Faulty coil , how do i fing out which one ?

[Brakebuster]

i suspect a faulty coil on the XJ8 ,

the car keep throwing its self into restricted performance, usually at high revving, or when hot after a long run ( usually half way there )

i actually have a known good one in the garage , but does anyone know how to diagnose a faulty 4 wire coil for your cars

i have software to run in the obd2 , but dont know what i'm looking for

BB

[BrianG]

Hi BB,
According to the Jaguar Heritage CD, in the Electronics section for explanation of the Diagnostic Trouble Codes (DTC) there is P0300 for general random misfire, P0301 for misfire cylinder no.1, P0302, P0303, etc., through to P0308 for misfire cylinder no.8.
(The CD says that when this fault occurs the Check Eng MIL light comes on and engine is limited to 3000 r.p.m.)

If you have the ODB2 code reader facility you may be able to find the problem if any of these codes come up when your particular fault occurs.

[springelec]

Hi BB,

Just trawled through the forum to see if anyone else had suffered ignition coil failure and your posting from 2007 popped up. The first sign was the dreaded 'restricted performance' message on the dash followed a lumpy response from the engine. Then came the realisation that the ECU limited engine revs to a little under 3000rpm. This is a permanent fault, so should be easy to find and fix. Took my XJR to my local garage who checked it using a generic scanner which claimed to find the fault with cylinder 3.

OK, so far so good. Error message on the dash, engine lumpy, faulty ignition, adds up so far.

Trouble is, which one is cylinder 3 ?. Depending upon where you start counting, it could be anyone of four cylinders.

Davji posted a note on this topic, but unfortunately confused the description by mixing the numerical firing order with piston banks A & B.

However, to use Daveji's reference point, i.e. the driver looking forward at the engine bay, if Bank A is on his right and Bank B is on his left, where are pistons 1 - 8 so that I can correctly identify 3.

Can you help or forward to someone who can. I've spent several internet hours on this and whilst the firing order is available, the piston lay out in what I believe is an AJ26S engine has proved to be impossible to find, so I believe this information would be very useful to other forum members.
(AJ26S fitted to XJR's 1998 - 1999. Mine's a Nov 1999 XJR)

Thanks

Springelec

[J44EAG]

I understand that Bank A is universaly known to be the bank where the forward most cylinder is nearest the radiator.

Mike

[springelec]

Hi Everyone,

Found a pdf on the AJ26 engine, some times referred to as the AJ-V8 engine for the American market. Page 43 provides the firing order information as:
1A, 1B, 4A, 2A, 2B, 3A, 3B, 4B.

Assuming Daveji is correct and Bank A is on the right and Bank B is on the left and pistons 1A & 1B are closest to the radiator, then 3A & 3B can be identified with ease. That narrows my search to only two cylinders instead of four which is an improvement over yesterday, but does appear to throw up a weakness with these diagnostic scanners in that they cannot discriminate between 3A & 3B. I may be wrong with this conclusion and would appreciate any members' advice.

Ordered the replacement ignition coil. A bit expensive at £80 each, but if it solves the problem, it'll be worth it. Also found a technical description of the signals between the ignition coil and ECU, so I'm hoping to fix the fault really quickly with any luck.

Cheers

Springelec

[Brakebuster]

almost


firing order is correct, and so is your assumption about the positions,

but

when it comes to a fault code from the ECM, the cylinders are counted A to H

so 1A is A , 2A is B , 1B is E and 4B is H , etc

i hade a coil fail on F , so it was the second cylinder on bank B from the front, if you follow my drift

replaced the coil ( 4 pin in my case ) ,and the car ran perfectly

hope this assists

BB

Radiator
B1=E A1=A
B2=F A2=B
B3=G A3=C
B4=H A4=D

Bulkhead

[springelec]

Hi BB,

XJR up and running again after fitting a new ignition unit to 3A.

I've also bought an Autel 509 scanner.

I'm hoping it'll make it easier for me to find faults like these in the future, but haven't used it yet. A bit worried I might need a computer science degree to use it, so I may be some time.

Anyway, my car's back to using all eight cylinders and it's fantastic ! !.

Cheers

Springelec