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1975 - 4.9 is firing badly. Distributor cap, or anything else..?

Discussion in 'Maserati' started by 71Satisfaction, Jul 3, 2020.

  1. 71Satisfaction

    71Satisfaction Formula Junior
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    Jul 15, 2012
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    Thanks for looking,

    - A week ago the Bora's engine kind of stopped running momentarily. This prompted me to fully replace the ignition switch.

    - Two days ago the Bora's engine had several seconds of running badly. I made a mental note of it.

    - Yesterday, driving up the street, the Bora's engine suddenly started running poorly .... sudden loss of power, firing badly, some small backfires. I could hardly get above 20mph, it seemed to have an rpm limit, all while firing badly with some pops of backfire.

    It idled OK, and it wasn't stalling, so I went around the block and returned to the garage. It starts OK, it idles OK, but under ANY load it sounds like doesn't fire properly.

    - I touched, wiggled and visually checked all spark plug and ignition wiring. It all looks intact, connected and good.
    - I have NOT replaced the distributor cap or rotor since I bought it 9,000 vigorous miles ago. Is this the obvious smoking gun?

    I checked it thoroughly - there was dust on top of the cap, I did my best to clean it all off. I opened up the cap to check, it looks mostly clean, minor crud on the contacts, the rotor looks OK too. There was some 'dust' and very minor amounts of soot. I cleaned it all up and tried driving it again.

    It drove BETTER, I could get up to 30-40mph, but still firing poorly. I went back to my garage, wired up a timing light and isolated the problem to intermittent firing of #3 cylinder. The intermittent fire occurred at idle and all rpms. All other cyls fired properly.

    I THINK the cleaning of the distributor cap improved the situation, it seems high time to replace them under a typical maintenance interval, and therefore a new cap and rotor may be all that is needed, so I will purchase them from MIE...

    But I while I wait for the parts, could it be anything else I am missing?

    What is the spark advance mechanism on these cars? There is no rubber hose on the vacuum port on the distributor, but there never was. That is no change from before. A sudden spark advance failure could happen inside the distributor (if a spring broke) but then #3 would get energy and fire normally...

    Affirmation, ridicule, ideas and discussion are all welcome.!
    Grazie,
    - Art
     
  2. staatsof

    staatsof Six Time F1 World Champ
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    The cap is off a Mercedes, nothing special. Probably the rotor as well. Check Ivan's website for the interchange list for Bora's it might be on it. A different cap than the points equipped dizzies I think. You might have a hairline crack in the cap keep checking.
     
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  3. thecarnut

    thecarnut Formula 3

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    It sure sounds like an ignition problem. Does your Bora have the dual contact points or is it late enough to have the breakerless ignition? Does you car have a switch to bypass the Bosch electronic spark booster? If so, switch to emergency mode and see how it runs. You might have a bad Bosch box.

    Ivan
     
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  4. thecarnut

    thecarnut Formula 3

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    Correct; cap and rotor are the same as a V8 Mercedes of that era. Just ask for a cap and rotor to fit a 1974 Mercedes 450SL. I doubt the problem is the cap. Even running on 7 cylinders that engine would be running better.
    Ivan
     
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  5. 71Satisfaction

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    Thank you gentlemen,

    I'm not familiar with a switch to bypass the Bosch spark booster, but I'll look at the Owner's Manual or surf around to inform myself and check for that option.
    Here are two pics, inside the distributor. I would assume this one is Pointless. This looks unlike the interior of distributors I've seen. This is before I cleaned the cap.

    - Art
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  6. thecarnut

    thecarnut Formula 3

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    Probably the toggle switch for "emergency mode" was only available on Boras with dual contact points, your car has the later breakerless ignition. Unplug the connector at the Bosch ignition box and spray it with contact cleaner. I wonder if the Bosch box is interchangeable with that on the Khamsin since both cars have a breakerless ignition. Worth exploring since you have access to a Khamsin.

    Ivan
     
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  7. staatsof

    staatsof Six Time F1 World Champ
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    What's the rotor look like? I'd replace that cap.
     
  8. jamespeter26

    jamespeter26 Rookie

    May 9, 2019
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    Here is my $0.02 contribution:

    A couple of months ago, I had an ignition problem with my 1982 Quattroporte, which also uses a magnetic pick-up (=point-less) Bosch distributor. My distributor looks very much like the photos posted above.

    I had misfires, etc. all the symptoms pointing at an ignition-related issue. The distributor cap looked just fine, I had replaced the wires the previous month, so we started by swapping the electronic box, then the ignition coil, to no avail. We eventually found out the culprit was the distributor sensor that small electronic device at the end of the green wire. For some reason it was malfunctioning.

    I don't know for Bora's but NOS Quattroporte distributors (Bosch 0237401003) are astronomically expensive, and I got quotes over €/$2,000 in both Europe and the US.

    After doing a bit of research, I discovered that the ignition system is entirely identical to the one used in the Porsche 928 and possibly other German cars. The distributor is a slightly different variant, and is not a direct replacement for a Maserati, but the distributor internals are identical. I ended up buying a NOS Bosch 0237401006 distributor, as used in Porsche 928s, and used it as a parts donor to repair mine and replace the faulty bits - most notably the sensor. Cost me a fraction of the price and solved my problem.

    Also, there is an excellent and very straightforward troubleshooting procedure in the Porsche 928 workshop manual, volume 1A, chapter 28. It is fully applicable to the Quattroporte 3 and possibly the Bora too if the ignition system is the same. Look at http://www.ligeti.com/928/
     
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  9. staatsof

    staatsof Six Time F1 World Champ
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    Sounds promising!
     
  10. 71Satisfaction

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    Thanks all,

    Yes, easiest things first:
    - I'm waiting to receive new cap and rotor. In the meantime, here's a pic of the rotor as requested. No smoking gun as far as I can tell.
    - I inspected, checked, and reseated the connector at the Bosch ignition box. Nothing obvious.
    - I'll get into the distributor internals and/or the sensor as shared by JamesPeter26 if the above doesn't solve the problem.

    I'll update when the new parts are installed and tested.
    Cheers,
    - Art

    Here is the rotor...
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  11. staatsof

    staatsof Six Time F1 World Champ
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    I doubt that would explain the suddenness of the symptoms. Is it possible that you disturbed that lead wire from the sensor? As I remember it runs out along the the left hand side on the the engine compartment then through a grommet I think (been a long time) and then becomes a part of the wiring harness that attaches to the ignition box on the LH side outside of the engine compartment.

    This wire is somewhat burned in my memory because I followed a 2 year wild goose chase which I thought was carburetion and turned out to be 180 degree out of phase wiring error of that sensor in the harness from the factory.
     
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  12. 71Satisfaction

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    - The misfire symptoms seemed to evolve over a two week period: One single misfire. Then a few seconds of misfiring. Then a constant condition.
    - It is possible the sensor wire was disturbed - assuming you are talking about the green sensor wire jamespeter26 notes above? I had done some work to, and cleaning of, the Bora the week prior. I will look for the green wire, I assume it emerges from the distributor housing, and trace it out. I know nothing about phasing..
    - I won't forget to have another close look at the Bosch ignition box connector.
    - jamespeter26, thank you for the link, I have pulled up the Porsche 928 Bosch diagnostic manual.. looking at it now.

    Grazie tutti,
    - Art
     
  13. staatsof

    staatsof Six Time F1 World Champ
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    Art ... in my case it was while I was restoring then entire back half of the mechanicals, the engine compartment. I had suffered some extreme heat damage from the thermal reactors on the way home from Oklahoma City to SF.
    Lots of stuff melted because I was ignorant of the admonition not to take the car over 4,000 ft elevation. I was excited at having an almost brand new Bora just took of for Kansas City to see some friends and missed that plaque in the engine compartment. That's why my car has so many wonderful heat shields.

    Anyway, that harness from the distributor needed to be remade and spliced a new one fairly close to the distributor, followed the original color coding and replaced long section of the harness show signs of heat damage. Even my LHM tank had the paint bubbled off of it in spots. The gas in my tank was churning when I arrived in Denver during an overly war day in early spring. I got towed to the Maserati garage in Denver for a case of vapor lock ... So 10,000 ft over Bertha pass even at night was a terrible idea. That's where I cut the belt to the air injection and all the problems cleared up.

    Well after restoring the cat it took me two years to figure out that somewhere in that piece of harness I replace they had swapped the two wire for the sensor violating the color code and so when I made it go straight through it causes all sort of very weird issues.

    Now I doubt that's what's going on with yours but it does demonstrate that if that sensor isn't perfect it can cause great issues. I was 180 degrees out phase and had to rotate the distributor quite a bit to get it running which I found odd at the time but I just assumed that I had made an error marking it. My cars were sent of to a well known Weber modification/testing place in LA recommended by Al Burtoni where they bench flowed them and tested every circuit. They found nothing. There was an enormous delay because once they arrive d there the Rodney King riots erupted and my carbs sat in a warehouse smack dab in the middle of everything. I truly wondered if I'd ever see them again. Just a wonderful 2 year long goose chase.

    Hang tough ...

    Having lots of fun? LOL :p ;)
     
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  14. 71Satisfaction

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    Today's update, with a new related problem:
    - Waiting for new cap and rotor, so still using "old" ones.
    - Checked wiring connections. Good & clean.
    - Cleaned the existing cap's exterior, there was grit that may have grounded out the spark(s).
    - Wanted to get the engine running and test the engine under acceleration, by hand-throttling it vs on the street, to see if I could isolate whether the spark advance springs inside the distributor maybe broken.

    The engine cranked and almost fired once, but didn't start. Tried until battery ran low. Hooked battery up to charger.

    Try again to start the engine, hooked up to timing light for diagnostic check:
    - Pulled out my induction timing light and hooked it up to positive and ground, then had my son crank the engine while I checked plug wires and coil for spark.
    - Timing light indicated no spark at any plug wires.
    - I also put timing light induction sensor around the coil wire and it shows no sparks.
    - I disconnected green sensor wire just for curiosity. No change, as expected. Reconnected, no change.

    So I have advanced from one misfire, to several misfires, to a lot of misfiring, and now no fire at all.

    The new cap and rotor won't help if there's no energy from the coil.

    - Failed coil? I'll check how to diagnose it.

    jamespeter26, I'll read through the Porsche diagnostic flow chart, see what I can figure out.

    Anyone else?
    - Art
     
  15. staatsof

    staatsof Six Time F1 World Champ
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    #15 staatsof, Jul 16, 2020
    Last edited: Jul 16, 2020
    If you become impatient and totally stuck perhaps a vintage Porsche shop that works on 928's could help you out rather quickly?

    If it ends up being the box you can find them used for $100-$200 guaranteed to work.
    Years ago there were people who would put a better more modern system inside the box to preserve originality. I know that this dizzy works with MSD stuff. A friend of mine had one on his Bora to let him change the advance in real time.

    If you had and knew how to work an oscilloscope I should think you could check if you're even getting a pulse signal. Pull the plugs and turn off the FP.
     
  16. thecarnut

    thecarnut Formula 3

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    I suggested some time ago swapping the box with your friend's Khamsin (assuming they are the same). That would be a quick an easy way of confirming (or eliminating) the box as the problem.

    Ivan
     
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  17. staatsof

    staatsof Six Time F1 World Champ
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  18. staatsof

    staatsof Six Time F1 World Champ
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    Looking around a bit, there plenty of places that will refurbish these boxes ... too many to bother listing here.
     
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  19. 71Satisfaction

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    Thanks Bob, Ivan, jamespeter...

    1.) The Green Wire Sensor:
    I sourced a Porsche 928 distributor Bosch p/n 0237401006 for parts and swapped in the 'green wire' sensor and plug. This got the engine running again, albeit poorly.
    - NOTE: The green wire is a coax wire and has a "polarity", meaning that the engine only started after I oriented the two wires correctly in the two prong plug at the wiring harness.

    Regarding this 'green wire' sensor - PelicanParts.com offers several replacement options from $50 to $90. Look up Porsche Ignition Distributor Wire - 93060290701 - Bosch 1-234-431-290.
    - NOTE: Porsche's standard wire length is 12.8cm. There is an optional part number 93060290700 that should get you a 70cm long wire. Since the spare 'green wire' I swapped in is working temporarily, I haven't yet placed my order for a new one.

    - NOTE: As far as I can tell, the failure at my 'green wire' sensor was a kink and breakage in the green insulation that shorted out the inner and outer coax wires. This obviously prevents the wire from triggering anything. Whether there was an actual short or not, the CDI box is now my main suspect.

    2.) The Bosch Electronic Ignition Box:
    Since the engine ran, but ran poorly, I turned to the Bosch CDI box (my part number Bosch 0227 3 0000 2 ) and I surfed around for a diagnosis or rebuilder.

    After some sleuthing, I concluded that PelicanParts.com ($309) and ECUdoctors.com ($375) outsource this work to outside shops. I found Bob Ashlock of AshlockTECH in Fullerton, CA. Visit or bookmark him at www.AshlockTECH.com.
    He's the actual rebuilder of the Bosch CDI boxes for $300. He offered me a free test and diagnosis if I just paid shipping. He also has an inventory of replacement boxes if you're in a hurry or have no 'core' to start with. We spoke and he felt at this point it's a reasonable possibility the problem is the CDI box (my Khamsin friend is out of town for several weeks, so no quick reference-check there).

    The only thing I wish I'd checked before I pulled and mailed my Bosch CDI box was the voltage supplied to the box. If that voltage (or maybe current) is low, it won't discharge properly. Either way, Bob Ashlock will give me a diagnosis and either repair it if needed, or return it if not.

    Photos:
    1.) The Porsche distributor Bosch p/n 0237401006 with the 'green wire' part pulled off.
    2.) The two prong plugs of the 'green wire' at the wire harness.
    3.) The Maserati distributor with the Porsche 'green wire', you just swap the metal bracket that holds it.
    4.) I believe the coax conductors of my original 'green wire' shorted out at the elbow where they emerge from try distributor.
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  20. 71Satisfaction

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    P.S....

    - It's also worth noting the illustrated parts catalog for the Bora (Table 7) shows the old style 'points' distributor.
    - A better reference is in the Khamsin catalog (Table 8, photo below). But even there, the 'green wire' has no part number... Go figure.
    Cheers,
    - Art

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  21. staatsof

    staatsof Six Time F1 World Champ
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    Glad to see you're making some progress. In my Bora that shielded wire disappeared into the wiring harness and that's where the swap in color coding happened. I don't think it was shielded all the way to the Bosch box. It probably should have been and that's how I got the wires reversed in polarity and YES it will still start but the dizzy has to be rotated quite a bit but it doesn't run perfect.

    Have you thought about having an entirely new sensor harness made up that goes the full distance? Perhaps mine was a one off mis manufactured thing? Wiring harnesses were never one of the Italians strong points ...
    The guy who owned my car barely drove it so I'm not sure he would even have needed to touch that with only 3K miles on the car.
    Have you also thought about having the advance profile modified to European specs while you have the dizzy out along with a full service?
     

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