'89 V12 runs like poop unless using 93 octane...
#1
'89 V12 runs like poop unless using 93 octane...
Lot of talk recently about how Americans waste money buying premium unleaded for cars that don't need it.
I've tried to run 87 and 89 through this car, and it doesn't like it one bit. Lots of rattle and knock taking off from red lights, especially when the engine has warmed up. So I put 93 back in it today for the first time in months, and it did great. All the noise went away.
I don't mind spending the extra $$ for a happy engine; just wanted to make sure I'm not doing anything wrong here.
Jess
I've tried to run 87 and 89 through this car, and it doesn't like it one bit. Lots of rattle and knock taking off from red lights, especially when the engine has warmed up. So I put 93 back in it today for the first time in months, and it did great. All the noise went away.
I don't mind spending the extra $$ for a happy engine; just wanted to make sure I'm not doing anything wrong here.
Jess
#2
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We don't have 87 or 89 in our market. The cheap fuel is 91.
My car has the rattle and knock with 91 but runs well on 95 or 98 (Uusually run 95 for cost reasons). I run 91 in my Jeep and it seems fine with it.
I run 98 pulp (premium unleaded pertol) in the bike because it doesn't like 91 or 95 at max revs.
I try them all in vehicles when I get them, they tell you what they don't like running on.
My car has the rattle and knock with 91 but runs well on 95 or 98 (Uusually run 95 for cost reasons). I run 91 in my Jeep and it seems fine with it.
I run 98 pulp (premium unleaded pertol) in the bike because it doesn't like 91 or 95 at max revs.
I try them all in vehicles when I get them, they tell you what they don't like running on.
Last edited by o1xjr; 09-28-2016 at 01:23 AM.
#3
Lot of talk recently about how Americans waste money buying premium unleaded for cars that don't need it.
I've tried to run 87 and 89 through this car, and it doesn't like it one bit. Lots of rattle and knock taking off from red lights, especially when the engine has warmed up. So I put 93 back in it today for the first time in months, and it did great. All the noise went away.
I don't mind spending the extra $$ for a happy engine; just wanted to make sure I'm not doing anything wrong here.
Jess
I've tried to run 87 and 89 through this car, and it doesn't like it one bit. Lots of rattle and knock taking off from red lights, especially when the engine has warmed up. So I put 93 back in it today for the first time in months, and it did great. All the noise went away.
I don't mind spending the extra $$ for a happy engine; just wanted to make sure I'm not doing anything wrong here.
Jess
#4
We don't have 87 or 89 in our market. The cheap fuel is 91.
My car has the rattle and knock with 91 but runs well on 95 or 98 (Uusually run 95 for cost reasons). I run 91 in my Jeep and it seems fine with it.
I run 98 pulp (premium unleaded pertol) in the bike because it doesn't like 91 or 95 at max revs.
I try them all in vehicles when I get them, they tell you what they don't like running on.
My car has the rattle and knock with 91 but runs well on 95 or 98 (Uusually run 95 for cost reasons). I run 91 in my Jeep and it seems fine with it.
I run 98 pulp (premium unleaded pertol) in the bike because it doesn't like 91 or 95 at max revs.
I try them all in vehicles when I get them, they tell you what they don't like running on.
Our 98 is equivalent to US 93
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ronbros (09-28-2016)
#5
In the EU we have 98, 95, 95-E10 and 95-E85 (the last two having 10% and 85% of ethanol respectively).
On my old jags (XK and AJ6 engines), I always put 98.
On the XJ with a modern V8 4.2 SC that I drive more often, I use 98 or 95.
But in none do I put gas-ethanol mix, in the long term the engines, gas tanks and hoses will not like it
On my old jags (XK and AJ6 engines), I always put 98.
On the XJ with a modern V8 4.2 SC that I drive more often, I use 98 or 95.
But in none do I put gas-ethanol mix, in the long term the engines, gas tanks and hoses will not like it
#6
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#8
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Back to the OP- what does the owner's manual say about required octane rating?
#9
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ronbros (09-28-2016)
#10
US manual calls for "Unleaded" fuel. That translates to 87 here. The lowest octane available.
I do not run on that. I run 91. "Premium" here. I Probably run 3-4, maybe 5 more degrees Advance without detonation than I could on "Unleaded".
I'd suggest in the strongest possible way that you do whatever is required to avoid that rattle and knock. Retard your timing, accelerate slowly or just park it. Detonation can and will burn pistons.
I do not run on that. I run 91. "Premium" here. I Probably run 3-4, maybe 5 more degrees Advance without detonation than I could on "Unleaded".
Lot of talk recently about how Americans waste money buying premium unleaded for cars that don't need it.
I've tried to run 87 and 89 through this car, and it doesn't like it one bit. Lots of rattle and knock taking off from red lights, especially when the engine has warmed up. So I put 93 back in it today for the first time in months, and it did great. All the noise went away.
I don't mind spending the extra $$ for a happy engine; just wanted to make sure I'm not doing anything wrong here.
Jess
I've tried to run 87 and 89 through this car, and it doesn't like it one bit. Lots of rattle and knock taking off from red lights, especially when the engine has warmed up. So I put 93 back in it today for the first time in months, and it did great. All the noise went away.
I don't mind spending the extra $$ for a happy engine; just wanted to make sure I'm not doing anything wrong here.
Jess
Last edited by JigJag; 09-28-2016 at 12:56 PM.
#11
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#12
#13
Here's the manual insert.
1986 Jaguar XJ-S manual rear insert page.
Specifically says "Octane rating 87 RON Unleded"
Crazy talk.
And while the US may supposedly use this AKI system I don't think I've ever seen a pump stating an AKI rating of its fuels. They all say ie.
97
Minimum octane rating
(R+M)/2 method
They are commonly 87, 89, 91, and occasionally 100. And trying to find ethanol free fuels is impossible when traveling but locally you can find one or two stations that sell ( Regular Unleaded 87 ) in an ethanol free version. I haven't seen e free higher grades in years now. Them corn farmers get subsidized heavily to grow corn for fuel additive. Gotta move a lot of ethanol to keep up.
1986 Jaguar XJ-S manual rear insert page.
Specifically says "Octane rating 87 RON Unleded"
Crazy talk.
And while the US may supposedly use this AKI system I don't think I've ever seen a pump stating an AKI rating of its fuels. They all say ie.
97
Minimum octane rating
(R+M)/2 method
They are commonly 87, 89, 91, and occasionally 100. And trying to find ethanol free fuels is impossible when traveling but locally you can find one or two stations that sell ( Regular Unleaded 87 ) in an ethanol free version. I haven't seen e free higher grades in years now. Them corn farmers get subsidized heavily to grow corn for fuel additive. Gotta move a lot of ethanol to keep up.
#14
I don't think I have a Marelli car. I've got a single "ignition amplifier" with LUCAS written on it sitting on top of the driver's side (LH) bank of cylinders.
Jess
p.s.: I'm also watching the "my car is idling rough" thread because mine also has a shake when idling at low-rpm that goes away immediately upon adding throttle.
#15
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Here's the manual insert.
1986 Jaguar XJ-S manual rear insert page.
Specifically says "Octane rating 87 RON Unleded"
Crazy talk.
And while the US may supposedly use this AKI system I don't think I've ever seen a pump stating an AKI rating of its fuels. They all say ie.
97
Minimum octane rating
(R+M)/2 method
They are commonly 87, 89, 91, and occasionally 100.
1986 Jaguar XJ-S manual rear insert page.
Specifically says "Octane rating 87 RON Unleded"
Crazy talk.
And while the US may supposedly use this AKI system I don't think I've ever seen a pump stating an AKI rating of its fuels. They all say ie.
97
Minimum octane rating
(R+M)/2 method
They are commonly 87, 89, 91, and occasionally 100.
I'm surprised by the stated 87 RON number. In the '80s, the difference between RON and MON numbers was usually around 10 points, so that would meant a fuel of around 82 AKI. I've never seen such a thing.
I wonder if it's a misprint and they actually meant 97 RON which would be around 92 AKI? That would match with the OP's observations.
Last edited by Mikey; 09-28-2016 at 07:58 PM.
#16
All that vacuum contraption and lower than optimal timing recommendations might make for less power but better economy figures.
#17
US manual calls for "Unleaded" fuel. That translates to 87 here. The lowest octane available.
I do not run on that. I run 91. "Premium" here. I Probably run 3-4, maybe 5 more degrees Advance without detonation than I could on "Unleaded".
I'd suggest in the strongest possible way that you do whatever is required to avoid that rattle and knock. Retard your timing, accelerate slowly or just park it. Detonation can and will burn pistons.
I do not run on that. I run 91. "Premium" here. I Probably run 3-4, maybe 5 more degrees Advance without detonation than I could on "Unleaded".
I'd suggest in the strongest possible way that you do whatever is required to avoid that rattle and knock. Retard your timing, accelerate slowly or just park it. Detonation can and will burn pistons.
nothing more, nothing less.
it has no bearing on octane in and of itself.
#18
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Good work. Failure of the advance systems often goes unnoticed and unrepaired
it will run with the big boys now on low octane fuel. Wonder what it would do on high octane?
The only purpose of higher octane is to eliminate pinging/knocking. If it isn't pinging on whatever you're using now, that's as good as it gets. A higher octane rating won't do anything for you
Cheers
DD
#19
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Yeah, in that era the V12 used several different crazily complicated vacuum advance schemes ....electric timers, dump valves, delay valves, regulator valves, etc. I'm sure part of the reason was to allow use of 87 octane fuel. Probably worked "ok"...for as long as all the gizmos stayed operational.
Haven't driven my present V12 enough to experiment by my old '88 XJS V12 was fine on 87 octane unless the coolant temp got a bit high or I was pulling a long grade. The I'd get a trace of pinging. For that reason I usually used 89 or 92. But, too, I was running without all the gizmos....vacuum hoses connected directly to ported vacuum.
Cheers
DD
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