Piston 6 hits sparkplug - Bad timing
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HT4100 4.1, 4.5, 4.9 Discussion, Piston 6 hits sparkplug - Bad timing in Cadillac Engine Technical Discussion; Its quite a story 88 sedan deville 4.5 liter engine. Engine was replaced with one purchased from ebay, the ebay ...
  1. #1
    mikeythegreek's Avatar
    mikeythegreek is offline Cadillac Owners Member
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    Piston 6 hits sparkplug - Bad timing

    Its quite a story 88 sedan deville 4.5 liter engine. Engine was replaced with one purchased from ebay, the ebay engine was new from cadillac but intake was multiport, so i switched it over. Could never get the timing quite right, ran retarded for a while and now more recently i guess a little bit above 10 degree mark. Im driving and I here this loud tapping.Got home , took out the plug and the gap was gone. So I was planning on the tune up I did it, but new parts (plugs, wires, cap, rotor, coil) didnt do the trick. With the new engine I didnt give it a new distributor, (from old 192k engine).

    If its overall timing issue why would it affect just cylinder 6? Any troubleshooting advice? Im going to replace the plug again start it but with obd 1 plug term A+B together, seeing how it will react. Or should I take off the pan and look for bolts on the bottom?

    I appreciate anybody's advice.

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  3. #2
    Edahall's Avatar
    Edahall is offline Cadillac Owners Enthusiast
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    Re: Piston 6 hits sparkplug - Bad timing

    One thing I do know is that the 4.5 with multiport had more differences than just that. They had different heads and higher compression ratio. This in itself is going to throw things off. Perhaps this is what is going on. The 1990 4.5 was just produced for 1 year and had the same heads and compression ratio as the 4.9.

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    mikeythegreek's Avatar
    mikeythegreek is offline Cadillac Owners Member
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    Re: Piston 6 hits sparkplug - Bad timing

    Figures, - I actually got 50k miles out of the engine so far. I guess I can either look for the actual 4.5l engine for that car or is it possible to convert it to multiport? I love the car too much, apparently its a continental version sedan deville, white with a blue stripe down the middle (like one big fat stripe) Hubcap on top of the trunk. Privacy window. Its a pimp mobile.

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    Edahall's Avatar
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    Re: Piston 6 hits sparkplug - Bad timing

    Did this engine ever run right? Also, are you using premium fuel? The multiport engine was higher compression and needed premium fuel to not ping. Do you have problems with excessive pinging? I bet your engine is running lean. You possibly need an adjustable FPR to dial in the extra fuel requirements of this higher power engine. This would be a lot easier than looking for the actual 4.5 engine. Converting to multiport is not worth it. You would not only have to change over all the electronics but also the transmission. The multiport cars had a electronic shifting transmission.

    What it comes down to, the multiport engine is not plug and play with the TBI engine. You'll have to find a workaround to make it run correctly.

  6. #5
    mikeythegreek's Avatar
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    Re: Piston 6 hits sparkplug - Bad timing

    It never really ran bad honestly, but yes always seemed like it could use some tweeking. even if i add a fpr wouldnt the psi change if so that would be an issue with the injectors. i guess its amazing i got away with it for this long. but aside all of this could it be anything mechanically done to stop the piston from hitting the sparkplug?

  7. #6
    Edahall's Avatar
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    Re: Piston 6 hits sparkplug - Bad timing

    What probably bent the tip on your spark plug was severe detonation from running lean. What's going on is the computer in your car is unable to compensate for this foreign engine. It thinks you have a 155 HP 4.5 engine in it but you have a 175 hp 4.5 engine instead. What you need to do is install an adjustable FPR to give your higher performance engine the fuel it needs. The PSI change won't be an issue with the injectors. Here's a FPR that works on our cars.
    http://www.aeromotiveinc.com/products.php?prod=13
    The P/N 13106 Aeromotive is the one that fits our engines. And the
    Aeromotive one will handle alcohol (aka, E85) if you should ever want
    to use it.

    Here is some info on how to properly tune your engine with a fuel
    pressure regulator:
    http://www.aeromotiveinc.com/pdf/13106.pdf

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