After all the changes were complete for the vapor lock project, I took the car for drive. It seemed to to go well….I took it up to about 60 mph and then while accelerating it backfired. Drove home and after a while took it out again and upon accelerating from about 25 mph I hear a couple of pops. Back to the garage and start troubleshooting.
My Autobooks Owners Workshop Manual has the following procedures for troubleshooting misfires
Pickup Gap
First up – I consulted the REOPUS website and Dave has a comment on there that he has best performance with the pickup clearance to timing rotor at 0.020″. Its tough with a flat feeler gauge to get this right, but after check and reset of this clearance. – still backfires
Timing
Next – checked timing, mechanical and vacuum advance. Its hard to find good information on timing this version of the V12 except at idle, but The Book has suggestions from Roger Bywater that the timing should be 33° BTDC @ 4,000 RPM. Then I checked the vacuum advance and did see advance with applied vacuum. Timing OK……problem not fixed. For reference here are the timing values for my car
With vacuum disconnected were:
10° @ 600 RPM
12° @ 1,000 RPM
18° @ 1,300 RPM
31° @ 2,600 RPM
34° @ 3,500 RPM
Injectors
Using a mechanics stethoscope, I confirmed that all of the electrical connections to the injectors were good as all were loudly clicking. I then had the great idea that maybe with all the surgery to the fuel rail and moving the fuel filter to the trunk that one or more of the newly installed input filter baskets to the injectors had picked up some junk and was now blocked. I pulled the fuel rail, removed all the injectors and took them back to the place that serviced them. All inlet filters replaced with new (again), but none of the removed filters were blocked.
Throttle Switch and Ballast Resistor
I then checked operation of the throttle switch and resistance in the ballast resistor
Since the connections at A and D are removed when the ReOpus ignition is used, I verified that the resistance from B to E, C to E and C to F were correct.
Spark Plugs and Wires
On the troubleshooting list is spark plugs and wires. I had replaced the plugs with NGK BPR6ES gapped to 0.035″ during the vapor lock project so I am assuming they are OK. My Magnecor wires are now almost 20 years old, so changing them seemed like a good idea. I replaced them with Intermotor Spark Plug Wires part number 55454 …….car still backfires
…….more to come……..
Ok……..it seems my vacuum advance module is bad after all. I was confused by this as I was getting advance and The Book mentions that some versions of these modules had bleed holes. After posting on jaguarforums, the consensus is that my module is bad. This may not fix the backfiring, but it needs to be resolved so I have one on order.
After re-installing distributor and checking timing…took car for a drive….NO POPPING………the issue was a bad vacuum advance module.