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

Discussion in 'Maserati' started by jamespeter26, Feb 4, 2020.

  1. jamespeter26

    jamespeter26 Rookie

    May 9, 2019
    Rome, Italy
    Full Name:
    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:

    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.
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  3. thecarnut

    thecarnut F1 Rookie
    Silver Subscribed

    Apr 22, 2006
    Full Name:
    The Car Nut
    I am confused .... does this engine only have 80 psi across all cylinders or did I not understand your post correctly? If it only has 80 psi then you already found your problem. The next question is why (pistons or valve leakage) .... and a leak down test should answer that question. When doing a compression test make SURE the accelerator pedal is fully depressed or you will get incorrect results. Do not assume the engine has 80 psi without getting a second opinion from someone that knows what they are doing.

    Is this the same mechanic that could not figure out that the noise the engine was making were popping carburetors? Perhaps it is time to look for another mechanic.

    boralogist and 71Satisfaction like this.
  4. AM101

    AM101 Rookie

    Mar 11, 2015
    It must be assumed that all your issues started with the carburettors, just because they are jetted correctly and everything such as float levels etc look right, they must be the start of your problems.
    Initially from your description the car must have been running very rich, and stalling when running slowly, the fact you have fuel in the air cleaner points to too much fuel, and / or fuel being blown back through the carburettors. Having to start with full throttle all point to a flooded engine.
    The rich mixture will cause carbon build up on the valves and stems, these will then not seat, causing low compression and more blow back through the carburettors. The extra fuel will also wash the cylinder walls causing piston blow past. Although I have never come across this in such a sort time.
    As Ivan said the best tool by far you have for this type of "old school" diagnostics is a cylinder leakage test ( it is the pre computer age plug in diagnostic tool) which can answer all your questions. All you need is a broken spark plug, compressor, common sense and a bit of time. Just need to make sure you have a workshop that understands these methods.
    If it was me I would look further at the carburettors checking the float level and condition of the floats for any punctures (this is now more common with modern fuels).
    However this is unlikely to solve your issues now, but you have to start somewhere. If you can get the engine running after this and establishing the cause to the low compression it may be possible with gently running and care that you may find the compression return, but if you continue hard driving, it is most likely to end with burn valves or worse.
    I think it is worth getting someone experienced with old engines to carefully work through the issues before you jump in and strip the engine.
    These are just my opinions, others may think completely differently.

  5. jamespeter26

    jamespeter26 Rookie

    May 9, 2019
    Rome, Italy
    Full Name:
    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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  6. carguy

    carguy F1 Rookie

    Oct 30, 2002
    Alabama (was Mich.)
    Full Name:
    Not sure why the mufflers would clog up, it's not unusual to have some fiber packing on the muffler housing around the pipes. Was this packing actually in the exhaust stream? The distributor issues you mention would certainly cause lack of power under load, lots of unburned fuel, starting problems, etc. I would still do a compression check, just to be sure the engine internals are okay.
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