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Thread: Cylinder never fires (plug, coil, injector are OK). Please help. :-(

  1. #1
    Join Date
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    1998 328i and 2001 330ci

    Cylinder never fires (plug, coil, injector are OK). Please help. :-(

    Hey all, I stuck on this one. I have a cylinder that does not fire, so i'm currently running on only five cylinders. I need help.


    Here's the car, and its background info.


    I have a 2001 330ci that is now only running on cylinders 1-4,6. Ie, cylinder 5 does not fire. I have determined that it is not the spark plug, not the coil, not the fuel injector via the following (if you care to know).



    Method for determining functioning coils: With the car running (yes it runs on 5 cylinders) I removed the wiring connection that goes to the coil on cylinder number 5 and can hear no change in motor performance (whereas removing any of the wiring going to the other coils causes degraded engine performance audibly). After then swapping coils from a functioning cylinder, we see the same misfire on cylinder 5 using this method.


    Method for determining functioning spark plug: Similar to above, I pulled two spark plugs (cylinder 5's and one from another cylinder) and swapped them. The same non-firing is occurring on cylinder number 5 using the method from above.


    Method for determining functioning injectors: The nonfunctioning cylinder's spark plug is wet at the tip.



    What should I check next? I was told recently by a mechanic that he did a compression test and that all cylinders were in spec. So more info on the car's recent history.


    It burned oil a few years ago and it burned up my catalytic converters (so i put in cat-less headers) and replaced the CCV system (about 200,000 miles).


    More recently the car had a misfire issue which i attributed to a possible vacuum leak, so I replaced the intake boots (found a small crack) and a few CCV hoses for good measure (while I inspected and cleaned out the CCV oil separator with solvents. I also inspected the DISA valve which is actuating correctly, and cleaned the throttle body a bit with cleaner (240,000 miles).


    At this point with 240,000 miles it still ran TERRIBLY with the MAF sensor plugged in. It almost sounded like a knocking sound would develop when the MAF was plugged in and if you let it idle for longer than 10 seconds like this, it would develop a misfire that would remain until you shut the car off and turned it back on (then the misfire was gone). However, with the MAF sensor unplugged (which, from my understanding, puts the car into a richer fuel map for engine safety) it ran pretty darn well (100mph no problem and felt nice)!


    I went on a three hour drive and when I got up into an area with a bit more elevation (2500 ft) vs my normal 600 ft, it lost the number 5 cylinder going up a hill. I made it all the way back home carefully and now, she is parked. Ideas?


    Any help would be greatly appreciated.

  2. #2
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    Perform a diagnostic scan for further clues, preferably with a BMW scantool/software, instead of a generic OBD2 scan tool.

    However, with the MAF sensor unplugged (which, from my understanding, puts the car into a richer fuel map for engine safety) it ran pretty darn well (100mph no problem and felt nice)!
    This observation seems to point to an intake leak, causing a fuel mixture issue.

    Have an intake smoke test performed with a professional smoke machine to reliably dismiss or confirm locations of intake leaks.

  3. #3
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    While I have no suggestions for you, I am suffering a very similar problem.
    I have a 2001 E46 5 speed Touring that has lost compression in cylinder 5 too. I have soaked the cylinder in ATF fluid and Marvel Mystery Oil, three times and can only get the compression up to 60 lbs with my foot in the pedal. After reading your post about knowing the injectors work as the tip of the plug is wet, I noticed my plug is dry. Now I'm wondering whether my injector is bad. Do you know whether , as opposed to bad rings, a bad fuel injector would cause really low compression? ( Seems like a dumb question as if there's no fuel there couldn't be any compression I would think.)

  4. #4
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    Quote Originally Posted by Mountainwoodie View Post
    While I have no suggestions for you, I am suffering a very similar problem.
    I have a 2001 E46 5 speed Touring that has lost compression in cylinder 5 too. I have soaked the cylinder in ATF fluid and Marvel Mystery Oil, three times and can only get the compression up to 60 lbs with my foot in the pedal. After reading your post about knowing the injectors work as the tip of the plug is wet, I noticed my plug is dry. Now I'm wondering whether my injector is bad. Do you know whether , as opposed to bad rings, a bad fuel injector would cause really low compression? ( Seems like a dumb question as if there's no fuel there couldn't be any compression I would think.)
    No, compression testing is measuring how much pressure is built up inside the cylinder when the piston rises towards the head. A non-functioning fuel injector would not affect compression.

  5. #5
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    Quote Originally Posted by MIKYZZ4 View Post
    Perform a diagnostic scan for further clues, preferably with a BMW scantool/software, instead of a generic OBD2 scan tool.


    This observation seems to point to an intake leak, causing a fuel mixture issue.

    Have an intake smoke test performed with a professional smoke machine to reliably dismiss or confirm locations of intake leaks.
    I'll get my Peake reader in a day or two and update the thread. I'll see if I can get it to a service station that has a smoke machine around here as well.

  6. #6
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    Quote Originally Posted by FnSquirrel View Post
    No, compression testing is measuring how much pressure is built up inside the cylinder when the piston rises towards the head. A non-functioning fuel injector would not affect compression.
    Unless there's an E46 model with direct injection we don't know about

  7. #7
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    Quote Originally Posted by Raddee View Post
    Unless there's an E46 model with direct injection we don't know about
    Lol. My bad. One more go around soaking the piston then its on to a leak down test . I'm guessing its a valve but IDK. Only has 146 K on it and was owned by 2 BMW tech workers before me. Seems odd

  8. #8
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    Quote Originally Posted by MIKYZZ4 View Post
    Perform a diagnostic scan for further clues, preferably with a BMW scantool/software, instead of a generic OBD2 scan tool.


    This observation seems to point to an intake leak, causing a fuel mixture issue.

    Have an intake smoke test performed with a professional smoke machine to reliably dismiss or confirm locations of intake leaks.
    I have an update...

    I have ~180 lbs of compression on all cylinders except for cylinder number five. Cylinder number five has 0 lbs. My question is this...does this indicate a valve issue, or could it be rings? Don't rings wear down over time, instead of just letting completely letting go? When i do the compression test, the needle on that cylinder doesn't even move.

  9. #9
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    A cylinder leakdown test will answer that question.

  10. #10
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    Go buy GM top end cleaner from a GM or chevy dealer. Put one ounce in the spark plug hole of the 0 compression cylinder. Put the spark plug back in and let sit overnight for at least 12 hours.

    Then run the car let the carbon clear out.

    Let car cool down to cold, check compression.

  11. #11
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    Get a spark plug hole adaptor for a quick disconnect air fitting

    Quote Originally Posted by MIKYZZ4 View Post
    A cylinder leakdown test will answer that question.
    The idea is to put compressed air into #5 cylinder with the piston at TDC....sometimes you have to put a breaker bar on the crankshaft pulley bolt and hold the crank...if the crank is a couple degrees øff TDC the air pressure can force the piston down. Also, some cams have a certain amount of overlap (both intake and exhaust open at same time for some amount of crank rotation) so you want to find the spot where both valves are closed, i.e., the power stroke. A leak down test is just a metered variation of this exercise that puts a number on the leakage.

    Once you've found the right spot and put compressed air into the cylinder through the spark plug hole, you need to listen for where the air leakage goes...and it WILL go somewhere if you have zero compression!!!

    You might need to remove the throttle body to air cleaner boot to hear intake valve leakage, but you should be able to hear exhaust valve leakage at the exhaust pipe. Bad rings you'll hear air leakage at the pcv port or the dipstick tube.

    Wouldn't be surprised to find a burnt exhaust valve leaking. At that point it's remove the head and accomplish a valve job.

  12. #12
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    Quote Originally Posted by FnSquirrel View Post
    I have an update...

    I have ~180 lbs of compression on all cylinders except for cylinder number five. Cylinder number five has 0 lbs. My question is this...does this indicate a valve issue, or could it be rings? Don't rings wear down over time, instead of just letting completely letting go? When i do the compression test, the needle on that cylinder doesn't even move.
    You can do a quick compressed air test into #5 or you can pull the cam cover and see if a valve is stuck, a cam lobe wiped, etc. I would do the compressed air test first.

  13. #13
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    Quote Originally Posted by SloopJohnB View Post
    The idea is to put compressed air into #5 cylinder with the piston at TDC....sometimes you have to put a breaker bar on the crankshaft pulley bolt and hold the crank...if the crank is a couple degrees øff TDC the air pressure can force the piston down. Also, some cams have a certain amount of overlap (both intake and exhaust open at same time for some amount of crank rotation) so you want to find the spot where both valves are closed, i.e., the power stroke. A leak down test is just a metered variation of this exercise that puts a number on the leakage.

    Once you've found the right spot and put compressed air into the cylinder through the spark plug hole, you need to listen for where the air leakage goes...and it WILL go somewhere if you have zero compression!!!

    You might need to remove the throttle body to air cleaner boot to hear intake valve leakage, but you should be able to hear exhaust valve leakage at the exhaust pipe. Bad rings you'll hear air leakage at the pcv port or the dipstick tube.

    Wouldn't be surprised to find a burnt exhaust valve leaking. At that point it's remove the head and accomplish a valve job.
    Hey Folks- Thanks for all the input. My leak down test has been put on hold. It was supposed to be done yesterday but my friend at the shop got hung up. I really appreciate all the expert input and as soon as I can I will report back.....based on everything I've read here I'm suspecting an exhaust valve which seems more likely than rings as I have no blow by.

  14. #14
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    Yeah if it is valves and not a ring issue then GM cleaner will not help.

    Your compression test with oil in the spark plug hole should tell you if it is rings.

  15. #15
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    If you fire the car up and remove the oil cap, do you have a lot of blow by? If you do, its the rings. If you dont, its a valve.

    Im betting valve.

  16. #16
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    Quote Originally Posted by dhurley34 View Post
    If you fire the car up and remove the oil cap, do you have a lot of blow by? If you do, its the rings. If you dont, its a valve.

    Im betting valve.
    Me too guys. As soon as I know I'll be back on here. Should get it done by this weekend. Thanks mucho for helping by replying!


  17. #17
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    Quote Originally Posted by SloopJohnB View Post
    The idea is to put compressed air into #5 cylinder with the piston at TDC....sometimes you have to put a breaker bar on the crankshaft pulley bolt and hold the crank...if the crank is a couple degrees øff TDC the air pressure can force the piston down. Also, some cams have a certain amount of overlap (both intake and exhaust open at same time for some amount of crank rotation) so you want to find the spot where both valves are closed, i.e., the power stroke. A leak down test is just a metered variation of this exercise that puts a number on the leakage.

    Once you've found the right spot and put compressed air into the cylinder through the spark plug hole, you need to listen for where the air leakage goes...and it WILL go somewhere if you have zero compression!!!

    You might need to remove the throttle body to air cleaner boot to hear intake valve leakage, but you should be able to hear exhaust valve leakage at the exhaust pipe. Bad rings you'll hear air leakage at the pcv port or the dipstick tube.

    Wouldn't be surprised to find a burnt exhaust valve leaking. At that point it's remove the head and accomplish a valve job.
    Right you are Sir!! Did the leakdown test today and put a scope into the cylinder. Piston and rings are fine. Looks like it is an exhaust valve...compressed air coming out the tail pipe. Only has @137,000 miles.so not sure how this happened. It is well taken car of, bought it from a BMW tech......so head is coming off this week or next. Darn!

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