[xj-s] Re: XJ-S Digest - The mysterious "surge"

[Walter Petermann <corsaro@brokersys.com>]

Craig Sawyers wrote:
> 
....
> 
> I too have the "surge" haunting me, but only after replacing the throttle
> position potentiometer (!).
> 
> With the '88 XJ-S, I notice it on deceleration, as the engine braking seems
> inconsistent, or a "negative" surge if you will.  Something is definately
> kicking in and out.  I've wondered if an improper adjustment of the throttle
> pot is part of the problem, as it coincided with with the replacement?
> 
> I do intend to try Walters suggestion relating to the oxygen sensors as
> well.
> 

  My original suggestion of disconnecting the 02's to see if the surging
  stops might not work. Most of the V12 ecu's will start to 'hunt'
  several percent when the o2's are disconnected. This should make the
  surging worse. If you have the 2 wire connector in the trunk (the one 
  that gets pulled for emissions tests), you could put a ground on it
  which will keep the ecu in open loop. If you don't have that connector
  (89 on ?) the only way I know of to put the car in open loop is to
  'temporarily' cut the ground on pin 23 of the ecu. This is the reference
  ground for the O2 circuits and without it the ecu gives up even trying
  to hunt and stays in a stable open loop. This should work up to the
  94's when, probably after a wild party, the Lucas engineers decided
  it would nice to have a 'limp home' system :). 

   Walter

---

References:

• RE: [xj-s] Re: XJ-S Digest - The mysterious "surge"
• From: "Craig Sawyers" <craig@sawyers.demon.co.uk>

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