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Thread: Can some help me understand why this won't go over 4000 RPM?

  1. #1
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    Can some help me understand why this won't go over 4000 RPM?

    It seems no matter what I do, this motor won't go much over 4000 RPM
    I have tried new fuel pumps, regulators, larger injectors, fuel filter, valve springs, removed timing, changed the MAF, endless tuning attempts and nothing seems to help get it over 4000 RPM at WOT. At part throttle I can get it a little higher, about 4400 RPM if I'm real careful. Since it used to rev easily to 5000 RPM, I am assuming I messed up the tune some where, although it does make a lot more power now.
    On the data log attached I am tuning for MAF only, I had just raised the the fuel pressure from 57 to 64, so it is a little rich. While raising did bring my inj duty cycle down to mostly under 100 (it would hit 140 before) it had no effect on the engine cutting out at 4000 RPM. It seems if my injectors were too small, I would have noticed a significant gain at 4000 with the FP increase?
    Other concerns, engine wants to go very rich at WOT .7 lambda. In closed loop, fuel trims will max out within a few minutes.
    Thanks for any help, I am pretty sure i have messed up this tune.


    99 Vortec 454 with 0411 conversion 24x with LS truck coil packs
    Very mild RV type cam, headers, BBK 80mm TB, CAI, 26lb LS1 injectors.

  2. #2
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    Post your tune and a log, 4000rpms is GM's factory P/N rev limit so wonder if something got missed during the 0411 swap and the truck thinks you're in P/N all the time.

    If you're at 100% IDC, you need injectors now. You want to stay below 90% (ideally even lower like 80%) so the PCM can actually control the injectors properly. 100% IDC is static, as in-wide open.

    BUT it sounds like you need to get your MAF and VE correct, if you're seeing .7 lambda then MAF, VE, and/or PE settings are not setup right.
    Last edited by ScarabEpic22; 01-23-2019 at 12:45 PM.
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
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  3. #3
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    Dang, I somehow didn't do those file attachments right. I hope this works
    Attached Files Attached Files
    Last edited by DB Cooper; 01-23-2019 at 11:22 PM.

  4. #4
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    I did replace the P/N switch a while back, as it was giving codes. I will recheck the tune and make sure it is still set up right. That makes the most sense as it feels like a rev limiter @ 4000 even when not under load and duty cycle is under 50%.

  5. #5
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    Are you getting any DTC's, possibly either of these P1514/P0068?

  6. #6
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    Log current gear the next time around, that will tell you quickly what gear the PCM thinks it's in. Will it shift at WOT? Cant tell if you're lifting at ~4000rpms to let it shift.

    Not related to rev limiter suggestions:
    I'd change your PE modifier to the same across the board, makes it easier to dial the VE and MAF curves in. Once you have a baseline VE/MAF, you can play with the modifier at certain RPMs if you so desire. You're at times rich by about 1-2 full points on the AFR scale, usually at WOT but also cruise, which tells me either the modifier is coming into play or the fuel curves need a little more work. MAF looks close though!
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned

  7. #7
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    Thanks for your input guys. I have added a gear pid, it seems to be showing the correct gear at all times, also the P/N rev limit is set well over 5000 rpm. It will not shift at WOT, it just won't rev high enough to get to shift point. I am lifting to prevent engine damage because my WB is showing crazy lean numbers when it starts cutting out. It often bounces dramatically rich-lean rich-lean.
    I have made the PE EQ Ratio table all the same as suggested.
    I am posting my latest tune and log files. The MAF tune is coming in nicely until the upper end. If you look at 09:59:36 to 9:59:56 I held it in second gear at part throttle until it started cutting out, I could get it to about 4300 RPM but no higher, it was cutting out most of the time. IDC never exceeds 40%. At 10:10:33 you will see a quick WOT from a slow roll, I lifted when it was cutting out severely at 3800, the IDC never exceeds 80%. This type of data is why I'm hesitant to change to a larger injector. Also, I see the gear pid does not show it down shifting into first, which it did. Does that pid only show the gear selected and not the gear it's actually in? Should I look for a different pid?
    Thanks again for your help.
    Attached Files Attached Files

  8. #8
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    I'm guessing you don't have any DTC's then. I didn't look at your current log. If you're going lean and it's starts cutting I'm not sure if the Cal airmass vs tps vs rpm table will cut like that. I do see that you're exceeding that table with you airmass in the log. I am pretty sure if it's not the issue, you'll still need to make adjustments to that table.

  9. #9
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    Dumb question, how do the plugs look? If it's going lean and cutting in/out/in/out, sounds like either spark, fuel, or a limiter table kicking in. Look at the table ericbedd mentioned, it's set to factory 02 Silverado 6L+80E settings and needs to be bumped up. ECM 14040 is the table, Engine Diags->Calc Airmass. ECM 14041 probably needs to be adjusted as well.

    That PID is for what gear the selector is in, i.e. if you put the shifter in 3/D it'll show D3. If in 4/OD, it'll show D4. Log "Current gear" to show what gear it's actually in (or the PCM think's it's currently in).

    No DTCs, at least per the log.
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned

  10. #10
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    I found that current gear pid this morning and added it. All seems normal, always shows correct gear. I have a few questions about ECM 10040 and 10041. I thought these just turned on the CEL, how do they affect how the engine runs? Also, this engine is DBC and 10040 says it is DBW? I went ahead and changed both to see what would happen. I first increased both tables by 15%. This seemed to increase the RPM about 200 before it started missing so I added another 10% to see if the trend continued, it did not. It did start throwing a DTC P0336 CKP code however with both settings. The sensor is fairly new, replaced about 1.5 years ago. I guess it wouldn't hurt to try a new one?

  11. #11
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    Make sure the Crank sensor clearance is a minimum of .030, https://www.eficonnection.com/home/p...ensor-shim-kit .
    https://www.eficonnection.com/home/p...or-minus-0-020

    Mine is around .035.

  12. #12
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    Thanks for every ones help!!! It was the crank sensor, new one installed and properly shimmed. MAF tune complete moving on to VE.

  13. #13
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    Glad you figured it out! Crank sensor clearance on the swap, noted for the future!
    ~Erik~
    2013 Sonic RS - manual, CGM, 6M, sunroof, mods in process
    2008 TrailBlazer 3SS AWD LS2, loaded, dropped, modded, SE22 Performance tuned. And then some...
    2002 TrailBlazer LT 4WD 4.2L I6, lifted, tires, exhaust, SE22 Performance tuned