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Thread: Low RPM, Low Boost Misfire, 2-3 seconds into PE, TVS1900

  1. #1
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    Low RPM, Low Boost Misfire, 2-3 seconds into PE, TVS1900

    Hi all - Has anybody seen a repeatable misfire at low rpm, low boost with injector pulse width spikes? It seems I have some sort of misfire going on when my truck is in the 2000rpm range and I get creeping into boost (2-3psi). If feels like a thump in the drive train when this happens. I see lean spikes in both O2's, as well as the WB in the drivers side header, which leads me to believe misfire. The interesting thing is I sometimes see quite a large spike in the injector pulse width. Could this be causing a misfire? I don't see any MAF, MAP, voltage spikes, etc. corresponding to the IPW abnormality. Who's telling the injector to spike pulse width????

    The other thing I noticed is this occurs right at 2-3 seconds after going into PE. Is there a 2-3 second clock for anything in the tune that might cause this?

    Before you ask, I was running TR6 plugs, original gap ~0.040. After I noticed the misfire, I figured it was spark blowout. So, I swapped in some BF7EF's with out of the box gap ~0.028". The problem is still there, maybe a little better. but not fixed. After changing plugs, I stayed on the throttle after a misfire and it cleared right up and ran smooth. It may have done this with the old plugs but I always let off.

    The attached log is after changing to BR7EF's. You can see it happens three times, circled in red. The third time you can really see the IPW act up.

    Low Boost Misfire.JPG

    2007 Silverado NNBS 6.0L L76 E38, TVS 1900, Kooks headers

    Thanks!
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  2. #2
    Senior Tuner 10_SS's Avatar
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    strange.
    You have Inj Delta drop spike at 24.032 with no other matching data, maybe the other channels arent updating fast enough to show what is causing it.
    T\You have an Bank 1 Intector pulse spike at 46:030 and your fuel pressure seems jumpier than what I'm used too.

    There could be something happening that the scanner just isnt fast enough so it's missing something. Maybe try reducing channels to MAP, MAF, Injector Pulse, fuel pressure, Inj Delta, and both O2 sensors see if it graps more info? Make sure to turn up the sampling rate on at least the MAF, MAP, Injecotr Pulse maybe it will be clearer what is happening.
    2010 Camaro LS3 (E38 ECU - Spark only). MS3X running complete RTT fuel control (wideband).
    Whipple 2.9L, 3.875" Pulley, kit injectors, supplied MSD Boost-A-Pump, stock pump
    LG Motorsports 1 7/8" Headers - No Cats, stock mid pipe with JBA Axle Back
    ZL1 Wheels/Tires

  3. #3
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    Good ideas! I was thinking along the same lines. In fact I already turned up the sample rate on the IPW in the scanner. I'll have to do the others too and get another log. Stay tuned.

    I was wondering about the fuel pump and the FPCM. I know the pump (stock truck pump, non-flex) is wayyy too small. There's a walbro 450, and upgraded FPCM, on the bench ready to go as soon as I get some time to install. So my thought about the fuel system was....could the FPCM be throwing up some sort of prediction that the ECM is reacting to?

  4. #4
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    Here is a new log with higher sample rate. This log shows a much better picture of the fuel pressure and Inj Delta. Any idea why fuel pressure spikes UP and Inj Delta spikes DOWN??? There is another event in the log that shows no fuel pressure spike, maybe a small dip, but does show the Inj Delta dip.

    Low Boost Misfire hi res.JPG

    This one made a good thump in the drive train.

    Low Boost Misfire hi res2.JPG

    How is Inj Delta calculated? It seems it should be based on fuel pressure and MAP, but fuel pressure spikes the opposite way and MAP doesn't move. Hmmmm
    Again, this happens like clockwork at 2-2.5sec into PE. Could it be volume related (fuel filter, fuel bucket...etc.)?
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  5. #5
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    Does your tune have "desoot mode" in the fueling tab?

  6. #6
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    No desoot in editor. However, the latest editor I have is a 3.5 beta. Some day I'll get the latest release loaded. If someone has a newer release and would like to check, the tune file is attached.
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  7. #7
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    Ever figure out what was causing the misfires?

  8. #8
    YOU NEVER TUNED THE OPEN LOOP VE your in open loop in boost!!!!!!!!! its trying to run off stock ve in boost you hav to tune your open loop and be in pe before your hit 100kpa which is equal to wot in na car why tune for 85kpa pe look at changes and tune your open and closed ve to match stop relying on maf only and i dont know ifyou have dod so copy and paste all your ve tables to match try what i sent your truck is jumping back and forth between open and closed loop tables and they are wildly different hence the wild delta numbers. you might have to retune your ve now that you know they all need to read the same i dont know ifyour closed loop is correct either. try this send me data log illl read it and try to help the second is the changed tabes do a partial throttle pull like youve been incase you need to add fuel later but dont do it by maf below 2500 rpm. your going ruin your partial throttle driveablility
    also your manifold volume is wrong which lid and which tvs 1900 are you running i can find the correct manifold volume and predicion coefecients why did you change those.. That can really throw out readings as well try both 2nd tunes and see how it does. the correct manifold volume for a zl1 tvs is 13487 on a zl1 but different on cts as the lid is smaller so is the volume.
    Last edited by jpierro79; 10-14-2018 at 03:51 AM.

  9. #9
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    Nope, haven't fixed this yet.

    jpierro79 - Good eyes! Yes, I know it's running MAF only and was going to re-enable dynamic air to stock settings as a first test. Haven't gotten around to it yet. I'm not following you on the open loop. Yes, of course it's open loop during PE, whether it's SD or MAF or hybrid. The VVE should actually be quite close to properly tuned, even though it isn't enabled. I'll run with it re-enable to try that first.

    To answer your question about the manifold volume, I can't remember exactly how I arrived at that number. I was messing with transients at one point and trying to fix a lean tip-in. It's a Magnuson TVS1900 Radix, for the trucks. There is no lid.

    If you are talking about the Dynamic>Prediction Coefficients, those are bone stock. The Speed Density>VE Coefficients were changed for the VVE tune.

  10. #10
    ok the lean tip in problem is cause your running maf down low. It becomes erratic. Tune in your low rpm up 75 kpa using a histogram with your dataloging. theres a great ls3 tutorial on how to do it ill send you the youtube llink.https://www.youtube.com/watch?v=CvYjDJo1rRQ you dont have do a maf fail as i found it makes it harder to get favorable results. just set your maf enabled at 3800 go back to stock maf settings and follow the rest if his tutorial and do not use it for anything above 75-80 kpa. Your vve is going to give you great low rpm response and you wont have that lean tip in. An exremley big name in e tuning tunes maf only this way and it just drives me nuts. Heres another great tutorial on how to do ltft and stft math but remeber multiply by percent half always when pasting to your VVE table so you dont over shoot.https://www.youtube.com/watch?v=Rhg5NSh8Dq8 ill share my zl1 tune with you you can see and get an idea how important it is to rely dial in your VVE and i get Zero lean tip in. the most it moves is .5 so leanest tip in is 15.5ish. also changing o2 offset and raising your o2 bank 1 and 2 to 600 on ill attach pics. my o2 are stock cause ive got my ve dialed in really well. look these o2 settings in the attached images youll see the second pic will help you to set your low airflow modes higher duringe vve tuning. changing lower airflow modes to higher 02 switching point here do not change the others as they will change your mixture stablity up high. I did not disable my maf to tune my ve because i have headers and I used a wideband also if you have headers you cant disable it completely because your low rpm will lean lope meaing it will want to take fuel out but will actually need more. So if you have headers you should leave maf enabled for sure but raise MAF enabled in point to 3800 and again tune up to 75kpa. if not and you only have catback you can build a vve your MAF disabled. you can set your o2 back to stock if you got your VVE tuned after your done and see how it idles. I hope this helps you get on your way to a solid tune. GM PE enrichment is cacluated by dividing 14.7 by whatever pe number you put in say 1.28. 14.7/1.28=11.48 afr. Thats a safe afr to shoot for after youve got your vve sorted out. The last airflow zone switches at 3250rpm. Tune at least up to here as much as you can with your ve table then use high rpm maf to do the rest. I promise you your truck will drive like its OEM once youve got it right. Only alot faster. after this though you must have a wideband to be truly on point. I like the ltft and stft math histogram more for tuning without wideband sorry for some reason every time i uplaod a photo its sideways even if i rotate and save. I cant find the manifold volume for that supercharger it might be in with your original boxing if not contact magnuson support they should have that somewhere. ive seen somewhere in a couple tunes peole used 11,700 for manifold volume other than that i really wish i could help you more. The problem lies in the fact that unless take off the truck and get a giant measuring flask and fill your supercharger with water and measure how much fits in it theres no other way to calculate manifold volume. the rotors only account for 1900cm3 that may or may not include the mass of the rotors themselves it may actually be less inside rotor section due to the rotors themselves.
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    Last edited by jpierro79; 10-15-2018 at 10:00 PM.

  11. #11
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    Ok, lots to digest!

    After skimming the first vid, I think I know what you were talking about with the 'OPEN LOOP VE' from two posts ago... You were talking about the VE Mode>Manifold Switch Closed and VE Mode>Manifold Switch Open, correct? Yes, I only updated the default, Manifold Switch Closed. However, I don't think these have anything to do with closed loop vs open loop fueling. They look like some variable length/volume manifold parameters, no? Since the truck, and most LS's, don't have any of this which does computer use? DOD is disabled so leaving those tables stock shouldn't matter either.

    Anyway, the Manifold Switch Closed table was 'tuned' with calculated GMVE based on fuel mass and wideband lambda. It's probably not perfect but much closer than stock. I can copy and paste that to all the other modes, but I doubt it will change anything especially if I left it MAF only.

    Regarding tip-in, yeah, I can see how enabling VE again will help that. I will do that. But, that's not the issue I'm worried about right now. It's during steady state, something is hiccuping. It's well into OL PE and not even thinking about switching back and forth to CL. It should be running straight MAF and not looking at which VE mode table to use. The MAF was tuned using LTFT + STFT and MAF depending on CL vs OL, respectively.

    Thanks for the idle tips. I do need to mess with O2 settings just a little for idling with headers. Before I changed plugs it idled close to stock, so it was quite happy on MAF only idle.

  12. #12
    its a blended calculation NOT MAF only. It only adds the MAF on top of the VE. change your predicted coefecients back to stock your hiccuping during a rpm between 2200-2400 and cause its happening at an exact rpm therefore the computer isnt calculating correctly. exact rpm and same throttle your predicted coefficents change how maf and ve communicate. If you change them you change you fuel. airflow dynamic read the description IT says it uses "FILTERED MAF CALCULATIONS" where do you think the other numbers are comming from in the equations for fuel?????
    Predicted coefficients then ve then maf then from sensors combined gives the ecu the numbers to spit out to injectors timing ect.ALSO your manifold volume is wrong you have a supercharger on it not the original manifold. IF you change the predicted coefficents you mess up the whole caculationgs. Change your maf back to stock rebuild your VE. Change your maf above 2500 rpm enable. If it doesnt idle right your VE table it WRONG. Please put your stock predicted coeficents back in and retune your lower rpm ve then tune your maf afterwards. thats the correct way. Just cause it idle with maf enabled down low better simply means you put the MAF in to alter the equations. YOU should NEVER do this practice its the easy way out of doing it right. if your using an lsa supercharger with a ctsv lid look up a stock sctv manifold volume that year. If itss from a zl1 use 13,487cm3 if its a radix ive seen between 11900-13000cm3. So clearly you can play back and forth with your maf and ve unless you set the other settings back to what they should be like i said and correct your manifold volume your problem will be there forever!!!
    Last edited by jpierro79; 10-16-2018 at 06:56 PM.

  13. #13
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    jpierro79 - I can't tell if you are messing with me or what. haha You seem to use a lot of HPT buzzwords, so you have the lingo down, but it's coming out a little scrambled. I appreciate the effort though, so thanks for that.

    1. Why do you insist it's not MAF only? My Dyn Air>Disable is set to 650 RPM! Sure, it may be filtered, but it sure as shat isn't using VE.
    2. MAF does not add to VE. I've tuned SD only and I've tuned MAF only. Both can sufficiently calculate air mass on their own, no matter what the other table says.
    3. Dynamic>Prediction Coefficients these are what was pulled from the truck when it was stock, haven't touched them. I pulled a tune repository file and there are some of the DOD Coeffs that are different, but that's disabled on my tune anyway.
    4. Exact RPM - it is NOT happening at an exact RPM. If you looked at the first log, you've got ~1700rpm, ~2200rpm, and I'm sure I could make it happen in between.
    5. Manifold Volume - my understanding is manifold volume is for transients. The problem I'm having is about as steady state as it gets. I fail to see how manifold volume, or any transient, has anything to do with it.

  14. #14
    ill tell you what ive dont ive pulled fuel from upper ve table and long behold ive had to add to maf above 2400 rpm which is exactly where mine is set to change. I have a zl1 though running a 3 bar factory map sensor so there might be a chance im wrong but often when you increase pressure like i have and you have with gm youll have two low rpm funky transitions mine are lean at 1500 and 2500 your problems are at 1700 and 2200. its all got to do with predicted coefficients and if ve was disabled above that rpm and maf was only then why when i pull from my ve do i have to add more maf above that point. I played with it for weeks. I can tell you right now if i pull anything from my ve at 2600rpm it will pull from my final fuel equations. Even though my maf is set to 2400. Im not messing with you but again i have 3 bar and a single maf table from factory. you have a high and low maf table from factory. Mine does NOT transition to nothing it always is part of equation. Maybe cause you have a high and low maf table yours becomes eliminated negating the need for a 2 bar map even though you have a supercharger. Mine on the other hand the ve always part of equation and heres the part i hate. Above 105 kpa even though ihave a 3 bar map it has almost no effect on my fueling even if expand the chart which to me is bs. believe me ive tuned in the sd only way and added 20 percent of fuel sd only above 105kpa with the maf disabled it did do crap unless i changed it at 105 kpa.
    Look Id love to debate gm tuning physics but they dont make sense and every damn car is different they use the same e38 ecu is 4cyl and 6 cyl cars. I pulled data from an 07 malibu it saod e38 ecu.
    You might be right in your case about the high rpm disable not including ve and using maf calculations then why are you having problematic calculations like i had until i tuned my ve above that rpm disable? im serious if i move my maf to 2200 rpm and pull fuel i end up with a lump in my maf not a rise a lump where a higher frequency calculates less air which you and i both know is impossible!! a maf requires more airflowing passed it inorder to increase frequency. If the VVE isnt blended after then why would a higher frequency read as if theres less lbhr air moving passed it????? I had a guy earlier had a zr1. It had a glitch at 3600 rpm at 239kpa yes like 16lbs of boost it was due to a transition calculation in a different zone all the way down at between 105 and 135kpa. He had a hole there he never tuned for but it messed up his sd calculation at 239kpa. To 99.9 percent of logic says no way in hell but heres the pic it makes a difference. Mind you its a 100 kpa away. your trucks calculations are about smooth transititions. Look take the info ive shown you and stated and tested and you can choose to believe what you like
    heres my tune with a log and above 5200 on my ve it curves down but my maf curves up and my calculated volumetric efficiency airflow reading doesnt change above 5200 cause on my Ve it slopes slightly downward the maf does not calculate airmass. Ve does It will change timing cause the calculated spark vs airmass on your high octane spark tables the VE table changes everything . This is why i stated tune ve first
    heres my tune with a pull and look at my ve and maf. My maf doesnt level off nor do my calculation of airflow jump. feel free to look it over and make your own conclusions.
    Heres mine MAF helps you mix fuel nothing else. the only place i had a slight issue was blending at 2500 rpm it required both Maf and ve cause with 18%overdrive pulley and headers with id1050x its what it took to get proper fueling. also ve tuning helps correct timing accuracy so i was able to add an extra 2 degrees of time up top with zero knock retard
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    Last edited by jpierro79; 10-17-2018 at 09:36 AM.

  15. #15
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    On the 3rd. miss you have a 5 psi jump in fuel pressure (This appears to be normal transition in pressure on the flow rate vs. fuel flow table 55.6 to 63.5 psi), 10 lb./h jump in flow rate, 3 ms injector pulse drop Bank 1, 8 psi Delta drop , and steady 99.6 % fuel pump command (pump is set for 99.0 % duty cycle for complete table) from one frame to the next with no visible fuel inputs changing? Time register 46.085 to 46.095? I'm not sure what you call the time indicator at bottom. Similar changes in other parts of log. One would think 02 would pick up. Maybe lacking resolution to see input change(s). Are you able to see misfires in data? Log misfires on each cylinder if possible in parameters.
    Last edited by DGS; 10-20-2018 at 06:40 PM.

  16. #16
    DGS very good on pick up in data log. A misfire will change a host of readings. If ecu does detect misfire true or false it will cause havock. It will revert back to VVE. The simplest most know equation for fuel. At the end of the day majority of peoples problems are tune related, but go back to basics. IF you havent had a problem before and now you do something has changed. Now ask yourself what has changed. If youve changed nothing with your tune then go directly to misfire counters and basic diagnostics like individual fuel injector disablement to find your issue. If it never ran right expect most likely scenario tune issue and follow up there. The other thing is you HAVE and or MUST use a wideband. I cant emphasize this enough. We do not have afr sensors only basic o2. If its not mechanical then it can be fixed.

  17. #17
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    DGS - Yeah, you saw the same thing 10_SS saw from the 2nd post. I have fuel pressure set to 400kpa in all modes for no other good reason than to eliminate transient variables. Since it's always set to 400kpa, I don't see how there would be any transitions going on related to the fuel pump mode tables. I'm not sure what the 99.0% vs 99.6% means. Aren't the fuel pump settings in the ECM just suggestions for the FPCM? I've never logged the FPCM outputs, but maybe this would be reason to do so. I'm leaning towards a fuel pump/electrical problem in the fuel system that is causing this issue. There is upgraded pump and FPCM on my bench waiting to go in as soon as I get a few minutes. That will tell us quick if that's the problem.

  18. #18
    Fpcm for those who have it controls flow but all you really need is a pressure reading to run gm ecu. It compensates by add injector pw during drop of pressure. So if you have a return system set it to read pressure but disable the codes that correspond to flow variance or psi range. Our fuel injector vs kpa rate chart corrects pw automatically based up our settings. Up grading fpcm is only reflashing it and for one hp tuners credit if your car has it wired in correctly you can alter any settings. I have flashed mine to run nothing but 52 up to a certain gpm then after that 58 only. If I was running non boosted app id run 48. Per my id1050x are rated their but for every psi of boost I like to add one psi of fuel pressure to keep a good spray pattern