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  1. #1
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    Exclamation Surge on DECEL 2000RPM 1500RPM

    Hello,
    Was wanting to reach out to you all to see if you have noticed this before;

    Gen4 with 17k miles

    First a list of mods on the car prior to the issue, then the recent round that presented the issue.

    Prior to Issue;
    • Gen 5 Intake Manifold
    • Smooth Silicone Bellows from Doug Shelby Engineering
    • Doug Shelby Engineering Catch Can


    Mods that presented the issue;
    • Full ARH 1-7/8 Long Tube Headers, and side pipe Exhaust System (system is Cerakoted)
    • New Upstream/Downstream Denso O2 Sensors
    • Prefix/Mopar Race Controller
    • NGK Iridium IX Plug LZTR5AIX (see story below for info)
    • Moroso Ultra 40 Wire Set from Doug Shelby Engineering



    Initially when ordering the PCM from Prefix I asked Dale Mathews (Prefix Product Engineer) if he had a recommended plug to use, knowing the mods I had with his controller. He provided me a Bosch Plug that was 1 heat range colder (at $6.XX per plug I was kind of impressed) so I installed it the setup. Dale programmed PCM on the bench so it would all be plug and play. I installed, used an Autel just for peace of mind to relearn my actual ETC system for idle. I noticed within the first 48hrs, 2 things;

    1. a lope to the idle, 5 sec of happy idle, then 2 sec of a drop off then cycling back and forth.
    2. Surge on decel any gear once I hit 2000RPM down to 1500RPM.


    So immediately I suspected perhaps the colder plug was loading up at idle, continuing to monitor for another 24-36 hours I decided to call Dale as I had a P0172 & P0175 (System too Rich Bank 1 and Bank 2) pending, discussing with him and asking if he had seen this as I wanted to switch to the NGK plug above. He mentioned to me they recently had seen that Bosch plug loading up at idle, putting it at risk of carbon fouling that they had since spec'd the same NGK plug to use as I referenced. So I told him I would order and give some feedback from street use as they use the Bosch primarily on their higher RPM track use builds. So I swapped them, and it immediately cleared the idle up 100%.

    Now onto the surge, once it starts to surge/buck if you ever so lightly give it slight throttle it's gone and smooth and performs awesome which to me doesn't support a restrictive exhaust, more rather than the fuel cut off in the tune. The vehicle drives and performs fine EVERYWHERE but this range (I could possibly say a surge down to 1300 but the fuel is so low being supplied it's not noticeable), I even again yesterday had a dealer in Kokomo, IN with a tech I know go in and reset the Adaptives. Now I have roughly 120miles on the car since I live 2 HRs from that area and I still have a slight surge. I do notice from a COLD START (vehice setting 12+ hrs) on initial start I may get a high idle, or a lope (as in 1800 RPM, then down then back and down to stay down). Vehicle holds smooth at 760 -7900RPM when monitoring with my scan tool.

    Given my background I still hunted all over for any form of vac leak, or line crack/split etc. I see nothing even spraying the lines with a soap/water mix while running to see if it's pulled in or not. Naturally when you see a surge around this area you think ATC/TPS perhaps has a bad spot, MAF issue, IAC (which the car doesn't have as it's part of the ATC system), restricted exhaust (hard to believe all is new) and a few others. However part of me wanted to reach out and share this to see if anyone who's equipped with similar mods, and or the PREFIX/MOPAR PCM has experienced this as the car was behaving flawlessly prior to the install so for me to just say ya the ThrottleBodies, etc are bad (when I was sweep data I don't see a drop out) and replace them without a hard code set isn't justified. It's almost as if the fuel cut out in the programming is just a slightly RICH and has too much fuel commanded still.

    During the trip yesterday I left my scan tool plugged in and left the special function screen pulled up monitoring Fuel Consumption Data, and Say for over 260 miles of driving I averaged 21.6MPG and seen instantaneous as high as 24MPG. So I can believe the rest of the tune is pretty on point, as if I were rich across the board I'd still have DTC's to support and notice the MPG data to be worse.

    Planning to give Dale a call Monday @ PREFIX and share info, but thought I'd reach out to see if anyone has a similar issue, story, insight to share.

    I could swap back to the OEM PCM I suppose to see if this removes the issue, and may do that depending on what I hear.

    THANK YOU ALL,
    Ryan



    Below are 5 links to various data on the scan tool at idle prior to the trip yesterday (after I swapped plugs to the NGK)





    Last edited by DARKNHT; 05-01-2021 at 02:29 PM.
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  2. #2
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    Your story reminds me of this one:

    https://driveviper.com/forums/thread...l=1#post434279

    I'd suspect it is in the tune, specifically related to the extra popping on decel introduced by the Arrow/Prefix PCM. 2,000 RPMs is right where that would start on decel from what I know of that calibration.
    2008 SRT-10 Coupe - Venom Red Metallic w/ White Stripes - 1/4 Mile Passes (YouTube)
    High Flow Cats | Gen 5 Intake Manifold | UDP | HPTuners | 3.55s | MCS | DSS Axles | McLeod RST | 11.027 @ 130.06 (Vid), 1.78 60' (+1,622 ft DA, w/ 3.55s & Hoosier Drag Radials)

  3. #3
    I agree - most likely tune - sounds exactly how everybody describes what happens as a result of the arrow/prefix decel popping tune

  4. #4
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    I just spent the day going over the car once more, verifying all bolts are secure and tight on the EXH system. Even did a once over on the Gen5 intake, even though it's been on the car since 2019. Found nothing... Drove for 30min, LTFT never went over 4.7 (both banks identical). I spoke with Scott w/ Prefix yesterday via FB Messenger. He swears if the programming was correct, then I have an exh leak etc. However given my automotive knowledge and background. I would think I would show supporting data, via O2 data switching, Fuel Trims etc but both are almost spot on to where I don't see anything of alarming or concern. Let alone 386 miles since install and no CEL/MIL. In addition soon as it's doing it, if I take the load off the car as in pull it to neutral and let off the gas the surge is gone, if I rev in neutral the surge is gone, and if I rev sitting at 0 mph the surge is gone on decel.

    I shot an email to Roanoke to see if they would be willing to go through the programming sequence (trying another dealer) to rule out a fluke at Button in Kokomo. So we will see, I really don't want to drive the car 6.5HR to Prefix just to verify, but I guess if anything if the tune needs adjusted it can be done live on the car should it come to that.
    "GOD made Vipers, so the Corvette could have a HERO..."

  5. #5
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    Swapped the OEM PCM back into the car and all is well again. Zero surge, however now there’s no longer the crisp response, the skip shift is back etc til this is sorted out.

    Im not sure which route to go… I couldn’t get Norwegian to respond to me from his thread with the solution for his situation.

    1. I have a tentative appointment next Tuesday with Roanoke to go thru the install/setup to rule out a mishaps from what was done Friday at Button Dodge in Kokomo.

    2. Say I do 1 and nothing if changed now I have 2 diff trips of 8 hours each invested, time, money etc just to still need the PCM to be adjusted. So I would think rather than send the PCM alone it’s better for the car to go with to Prefix to adjust it to the actual car not adjusting a median value. Which would then involve 12 hours round trip, hotel, money etc all possibly for a concern I supported and pinpointed in the beginning?? I feel should this be the case some form of compensation would be warranted. I have their oil lines maybe they will install lol.

    The reason why I question the fuel cut off in the tune has been covered, but then I just seen SneakySnake posting on IG Dick Winkle’s giving him a fresh new 9.0L Extreme update. Perhaps it shares some fuel calculations with my tune and it’s too much for a stock cube engine with only a G5 intake and exhaust. I don’t know… #Crossroads

  6. #6
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    My $0.02:

    You are wasting your time with another dealer appointment - it won't fix the issue you are having.

    You already know what the problem is - it is a calibration issue. You know this because the car no longer has a problem after simply swapping the stock PCM back in place.

    The only thing the dealer must do to make sure the new PCM works correctly is the throttle relearn, which syncs the PCM to your gas pedal and throttle bodies. Those parts have design tolerances, and the relearn process makes sure the PCM knows what those tolerances are on your car. That's it. If they didn't do it correctly, the car wouldn't run right at all; likely it would go into limp mode, which would throw lights on the dash and be nearly impossible to drive. Since that isn't happening, there is nothing more your average Viper tech can do.

    Prefix also doesn't need your car to fix this issue. Simply describe your problem, and tell them the stock PCM fixes the issue entirely. Then tell them you are shipping their PCM back to them and want the deceleration fuel cutoff parameters put back to stock so you no longer have to deal with the surging issue.

    History lesson: the Mopar PCM was the only game in town for many years for the Gen 4 Vipers. It was essentially the same basic idea as the Arrow/Prefix PCM - it allowed you to run headers without throwing codes. That calibration, however, got rid of all exhaust popping on deceleration, which apparently was a big deal to some. Enough complained that Arrow/Prefix decided to add it back in when they released their calibration a few years back, only this time they turned it up to 11. They said "You really want exhaust popping? We'll give you exhaust popping."

    My firm belief is that the issues you are having are the direct result of the calibration changes they made so your car can sound like my idiot neighbors around the 4th of July when decelerating.

    They have the source code, and Dick Winkles will know how to do what I described above.

    I'm likely missing a few details here, but this seems pretty cut and dry to me. If it is only happening on decel under 2,000 RPMs, it is the extra exhaust popping they added to the calibration.
    2008 SRT-10 Coupe - Venom Red Metallic w/ White Stripes - 1/4 Mile Passes (YouTube)
    High Flow Cats | Gen 5 Intake Manifold | UDP | HPTuners | 3.55s | MCS | DSS Axles | McLeod RST | 11.027 @ 130.06 (Vid), 1.78 60' (+1,622 ft DA, w/ 3.55s & Hoosier Drag Radials)

  7. #7
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    Here are two links that go along with the history lesson:

    https://driveviper.com/forums/thread...xhaust+popping

    Pay attention to this one about the popping: https://driveviper.com/forums/thread...l=1#post137521
    2008 SRT-10 Coupe - Venom Red Metallic w/ White Stripes - 1/4 Mile Passes (YouTube)
    High Flow Cats | Gen 5 Intake Manifold | UDP | HPTuners | 3.55s | MCS | DSS Axles | McLeod RST | 11.027 @ 130.06 (Vid), 1.78 60' (+1,622 ft DA, w/ 3.55s & Hoosier Drag Radials)

  8. #8
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    Quote Originally Posted by Steve M View Post
    Here are two links that go along with the history lesson:

    https://driveviper.com/forums/thread...xhaust+popping

    Pay attention to this one about the popping: https://driveviper.com/forums/thread...l=1#post137521
    Thank you for reaffirming my thoughts. I’ve been out of the automotive service field since 2012, an am never a bragger/boasted of knowledge while I try to remain humble.

  9. #9
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    It sounds like you have the data you need to make your case with them...it seems like their position is to push back on the customer, because it couldn't possibly be something that they did. To be fair, I'm sure there is no shortage of people out there that have no business wrenching on a car that end up inducing problems that they don't even realize. I don't get the impression that is the case here...you've been thorough, so hopefully that works in your favor.

    Stick to your guns, and definitely let us know when/if you get the problem resolved. As you've already found out, this community is only beneficial if people share info.
    2008 SRT-10 Coupe - Venom Red Metallic w/ White Stripes - 1/4 Mile Passes (YouTube)
    High Flow Cats | Gen 5 Intake Manifold | UDP | HPTuners | 3.55s | MCS | DSS Axles | McLeod RST | 11.027 @ 130.06 (Vid), 1.78 60' (+1,622 ft DA, w/ 3.55s & Hoosier Drag Radials)

  10. #10
    Prefix is a standup company, and I'm sure will right any wrong that they have caused.

    I don't think you have a case for reimbursement for bringing your car to them though.

  11. #11
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    Quote Originally Posted by Steve M View Post
    It sounds like you have the data you need to make your case with them...it seems like their position is to push back on the customer, because it couldn't possibly be something that they did. To be fair, I'm sure there is no shortage of people out there that have no business wrenching on a car that end up inducing problems that they don't even realize. I don't get the impression that is the case here...you've been thorough, so hopefully that works in your favor.

    Stick to your guns, and definitely let us know when/if you get the problem resolved. As you've already found out, this community is only beneficial if people share info.
    For sure, I definitely will update the thread with the resolution.
    "GOD made Vipers, so the Corvette could have a HERO..."

  12. #12
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    Quote Originally Posted by 13COBRA View Post
    Prefix is a standup company, and I'm sure will right any wrong that they have caused.

    I don't think you have a case for reimbursement for bringing your car to them though.
    I don't knock them at all, and will continue to support them as a company and buy their product, flying their flag. I don't want to be misread here, just felt resistance that it couldn't be the product. While I do get plenty of PCMs are in the field without issue. Thus while I am willing to let Roanoke verify a completely diff dealer with a known Viper history walk thru the setup to give them (Prefix) the peace of mind to know it was done correctly. Prior to taking the car on a trip to Prefix or sending the PCM to them for an adjustment. (If the adjustment will be a cold calculated number change, then I will just send the PCM to them. If they are willing to adjust to the car specifically then I'll take the car and invest the time).

    To clarify I have been in communication with Scott Rickford @ Prefix the past 24 hours and we are moving forward working on a sensible approach and solution that will hopefully be addressed by end of next week.
    "GOD made Vipers, so the Corvette could have a HERO..."

  13. #13
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    Update....

    Went to see Dave (technician) at Roanoke this morning at 9AM. He confirmed the surge, and confirmed the pedal was learned, however re-learned the procedure one more time. Test drive, and verified surge is still present. Dave then spent some time on the phone with Scot Rickford @ Prefix (all behind the scenes). Scott sent me a message on my phone, asking my to call him.

    I called Scott, and he apologized upfront and wanted to tell me personally. We need to send the controller back to him or bring the car for live immediate fixing and verification. Ultimately I have decided as it's just a parameter adjustment with the Fuel Cut Off (decel popping) that I am Priority Mailing the controller back to Prefix today, it's scheduled for delivery on FRI. They will make the adjustment, we discussed going with a 50% value from where it is now. They will mail back, and I will install and review, if still unhappy I will send the controller back and have the decel popping completely removed. So I should have the first revision back and in the car I would think be the end of next week.

    Again Scot was more than professional, with discussion, explanation and apology for the problem I am experiencing and is motivated to get it corrected for me.

    Til the next update, hope everyone is have a wonderful time!!
    "GOD made Vipers, so the Corvette could have a HERO..."

  14. #14
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    Good info DARKHT...I am betting that all will be well when you get the module back from Prefix.
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