FF13 Fault Code. V12 5.3

[xjscharlie]

Hello Folks,
Experienced a loss of power on my 91 V12 5.3 and the fault code FF13 is flagged. Occasionally the engine will cut out but so far has always restarted. Has anyone experienced this fault and can advise of possible causes and investigative procedure. Thanx in anticipation. Charlie.

[AndyF]

Hi Charlie

I am sorry to hear that you are getting FF13. Here are my thoughts - apologies if I am teaching you to what you already know:

The FF13 fault code is for "Powertrain Control Module Fuel (PCMF) Manifold Absolute Pressure Sensor (MAPS) or signal pipe signal error". What does this mean? - well, the engine is controlled by an ECU, mounted in the passenger footwell, and connected via a small diameter red vacuum hose to the intake manifold on the RH (A) bank, at the back. This small pipe allows the ECU to monitor the manifold vacuum as it changes under load and adjust the ignition accordingly.

So - is the pipe intact? Cracked or split (as mine was - note small cable tie "fix" in the image below)? Is the pipe blocked with gunk? Pull the pipe from the back of the intake manifold and ensure that the port on the manifold is clear.

Is the engine giving the correct vacuum level at idle? - this can be checked by hooking up a vacuum gauge to the spare port next to the ECU port. It should read about 20" Hg at hot idle (mine read 20.5"), 750rpm with all loads off. Note I had a ~3.0inch zero offset error in my gauge - hence the reading below

There is also a Manifold Pressure Control System on the 5.3 - when the engine coolant is below 45 degC, the manifold pressure signal to the ECU is switched by a solenoid vacuum valve, via a delay valve, to a port in the A bank intake throttle housing. When the coolant is above 45deg C (as measured by the coolant temperature switch located at the rear of the A bank coolant rail) the solenoid vacuum valve is closed and allows full vacuum to be available to the ECU.

So another question would be - does the issue happen when the car is cold or hot? If the temperature makes a difference, maybe either the temperature sensor is not working, or the solenoid vacuum valve / delay valve are not working properly.

The most comprehensive information can be found in Chapter 4 of Supplement C to the Jaguar XJ-S 5.3 & 6.0 Repair Operation Manual.

Have a good search on the forum here for other FF13 investigations and it is also worth having a look at what the US XJS owners are doing on the Jag-Lovers forum too.

Hope this helps - we'd all love to hear how you get on.

Kind regards

Andy