Jaguar Repair: Resetting the ECU, spark plug wires, 1986 jaguar xj6

Question
QUESTION: Hello Howard,

I have been reading a lot of your answers on here and they've actually helped me about quite a bit! Thank you!

I am working on getting a 1986 Jaguar XJ6 Sovereign running properly after sitting for 5 years. I have the car running OK now but I was wondering how would I reset the ECU?

Thank you again.


Justin.

ANSWER: Hi Justin,
No reset on the ECU. What is wrong and why are you trying to reset the ECU?
Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks for the quick reply Howard.

I am trying to reset the "service interval" after putting a new oxygen sensor in. I've also got the motor running alright but under load there is no power it simply sputters and struggles.

I've taken a look at the spark plug wires and the coil wire has a resistance of about 7k... I'm going to get replacement spark plug wires tomorrow morning.

So far, I've replaced the following in attempts to make the engine run like it should:

old gas with new, fuel filter, oxygen sensor, alternator (was seized due to rust from sitting outside for 5 years) and the engine belts.

I've checked the following and they appear to be in working order:

fuel system (rail, injectors, intake, pump, no leaks)
electrical system (battery, alternator, ignition, distributor)
all cylinders are firing (checked by unplugging spark wire 1 by 1)

compression of the cylinders is 120 dry except cylinder # 4 which is 90 dry, 120 wet)

If there's a step by step for resurrecting a jag that's been sitting for 5 years I'm sure I've checked most of the steps off so far... Let me know if there is anything here I'm missing.

Thank you,


Justin

Answer
It sounds like you are on the right track. I don't like to do a cylinder kill test on electronic ignition by removing a plug wire because of the chance of when you pull a plug wire the coil charge looks for the next best place to jump and sometimes that is down the coil tower to the primary winding which is connected to the ignition module which can destroy it. In the dealerships I was spoiled because I had the use of a scope to do that.

On your compression tests, did you open the throttle? (your readings are a little low) In the dealerships we often received cars that had been in storage and our standard procedure was to change all fluids including brake fluid. Change the fuel filter. Charge or replace the battery and run fuel through the system to purge the fuel lines. Test the fuel pressure at the fuel rail (32 PSI with the engine running and 42 PSI with vacuum removed from the pressure regulator). Test the fuel return system on Ser III cars. Run a compression test (Dry throttle open) If a cylinder or more were low we would run a wet test (throttle open). Clean or replace the plugs. Run a cylinder kill test on the scope and only check the ohms of a wire if we see a high spike on the scope for a cylinder. As I remember we used a rough rule of thumb at 5K per foot of wire.
We warmed the engine up and use CO equipment to sniff the radiator for CO (a test for a leaking head gasket) We pressurized the cooling system and looked for any leaks and pressure tested the radiator cap. Examined the belts and tension. Set the ignition timing, Checked the charging system at a fast idle (13.8v to 14.5v) Checked the operation of all electronic equipment. Tire pressure and look for dry rot. Check brake pad thickness then road tested the car. While driving the car we would check the AC for operation and recharge the system if needed. That's about all I remember doing.

All this was done on long term storage cars but was not all done on cars only stored for a winter or such. We would have considered 5 year as a long term.

If your #4 compression test was accurate you do have a problem and the wet test indicates a ring problem. However since it was stored for so long I would run it a while and recheck just in case it is just a ring stuck in a groove, which can happen on a stored car. If allowed to idle too long with a cylinder at only 90 PSI it will pump raw fuel into the exhaust and over heat the first CAT and maybe damage it. As you rev higher a low cylinder will start firing and not dump raw fuel into the CAT. Most cylinders will start misfiring at below 100 PSI.

If you have to purchase a new battery be sure to buy a "Deep charge" battery (diesel or marine).

Howard

The service light reset unit is in the trunk (boot) to the left of the ECU. (a push button)