS (Northstar)
and it has been runnning on regular, since forever, with no
problems or knock.
With regard to gasoline detergents, No one has convinced me, nor
provided proof, there is any variation, within a brand, from
regular to premium in the detergent additives. In other words,
regular Chevron contains the same amount of Techron as premium
Chevron. There is a variation from brand to brand in the additive
packages which include detergents. Thinking your engine will run
cleaner on premium than it will on regular is another one of those
fairytales promoted by unknowing car salesmen and gas retailers to
push the sales of the higher cost premium.–
lockheed
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
In reply to a message from Kirbert sent Sat 3 May 2008:
Kirbert, you could encounter knock under load conditions,
such as while pulling a trailer up a long hill, or in
especially hot weather, or if you happened to get gas that
wasn’t up to spec, or if someone inaccurately set
distributor timing, etc, etc, so the knock sensor still has
it’s uses.–
The original message included these comments:
Here’s an oddity: My 2002.5 Mazda Proteg�5 supposedly has a knock
sensor, although I dunno where it is or what it looks like. The
I dunno why anyone would fit an engine with a knock sensor when the
engine runs the same on regular as it does on premium.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
25
WayneC wrote:
Kirbert, you could encounter knock under load conditions,
such as while pulling a trailer up a long hill, or in
especially hot weather, or if you happened to get gas that
wasn’t up to spec, or if someone inaccurately set
distributor timing, etc, etc, so the knock sensor still has
it’s uses.
Towing a trailer with a Mazda Proteg�5 would be laughable!
Especially up a hill! And, of course, it doesn’t have a distributor
nor any timing adjustment.
It just perplexes me that, as long as they were providing a knock
sensor anyway, they didn’t go ahead and advance the timing so the car
could take advantage of premium fuel. When you used regular fuel, it
would resort to running just as it does now. I’m wondering if it was
only so they could claim in the specs that the car runs on regular
gas.
In reply to a message from lockheed sent Sun 4 May 2008:
I have been to many refineries, and you may notice that most
operate under some genreic name instead of the primary brand.
Any day of the week, you will see fuel distributed to the pipeline
network, and loaded locally into tanker trucks. The stuff that
goes to the pipeline, unleaded regular for instance, will end up at
some remote depot for further distribution. At this point, as well
as at the refinery location, each load will have the additive pack
added according to the customer specifications. That is why you
will see tanker trucks with brand name, or no name loading at the
same facility. They essentially have the same fuel, with somewhat
diffrent add packs.
But I wonder how different are the additives? The grandfather of
them all is Techron, and I would wager that all others are a minor
variation on their formula, and may very well be manufactured by
Chevron.
You will note that when you buy gasoline futures, they are not
brand specific. Unleaded is unleaded.–
The original message included these comments:
For what it’s worth, my wife’s daily driver is a 97 STS (Northstar)
and it has been runnning on regular, since forever, with no
problems or knock.
With regard to gasoline detergents, No one has convinced me, nor
provided proof, there is any variation, within a brand, from
regular to premium in the detergent additives. In other words,
regular Chevron contains the same amount of Techron as premium
Chevron. There is a variation from brand to brand in the additive
packages which include detergents. Thinking your engine will run
cleaner on premium than it will on regular is another one of those
fairytales promoted by unknowing car salesmen and gas retailers to
In reply to a message from uncle sent Mon 5 May 2008:
Uncle,
My point was that there is no difference in the additive package, a
particular brand uses, that goes into regular gas and premium gas.
The only difference is the octane of the gas. One of the
respondents to this string had stated that premium gas has better
additives than regular gas with respect to detergents. No one has
demonstrated or proven to me that the additive package is any
different (including detergents) from regular to premium within a
particular brand - be it Shell, Mobil, Chevron, Texaco, or whomever.–
lockheed
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
In reply to a message from Geoffrey Green sent Sun 4 May 2008:
What is Tier 4 grade gasoline? How do you know what tier or grade
their gasoline is?
Lee Murray–
The original message included these comments:
The 4.0 is different than the V12 as far as engine management (running) is concerned. Much more so with the AJ16 4.0.
You should use Tier 4 grade gasoline and of the octane listed in the owners manual. You will never hear the engine pings, knocks and rattles equipped with a knock sensor. Unless you go far down in fuel to bad gas or kerosene.
Top tier gasoline refers to the additive package. See:
What is Tier 4 grade gasoline? How do you know what tier or
grade their gasoline is?
We tried to deal with the customer dissatisfaction and make the cars work properly with the bad gasoline in the 1980s when I was head of the Jaguar dealer service department. By using only tier 4 gasoline you will eliminate engine fuel running problems and help keep quality fuel on the market. The reason for specifying additives is found in the following report:
Please pay attention to the two sections: Amendments to PTD Requirements and Opportunity for Public Participation. Write to the EPA with your feelings about how the Bush administration works. No politics flames, just pointing the correct administration to the rule change that may affect your driving.
I have two 96 XJS convertables with the 4.0 engine. I have two guru mechanics. One in Scottsdale Az and one in Goshen Oregon (just south of Eugene Ore.) Both have told me to run premium, and one added, "and use Octane Booster at each fill up. One car has 60k and the other has 80k. Both run peacefully, and I’m happy with that. TRUNK LID WOULD NOT UNLOCK. on one of them. The Goshen mechanic didn’t have to “drill” a hole. Yippeeee!! Bill for accessing. Opening with ‘tools’, and lock & electric motor replacement came to just over $600.00 Did require my having to add another key to my ring. Shop is called British Motor Co… Phone 541-485-8542 He’s very busy. Let phone ring…
Only use 91 or 92 octane
I have used octane boost and it does give a little extra
Best of luck
David
Akm190
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
32
Only use 91 or 92 octane
I have used octane boost and it does give a little extra
A little extra what?
In general, if you can tell a difference, you needed the octane boost. If you
can’t tell the difference, you’re wasting your money. But the difference
should be in what you hear – unless the engine has knock sensors.
Interesting stuff, but, so many variables as usual.
I have no intention of defending oil company profit, aka “rip off”?? The numbers reported are certainly huge. No question there. But, so is the investment. It costs tons to find the crude, transport it, refine it and distribute it. Figuring out the real value of a refinery property for tax purposes is herculean.
Bad gas a such isn’t anywhere as prevalent as it once was, at least in CA. Most was the result of old and dirty leaking under ground tanks. Now gone.
Most areas use gas from a limited number of refineries. We have two large ones and a smaller one. so, no matter the brand, the fuel came from one or more of these As stated, minor differences in the additive packages.
My LT1 does have a knock sensor. But, I find 87 runs just fine in it. But, caveat, my ears are definitely impaired.
Not sure about my 94 4.0 Jeep 6. I suspect it does. But, I also suspect that it’s EFI is Bosch Jetronic or very simlar. ONe day, I’ll research that. It also does just fine on 87.
Kirby, No idea as to the architecture of the engine in your Mazda. But, it’s knock sensor may look like a diaphragm bellows with a wire attached. Dependaant on it’s management system, it can assure maximum timing from the 87 sans a knock.
My Jeep refused to run on an empty tank!!! A whole other story…
I have two 96’ XJS’s. Both under 82k miles. Both converts. Both 4.0 L engines. I have two reputable Jaguar mechanics, abouyt 1,500 miles apart from each other. Both say, use Premium, and then add Octane Booster. So I have been doing so on both. No ping. Engine runs better. (where’s my crystal ball to tell me the difference?)
Wait, you’re running premium AND THEN ADDING AN OCTANE BOOSTER?
OK, you can cut out the octane booster immediately. I have the timing bracket on my AJ16 and I use premium fuel, however I understand there are some people who run regular with no perceived issues. I believe the bracket takes full advantage of the premium fuel whereas the standard engine will indeed work fine on regular. Your results may vary, but ditch the octane booster!
Wasn’t in the old days these XJS’s were made that premium was to be 100%
octane? Well, sometimes, I only find it to be 93 or 91. So adding Octane
booster is by my two different guru’s recommend this??? And they are
not selling it to me. One’s in Scottsdale, and the other is in Goshen
Oregon.
“ditching the octane booster” leaves me confused. Are you a Jaguar
experienced mechanic? I need to know, be cause I am 83 years old and don’t
know s–t about “mechanical things”.
Thanks Veekay