Misfire

[Flappers]

Hi again Can anyone tell me how I set up the TB butterflies and replae the pressure regulators on the V12 HE please? The rough start and now big missfire has returned on the opposite bank.

[mike020150]

Unless someone has been fiddling, it's unusual to find that the butterflies require adjustment. When closed, the stops need to be set equally with a .002" clearance between each butterfly and its housing. Smaller clearances risk throttles jamming. Larger clearances lead to excessive idle speeds. Changing the fuel pressure regulators is a straightforward task, albeit that like most V12 jobs, access could be easier. Remove any fuel pressure in the system beforehand by cranking the engine for a few seconds with the fuel relay terminal 85 disconnected. Before removing them, clamp the fuel hoses to minimise fuel losses and risk of fires later. Then, undo each regulator bracket and finally remove the regulator from the bracket. There is more than one type of fuel regulator fitted to injected V12s so ensure you buy the correct type. Some are getting difficult and expensive to buy new. If your regulators are by Bosch and are marked 0280 160 200, FWIW, I have a brand new one I had to import from the USA. It cost me £175 but could be yours for £155 if it helps. If it's of interest send me a pm. Mike.

[davidr]

Its also worth checking the rubber bushes that the throttle spindles run in. If they are worn then the throttles will be sloppy.
The process for setting the butterflies is well covered in Kirby Palm's "Experience in Book : Help for the Jaguar XJ-S Owner". I know its an XJ-S book but there is so much in common with your HE it's worth having and its free!
http://jag-lovers.org/xj-s/book/Jaguar.html

[Flappers]

Thanks, it's been ongoing for ten years now. Let's hope this finally fixes it. I could have bought another engine with the thousands spent trying to find the issue...

[Flappers]

Unless someone has been fiddling, it's unusual to find that the butterflies require adjustment. When closed, the stops need to be set equally with a .002" clearance between each butterfly and its housing. Smaller clearances risk throttles jamming. Larger clearances lead to excessive idle speeds. Changing the fuel pressure regulators is a straightforward task, albeit that like most V12 jobs, access could be easier. Remove any fuel pressure in the system beforehand by cranking the engine for a few seconds with the fuel relay terminal 85 disconnected. Before removing them, clamp the fuel hoses to minimise fuel losses and risk of fires later. Then, undo each regulator bracket and finally remove the regulator from the bracket. There is more than one type of fuel regulator fitted to injected V12s so ensure you buy the correct type. Some are getting difficult and expensive to buy new. If your regulators are by Bosch and are marked 0280 160 200, FWIW, I have a brand new one I had to import from the USA. It cost me £175 but could be yours for £155 if it helps. If it's of interest send me a pm. Mike.

Hi Mike.

How do I test if these are working correctly, I don't want to replace them if they are still good units?

[mike020150]

The simplest regulator test is to disconnect the vacuum line and with the engine running, check first that there is a vacuum in the pipe. If not, find the leaking pipe and correct it. Then, try connecting rubber piping to the regulator vacuum inlet and check it can hold a vacuum. Do this either crudely by sucking on the pipe or by using a vacuum pump such as one used for brake bleeding. If the vacuum element of the regulator is working OK, move on to test fuel pressure. First depressurise the fuel system so you can fit a pressure gauge to a convenient point. Then, with the engine running, the reading should be approximately 35psi (earlier injected V12s operated at a lower pressure with two regulators), certainly a consistent reading whatever the engine revs are. If that's the case, the regulator is working OK. Mike.