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500+ hp LT1, new motor, misfire fixers help plz :)

This is a discussion on 500+ hp LT1, new motor, misfire fixers help plz :) within the LT1 forums, part of the Vehicle Specific category; Hey everyone. I'm in the weeds bad and need a miracle. I would first like to apologize for the novel ...

  1. #1
    Junior Member
    Join Date
    Mar 2009
    Brighton, MI

    2000 CAMARO SS

    500+ hp LT1, new motor, misfire fixers help plz :)

    Hey everyone. I'm in the weeds bad and need a miracle. I would first like to apologize for the novel I about to write. I have been to 5 performace shops here in southeastern Michigan and all 5 shops returned the car to me and said they could not figure it out. (This includes livernois motorsports which I was told were a very 'smart' shop that could fix anything....ERRRR wrong)

    Straight to the point.


    1995 camaro a 383 LT1 stroker, 12.5:1 compression (checks out very good), estimated to be 500 h.p. + by Lloyd Elliot stage 3 heads and cam, pacesetter long tubes, no cats, SLP loudmouth cat-back, 30lb injectors, msd opti, msd 8.5mm wires, autolite plugs, msd coil, stock MAF, PCM tuned 3 times by pcmforless (Bryan Herter), LT4 intake manifold, new walbro 255 fuel pump (pressure is strong and check out to be holding perfectly), cold air intake, egr removed (block off plates could be bad seal??), AIR pump deleted, (I think thats enough background) (THhis motor just dropped recently in btw.

    Started right up, broke in the cam, maybe has a total of 40 hours total run/idle time on the motor since it was new.

    PROBLEM1: (Dies when motor gets hot)

    For a while the car would start and hold an idle with no problem. Now its a tough time to get it to start (20-25 turns before it finally starts, have to gas it to get it to hold an idle.) Once its started it would hold an idle and rev while the motor was still cold. As soon as the car get warm, big trouble happens. It starts bogging down, slow response when giving it gas, misfires throughout any motor rev, eventuially when it gets too hot under the hood it will simply die. Starting it after it dies is simply not an option. What would be a list of reasons as to why it would run horrible once it reaches operating temp.

    1. bad coil?
    2. bad ICM?
    3. Bad coil wire?
    4. Bad opti? (Or would the opti make it bad regardless of temp?)
    5. BAD o2 SENSORS? How do you know if the o2's are bad? What happens?
    6. bad spark plug wires?
    7. Wrong gap on the spark plugs? (12.5:1 compression blows my spark out so I have it set at .030-.035 (I think stock calls for .040-.045??)

    When I installed the brand new msd opti was I supposed to mark the position of the crank or was it ok to just line up the little key-hole on the optispark with the dowel that stick out of the motor by the crank???? What if that dowel is sticking out too far, would that destroy my opti immediately? How far out should that dowel pin be (Anyone have a link to a picture of a dowel properly sticking out that I could see?) I did not mark the crank and its quite possible I rotated the crank to install the new opti. I did line up the dowel on the motor to the opti corectly and it fit nicely but if there is something else I needed to do or check, I might have failed installing the opti correctly.

    Also I was getting a major misfire/backfiring right at 4000-4200 rpm's consistently when accelerating soft or hard in any gear. At any rpm lower than that, the car would run very good and hardly could notice any hesitation but as soon as I hit 4000 rpms (BOOM, POP, BANG, Smoke out the exhaust, car didn't stall, just had to catch it and anything under 4000 rpm's the car would run, shift and drive like nothing was wrong. What could this be:

    1. Vacuum leak? (Bad egr block-off plate sealed?
    2. opti?
    3. weak spark?
    4. weak fuel pressure? (it was weak/leaking pressure but that is now fixed, however the car hardly starts right now and I have to gas it all the time just to keep it running.

    I checked all my grounds, checked the compression, checked the new fuel pump and pressure is holding strong (44 psi), I have another new MSD opti showing up this week, new msd coil, (stock 90,000 mile ICM , what would a bad ICM symptoms be?), new plugs, new wires, new 02 sensors literally going in tomorrow night.

    Oh, can you tell me what this mean.... I have MSD coild p/n 8226. I had it tested and this is the results: primary=2.46, secondary=8.54. What do these specs tell me? I can't find a chart to let me know if these numbers are good or out of spec. Can anyone let me know if these numbers are good or bad? This is a new coil (10 hours of use).

    Last thing is I just noticed and I'm done, I promise. I just found out my lower left vacuum tube that connects to the lower left back of my 58mm BBK throttle body was missing the vacuum hose that connects to my purge canister (Apparently I lost that stock hose that goes to the purge canister and was driving around with these both wide open. Could that be the vacuum leak that was causing the misfire at higher rpms? I noticed if I plugged the hole on the throttle body with my finger while the car was running it would run so much smoother and when I released my finger it would run a lot rougher. I did buy a new vacuum hose to connect the throttle body to this 'purge canister' thing so hopefully that would be one of hte many problems causing me al the issues.

    If you have any advice, suggestions, want to come over and I will PAY you to help me trouble shoot it, let you drive it for a week if you are able to pin point the problem and get it running , pretty much anything you can give me would be so appreciated. I have lost all hope and after I put all these new parts on, I am out of ideas.

    Thank you so much for reading my auto-biography, again I apologize for the length, I'm just desperate and have been tirned down by 5 performace shops so you guys are my last hope.

    Sincerely... Joel
    Brighton, mi 48116

  2. #2
    Senior Member JaycenK's Avatar
    Join Date
    Nov 2008

    1997 Camaro Z-28

    Hey sorry to here about the problems.
    1st off I have had a conversation with brian at PCM and the likley hood of a bad pcm if he is able to program it is low but I have had crazzier crap happen.

    2nd your a little high on the CR. 12.5 is at the edge of pump fuel and you didn't mention what fuel you are useing?

    3rd off one item that is not to hard to check is the injector plugs on the pcm wire harness. I had a simmilar back fire problem that no one could figure out on a 83 starion and years after the car was in the junk yard I found out that all it was is bad injector plugs that caused miss backfire and black carbon rich exhaust. With 90 k and it being that old it's worth a few minutes to check them out and maybe just replace them if you see anything abnormal with them.

    as for the opti if it were missfireing it should throw a code. have you had the pcm scaned for codes? or even had it data mapped or data logged? is that were you got some of the numbers from?

    The engine control modual usually dosen't causes misses in and lt1 but like I said earlier never write anything off. it could be going bad. coil is a quick 50 bucks to replace and if you find them cheap even 40 bucks.

    02 sensors would make it run rich all the time I belive so Not sure thats worth chaseing but you should have bought a new set with the new motor.

    you can do some quick test with a multimeter on the MAP, TPS, MASS/AF.

    Did you do an after market fuel pressure regulator? or MASS/AF?
    Last edited by JaycenK; 07-21-2009 at 07:50 AM.

  3. #3
    Junior Member
    Join Date
    Mar 2009
    Brighton, MI

    2000 CAMARO SS

    1. I have 110 octane in it right now just to rule out the whole 'bad gas' theory I have been getting.

    2. I am really interested in the idea you have about checking the fuel injector plugs. The injectors are brand new but the clips/plugs I have never tested. How do I test them? Are you talking about using a test light to see if they are getting power to the injector or using a voltmeter of some sort to test for a specific range/reading? How would I test them to make sure they are working?

    3. I have heard the opti can go bad and won't throw any kind of codes sometimes. Eitheway MSD is shipping me a brand new opti this week.

    (Oh, heres a little something I just figured out)

    So I bought the vortech intake elbow (metal piece to replace the plastic elbow that hooks to the Throttle body...) When I installed it I must have completely forgot that the vacuum tube going to and from the opti needed to be plugged back I never had a vaccuum tube connected at all. I heard the air inside the opti 'ionizes' or something causing it to send bad signals so I'm thinking now that I have rigged a vacuum into the new intake elbow, when I have the new opti put back on and everythign is vented properly, maybe this will help get me going). Any thoughts on this?

    4. should I replace the ICM?

    5. I have a new coil. MSD 8226

    6. I have 2 new o2 sensors so they will go on with the new opti.

    7. How do I check these "you can do some quick test with a multimeter on the MAP, TPS, MASS/AF. " DO you know a part or mutimeter I can buy at autozone and how to check each of these sensors?

    Thanks so much guys.

  4. #4
    Junior Member
    Join Date
    Jul 2009

    1996 LT4 Corvette

    By chance did any of the exhaust get welded while on the car? Bryan can tell you welding on a car with the computer in CAN cause issues with the computer, as we traced one down together once. Ended up being that, and it never threw any codes.

    Also, I'd run a vaccum gauge on it just to be sure. It's possible it's a vaccum problem, but most likely it would have shown up right from the start. Also if it runs fine when cold, and bad when hot, it sounds like when it enters closed loop is when your problems start.

    There is a unit for testing injector plugs and injectors themselves. Can't recall who makes it but your local parts store may have one for rent. Comes with multiple adapters for checking different cars. It tests the wiring for the plug and the injector for firing. Not a bad idea to check, but once again, it would typically show all the time, not just when hot. Not sure how deep the hole is for the cam dowel, but if you got the cam from Elliot, they are competent enough to know how far the dowel needs to be (.620" long) and i believe the max is .7", but that is for stock opti, the MSD will retain the min, but the max may take longer.

    MSD optisparks are a solid piece. not likely to cause a problem, but yes a bad optispark can cause what you're describing rarely without a code though. I'd do all the other checks before ripping the front of the motor off to replace the optispark. You CAN put them on wrong, it has been done, but very unlikely the case here, as once again a wrongly installed optispark would cause issues the entire time, and not just when hot.

    I believe you are looking at a sensor/fuel problem more than a mechanical issue. I don't believe there is a test for the MAF sensor. These you can get for around 100 new, but i wouldn't do that yet. The TP sensor you can check with a multimeter to see if the resistance is smooth through the throttle range. A bad spot in the TP sensor could cause what you are describing especially at a specific spot like you describe. Not sure about the MAP sensor as that will be a resistor type reading as well, but you need vacuum to check it. Maybe the local parts store can check it for you as well, again same as the TP sensor, a bad spot in the range could cause issues. A typical Haynes manual should have the tests for these in it as well.
    Last edited by Rottie; 07-31-2009 at 08:41 AM.

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