Recently purchased a 1991 XJS convertible that had been parked for 10 years or so. 27K original miles, great condition except for sun damaged top & seats. Wasn't running when purchased but was told "ran great when parked". Replaced fuel pump, filter, and battery and v12 eventually fired up. Replaced all fluids and set about fixing interior.


V12 ran great at first, but now seems to run a little rougher. When running, if you put you hand in front of air cleaner intake on driver side, there is very strong suction. Little or no suction on passenger side. Was worried that maybe passenger bank wasn't firing so dug into valley and checked cap and rotor for burn through. Both appear to be original Marelli, very good shape with no sign of issues. Went ahead and potted rotor and replaced all. Next swapped ignition modules and no change. Checked both coils, both have good spark. I can pull A bank plug from cap and engine will run, ditto if I replace A bank plug and pull B bank plug - so it appears both banks are running. I am just confused as to why I have so much air being pulled into the driver side air cleaner and seemingly none on passenger side - I would have expected them to be equal when car was running. Is this normal?


Sorry for the newbie question, just that this is such a beautiful car and I'm worried after reading the posts about bank failures and meltdowns.

 

Perfectly normal, no worries.

Cheers
DD

 

Doug,


Wow! Thank you very much for your reply!


john

 

Rad hoses! Check them especially the heater hoses against the bulk head.

 

Regarding the uneven air flow have you changed or cleaned the air filters? If one or both get clogged up it can lead to rough running and high emissions.
The easiest way to check is to take both filters out, replace the covers and see if the difference is still there.
Obviously don't do this in a very dusty environment!
It could also be a sticking throttle butterfly.

 

These cars can feel that way at idle, because of the balance tube at the rear of the engine. But I bet if you were to do the same thing, opening the throttle just a little, you would feel something entirely different. There are a few things that can cause this kind of thing on a Marelli car in my opinion. Maybe the amps are getting hot (located on top of the radiator cover up front) and breaking down, the coil(s) are getting hot and breaking down, or the wiring itself is breaking down under heat. I have recently started driving a 89 Marelli car that had been sitting a while. I noticed today that it too, developed a erratic miss. I built a whole new ignition harness, so feel pretty sure that isn't it, but if you are getting spark on both banks, and the miss is erratic, knowing what I've learned since owning this car, those are about the only things I can think of. Of course, one of the biggest differences in the way this car ran once I did get it running, was all new plugs.

 

Spark plugs - please replace them all,if not already done. My car sat for 2 years while I restored its clothes, ran like a dog when started 4 pots not firing, (it had new plugs just before I started the painting), took all plugs out cleaned them and it ran better, after a good long highway run was running like it should be.

 

I'm new to the XJS forum, but I have been reviving an 87 coupe that had sat for 9-10 years. I was having a lot of problems with rough running. Finally pulled my surge tank and it had at least a cup full of black sludge that the pump was trying to suck through the surge tank pickup filter. I pulled the surge tank and gas tank and did KBS coating on both of them. Also the contaminated fuel had screwed up my injectors so sent them off to Jaguarfuelinjectorservice.com. Now I am smooth as silk.

Anyway, it would probably be a good idea to at least check the surge tank.

Good luck.

 

Another thought on the seamingly low intake pressure felt on the passenger side. The passenger side also contains the AAV pump and plumbing. There is a bypass hose for the AAV that attaches to the back side of the passenger side airfilter housing. some of the air going in the the right bank is coming from this fitting, it is behind the airfilter (bad design, allows unfiltered air into the right bank) so it is going to be an easier place for that bank to suck air from, especially if the rubber fitting has come off the back of the housing. Even if it has not come off, the air pump is always pumping air, so once it is no longer called for during startup the air it pumps is bypassed into the airfilter housing.
Something to check, you are probably getting the same ammount of air into both banks it's just coming from multiple sourses.

 

Hey I seem to be have the same question ....... when running and I pur my hand on the left side it has lots of vacuum abd engine will almost die but when i put my hand over the right side no vacuum and no change to engine speed

 

Normal

Cheers
DD

 

is your xjs still running rough ?

 

mine was smooth as silk until about a week ago