Marelli Fires in Ferraris?

The American Ferrari V-8 Marelli also runs as two separate 4 cylinder systems, and single side ignition failure with cat overheat/fire is well known, and not uncommon. It often involves coil or coil controller failure.
It happened to me 3 times.
best
rt

 

Three times?!! Over how many miles, or how long?

 

I've had two........it shatters the header kinda like a pipe bomb......


better have a fire extinguisher handy,.....

 

Over 3 years use as a daily driver; I got so spooked about it I replaced the Marelli system with the most reliable single distributor ignition system I could devise; for me, it's about driving the car, reliably.

 

how long between when you lose half your power to when it goes boom?

 

Hi. Carnicero started this thread at my request, because I (and others) were wondering if the Jaguar XJ-S was unique in having cat fires due to Marelli ignition problems. The response here was such that I decided to log on for a while even though I don't own a Ferrari. Fact is, I don't own a Jaguar any more either, and I never owned one with Marelli ignition, but I was instrumental in figuring out what was causing the fires -- and how to prevent them.

First off, I'd invite you all to visit this web page:

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

There are pictures there of the normal failures as well as some pictures of some unique failures. The fixes for the common failures is mentioned: for the rotor, squirting silicone sealant into the opening on the bottom of the rotor prior to installation has proven 100% effective so far, not a single report of trouble on a rotor so treated. For the cap, the installation of a section of brass tubing around the center carbon brush; to the best of my knowledge, nobody has even bothered, they just buy a new cap since it is possible to find caps with the proper metal sleeve surrounding the carbon brush.

I sincerely apologize if this is wasting Ferrari owners' time because their failures are completely different. On the off chance that the Ferrari failures are similar, though, I'm sure somebody here would appreciate knowing about the simple silicone fix.

-- Kirbert

 

I recently had one bank of cylinders shut down on my Mondial t. Prior to the shutdown, I had intermittent periods of the car sputtering, especially when cold. After it shut down, I had it towed home and was trying to determine if the shutdown was caused by one of the infamous electrical gremlins well known to the Mondial t/348 crowd. After reading this thread, however, I am starting to wonder if my problem was Marelli ignition-related. I had no fire, but distinctly recall misfiring right before one of the cylinder banks cut off. After it stopped, the engine would turn over, but only one of the banks would get fuel (or power) resulting in the car not generating enough power to drive it.

For those with experience with the ignition issues, does this sound similar to the symptoms? I have looked at the fuses and electrical plugs and haven't seen any telltale signs of failure.

Your responses are appreciated.

 

Can anyone explain to me why on EARTH Ferrari used a dual ignition system? Seems to be nothing but an accident waiting to happen.

Birdman

 

It's not just Ferrari; lots of companies went that way. The reason is simple enough. When generating a spark, time is needed to build up energy in the ignition coil. The combination of high rpms, lots of cylinders, and high compression ratios make it really difficult to build up enough energy between two successive sparks. By having two separate ignition systems, each one serving every other spark, the time to build a charge is doubled.

All of this is largely history today. Most cars use distributorless ignition now, with a separate ignition coil for each two cylinders, firing those two cylinders at the top of every stroke, the top of the exhaust stroke being "wasted". With such a system each coil has gobs of time to build up a charge, so the coils don't have to be nearly as fancy as they were when they had to fire the whole engine.

The distributorless ignition doesn't necessarily avoid the cat fire issue. On a V12, for example, often there are simply two 6-cyl distributorless ignition systems siamesed together. Hence, there remains a possibility that one half will fail while the other continues to operate. One can hope that most of these electronic ignition systems are more reliable than the aftermarket rotors sold for use in the Jaguar XJ-S with Marelli ignition. Like I said, you can hope.

There are things that can be done. Perhaps the most straightforward is to put some sort of temp sensor on the cat that will at least warn the driver, or possibly shut off fuel to that side of the engine. The poor man's method is to just rig a piece of insulated wire in the area. When the insulation burns off, the wire shorts to ground (or another wire), lighting a warning light or buzzing a buzzer or whatever.

In hindsight, yep. One might ask: why hasn't somebody like the NHTSA jumped in and forced the makers of these things to recall some cars and make corrections to prevent such fires? As far as we (on the Jaguar XJ-S forum) been able to tell, nobody at the NHTSA has even figured out what's causing the fires. And Jaguar has not acknowledged the problem at all; no recall, no TSB, no part redesigns, no nuthin'.

 

I forgot to mention: The effects of losing one half of a dual ignition system should be significantly different on a V12 than on a V8. On a V12, each bank is essentially an inline six, balanced and evenly firing independently of the other bank. Hence, if one half of the ignition system fails, one entire bank no longer gets any spark, and 100% of the fuel and air going through that bank are dumped into the catalytic convertor while the other bank runs normally. A V12 runs quite smoothly under these conditions -- at least until the fire starts. If the catalytic convertor is hot and operational, it will get much hotter in a hurry. If not, the results may be far more benign, as that bank's exhaust tract merely fills up with liquid fuel that never ignites.

In a V8, the effects will be altogether different. Each bank of a V8 is *not* an inline four, balanced and evenly-firing on its own. In fact, the firing order on a V8 fires two cylinders in succession on each bank. Hence, if two separate ignition systems are used, each one would be expected to fire two cylinders on each bank, not an entire bank. If one ignition system fails, you will lose ignition on two cylinders on each bank. You will then have 50% of the fuel and air going through the engine dumped unburnt into the exhaust tracts on both sides. If there are catalytic convertors there, both sides will get very hot in a hurry -- 50% is still enough fuel and air to cause a catalytic convertor meltdown and fire in short order. If there are no cats there, the unburnt fuel and air mixture will still likely be ignited by the very next cylinder that does fire, causing a horrendous backfire -- depending on how much throttle is applied at the time -- more than likely doing significant physical damage to the exhaust system.

 

Kirbirt -
Actually, a Ferrari does have two independant operating 4 cylinder engines per side. This is due to Ferrari's use of a 180 degree 'flat' crankshaft as used in racing engines. You are correct though, that most other street V-8s use a 90 degree crank which would not allow smooth single side running. I can tell you that a Ferrari running on just one side is as smooth as glass, quiet and way down on power. It takes the cat around 30 seconds to a minute to glow depending on how warm the car is already.
I know this failure mode all too well.
best
rt

 

This is why I'm coating the headers:

http://www.ferrarichat.com/forum/showthread.php?t=71003

The distributor ate a rotor contact button and then it burned a hole through the header. If you look closely in the top left of the pictures you can see the two 90 degree bends that were replaced.

Bill

 

You get better ignition timing on 2x4 cyl distributor caps than on 1x8. At least this was the reason I was given for when Porsche went from a single distributor to twin on the 928?

Also, from personal experience, if you lose 1 ignition system on a 208, you can still get home as a 104...without catching fire!