Well after driving a bit the other day i experienced the dreaded marelli bank failure on my way to work. I noticed the loss of power right away and pulled over and shut the car down. There was some smoke coming from the right side of the engine compartment and a faint smell of burning rubber. I believe I had a small cat fire but fortunately I realised what was happening a shut the car down before to much fuel poured into the exhaust. Anyway after getting it home I found the roter had arced through to the bottom and replaced it. After that the car started right up with full power. I thought everything was great until i took it for a drive and noticed it would not shift out of first gear. I'm thinking that maybe a sensor or a vacuum line burned up from the cat overheating. Any suggestions on what might cause this or anything else I should be looking out for?

Thanks

1990 xjs 5.3 v12 convertable marelli

 

The vaccum line to the transmission modulator is on the right side. It probably melted. Take a look. As I recall it originates at the rear of the RH inlet manifold....one of several vac hoses there. Trace it back to the trans


Cheers
DD

 

Doug’s right and it is a PITA to get at mine was melted through from exhaust heat when my car arrived - if you need to replace it be careful running it back to the trans, run it under the heat shielding and keep it away from the exhaust, there is not a lot of room to get your hands between the trans and tunnel but persevere and use cable ties to keep it secured.

 

hmm. on one hand, that vacuum module shouldnt control shifting, but shift firmness and line pressure.

on the other hand, i dont see what else it could be.

 

If there's no vacuum to the modulator the trans won't come out of first gear until about 40-50 mph....and then with a bang! You'll think you've got a full-race tranny :-)


Cheers
DD

 

So just how common is this kind of failure? Should I locate a spare Marelli cap and keep it in the car just in case (along with a fire extinguisher)? I've got about 99.2K miles on a well maintained '91 coupe.

Or is the fix described here sufficient insurance (have Marelli parts installed now):

http://www.jag-lovers.org/xj-s/book/Marelli_pix.html

Thanks.

 

The marelli system is flawed only in that the consequences of failure are so severe. Annual checking of the cap/rotor condition will prevent the worst from happening, I think.

Increased resistance from worn spark plugs and/or faulty spark plug wires will exacerbate the situation....so bear that in mind before postponing checking/replacing them.

Genuine Marelli caps are no longer available. Some people have had problems with aftermarket replacements, others not. Some suggest keeping the original cap as long as it still works well...perhaps with some "dressing" of the contact terminals every few years

As of a couple years ago the gneuine Marelli rotor was still available under the Jag part number. I'd buy one and use apply the silicone sealer to insulate it

Cheers
DD

 

max line pressure + max shift point. so that solves that mystery.

 

Thanks for the info guys. I'm going to pick up some vacuum line on my way home today and get into it over the weekend. I'll post my results.
I think the Marelli design isn't that bad if it is maintained properly. It was on my list to pop in a new rotor and do the silicone squirt thing soon.....It should have been higher on my list lol. I opted to keep the original cap. My car has under 60k on it and the cap contacts cleaned up nicely. I think the main failure with these is due to the rotor shorting out on the middle post not the cap itself. I have seen a few places that have new old stock Marelli caps for sale. But they are all asking several hundred dollars for them. I think next go round I'll go for an aftermarket cap and just change it every year or so to be safe.

Thanks again,
Dan
1990 xjs 5.3 v12 convertible marelli

 

@Dan

Glad you got stopped before anything worse happened. I was also told if the right hand bank failed there was a good chance to melt the transmission line. It was my left hand bank that failed, and I "only" set my steering rack on fire.

As Doug said, the preventive maintenance + yearly inspection + knowledge should keep you safe. The only concern I still have is "what happens if you have a marelli failure while the cruise control is set?" (I think the car would note the drop in speed and open the throttle further......?) I think I'll leave my already non-functioning cruise control in the box in the garage, just in case :-)

 

Common enough that it happened to both of mine. And now yes, I keep a decent toolkit, spare cap, and fire extinguisher in the trunk (boot).

Anecdotal evidence, small sample size, etc. etc.

 

Well I found out the source of the trans not shifting. You guys were right. Where the vacuum line goes into the modulator the rubber elbow there completely melted into nothing. The vacuum line itself didn't seem to bad but I'll probably change it anyway since i bought some on my way home. I pulled the modulator out to get the melted elbow off of it. Is there anyway of checking the integrity of the modulator now that I have it out? I'm worried something in it may have got toasted too. It would be nice not to have to buy a new one if this one is still ok. Thanks again everyone! This is why this forum is so great

Dan

1990 xjs 5.3 v12 convertible marelli

 

i feel like it needs said that if you lose one whole bank due to marelli failure, UNPLUG THE CORRESPONDING FUEL INJECTORS BEFORE YOU TURN YOUR JAG INTO CRISPY BITS!

 

damn.... :-(

 

You can not just unplug 6 injectors on one bank, the ECU averages the O2 senor inputs from both sides so you will over fuel the other bank.

 

or when doing a complete rebuild,, you have no rubber or neo hoses that can burn, no injector hoses, injectors mounted in O-rings, all fire resistant lines ,all metal, even in the trunk and fuel pump+ filters..

when you gonna do it might as well do it right!

and YES a fuel fire driven by a hi-pressure pump can get very interesting quickly.

when doing your own car you are not held to, somtimes poor, factory engineering.

 

some pix of my old system.

 

pic of consol switches,, right ot left

Fuel pump relay
ignition relay
computor, relay
spare

Master power large relay

 

That's all fine and well to make those changes but let's not forget that Jag fires can be very easily avoided by simply taking care of the car, annual inspections, and replacing fuel hoses every 5-7 years :-)

Cheers
DD

 

I'm very new to the 1990 XJS Jag I just bought, the more I read the more I think about selling it. I never dreamed a car could have so many problems.
My Wife is driving it and now Along with all the other potential problems I have to worry about her burning up in it. I don't understand how a car manufacture could put out this kind of car.
"1990 XJS Convertible for sale" LOL