Page 2 of 3 FirstFirst 123 LastLast
Results 21 to 40 of 46

Missfiring at 5000 rpm

This is a discussion on Missfiring at 5000 rpm within the General Help forums, part of the LSx Technical Help Section category; Springs are funny sometimes. I had 8 broken springs and the engine never skipped a beat. I only took it ...

  1. #21
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    Location
    Arizona
    Posts
    12,552
    Springs are funny sometimes. I had 8 broken springs and the engine never skipped a beat. I only took it down because the engine had a misterious squeak. Turned out to be a roller lifter squeaking on a cam lobe that was half gone. I found 8 broken springs while I was in the process.

    These were high end Pac racing springs in a brand new set of AFR heads supplied straight from AFR. They were only on the engine for 2 months.

    It wore a roller cam lobe down because AFR supplied the heads with solid roller springs (400 lbs. seat pressure) after specifying a hydraulic roller cam for the engine through Comp Cams. The cam was also ground out of cast iron rather than billet steel like most rollers. Completely AFR's fault, but that's another story. Still though, I shouldn't have had 8 broken springs with only 10 dyno pulls and maybe 1,000 street miles.

  2. #22
    Senior Member redbird555's Avatar
    Join Date
    Mar 2009
    Location
    pompano beach florida
    Age
    27
    Posts
    1,008
    2002 Camaro Z/28 Pewter

    hey jones I had someone suggest crank walk could be causing the reluctor wheel to be misaligning with the crank sensor and thus causing issues with spark and fuel. I dont think this is the case because the problem is so exact and occurs at the same rpm every time but again I'm not sure so I'm just bouncing off ideas. I'd also think the crank walking would create some audible noise from the motor as well as me noticing metal in the oil (which there was none) when I changed the oil 200 miles ago. I should also add that when the motor has the issue the injector pulses do not go to 0 so its not cutting fuel its just cutting spark and hptuners WILL NOT pickup anything wrong it shows that the engine parameters are all fine as far as fueling and sensors go the dyno is the only thing that picks up a reading withe the graph and widebands. This is why were thinking pcm because the pcm doesnt actually see any problems however it may be sending a mbad signal to the engine at 5900 rpms but since its follwing the tune (just not correctly) its having problems.

  3. #23
    None Shall Pass Knight's Avatar
    Join Date
    Jan 2010
    Location
    East of Cleveland, Ohio
    Posts
    3,828

    Black
    99 WS.6 - Modified

    Quote Originally Posted by redbird555 View Post
    hey jones I had someone suggest crank walk could be causing the reluctor wheel to be misaligning with the crank sensor and thus causing issues with spark and fuel. I dont think this is the case because the problem is so exact and occurs at the same rpm every time but again I'm not sure so I'm just bouncing off ideas. I'd also think the crank walking would create some audible noise from the motor as well as me noticing metal in the oil (which there was none) when I changed the oil 200 miles ago. I should also add that when the motor has the issue the injector pulses do not go to 0 so its not cutting fuel its just cutting spark and hptuners WILL NOT pickup anything wrong it shows that the engine parameters are all fine as far as fueling and sensors go the dyno is the only thing that picks up a reading withe the graph and widebands. This is why were thinking pcm because the pcm doesnt actually see any problems however it may be sending a mbad signal to the engine at 5900 rpms but since its follwing the tune (just not correctly) its having problems.

    It is a curious problem. I would side with your thinking as well. As you stated, you have the other PCM, so I'd definately swap it. Be sure to let us know what happens.

  4. #24
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    Location
    Arizona
    Posts
    12,552
    Crank walk would be due to a worn thrust bearing. That would cause low or no oil pressure in most cases.

  5. #25
    Moderator Cutlass's Avatar
    Join Date
    Apr 2008
    Location
    Madison, WI
    Posts
    6,998

    1999 Formula WS6 M6-sold
    2001 Silverado Z71

    I would tend to learn more towards a sensor problem like MAF, Crankshaft Position, MAP, or maybe Camshaft Position sensor. Or a mechanical problem like FBJ said: weak valvesprings...or lifter problems (like maybe there pumping up?)

  6. #26
    None Shall Pass Knight's Avatar
    Join Date
    Jan 2010
    Location
    East of Cleveland, Ohio
    Posts
    3,828

    Black
    99 WS.6 - Modified

    Been brainstorming a bit more last night......wondering if it's not a frequency interference that occurs at that rpm, interfering with one of the sensors. Would probably be on the more rare side, but something to consider.

  7. #27
    Senior Member redbird555's Avatar
    Join Date
    Mar 2009
    Location
    pompano beach florida
    Age
    27
    Posts
    1,008
    2002 Camaro Z/28 Pewter

    thanks guys i dont have the car here so its hard to test all of these things haha but i am passing it along to the shop. as far as electrical interferance goes the only thing that has changed recently on the car is the addition of a truck 130amp alternator which didnt have any issues till almost 2 weeks later when this started occurring. I tested the maf myself by simply unplugging it and forcing it to run in open loop and the problem persisted so that cleared that out. The crank sensor is still a possibility and were checking into that now but usually in my experience a crank sensor will cause the engine to run like crap all the time.

    After we eliminate the electronics I think we'll probably pull a valve cover the fact that the misfire occurs on both banks at the exact same time and leans out the same amount doesnt really tell me valve springs but who knows. The other thing is that when I got the engine it had 8k on it but it had sat for a while so before i dropped it in my car I tore the heads off and put in new lifters and valve springs so now those have about 2500 miles on them and the engine runs quiet as a mouse so I doubt its anything inside the engine. For a problem to be that pronounced up top I'd think you would have some other signs of issues down low. After they get back in the shop from the holiday weekend theyre going to swap the pcm to a known good one and swap the crank sensor for a spare and see what happens.

  8. #28
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    Location
    Arizona
    Posts
    12,552
    You can have broken valve springs and never know it. Like I said I had 8 broken and the engine still ran like a top, idled great, no noises, and cruised fine without skipping a beat. They usually don't show their weakness until high rpms.

    We run in new flat tappet cams with "break in" springs all that time that barely have 80 lbs. seat pressure to ensure the cam gets a fair break in chance before installing the required springs. Engine runs fine varying rpms from 2-3,000 and will rap up without a problem. A long hard dyno pull however will show a rapid torque drop off (valve float).

  9. #29
    Moderator Cutlass's Avatar
    Join Date
    Apr 2008
    Location
    Madison, WI
    Posts
    6,998

    1999 Formula WS6 M6-sold
    2001 Silverado Z71

    Quote Originally Posted by redbird555 View Post
    as far as electrical interferance goes the only thing that has changed recently on the car is the addition of a truck 130amp alternator which didnt have any issues till almost 2 weeks later when this started occurring.
    It wouldn't be a bad idea to test voltage with a meter as the RPMs climb, just to make sure there isn't any voltage spikes or drop offs.

  10. #30
    Senior Member redbird555's Avatar
    Join Date
    Mar 2009
    Location
    pompano beach florida
    Age
    27
    Posts
    1,008
    2002 Camaro Z/28 Pewter

    Well I finally got home from college and got the car over to Lashway motorsports down here where we tracked down the issue to a bad crank sensor they got the replaced and I also had them dynotune the car since they gave me a deal. With bolt ons only through an AUTO, with 18" wheels and 3.42's the ls6 kicked out 370 whp on a MUSTANG DYNO, I think on a dyno jet I would have easily met my 380-385whp gial so overall I'm happy!

  11. #31
    O U 8 1 2 Spaz's Avatar
    Join Date
    Nov 1999
    Location
    over here...
    Age
    39
    Posts
    25,693

    []D [] []V[] []D
    1999 trans am

    my dad just had the same thing happen... he had an audi R8 try him and and got on it (he destroyed the r8) and in the upper rpms he was breaking up but didn't feel any loss... he has dual spring, valve springs and the outer srping broke... i'd check your springs...

  12. #32
    Smiles for 9.5 Years cammed goat's Avatar
    Join Date
    Jan 2009
    Location
    Paterson/Ridgewood, NJ
    Posts
    11,474

    Phantom Black Metallic
    2004 GTO M6

    I like those numbers.

  13. #33
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    Location
    Arizona
    Posts
    12,552
    Those LS6 engines are strong for something that idles so smooth.

    Glad to see you got it figured out.

  14. #34
    Senior Member redbird555's Avatar
    Join Date
    Mar 2009
    Location
    pompano beach florida
    Age
    27
    Posts
    1,008
    2002 Camaro Z/28 Pewter

    ya guys I was pretty happy to finally get it all figured at 5500 rpms the crank sensor count was out quite a bit and then would get back in line a few hundred rpms later... but ya again like i said I'm happy with the ls6 maybe one day I can get it on a dynojet just to see what happens does anyone know what the approximate difference between the two is

  15. #35
    Smiles for 9.5 Years cammed goat's Avatar
    Join Date
    Jan 2009
    Location
    Paterson/Ridgewood, NJ
    Posts
    11,474

    Phantom Black Metallic
    2004 GTO M6

    LS6 has:

    slightly more aggressive cam than LS1
    intake manifold has larger ports than LS1
    I believe the throttlebody is larger than the LS1
    head ports are larger (243) than LS1

    Others will post what I have missed.

  16. #36
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    Location
    Arizona
    Posts
    12,552
    Quote Originally Posted by cammed goat View Post
    LS6 has:

    slightly more aggressive cam than LS1
    intake manifold has larger ports than LS1
    I believe the throttlebody is larger than the LS1
    head ports are larger (243) than LS1

    Others will post what I have missed.
    More compression, lightweight valves, better combustion chambers,

  17. #37
    O U 8 1 2 Spaz's Avatar
    Join Date
    Nov 1999
    Location
    over here...
    Age
    39
    Posts
    25,693

    []D [] []V[] []D
    1999 trans am

    better cooling passage...

  18. #38
    Senior Member redbird555's Avatar
    Join Date
    Mar 2009
    Location
    pompano beach florida
    Age
    27
    Posts
    1,008
    2002 Camaro Z/28 Pewter

    Quote Originally Posted by cammed goat View Post
    LS6 has:

    slightly more aggressive cam than LS1
    intake manifold has larger ports than LS1
    I believe the throttlebody is larger than the LS1
    head ports are larger (243) than LS1

    Others will post what I have missed.
    Lol I knew what the differences were between the ls1 and ls6 because I got this motor as just a shortblock and tracked down a set of original ls6 heads along with an 03 cam because it had an 01 smaller cam in it at the time. When I said the difference I meant the difference in what a mustang dyno reads compared to a dynojet because i know the mustang reads lower by an amount.
    Quote Originally Posted by Firebirdjones View Post
    More compression, lightweight valves, better combustion chambers,

    This is all correct. The ls6 uses sodium valves exhaust and hollow intake valves, along with a more agressive cam (02-04 is bigger than 01). The 243 heads give slightly more compression and then of course the intake. The tb is the same for the two motors however.

  19. #39
    Moderator Firebirdjones's Avatar
    Join Date
    May 2006
    Location
    Arizona
    Posts
    12,552
    In that case I wouldn't worry about it. Not worth the trouble to pay for more dyno time just for chest beating. Tuning is what they are meant for.
    Run that baby at the strip and see how it does, those are the numbers that count

  20. #40
    Senior Member redbird555's Avatar
    Join Date
    Mar 2009
    Location
    pompano beach florida
    Age
    27
    Posts
    1,008
    2002 Camaro Z/28 Pewter

    We are trying to get a track outting down here together but I would really like to have my 3600 stall thats sitting in my room installed before i go oh well. I'm still very happy with the setup 370whp on a mustang dyno is easily over the 380 goal I wanted on a dyno jet but when I go to the track the true colors of the motor will shine

Page 2 of 3 FirstFirst 123 LastLast

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. If you had $5000 to spend on a 94 Z28....
    By hix5000 in forum Camaro / SS
    Replies: 18
    Last Post: 05-22-2009, 03:32 PM
  2. WTB: LS1 Car $5000 or under AND WTS: 94 Formula
    By tford0688 in forum Vehicles For Sale / Trade
    Replies: 0
    Last Post: 01-28-2009, 08:47 AM
  3. Replies: 6
    Last Post: 09-12-2006, 11:49 PM
  4. $5000 and what to do
    By ttocs in forum Camaro / SS
    Replies: 4
    Last Post: 06-22-2006, 12:02 PM
  5. looking for an ls1 for around 5000
    By chevy_muscle in forum Vehicles For Sale / Trade
    Replies: 0
    Last Post: 02-28-2006, 06:39 PM

Bookmarks

Posting Permissions

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