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Thread: Turbo 5.3 Random Misfire

  1. #1
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    Turbo 5.3 Random Misfire

    Here is the backstory so you all know more information. The truck is an 87 S10 backed by a 700r4 with 3.73 gears. The motor is a 2000 5.3 with roughly 200k plus miles. The motor has a TSP 220/220/114 lsa cam with beehive springs and hardened pushrods. I know this cam isnt the perfect choice for a turbo but it was what was in it when it was NA. The turbo is the infamous On3 76mm. The injectors are decapped truck ones roughly 78 lbs. Walbro 400 in tank pump. I am running an intercooler and a 60mm external wastgate.

    I recently had developed a slight miss so I installed all 8 new NGK TR6 plugs and gapped them to .025. I also fixed the exhaust down pipe and installed a hooker maxflow muffler. I also wrapped all the underhood exhaust with header wrap. Following this work I took the truck out and it ran the best it ever had. The truck on about 8 lbs ran smooth and spooled very quickly. I was doing some tuning to the truck trying to eliminate some KR that I was getting and the truck was getting better and better but I shut down the truck lowered some timing where I was getting knock then fired it up and it had developed a miss even though minutes before it ran great. The truck now runs better when its dead cold and starts to miss more and more as it warms up. I have installed new plugs hoping they were just fouled or partially fouled. The truck just misses a lot mostly under load. This make me thing weak spark syptoms so I started with plugs but that didnt help one bit.

    The truck misses out of boost mostly. Doesnt throw any codes except the Maf code.

    I am running 2 bar speed density
    I am running a wideband and under boost I am 10.5 to 1

    I have attached the most recent log and my current tune. Has anyone ran across this and can point me in the correct direction?s10 turbo mod tuneafter help5.hpts10 4 21 run like shit.hpl

  2. #2
    Tuning Addict 5FDP's Avatar
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    Did you check compression on the engine yet?

    Bore scope the cylinders for possible piston damage?
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Quote Originally Posted by 5FDP View Post
    Did you check compression on the engine yet?

    Bore scope the cylinders for possible piston damage?
    I have not checked compression yet. I will try that and see. I dont have a bore scope. The truck doesnt smoke and when I pull the oil fill cap I dont get any smoke. So i assume the pistons dont have any holes. The plugs when I pulled them were all dry and not oil covered. Would excessive blow by cause KR?

    The knock sensors are only a couple months old and they are from autozone if that matters.



    Did anything in my tune or log look wonky or something I should look into?

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    Check your plug wires. Mine did the same thing, had burnt one right through my heat boots on the turbo headers side (on3 turbo) also.

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    Quote Originally Posted by bigredtruck View Post
    Check your plug wires. Mine did the same thing, had burnt one right through my heat boots on the turbo headers side (on3 turbo) also.


    I just checked the plug wires. I found one that was burnt through. I changed it out with a longer one. I will report back with results. Thanks

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    after replacing the burnt spark plug wire I took the truck out and it runs way better. I spent the better part of 2 hours going up hills and getting my VE table in the non boosted regions fixed. This fixed my KR problem in the non boosted regions. The turbo lights up quicker and sure is a lot more fun to drive.

    s10 ve fixed in boost bad.hpl s10 turbo mod tuneafter help5.hpt


    Would someone care to take a look at both of these and help figure out why im getting KR in boost? I dont believe my timing is aggressive and Im running 10 to 1 AFR in boost.

    My intitial stabbing of the throttle is throwing the AFR way lean. Would this be fixed in the transient fuel area or somewhere else?

    Thanks again for the help.

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    Just curious, what map are you running?

    If it's a cobalt map the offset setting should be 10.33 and not 8.01.

    If you are running 10.1 in boost you have some major fueling to work on. You are commanding 11.9-12 afr in PE so you have a major error there. Commanded AFR needs to match actual AFR. Over fueling can cause tons of knock and so can under fueling.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Quote Originally Posted by 5FDP View Post
    Just curious, what map are you running?

    If it's a cobalt map the offset setting should be 10.33 and not 8.01.

    If you are running 10.1 in boost you have some major fueling to work on. You are commanding 11.9-12 afr in PE so you have a major error there. Commanded AFR needs to match actual AFR. Over fueling can cause tons of knock and so can under fueling.


    I am running Mfr. #: 12615136 2 bar map from summit.

    I just took the truck out and here is the most recent log.s10 4 23 less KR.hpl

    At 19:23:0 to 19:23:09 The truck pulled great . Other than having to lift for the shifts it ran great.


    Do i need to work on my PE map or the Boost enrichment map? The truck has started to lean out a little. Its tough without logging AFR with the scanner.

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    After taking the truck out for the last time of the night. Here is the final log.s10 4 23 last of night.hpl The part at 20:10:12 Is the KR part that's frustrating.

    Also. Do the PE and BE tables reference the VE table? For example if I am commanding 11.9-12 in PE and the truck goes 10:1 on the WB does it mean that I should lean out the VE table in those areas?

    Im assuming this is what could be causing my KR problem.

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    Yes, you have to remove fuel via the VE to get your real AFR to match the commanded AFR.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Thanks. I will give this a try and report back on the results.

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    Quote Originally Posted by itsforsale2 View Post
    Other than having to lift for the shifts it ran great.
    That m0tha-phuking TV cable, aye?

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    Quote Originally Posted by Mr. Smith View Post
    That m0tha-phuking TV cable, aye?
    Yes!!! When this tranny blows it will not be getting fixed. I am over trying to change shift times with weights and springs.

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    Quote Originally Posted by itsforsale2 View Post
    Yes!!! When this tranny blows it will not be getting fixed. I am over trying to change shift times with weights and springs.
    Ha, me too. I feel your pain. I've had to back off the gas with every WOT upshift for the last 3 years and lost a race because of it (I was winning/pulling until I backed off completely) against a Chrysler 300C which I would've chewed Wanted to go 4L60E but I already had the 700 (which worked perfectly before my engine swap) + had to buy an adapter for the 4L60E swap and couldn't be phucked with the wiring at the time... Big mistake/regret.
    I think the problem with mine is the cable is stretched. But like you, I'm over it and looking forward to the trans blowing.
    Btw, I came real close to rear-mounting a T76 turbo a year or two ago too.. but didn't bother in the end.. all because of that phucking TV cable / upshift prob. One day..

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    s10 log file 4 27 2017.hpls10 turbo mod tune smooth VE.hpt

    Attached are my most recent log and tune.

    I have since started to log with my wideband so its easier for others to see whats going on and possibly help me with my tune. I dont hear any knock but the truck is a little loud. It seems that its only when boost starts to creep up. I haven't messed with my spark tables too much since all I kept doing was lowering my spark it it didnt get better. The truck does pull really great though. The only problem i'm having with the truck is the one rear tire seems to be wearing at much higher rate than the front ones.

    Does anyone see anything in the tune that would cause this knock? Maybe its phantom knock. I don't know but I don't want to be deadening my knock sensors if its real.

  16. #16
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    Just minor thing I noticed, you set burst knock to 0 meaning it's always going to be active. Set it to 8 to stop it from working, it's possible it's burst knock related but only a guess there.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Looks like real knock to me, but thats just an opinion! If its false, its usually happening at unexpected times/load/throttle combos, but yours is happening pretty much when you'd expect, eg. throttle on transition, boost transition etc. Just take a chunk out of the timing in that area as a test (not one degree, but several!) and see what happens to it..
    99 TA, Texas Speed LS376, PRC heads, 233/239 cam, Fast 92mm, 95mm TB, card style MAF, Tick TR6060, Strange 4.11 12 bolt axle & clutchpack diff, Strano springs/dampers, Vette 18" wheels, Vette disks, CTS-V calipers, 16lb flywheel, long tube headers, no cats.

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    Quote Originally Posted by 5FDP View Post
    Just minor thing I noticed, you set burst knock to 0 meaning it's always going to be active. Set it to 8 to stop it from working, it's possible it's burst knock related but only a guess there.
    I don't think that's a "minor thing". That most likely is his spark retard problem right there.
    Like you said, he set BK Enable to 0... and his vs. RPM table from 400 to 2,400rpm at 8 degrees... So BK is kicking in and pulling 8 degrees timing...


    @Itsforsale: Set your BK Enable to around 7 and your BK vs RPM to 0.. that should sort out your problem.

    Swear just the other day I was going to make a thread regarding Burst Knock after seeing so many threads saying "0 your BK tables to get rid of BK" (which isn't entirely correct because if you 0 "BK Enable" without 0-ing "vs. RPM", you'll just increase BK sensitivity/"paranoia") + also wanted to warn those who were planning on setting their BK Enable to 8, as I ran into a problem/glitch for 5 mins after setting it to 8 where I couldn't close a warning window which kept popping up (after closing it). I hit "No" and "X" 73 times, couldn't close my Editor... nothing. Somehow got rid of it after clicking on "X" really fast I think.. and maybe punching my keyboard a few times.

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    Thanks guys. I will give this a try and report back.

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    I have done what dermotw and mr smith said. I still have the same results. here is the most recent log and tune. I even tried pulling 5 degrees across the entire spark tables. Bother low and high are the same. I also zeroed out the IAT, ECT, and egr spark correction tables make sure they were not interfering.

    s10 turbo mod tune smooth VE.hpt s10 log file 4 28 2017.hpl

    Should I zero my boost enrichment and use just the VE table. It seams that over 100 kpa It would read the VE section and account for positive pressure anyway?

    I also have a sneaky suspicion I am getting KR from the trans taking so long to shift. Its causing vibration that the Knock Sensors are picking up. This is something that would be impossible to see from your end.
    Last edited by itsforsale2; 04-28-2017 at 06:53 PM.