Page 1 of 2 12 LastLast
Results 1 to 15 of 18
  1. #1
    Newbie
    Join Date
    Jun 2017
    Location
    Canberra
    Posts
    13

    Default 308 misfire/backfire at 3000rpm?

    G'day everyone, I'm desperately chasing some help from the experienced 304/308 guys, I've recently installed a fresh rebuilt 308 into my VH commodore, engine is 308 304 heads all machined and fully rebuilt, 4690 crow cam 234/244 i think?, come racing single plane, holley 650 HP street, msd ready to run distributor, msd leads, now this engine and combo was run in and dyno'd at Westend Performance before install and had no issues at all, now after installing in the car which is also fully rebuilt all the wiring is new to, sent it off to a tuner to be tuned again here in Canberra as it was running a little rich, and came across this random backfire/mis at around 3000rpm now I'm not sure it's a misfire but the engine definitely hesitates and backfires at the same rpm every time, it will rev fine up to and beyond this but it's in the same spot every, so obviously we went chasing ignition timing first, then fuel, even changed distributor and carby separately and together, checked rocker adjustment, coil, power to coil and distributor, earth's, ect.. We have checked all the obvious stuff twice over, now he is in the process of checking cam timing but I'm not sure that is going to be our issuer, but we are running out of things it could be, has anyone come across anything like this before? Any help or advice would be appreciated, cheers.

  2. #2
    Do you ever leave?
    Join Date
    Jan 2008
    Location
    Just outside the A.C.T.
    Posts
    1,646

    Default

    Where is the car getting tuned ??

  3. #3
    Do you ever leave? DR327VK's Avatar
    Join Date
    Jan 2009
    Location
    ADELAIDE
    Posts
    2,792

    Default

    That's biggish cam or real mans cam! It will need good CDI ignition system eg crane or Msd!
    Had faulty spark plug did some think like this & fault coil can do same thing!
    SA AUTO TEK
    https://www.facebook.com/SA-AUTO-TEK-1043624872327176/


    My Channel You Tube - VK 327 Stroker E85 Fueled since 2008
    http://www.youtube.com/user/DR327VK#g/u

  4. #4
    Do you ever leave? DR327VK's Avatar
    Join Date
    Jan 2009
    Location
    ADELAIDE
    Posts
    2,792

    Default

    Once the cam was bedded in was the inner valve springs installed & valve lash redone?
    SA AUTO TEK
    https://www.facebook.com/SA-AUTO-TEK-1043624872327176/


    My Channel You Tube - VK 327 Stroker E85 Fueled since 2008
    http://www.youtube.com/user/DR327VK#g/u

  5. #5
    Do you ever leave? paulzig's Avatar
    Join Date
    Oct 2008
    Location
    Gold Coast
    Posts
    15,420

    Default

    Tried changing the spark plugs?

  6. #6
    Newbie
    Join Date
    Jun 2017
    Location
    Canberra
    Posts
    13

    Default

    The car is being tuned at a new shop here in Canberra ''Totally Tuned'' the bloke there has been awesome. And we have actually found the issue turned out to be the dizzy after all despite changing it out for another one and it doing the exact same thing, probably a 1 in a million thing to happen haha.
    Originally swapped out the Msd ready to run with an electronic one he had laying around, did the same thing, so we started chasing other possible causes, changed carb, fuel, 3 sets of leads with 3 sets of plugs, valve lash, cam timing, and everything else we could think of, but still same thing at the same RPM every time, came full circle back to the distributor, thought we might try to get a hold of a good old fashioned Bosch point's dizzy, got one that had definitely seen better days covered in dust and grease, slapped it in, put it on the rollers again, and boom it was GONE! I almost fell over!! Has a bit of a flutter as it rolls over into secondaries but with a reconditioned regraghed one from scorcher and a final tune hopefully it'll be mint!

  7. #7
    Newbie
    Join Date
    Jun 2017
    Location
    Canberra
    Posts
    13

    Default

    Actually I'd be keen to know what others would do in my situation, I'm no specialist when it comes to distributor's I don't fully understand them. But the MSD ready to run was brand new and performed great on the engine dyno but for some reason has an issue now? I remember Sam at Westend did change the springs and something else in it at the time not sure if that would have anything to do with how it is working now because of different load on the engine or whatever? But the tuner here believes there could be something wrong with the internal module or something? And I don't want to just jump ahead and buy a reco Bosch unit if I could possibly fix the msd unit but on the other hand don't wanna waste more time and money on msd if it's still just going to be garbage?

  8. #8
    Newbie
    Join Date
    Jun 2017
    Location
    Canberra
    Posts
    13

    Default

    Actually I'd be keen to know what others would do in my situation, now I know bugger all about distributor's don't have a full understanding of how they work, but the MSD unit performed great on the engine dyno but has an issue now for some reason? I remember Sam at Westend changed the springs and something else in it at the time not sure if that might have anything to with it because of different load on the engine or something? But my tuner here said all the timing seemed fine with it, total timing was all in before we were getting the backfire at 3000rpm (not sure what that means) and he believes the internal module is playing up? Now I don't want to just jump ahead and buy a reco Bosch unit if my MSD unit might be fixable but on the other hand I don't want to waste more time and money on the msd if it's still just going to be garbage?

  9. #9
    Do you ever leave? EH179's Avatar
    Join Date
    Jan 2008
    Location
    Ipswich. QLD
    Posts
    3,842

    Default

    Depends how much stuffing around you are prepared to put up with.

    No-one on here could say with certainty, what the problem is. You could try and ask MSD?

    Factory Bosch HEI FTW!

  10. #10
    Do you ever leave? HQ308Ute's Avatar
    Join Date
    Dec 2011
    Location
    Adelaide
    Posts
    2,572

    Default

    with those MSD's, i'd say it could be noise.

  11. #11
    Not the Kingswood! hq308's Avatar
    Join Date
    May 2010
    Location
    The Riff
    Posts
    2,154

    Default

    The fact that the issue occurred with 2 totally different HEI dissys but didn't occur on the engine dyno or with the points distributor to me points to an issue related to your car. The only things I can think of are either a voltage drop in the ignition circuit or being that the issue occurs at a specific rpm there could be an issue with the tach ( assuming one is fitted) or any other accessory connected to the coil.

  12. #12
    Newbie
    Join Date
    Jun 2017
    Location
    Canberra
    Posts
    13

    Default

    hq308 we actually thought the same thing and tested all the electrics while running on the dyno and didn't appear to be any voltage drop, I do have a tach a dakota digital tach, fairly basic and didn't seem to have any issues with it?

  13. #13
    Do you ever leave? DR327VK's Avatar
    Join Date
    Jan 2009
    Location
    ADELAIDE
    Posts
    2,792

    Default

    faulty alternator can make the voltage spike and cause glitch in the ignition?
    SA AUTO TEK
    https://www.facebook.com/SA-AUTO-TEK-1043624872327176/


    My Channel You Tube - VK 327 Stroker E85 Fueled since 2008
    http://www.youtube.com/user/DR327VK#g/u

  14. #14
    Do you ever leave?
    Join Date
    Jan 2008
    Location
    Just outside the A.C.T.
    Posts
    1,646

    Default

    Ken is a good bloke, glad you found the problem.

    Another vote here for the Bosch HEI in front of the MSD.

  15. #15
    Part of the furniture gtrboyy's Avatar
    Join Date
    Dec 2007
    Location
    sydney
    Posts
    1,084

    Default

    Diode in alternator charge light?

    Being a vh a wiring issue would not be a surprise.
    Last edited by gtrboyy; 20-06-2017 at 07:58 PM.

Page 1 of 2 12 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. cleveland 351 misfire
    By michael giles in forum Ford V8's
    Replies: 13
    Last Post: 26-08-2014, 02:24 PM
  2. 350 misfire.
    By Sam I Am in forum Chevrolet
    Replies: 2
    Last Post: 26-01-2012, 09:45 AM
  3. Ocassional Misfire
    By Razor in forum Ford V8's
    Replies: 7
    Last Post: 24-12-2010, 03:47 PM
  4. WTB: 3000rpm Trimatic Hi Stall
    By VHPirie in forum Wanted (cars & items)
    Replies: 2
    Last Post: 10-08-2010, 11:34 PM
  5. Wanted 3000rpm Stall
    By Brody james in forum Wanted (cars & items)
    Replies: 0
    Last Post: 04-01-2010, 05:26 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •