By retarding timing, and losing some performance, how well do the six and double six motors run on 87 octane gasoline (regular fuel)?

 

As it says in the header - THIS SECTION IS NOT FOR TECHNICAL QUESTIONS.

From your previous posts and your profile, I can't work out which model you have. Please confirm and I'll move this question to the appropriate tech section.

Graham

 

These vehicles are designed for maximum performance and pleasure of driving. The use of lesser fuel will drop fuel economy and performance. I have seen a drop in as much as 3 MPG on lesser fuels and then there is pinging and engine detonation which eventually ends in very big repair bills. If you drive a Jag casually and not drop the hammer they get reasonable mileage if tuned and maintained.

 

Thanks Graham, this answers my questionn

 

The answer to this post is simple.... pay now or pay more later!... never run a Jag engine on 87!!!

 

About 20 years ago I owned two XKE's and 1 XJ6 AND 1 XJ12C. Since 1998 I have owned a 1998 Lincoln TC (premium fuel). In all of these cars I have run Regular fuel without a knock or any other problem. I just retarded the ignition a few degrees. I was just wondering if any other person had the same experience. I am trying to buy an XJS Coupe 1995 or 96 model and was wondering if I could still burn regular?

 

I've moved your question from General Tech Help to XJS forum. Members here with the same model should be able to help.

(also left a redirect in General Tech Help so you get double the chances of a reply)

Graham

 

A '95-'96 XJS 6 cylinder (not sure about V12) will have knock sensors that automatically retard timing if pinging/knocking is detected so you should be OK. There's no way to manually retard the base timing.

If you're an ultra-gentle driver and never go up any hills the knock sensors might never have any knocking to detect!

Cheers
DD

 

I run my '96 4.0 on 89 octane quite a lot. In hot summer I usually use the high test. I do drive this old car quite gently though.
RagJag

 

Thanks for the info. Glad to know about the knock detector. About 1960 I owned a Facel Vega Facillia. a 4 banger. I had to use French gas of a low grade. In about two years, the #1 PISTON LOOKED LIKE A RAT GOT INSIDE AND GNAWED OUT A 1 1/2" CIRCLE ABOUT 1/4 DEEP. That's the result of detonation.
Just as an aside. On the XJ6 I chucked the lucus Electronic distributor and use a Crystler distributor with a separate electronic box. A friend turned down the case and I reversed the counter weights because of opposite rotation. Worked like a champ. Why? Lucus reliability, Lucus cost 1960ish $500, Crystler $15 and parts available in Kmart
Have a Good day motering

 

When I was (even more of) a noob, and tried to skimp on some $ by filling up with regular, I heard these subtle, muted *tock*tock* sounds when using kick down. Yeah, that's called knock. As the man said, pay now or pay later.

 

you are going to retard timing and mess with your engine performance to save 40 cents??? I am constantly amazed at people who MUST cross the street to save a penny and HAVE to pay 80 dollars instead of 88 for a fill up.

the same people go to the same store, buy milk no matter its price, and are willing to buy dr pepper instead of dr.check. You people all blow my minds that you are so ridiculously cheap on your cars but will spend an extra 80 cents to make your fries a large.

seriously quit it. Oh and stop going to "gas-a-go" and "BIG BOY GAS" knock off gas stations to save an additonal 5 cents for crappy fuel with less detergents. Go to top tier gas stations and put gas that the engineers intended to go into your car. No to mention the v12 is known for running hot to begin with. I just am astounded that someones thinks they found a shortcut or cheat and think there are no negative repercussions. You sound like you genuinely think you have a brilliant idea and all the engineers that have been designing cars for the last 100 years are just messing with people to let gas stations earn more money.

more importantly, retarding timing is reducing efficiency in order to let you use lower octane. The money saved is more than offset by the loss in mpgs because your engine is running retarded now. You are either doing the same or losing more money than if you would just put the right gas in it. I ask you either educate yourself a bit better or at least leave poor innocent jaguars alone.

 

im sorry, i really want to be helpful on this forum but this is one of the dumbest things I have ever heard on this forum. I feel like im chatting on a redneck truck forum or one for teenage ricers.

ITS LITERALLY LIKE A DIFFERENCE OF $10 dollars in a 350 mile trip. Not to mention you aren't even saving the 10 dollars because your range diminished to 250 miles


I just rebuilt the entire upper half of my girlfriends land rover when all i wanted to do was simply change the head gaskets because the previous owners "saved money" with this kind of B$. "sometimes we put 91 in it and sometimes we put 87, we tried to balance it". People act like they are giving their cars a ****ing cookie by giving it the fluids it is designed to use. If you can't afford 91 octane gas don't buy a car that requires it or buy ONE LESS CHEESEBURGER OVER THE COURSE of 2 weeks. there is just NO excuse

 

I don't know about Tx but up here you may have a hard time finding 87 without ethanol in it. I honestly don't know if it matters whether there is, but I avoid ethanol in the older engines.

 

I just rebuilt part of the drivetrain and I must say that if you want to save a couple of bucks the gas is not the way to do it.... Knocking and missing will drop raw gas into the cayalytics. The cats on a V12 cost $600+ each, right/left,front,back! That could cost you up to $2400 for a set of new cats. I just replaced the four front cats... I had a misfire which dropped raw fuel into the cats and melted the interior... use the fuel that engine was designed for and enjoy the car a little longer.... going on the cheap for gas is WRONG, WRONG, WRONG! Also, always buy name brand at a station that has good turnover. On a trip from Florida to NY I foolishly bought gas at "El Cheapo." The most expensive gas ever... clogged the injectors, they stayed open, and raw gas blew the engine..... NOT EL CHEAPO!

premium gas all the way or sell the car!

 

I prefer to use the correct octane and quality fuel as well, but are you attributing this....

.......to using lower-than-specified octane?

Sounds more like a Marelli ignition problem to me.


Cheers
DD

 

The blown engine was caused by the injectors sticking open and raw fuel going all over and exploding.... really stinko! Never again will I buy off brand gas and never again at a fly by night gas station!

 

The octane rating of gas has nothing to do with quality. It's strictly a measure of resistance to detonation, nothing more. 91 fuel is not higher 'quality' than 87.

 

The statement was about buying off brand gasoline. Nowhere was octane mentioned in the snippet you quoted.

The remark about premium was an aside in an earlier post, and still was not an integral part of the admonition to avoid off brand gas.

 

Thanks. Your ongoing assistance is greatly appreciated by some, I'm sure.