1990 Marelli all 4 cats glowing!

I know the typical Marelli failure can result in burning red cats on one side. But all 4 just lit up! Cap and rotor, coils, leads, plugs, injector harness, are all new. I just finished the throttle linkage adjustment per the “Book”. Bank B butterfly was a little out of adjustment. Once everything was adjusted I decided to start it up with the air cleaners and outer covers off. This is where I should mention that I forgot to plug in the air intake temp sensor. About one minute later, and the car running a little smoother other than some misfires (I’m thinking injectors) all 4 cats lit up and it smoked the garage out. Got it outside and shut her down. Has anyone experienced anything like this or did I just smoke the cats because I left that sensor unplugged. :crazy_face:

Should also mention there are NEW exhaust leaks at the doughnuts at the manifold and the down pipe on both sides and silencers are coming apart from the inside out. Firing metal like a machine gun. I’m thinking the cats are all clogged but that’s just a thought. Any thoughts?

Once I ran my Marelli Jag for hours to perhaps days and nothing like that happened, in fact I never noticed until the next time I looked under the hood and at the air intake trumpet on the left for actually no reason and saw that it wasn’t connected. The reason I don’t know how long it was off is that I didn’t remember how long it was that I had taken it off.

Well, Paul I started thinking last night and I think the cats are just clogged and the silencers are full of junk. They even make a strange sound out of the tailpipes like there’s something blocking the exit. My mechanic friend agrees and said to bring it down to the shop and put it on the lift. I guess now is the time to do the exhaust. Or at least remove and inspect.

Whatever clog you may have had is melted away. When all four cats glow, you have raw fuel going in from both banks. That means you’re running on 10 cylinders or less, or an injector is leaking fuel in full time.

That seems to be what happened on mine when it was towed and dropped off. Both pipes dug into the gravel and got clogged and now it runs funny with funny sounds. Of course I can’t get it lifted to observe the cats.

Sounds like you could be right about that John. I wondered if a clog could live through that inferno :joy: I do have a misfire or two. Slightly firmer feeling one on the B bank exhaust and a little smoother on the a bank. The injectors are definitely suspect. When I redid the fuel lines I magically put the injectors right back in without cleaning them (like the forgetful person I am) and the car hadn’t ran in over 20 years. I’m considering getting those things out and cleaned.

1 Like

That also includes whatever was called ‘catalytic converter’. No reason to look any further, these CATs now may only work as an expensive self-propelled underside neons.
People are paying fortune for those gadgets, don’t waste your chance…

Are you saying to sell the cats now? Don’t think I could do that. I’m going to gut whatever is left of them and replace the rears with new cats. I have to pass emissions in California.

Your CATs are made of a ceramic substrate with tiny square holes allowing the air passing through it. The substrate is ‘soaked’ in something called washcoat - solution of fillers and surface ingredients and Platinum group metals dissolved in acid. The main problem with cars having CATs and not having Lambda sensors is the scenario like yours I’m afraid. The disintegration temperature of the coating is much lower than the melting temperature of the ceramic substrate, so in consequence you may have bare ceramic substrate left inside. If these can be sold - I say go for it.
The only uncertainty is the definition of ‘the glow’…

1 Like

The “glow” looked like the inside of a volcano.
Plus my car does have lambda sensors.

Yes, let’s say it has… One of the very first ones. As per your example - it seems that Jaguar’s design failure mode was not considering burnout scenario in 1990…

If the glow suggest that they went above 1k C. over few minutes, I would expect all the PGM being in the atmosphere now…1

My car is Lucas, but i still found chunks of old burned out catalytic bits down my exhaust pipes between cats and box mufflers.

My car is going up on the lift and we are going to do a full exhaust. 2 1/2 inch through and a y pipe with Vibrant mufflers. Hopefully we can cure the exhaust blockage issue.

1 Like

When I got rid of all 4 Cats (live in state with no smog check) no noticeable change, except exhaust is now a bit smelly.

When i got rid of mid mufflers, oh boy. Night and day. Definitely more power, and an actual exhaust sound.

I’m about to replace rear mufflers, power should not change, but should sound deeper.

One issue with 2 1/2" pipes, very little wiggle room between trans and heat shields. Ive adjusted 10 times, still get an annoying rattle (hitting heat shield) on hard acceleration from a stop.

Sounds like hamster squeaking its wheel! :frowning:

That’s some good info! I have the options to go to 2 1/4 if I have to do maybe I’ll do some measurements! My mid mufflers are so clogged when you hit them with a fist they sound like a sound like a rain stick.

Those mid mufflers arent flow thru either. Most restrictive part of the exhaust. But makes car whisper quiet. Flooring it, you hear a pfshhhhhhhhh. I couldn’t WAIT to get them off. First time i could spin tires from a stop! Not continuous though, id need a higher ratio diff for that.

Well I think most would be impressed with the sound this system is going to make and like you said I think this car is going to really love having some straight through exhaust. Maybe some others on this forum will want this same custom exhaust? Just head out to California we’ll take care of you.