# 8 misfire
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Northstar Engines and System Technical Discussion Discussion, # 8 misfire in Cadillac Engine Technical Discussion; WE have an 02 DHS with a 4.6. We started getting service engine soon light. Caddy dealership says throttlebody and ...
  1. #1
    cj489 is offline Cadillac Owners Member
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    # 8 misfire

    WE have an 02 DHS with a 4.6. We started getting service engine soon light. Caddy dealership says throttlebody and injectors needed to be cleaned. Also had two crank sensors which were bad. Thought I would change the sensors myself but did not have proper tools so took it to another dealership as the first one ripped us off before. So one thousand dollars later and the # 8 still misfires. New coil pack was installed on the rear but # 8 blew within minutes. Need help

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  3. #2
    darcy is offline Cadillac Owners Member
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    Re: # 8 misfire

    I just a problem with my 94 4.9 missfiring. the wires were only a little over a year old. i thought they were ok. found out that when you put in new wires and cap you have to put some dioelectric grease on or they will rot out. I found one of my plug wires did rot out. just something to look at.

  4. #3
    JimD is offline Cadillac Owners Connoisseur
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    Re: # 8 misfire

    Quote Originally Posted by cj489
    WE have an 02 DHS with a 4.6. We started getting service engine soon light. Caddy dealership says throttlebody and injectors needed to be cleaned. Also had two crank sensors which were bad. Thought I would change the sensors myself but did not have proper tools so took it to another dealership as the first one ripped us off before. So one thousand dollars later and the # 8 still misfires. New coil pack was installed on the rear but # 8 blew within minutes. Need help

    Pull your trouble codes (DTCs) and list them for us to see. In particular, the "P" codes.

    You have not explained why a coil was replaced on the 'rear'. Number 8 cylinder is in the 'front' bank.

  5. #4
    cart69's Avatar
    cart69 is offline Cadillac Owners Fanatic
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    Re: # 8 misfire

    number 8 is the front bank tranny side, or the farthest right plug on the front looking at the car.

    my 94 had a similiar problem turned out to be wires. i replaced the plugs and it was fine for 40-50 miles then it started missing again

  6. #5
    cj489 is offline Cadillac Owners Member
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    Re: # 8 misfire

    Changed out the spark plug boots but still have the misfire on # 8 which I found was in the front bank after reading the proper book. Replaced the coil pack and still had the misfire. Could the computer be sending the wrong message to the coil pack? Could the throttle bady sensor be bad but not throwing a bad code?

  7. #6
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: # 8 misfire

    Have you tried just replacing that spark plug? If that doesn't do anything, you can depressurize the fuel rail, pull it off, and switch the #8 injector with the #6 injector, to see if the misfire code follows.

  8. #7
    infin1ty is offline Cadillac Owners Member
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    Re: # 8 misfire

    My '97 set a #8 misfire code. Had newer wires and plugs within 15k miles. Replaced #8 plug only - problem was solved.

  9. #8
    cj489 is offline Cadillac Owners Member
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    Re: # 8 misfire

    I have replaced all the plugs, wires. When I replaced the coil in the front it ran fine without showing any codes then shot all misfire but only the # 8 was misfiring. I'm wondering now if there is a short or something not being grounded properly.

  10. #9
    cj489 is offline Cadillac Owners Member
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    Re: # 8 misfire

    new problem: We drive the caddy to Tampa for the weekend and on the way home the misfire clears up, running like a top. Pull it into the garage shut it off, start it back up misfire has returned. Is there some typ of command in the computer gone array?

  11. #10
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: # 8 misfire

    Quote Originally Posted by eldorado1
    you can depressurize the fuel rail, pull it off, and switch the #8 injector with the #6 injector, to see if the misfire code follows.
    ^^^

  12. #11
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: # 8 misfire

    Quote Originally Posted by darcy
    I just a problem with my 94 4.9 missfiring. the wires were only a little over a year old. i thought they were ok. found out that when you put in new wires and cap you have to put some dioelectric grease on or they will rot out. I found one of my plug wires did rot out. just something to look at.
    It takes a lot longer than one year for rubber to rot. The purpose of dielectric grease is to prevent the boot from sticking to the plug. Not to prevent rot. If that were the case, then the entire wire should be coated, right? Infact new A/C Delco wires come with a message in the box that says not to use dielectric grease because the boots are coated with something at the factory. If your boots or wires were rotted in less than a year, there are other factors at play. I know that coolant (Dex-Cool anyway) does not play well with rubber (serp belts).

  13. #12
    PAULSTSMAN1's Avatar
    PAULSTSMAN1 is offline Cadillac Owners Fanatic
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    Re: # 8 misfire

    With the 4.6 Northstar several things can cause a misfire. Some questions you might ask your are:

    1. Are you losing Coolant? Could there be a HeadGasket issue?
    2. Did you change the Fuel Filter? Dirty Fuel, or Pressure problem?
    3. Did you see what the Spark plug you removed from Number #8 looked like.
    4. Why did you change the Coil? Was it tested and found to be defective?

    Recently I had a similar problem, my car has 109500 miles on it and I ran out of fuel, then the misfire malfunction started. I took my car to Tune Masters, paid for a diagnostic and found out #3, and 4 were the culprits. I was way over the 100K tune up recommended time, so I had all the plugs replaced, and the fuel filter. The plugs came out looking somewhat ashend, and old.

    Bottom line, the car is now running like new! So much power, fuel economy up, and so Cadillac quiet.

    Tune up and Speed shops that have OBII and III systems can figure out if your issues are electronical or fuel related. I find when I experience these problems private repair facilities can be much better than the Dealerships. Dealers techs often have a pull/replace mentality. You have already spent way too much money and time, not to have a decent diagnosis and resolution.

    I hope this helps!

  14. #13
    cj489 is offline Cadillac Owners Member
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    Re: # 8 misfire

    Whole new ballgame: Driving down the road 35 mph hear several pinging noises car dies we pull off to a side road and try to start the car but sounds like fuel pump problem. Tow driver arrives he tries to start it says sounds like a fuel pump. Towed to the mechanic and left for the weekend but we did return to gather things out of the vehicle. I thought one more time, vehicle starts but now is banging shut it off immediately. Mechanic looks at car on Tuesday says rods are knocking but it's full of oil and he has know idea. @001 4.6 had a ring problems being too soft, could this be the problem and one of them was broken or split. Please help.

  15. #14
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: # 8 misfire

    Does the fuel pump prime for a couple seconds when you turn the key?

    How severe is the knocking?

    I know you said you replaced them, but it sounds suspiciously like an out of time/bad crank sensor. Run it out of time enough, and it will sound like your engine's rattling apart. Running it lean or out of time is obviously not good for it either, so get it looked into.

  16. #15
    cj489 is offline Cadillac Owners Member
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    Re: # 8 misfire

    yes the fuel pump primes when you turn the car on, you can actually hear it. We are in touch with Cadillac and they claim we have to get the car to their shop in order for them to figure out what is wrong, duh. Thank you to everyone who has answered any of these posts. If I ever find out what has happened it will be on here.

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