Okay, I have a 1994 6.0 L V-12. It runs/idles well, but has no power, like it's running on 6 cylinders. Definite fuel smell also when driving. The exhaust on right side at the tailpipe is much hotter than the left, although I can feel exhaust coming out both sides. Ideas? Can someone point me in the right direction?

Thanks,
Bill

 

It's quite possible you have a Marelli ignition failure. Begin by removing the distributor cap to inspect the rotor. That's the most common failure point. But, there are other possibilities

Don't drive the car!

Cheers
DD

 

Unless you want it to burst into flames.


How old is your ignition system? coils/amps/dist cables etc? There are some fairly simple ways to identify which part is weak and starting to fail, swap the electrical plugs on your ignition coils and see if the exhaust is cooler on a different side for example.

Or alternatively spare yourself the headache and/or fire hazard and just do it all once with a complete set of new ignition parts.

VE520225 Cambiare is a good interchange part for the ignition modules, and if your coils are the type with the nipple inside the socket I have a new set that was incompatible with my cables.

 

Thanks, guys. I have just replaced the spark plugs, dist cap, rotor, HT leads. There may be an issue with the exhaust/cats. Still not sure what the problem is.... I'm going to have it towed to my favorite shop and let them diagnose the problem. I'm also going to have them install a custom exhaust. Since I'm in SC, don't need to run the cats at all.

 

What the guys are saying is that one half of the engine may not be firing at all. Because the Marelli ignition system you (I suppose) have, has a well known failure mode that causes this. It may be the amplifier (one per bank) or the distributor (a double layer affair) or the wiring. This failure (no spark to one bank of the V) is what to test for.

 

Hi drbill

Following on from what 'Greg' said inside the 'Marelli' Distro Cap is a Double Stepped Rotor

'A Rotor Arm that is stepped with a blade at each end'

So although the Blades are at opposite ends, they sort of sit one on top of the other

One end of the Rotor runs the 6 cylinders on 'A' Bank

The other end of the Rotor runs the 6 cylinders on 'B' Bank

So as 'Doug' said, its just like having Two 6 Cylinder Engines which are joined together

What can happen and may have happened in your case

Is that the Insulation between the upper Blade on one end of the Rotor (The Top one in the joined together Step)

May have broken down and allowed the HT to Track to Ground via the Distro Spindle, which would disable all the Cylinders on 'A' Bank

At which point you would now be running on only half the Engine but the V12 Engine is so smooth that even running on just 6 cylinders

It may take a little while to even notice it apart from having a sudden loss of power

So assuming 'A' Bank has shut down (in which case stop and turn off the Ignition ASAP!)

Raw Fuel will still continue to be Pumped in to 'A' Bank (or which ever side has now shut down)

Which would then send unburned Petrol into the Hot exhaust of which ever Bank of Cylinders is no longer running

Where in the event this happens then it could cause a fire!

Always carry a Fire Extinguisher in an XJS

Although there are a couple of other things that could cause a Bank of Cylinders in the Engine to shut down, one of which is Coil Failure

Of One of the Two Coils on a 'Marelli' System Car

Don't try swapping the Plugs on the Coils as the Engine won't Start (ask me how I know!)

Or the Failure of one of the Banks of Cylinders on the Engine could be down to

One of the Two Ignition Amplifiers on the Closing Panel over the Rad

There 'was' a know issue on 'some' of the 6 Litre XJS that the Bonnet/Hood Lining could 'Push Down'

On one of the Ignition Amplifiers causing a possible failure over time

I think there was a Service Bulletin issued as to where it could be relocated to prevent it causing a problem (Doug would probably know)

 

Ah yes, thanks guys! There is definitely no spark on the B bank. Since new rotor, my guess is the amplifier. Definitely won't drive it until fixed. Sure don't want a fire.

 

Update: 'twas the coil for the B bank. Replaced both and now she's running perfectly. I do have another question: has anyone upgraded their exhaust for one of these 6.0 liter cars? Since I'm in SC, no inspection, so I can pretty much do whatever I want..... thanks for all the help!

 

Super !!! Oh, how I wish I was free of inspections. but, I got both my cars through !!!


Go shopping and fid a muffler shop in your area that builds custom systems, for the hot rod and muscle car folks. Not bound by mere replacements.


A talented one can redo it from the manifolds on back. X or H pipe, Turbo type mufflers, aye or nay on the rear resonators and an under the cage route. Sans cats means a bit on performance and a lot on $'s.


Carl

 

Good work

What did you have in mind?

Many have gone to lower restriction systems to pick up a couple horsepower and a sportier exhaust tone....the later sometimes problematic on the Jag V12, which can end up sounding a bit odd and nothing like the exotic Italian V12s

Cheers
DD

 

I've attached a pic of the x-pipe arrangement I had built for my V12. Not seen are the rear resonators. I am happy with the sound; much better than my other V12 which didn't have the x-pipe but was otherwise similar

Cheers
DD

 

I've got straight pipe (side exits) that work fantastic on the highway, neighbours complained so I had to do high-flow mufflers which isn't as nice but overall from my exhaustive research into the subject the best thing after gutting/removing the Cats is to retain the entire system as a straight pipe setup (with x-pipe preferably) leading to the rear resonators.

Delete all the cat/muffler garbage in the middle but keep the last two units for that raspy V12 sound otherwise you'll end up like me with people asking if I put a chevy 350 engine in there.

 

Doug, Carl and Vancouver,
Great input; just what I was looking for. We have a couple of shops there who can do the job. I'll show them that picture; want to try to get the "right" sound. Don't want anyone complaining about the loudness, just a nice rumble.

Thanks,
Bill

 

Found it..this is what I mean by retaining that raspy v12 noise. This guy has straight pipes with rear resonators and better air intake but thats mostly beside the point.

 

That's a bit lairy, is he running on slicks?
Mine has the centre boxes removed and TWR quad tailpipes; not add ons but proper silencers (mufflers) with twin pipes.
Sounds really good but not loud enough to annoy the neighbours.
I also have twin intake air filters which give a slight increase in induction noise.

 

Now that's loud! Not sure if it's the sound I'm after; it almost sounds like a "tuner" car. I do like his manual gearbox.

 

I reckon that setup could be done whilst retaining the factory tail pipes, no? I'd love to hear it running if you have a video.

Thanks!

 

I'll see if I can a decent recording device; last time I tried it, it sounded more like a lawn mower when I played it back!

 

As Steve mentioned, removing the centre boxes and replacing them by pipes, while leaving the rear tunnel silencers in place, gives much more sound, and is a very easy thing to do.
Simply Performance make the pipes so that they are a straight swap for the under car silencer boxes.
Use this link and scroll down to see them:
Performance parts |

 

Thanks! Looks like just what the Dr. ordered. I wonder if those parts can be adapted to the 6.0 cars?