Hi Everyone,

Still plugging away trying to fix my XJS. It is a 1989 XJS Collection Rouge V-12 US car LHD with 67,000 miles on the clock. I had some idling issues (slight misfire) that I have seemed to work out. However, I have a new problem which seems to be a vacuum leak.

In the 4 months I have owned it, I have replaced the fuel regulators, replaced all plugs, leads, dizzy cap, rotor, coils, rebuilt the injectors and put new hoses on the fuel rail, new fuel lines under the hood (all 4), new fuel pump, new fuel filter, and new AAV. This left me with a better running engine but, it had a very slight misfire. Someone suggested that I check the throttle bushings and clean the butterflies. Sure enough, the throttle bushings were gone. I replaced those. I set the butterflies at .002 inches, and noted that the throttle rods were not even. Using calipers, I sorted that out so they both open the same amount. I took the airboxes off and used new gaskets when going back on and they are nice and tight. All of this left me with an engine that on start up idles at 2,000 RPMs. Once the engine warms up and piston moves in the AAV, the idle oscillates rapidly from about 1,400 RPMs or so, to 800 then back and forth. Someone suggested this was due to a massive vacuum leak. I experimented and closed the throttle screw on the AAV entirely. I even blanked it off and disconnect the hose from the airbox. I noted that the idle came down a little. Now, if I put my hand over one trumpet, I get the idle down to about 850. It should barely even run. I even tried to cover one trumpet with some cardboard and my hand over the other. Gets the RPMS down to 750 where they should be. With both trumpet blocked like that, it should die but, it doesn't'. So, it must have some sort of vacuum leak as was suggested. I have been all over this thing. I went with the nuclear option, and started replacing vacuum lines with new ones. No change. Full disclosure - I haven't done them all yet. I bought a vacuum tester and started to try and pull a vacuum on the hoses remaining. Most of them hold a vacuum. One does not. It leads to some type of switch on the air pump. The ones going to the fuel regulator on the B bank, also don't hold a vacuum. Not sure if it is supposed to. The one on the A bank does a little, then I smell a little bit of fuel. The ones leading to the distributor don't but, I have a Marelli ignition system. Any help, advice, encouraging comments are appreciated! Thanks so much!

 

Injectors installed with new seals, squarely inserted into the manifolds?

Intake manifold bolts tight? New gaskets?

Not too long ago, fighting a weird high idle problem, I discovered that the .002" and .003" blades on my feeler gauge were stuck together.....meaning I set the throttles to .005". That one messed with me for some time before I figured out what happened. :-)

If you entirely disconnect the throttle linkages from the throttle bodies does anything change?

Cheers
DD

 

New seals for injectors used from the Mr. Injector kit. They appear to all be seated. I looked at my other XJS which still has the originals and they look the same. I double checked the feeler gauge. I’m about to pull the fuel rail and try putting it back. I’m seriously running out of ideas, and I want to fix it myself.

 

The vac spigots of the FPR's should hold vac. I usually test without the short hoses.

There should not be any fuel smell, if so, that FPR is faulty. I know they be new, but new never means faultless, sorry to dampen the mood.

I dont follow the caliper method with the rods. The at idle and "just off" idle is the critical area. Once the engine is at or over 2000rpm, the disc balance is of no consequence.

The spacer on the capstan ear at idle when setting the rods is also needed. Without using it, too much guess work, and odd idle behaviour is your friend.

 

Doug,

Thanks so much for your response! You were right. The butterflies were gapped a little too much. I watched a video on proper resistance on feeler gauges, and as it turns out I had set them wrong. I adjusted the butterflies and now the problem is h gone! Thanks to everyone else for your feedback and wisdom as well!

 

Gotta love an easy fix !

Cheers
DD

 

Agreed Doug.

As I have stated for a good many years, these are simple beasts, and easily lived with, if that systematic SLOW process is followed.

Good to hear its sorted and assuming its no longer "for sale", mm.