1995 XJ6 DVP 90K miles

Saturday June 2

Hi everyone,

Can someone help me?

I have replaced the ECU due very poor gas mileage 11.9 MPG and accelerating problems at low speed

Now that I have installed another ECU (used but garanteed to be perfect) my engine idling speed whic was before perfet à 800 RPM is now double that speed at 1600 RPM

Engine seems to work a bit better but far more too much trafic on this Saturday to really test the car properly on the freeway.

Tomorrow I will make another MPG test but this high idling speed bothers me and I do not know how or where to adjust it.

Thanks for your help

Claude
Durham NC

 

When replacing the PROMS or the ECM you will need to do an engine setup for the system to operate properly.

The setup is outlined in the T493 recall. The ECM needs to learn the parameters for certain sensors.

bob gauff

 

The ECU "learns" the voltage signal from the throttle potentiometer at idle. Your replacement ECU has learnt a lower voltage on the original car than occurs on your car. The ECU does not therefore recognise when the throttle is actual closed. It effectely thinks that the driver is holding the throttle slightly open. The ECU therefore does not try to control the idle speed to its programed value by controlling the position of the idle speed control valve (ISCV). You need to take the car to a Jaguar dealer or good independent Jaguar specialist who has either Jaguar service dianostic tools such as WDS or IDS or a good quality aftermarket service tool like Autologic. The technican will also need to know how to perform a throttle adaption test with this equipment. Bear in mind that these cars are now at least 15 yearts old so main dealers may not see them very often. It might be worth checking that they know how to perform this test before you turn up.

By the way, i think that it is actually most unlikely that the original ECU was the cause of your poor fuel consumption, unless it has suffered water ingress into the main harness connectors. It is much more likely that the cause is a failed lambda sensor. This should be possible to check by any garage that has a fault code reader. If you end up needing to replace one or both of the lambda sesnors, then it would be best to do this before you have the throttle adaption test performed. If you change the lambda sensors it would be worth having a lambda sesnor orientation test performed if the sensors are replaced, even if they are done one a ta time so there is no chance of the getting the front and rear sensors mixed up. the lambda sensor oreientation test can be performed with the same equipment as used to perform the throttle potentiometer adaption test. Both test can be performed in under 5 minutes on a full warm engine by someone who knows what they are doing.