[xj-s] 1986 XJS - Hesitates under hard acceleration

Just bought a 1986 XJS with 86K miles and all is well except that
is hesitates under hard acceleration from stop. However, if I rev
the engine while in park/neutral, the sympton does not occur.

The car performs flawlessly otherwise. Normal acceleration causes
no hiccups and it starts on the first turn of the key. I was told
the car was driven less than 100 miles in the past year. It’s got
great oil pressure and normal engine temps. Drivetrain is all
original…no funny business there.

Any ideas?–
JamesPik
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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In reply to a message from JamesPik sent Mon 25 Sep 2006:

First thing to do is run it low on fuel and stick a whole
bottle of injector cleaner in it. Then run it almost out of
gas give it a couple of Italian tune ups and change the fuel
filter. If that don’t cure it then you have a weak spark for
some reason it won’t jump the plugs at WOT take out the plugs
how ever many you have and put new ones in at the correct gap.
We need to know what engine you have.
And is it US spec or Euro spec.
During The hesitation is there any popping back into the air
filters you notice. Or does the engine seem to die flat when
you flour the gas pedal, is this dependent on revs.
Have you read K Palm’s holy bible for worshippers of the XJS.
I think you can download it here.–
Bassmec, XJS V12 1977 Coupe
Ipswich, Suffolk., United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from Bassmec sent Mon 25 Sep 2006:

Thanks for the reply. This is a US spec engine.

It had gotten down to less that half of a tank of fuel (bad gas?)
and I refilled it with 93 octane. The problem appears to have gone
away. No hesitation and its seems that I have more power and a
smoother idle.

Whew! I will try some injection cleaner too.–
JamesPik
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from JamesPik sent Mon 25 Sep 2006:

Is it a straight Six or a V twelve.–
Bassmec, XJS V12 1977 Coupe
Ipswich, Suffolk., United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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JamesPik wrote:

Just bought a 1986 XJS with 86K miles and all is well except that
is hesitates under hard acceleration from stop. However, if I rev
the engine while in park/neutral, the sympton does not occur.

The car performs flawlessly otherwise. Normal acceleration causes
no hiccups and it starts on the first turn of the key. I was told
the car was driven less than 100 miles in the past year.

Italian Tune-Up.

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