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Thread: Why Do I Have Engine Knock

  1. #41
    Ok I finally was able to get around and take off the exhaust to knock out the guts of the cat.

    Which was badly melted. Which means the other one probably isn't too great even though it passed my backpressure test.

    Also, I did have time to do a quick test drive and log the data, which I uploaded here.

    One thing to note is I forgot to reconnect the bank 2 O2 sensor so disregard the flat O2 reading and probably fuel trims on bank 2.

    The most important thing however is it ran much much better. Its far from 100% but it only knocked a few times and then spark retard decayed quickly enough so it really didn't cause me to have a substantial and/or continuous loss of power.

    I think at this point other than readjusting the valves, hooking back up the O2 sensor and a few other minor things. I am ready to start tweaking the tables.

    Or is there something else I am missing here.

  2. #42
    Advanced Tuner
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    Mar 2011
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    I would do to many tweaks till you either gut the other cat or replace both cuz that will throw off your tune. it will make the airflow from bank to bank be different. also get a log with the o2 sensor hooked up. doesnt like look it was trimming at all. i think the knock might be false knock or knock due to it using the saved trims and running a little leaner on the side without the cat.
    My setup is a 356ci with a 260/268 (212/218 at .050 lift) duration cam with aluminium corvette heads and flat top pistons running 11.3 comp. ratio. with tuned port injection and vortec crank pick up and dizzy running a 411 pcm and 60lb bosch injectors, 1.6 ratio roller rockers. For transmission its a 4l65e built with the monster in a box mega ss kit. All in a 92 chevy ext cab 4x4 pickup with a 98 cab now installed with a third door! running only e85

  3. #43
    hi wyochimneysweep

    Damn, I should have known it would have been too simple to just have gutted the one cat

    Ok well I am planning on doing the O2 sensor today and hopefully adjust the valves as well. Ill get another log and post that.

  4. #44
    Ok finally got the valves readjusted and reconnected the O2 sensor. I wound up doing like 1+ turns from what I felt was zero lash by spinning the push rod. I did 3/4 of a turn last time and they still chattered. Now it sounds like a typewriter. If anything I still think I might have a couple loose ones.

    Unfortunately, on a few of my exhaust push rods there was rubbing that caused a little divot. Some barely removing any material but there was one that definitely has me worried.

    It is caused by the guide "fork" that are under the rocker arm stud. I have a feeling I am going to have to replace all push rods and widen the guide forks.

    Also I posted a log file. It isn't much more than just running at an idle. I heard a rather loud knocking that I am pretty sure is coming from the exhaust but not being sure I didn't want to risk it.

    But I did see some issues with the fuel trims and O2 sensors being vastly different from one another at times so like wyochimneysweep had predicted I need to get both exhausts with the same flow/backpressure before I can determine if its tuning time or yet another mechanical to fix.
    Last edited by knowledge; 07-22-2012 at 07:11 PM.

  5. #45
    Oh still trying to work out my options on the exhaust. I think best case ( cheapest short term ) is to tow it to a muffler shop and have them weld in two new cats and hopefully a couple of O2 bungs. The more expensive but right was is to have it towed 80 miles to a good and cheap muffler shop and have them do an entire true dually stainless steel exhaust, manifold back including two new cats two mufflers instead of one. So Ill be calling around tomorrow getting quotes.
    Last edited by knowledge; 07-22-2012 at 07:07 PM.

  6. #46
    Not sure if anyone is still interested or not but I do have a note worthy update. I found out the source of the rubbing of my push rods. Its because even though there were holes in the guide plate for the rocker arm studs to go through, there still was enough play to make it cockeyed enough so that one of the push rods would bottom out. In my case the exhaust.

    Anyways redid all the rocker studs while holding the guide plate down and that should fix it. Now I still need to get some new cats on. Got to borrow a buddy's truck and trailer for the 80 mile journey...

    Oh and I also learned that when using push rod guides make sure you have hardened rods.

    Anyone know of some decent rocker arm stud nuts. I don't believe I need poly locks but not exactly happy with just regular lock nut either. They seemed a little too easy to back off. Is there some happy medium??

  7. #47
    Tuner mcdonald77's Avatar
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    Aug 2011
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    good read and I appreciate that you keep updating. I try to do this also. I always find threads with problems, then no fix. Keep it up!
    If you need pinouts for GM 98-09 PM me your email address with year, make, model and what you need.

    2000 GMC Jimmy 6.0L w/ L92 heads and LS3 intake- Project has been parted.
    1998 Pontiac Firebird Formula 411 ecu swap/ 6.0L w/ L92 heads and LS3 intake 224/230 595/595 cam. SOLD
    2006 Blue TBSS, 403 w/ Magnuson 2300 and 4l80e swap.



  8. #48
    Advanced Tuner
    Join Date
    Mar 2011
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    384
    the stock lock nuts should be fine....or go with poly locks for a piece of mind
    My setup is a 356ci with a 260/268 (212/218 at .050 lift) duration cam with aluminium corvette heads and flat top pistons running 11.3 comp. ratio. with tuned port injection and vortec crank pick up and dizzy running a 411 pcm and 60lb bosch injectors, 1.6 ratio roller rockers. For transmission its a 4l65e built with the monster in a box mega ss kit. All in a 92 chevy ext cab 4x4 pickup with a 98 cab now installed with a third door! running only e85

  9. #49
    Tuner in Training
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    Byram, MS
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    Old thread, but did you figure it out?