Help needed to diagnose a possible engine failure - Maserati V8 tipo 107

Hi all,

I am once more asking for your kind help to help me troubleshoot and hopefully solve a mechanical problem that kept my Quattroporte III from starting for almost a month now. The mechanic and I are running out of ideas so really, I would be most grateful for any help.

Bottom line: the current engine condition is described by this video: https://drive.google.com/file/d/12bgFvco8e8QFlWYJPmdsAChrLImRXuNc/view

A bit of background: it all started with a full carburetor rebuild, performed by a professional two months ago. After that, the car started lacking power, especially under load. Typical symptoms were hesitation and stumble upon start after a red light, car running rich (fouled plugs, very poor mileage). At first, it negatively impacted driveability and mileage, but didn't prevent me from driving another 500 kilometers including highways at 130 km/h.

The first time the car stalled was during a demanding uphill segment, and I had to wait 15 minutes before I could successfully restart it. There was a lot of fuel in the air filter box.

I initially suspected fuel delivery issues, so I replaced fuel lines, pump, and pressure regulator, and can confirm the Webers now receive 2.75 psi of fuel. No difference. I also replaced a couple of vacuum lines which were cracked.

I also suspected a weak ignition coil, and replaced it with a new coil, same exact reference. No difference.

A few weeks later, the car stalled again at a red light, after a really difficult 80 kilometers. As I slow down and and put the gear in neutral, the engine stalls, and there is no way to start it again this time. I parked it nearby, came back the next day, replaced spark plugs on the spot. After that, I managed to crank the engine a couple of times, but I really had to floor the accelerator pedal to avoid stalling. I could drive less than a kilometer, but again, flooring the accelerator achieved only a measly 15 km/h. As soon as I released the pedal, the car stalled again. After a few attempts, the engine no longer started at all and I had to push it to another parking spot.

Car gets towed to the mechanic the next day, who confirms that we have a spark, double-checks ignition timing, does a few usual checks. And tells me the engine is getting too much fuel - most likely a carburetor issue.

Car gets towed from the mechanic to the carburetor shop, who re-opens all four carburetors, verifies that everything is in order. All jets are factory spec, choke is not engaged, floats height is correct, needle valve operates correctly. And I get the call no one wants to get: "This is not a carburetor problem, you have a problem with your engine. The engine is not aspirating air, it is actually blowing air through the carburetors. And by the way you have 80 psi of compression on all cylinders. Car needs to go back to the mechanic." This is the day when I shoot the video at the above link.

Car gets towed back to the mechanic again. Both him and I can think of nothing else than a timing chain having jumped a few teeth, and my only hope was that the pistons hadn't hit any valve yet. The logical next step was to open the four cam covers, and adjust valve/camshaft timing. Possibly replace chain tensioners. And then check compressions again.

This was done today, and the mechanic confirmed that cam timing was perfectly correct and did not require any adjustment. He also opened the distributor, and says it looks in order.

I am really running out of ideas here. Could you please look at the video and tell me if that makes you think of anything? The noise, the speed at which the engine is cranking, the carburetors blowing air... ?

Thank you very much in advance for your time.

 

Ivan, Mark, many thanks to both of you for stepping in. Your recommendations are helpful and sensible. I will definitely do a leakdown test as soon as possible.

I think we finally found the origin of the problem and… it was in the exhaust! All mufflers were seriously clogged to an extent, but especially the rear one. Look at these photos! No wonder why the air was flowing back through the intake. As soon as we removed the exhaust lines, effectively exposing the exhaust manifolds to the open air, the engine started immediately and would not stall. No more liquid fuel in the air box, no more intake backfire.

So I’m good for new mufflers, but I was relieved to see my engine come back to life. Of course, we still have to find out if driving with clogged exhaust lines caused internal engine damage, especially in light of the low compressions.

I really don’t understand how we can have low compressions on all cylinders, instead of just a few, but this seems to point at a general issue (as opposed to something located in a particular part of the engine).

I wonder if these low compressions couldn’t be caused by the fact the engine has been running so rich, with exhaust gases backflowing, etc. This probably led to a good amount of carbon buildup, which might have reduced the valves’ ability to seal.

Do you see any reason why I should not make an oil change (perhaps even two in a row, with 15 minutes of idling in between, to gently clean the internals) followed by a tankful of fuel supplemented with a fuel system cleaning additive (like Redline SI-1) to see if this helps eliminate a bit of carbon buildup and restore engine compressions?

We also found a secondary problem that needs to be solved. I was suspecting something wrong with the ignition system. The coil had already been replaced, so it could be either the ECU or the distributor. The mechanic had another Quattroporte being restored in his workshop, and he was kind enough to temporarily replace these two components with those of the other car.

The ECU didn’t make a difference, but clearly, my distributor’s magnetic pick-up sensor seems bad. With the other car’s distributor, the engine settles to a relatively smooth idle, but as soon as we put back my own distributor, we got misfires and unburnt gasoline smell in the exhaust. The engine could idle, but roughly.

The mechanic recommends keeping the stock distributor and replacing the sensor only. I am still hesitating between this, or replacing the magnetic pick-up with something like the Crane XR-700 or XR-3000 system (optical pick-up), which has quite a lot of success on this forum and a good reputation for reliability among Ferrari 308 owners in particular. Any thoughts on this? I am not particularly interested in originality, but I do care about reliability.


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