The rear sensor is the Tach signal (engine speed) for the Marelli. The Tacho is run off the coil.

That shieled wire is the Tach pulse for the Lucas so the ECU knows engine speed (in pre-Marelli this pulse came from the ignition amplifier). Without this signal the ECU will not fire the injectors.

TPS unplugged will look like idle to the ECU, if you were to rev it with the TPS unplugged then the ECU would be confused and not adjust timing or fuel.

 

I have been through everything listed so far, thank you all for your input. While checking the sensor gap on the front I noticed the sensor was rubbing on the alt. pulley so I started pushing around on it. I was able to move it more than I thought acceptable so I took the belt loose. The alt. pulley will spin freely around the shaft and can be moved forward and back close to a quarter inch. The timing disc seems to be firmly mounted, somehow. I have started taking the pulleys off, I don't know if this will correct my original issue but I know it will correct this new one. I'm also thinking I should change the front seal, a lot of oil on the front of the engine. What do you think?

 

I assume you mean the alt pulley is loose not the sensor.

Is the sensor firmly mounted?

Fix one thing at a time you do not need to remove all the pulleys, although if the alternator needs rebuilding do this as a bad (noisy) alternator can cause all sorts of weird problems on a running engine.

 

The sensor is firmly mounted. The alt. pulley/crank damper is loose, with the belt off it spins freely on the crankshaft. From what I could find online, the crank pulley, alt. pulley/crank damper and the timing disc/trigger wheel should be bolted together as an assembly. Looks like 3 bolts and a pin. Thats why I'm not sure how the crank damper could be spinning so freely. Taking the pulleys off would be the best way to check the woodruff keys. I need to fix the crank damper anyway and if the crank seal comes out the front, then I might as well change it while I have the pulleys off.

 

The front seal on the V12 does simply pop out the front. There are even two slots in the timing cover to assist this operation. Dont WHACK it in too hard when refitting the new seal, as I simply forget if there is a ledge to stop it going all the way in, or I may be thinking of another Jag engine, dunno, its been a while.

Whilst in there have a look up on the RH side of the front face of the timing cover. There is a "rubber" bung there for the timing chain tensioner ratchet release. These shrink with age, also turn hard as hell, and LEAK profusely.

 

Sorry I misunderstood what you said. In that case I would definitely do the front seal while you are in there.

Grant, what did you use to plug the timing chain access hole?

Be careful with that bung, when I removed mine some of it went inside the timing cover, luckily it was my spare engine.

 

While I was bumping the engine around, to get to the crank pulley bolts, I found a position where I couldn't see a trigger finger. Close examination showed one is broke off. and the damper needs to be replaced.

 

Originally a rag, stuffed in the hole. We were part way around Australia, and Far North Western Australia when it did its thing. Not much up there but us strange Jag owners HAHA.

The old one got levered out as best I could in 50C temps, and most of it fell inside. Got a new Genuine bung in Perth some weeks later, and RTV coated, and pushed it in. Still there. I was seriously tempted to leave the rag in there as NO oil escaped.

As for the bits, weeeeeeeeelllllllll, dunno, some strange looking crumbs come out with oil drains sometimes, Jags keep going mate, FAITH, and JD, solid as they come.

 

Thanks Grant, given me the idea of machining one from aluminum and RTV.

 

OK - you need all 3 fingers on the wheel as each one corresponds to TDC on all 6 pistons on the A bank the ICU will not fire if it does not see the pulse.

 

When you redid the wiring did you replace the wire to the plug that go to the coil? The original white wire are brittle and crack with age. Wiggle the wires around and see if you get it to start or improve. It occurred on my '91 years ago and would stop me dead. I would get out and wiggle them and it started up. You can buy the plug end pieces on line so you can have a new wiring system complete.
Good Luck!

 

I ordered a new damper and trigger wheel today, should be here by monday. I will move rebuilding that harness up on my list.

 

The new damper and timing disc did the trick. Thank you all for your help.