1994 XJS V12 6.0Lt Marelli – Lack of Power, Cutting Out

1994 XJS V12 6.0Lt Marelli – Lack of Power, Cutting Out
Where do you start

  1. The poor mode – Car started fine and, in a few mins, went into lack of power, cutting out, and Tack quit, motor ran OK but with little power
  2. Shut motor off and re started ran fine
  3. 20 mi later same thing for a few seconds and again in a mile or so
  4. 5 mi later went into poor mode, limped home
  5. Started the car next day, fine for few mins and went into the mode and motor quit

Started to check things
a) Looked and cap and rotor, looked fine
b) No spark out of coil or at plugs
c) Came back in few hours and started up, in the poor mode and quit
d) Came back next day and started ok for one min, seems to be getting worse, B bank no spark, cold
e) Checked 12V to coils OK
f) Disconnected front coil B bank and ran the same, plugged back in and ran fine for 2 mins
g) Changed coil to cap wires, no change and then quit
h) Put orig wires back on and would not start

Where do we start, checking procedures and how do we check components?
Coils, Front cam sensor, back crank shaft sensor, Ignition amps or Ignition ECM module
Need to get head around which components controls what and in which order?
Any help Thx Terry

Is your on board display showing any codes?

Hello Terry - sounds like you have a coil that has gone open, so not firing plugs - you said B bank changed nothing when removed HT lead (main cable from coil to distributor) - you could change HT lead, at coil location, with the other coil for the A bank - if your B bank spark plugs are now firing, and your A bank spark plugs are not firing, then you know the coil is bad - if B bank is still not firing, then check change the HT lead complety over - use B bank lead for A bank and A bank lead for B bank - B bank still is not firing then open distributor cap to check carbon button inside cap top and check rotor condition.

As far as engine codes came up with F44 A bank right side oxy sensor but after the engine completely quit it came up on display ENG CODE but did not display code number

After engine completely quit changed both coil leads and nothing Looked at cap, rotor all looked good Rotor is new 1000km ago I think we are looking for a component that is failing periodically?

Usually, when a coil is going bad, it is because heat has dissipated the insulation on the internal windings and the coil can not produce the high voltage for the spark since the windings are now shorting themselves out, or have blown them selves open - this will mean that you have to install new coils - this generally lets you start when the coil is cold, then stops working when the coil is electrically hot inside - some people have placed an ice pack around the coil, when it shuts the car off, to prove this to themselves before they replace the coil - using an ohm meter, you can check the coil like this: with all the wires disconnected from the coil, place the meter leads on the positive “+” and negative “-” terminals, with the meter set for low ohms - you should see a reading some where between 0.4 and 2.0 ohms - if less or more then bad coil primary winding; now place the one meter lead on the HT (distributor lead connection) terminal and set the meter on high ohms - you should see a reading between 6,000 and 20,000 ohms - if less or more then bad coil secondary winding - these ranges are general ranges for coils - I do not have my service manual near me at this time, so I can not give you a better range of what your coils should read.

I did check coil for conductivity, which there was, but don’t remember what the reading were. Will check again to see Thx

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I didn’t read every post here very carefully - has the possibility for partially blocked exhaust track been tested?