I tested my AFS/MAF sensor to diagnose my FF 44 code. Im checking all my components to rule things out. Sensor checked out OK, but when I reconnected the plug and tried to start engine, ALL of the engine electronics were literally randomly clicking on and off. Needless to say the car won't start now. It ran fine before I tested the sensor. I also replaced the o2 sensor just before the test. The car has never done this before. HELP!!!!!!!!!

 

Hi 91calijag,

Welcome to the Jaguar Forums! It's great to have you with us.

When you say the "engine electronics were literally randomly clicking on and off," do you mean the lights in the instrument cluster are turning on and off? My first instinct is that you may have blown a fuse while disconnecting and reconnecting the MAF sensor or other components, so check all your fuses.

Jaguars do not like low battery voltage so that would be another to check. If the static battery voltage is less than 12.5V, or if it falls below 11V while cranking, it needs to be recharged or replaced.

In diagnosing FF44 after replacing the O2S, are you following the diagnostic flow chart in this manual?:

AJ6 4.0L Engine Management System / OBDI Diagnostic Guide

The EMS grounds mentioned in the diagnostic flow chart are the two on the intake manifold and the one on the firewall/bulkhead behind the cylinder head. Cleaning all the engine bay grounds, including the engine ground strap, should be a part of regular maintenance on any Jag.

Cheers,

Don

 

Hi Don,, thanks for the response.
No, I mean the electronics under the hood, like the air pump clutch, several relays i can hear clicking, the fuel pump. It literally sounds like morse code tapping away. Anyhow, common sense kicked in and after thinking about it, the only device that controls all of those relays and such is the ECU. So I pulled the ECU and opened the box and sure enough, it has a couple blown circuits. So i need to find one. I did find one locally but it goes to a 93 XJ6 which i don't think is compatible with mine. Would you know off the top of your head if a 91 and 93 ECU are compatible?? They look identical but the part numbers are different.

And yes reference the FF44 code. Under the diagnostic notes, not the flow chart, The MAF is listed as a possible issue, but more than likely not the culprit. It tested out OK...
Thanks
Marco
91 XJ6 Base.... trying to keep her from the scrap yard!!

 

Hi Marco,

I don't think the '93 ECM would work optimally with a '91 engine because the fuel injectors were changed in '93 and the fuel mapping is different. The newer injectors have two orifices that spray fuel directly on the backs of the intake valves, so they are more efficient and their fuel flow rates are actually lower than the earlier injectors. A '93 ECM might cause a '91 engine to run lean. However, the '93 ECM has adaptive fueling capability, so given time it might adjust the fueling to work reasonably well. I can't think of any other major difference between the '91 and '93 EMS.

Check your VIN against the listings at jaguarclassicparts.com for suitable ECM part numbers.

Please keep us informed!

Cheers,

Don