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Thread: C7 Z06 Hesitation at WOT

  1. #1
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    C7 Z06 Hesitation at WOT

    I think I may have an issue with my low-pressure fuel pump. My HPFP and fuel pressure sensor has been replaced but still have hesitation at higher RPM WOT.

    There was a similar thread but no conclusion...

    https://forum.hptuners.com/showthrea...Pressure/page2


    Here is the timeline of events:

    -2016 C7 Z06 w/Z07 5135 miles

    *Took my vehicle for a hard drive and noticed some surging past 5000 RPM, 4th gear and 5th 130MPH (Mexico has the best straight roads)
    *Proceeded to put the vehicle on a dyno and found that fuel pressure ranges were around 2100 PSI at WOT same conditions as above
    *Fault code popped up P228C fuel pressure regulator control performance -low pressure
    *Took the car to the service centre (was assured that they have 4 exclusively trained techs for the higher end performance vehicles
    *High-Pressure Fuel Pump was replaced (plus a few gaskets, as the supercharger was removed)
    *Collected the car, proceeded to the same heavy load conditions as the first * line. Reduced power and engine light illuminated. Proceeded to turn the vehicle off, opened the hood. Closed hood, locked vehicle, unlocked vehicle, started vehicle (limp mode no longer present) engine light still illuminated.
    *Called service advisor, was waiting for me (Munday Chevrolet) and returned the vehicle immediately this is 20 minutes after all of the above was repaired.
    *Spent time with said service advisor and politely requested to talk to the technician who performed work on the vehicle.
    *Was finally introduced to the tech who worked on my vehicle
    *Discussed PIP5279A with the technician. He was bewildered when I spoke about lash caps, clearance on the HPFP spacers and perhaps, we should replace the high-pressure sensor since it seems like a common problem. (P228C, an abundance of info on that)
    *replaced pressure sensor thumbnail_image1_4ca702cdd59c79b59f54c7ff155c0fafec314dab.jpg
    *Got the car back. Felt a small hesitation again higher up in RPM around 120-130MPH and just let off as I did not want to trip the CEL and reduced power mode. may be pointing to the low-pressure fuel pump that should be between 50-70PSI


    -Has anyonbe had this issue or heard of it before. Might need to get it on the dyno and see what my LPFP psi values are showing...

  2. #2
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    *Update

    Put the car on the dyno to datalog while I get the hesitation. lpfp pressure was low 59psi and the high pressure was around 2700psi. Took the car to the service department and provided them with the info. Hopefully replacing the lpfp will solve this problem. Attached the data and some screen shots.


    -Would someone mind taking a look and providing their 2 cents?

    Screenshot (4).png
    Screenshot (6).png
    Attached Files Attached Files

  3. #3
    Senior Tuner Ben Charles's Avatar
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    I don’t see fuel pressures in the data log!!!

    Log desires fuel pressure
    Actual fuel pressure
    Desired HPFP
    Actual HPFP

    Low side at WOT runs around 81psi and 2900 psi at WOT

    If dropping to 59 psi not end of world, but for sure running out of low side..

    What’s injector puslewifth?? Probably around 6-7 msec I bet

    Could just be out of fuel

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  4. #4
    Senior Tuner Ben Charles's Avatar
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    Also what lashcap?? If the 80 thousandth one it’s bottoming out I bet on te lt4 pump..
    This is something you have to measure on EVERY setup

    All cam grinds that manufactures use are from a 14 vette and tolerances change slightly with cam manufactures

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    Quote Originally Posted by Ben Charles View Post
    Also what lashcap?? If the 80 thousandth one it’s bottoming out I bet on te lt4 pump..
    This is something you have to measure on EVERY setup

    All cam grinds that manufactures use are from a 14 vette and tolerances change slightly with cam manufactures
    Ben,

    Thanks for your reply. The vehicle is bone stock with no tune. I took the Vehicle to corvette world Houston and the gentleman who put the car on the dyno just provided me with the file. I had no idea anything was missing from the log. The screenshots is what he showed me and the pressure was 59 at WOT, the HPFP pressure was 2700 and he said the boost was at 1.3 PSI. basically the fuel was not available and the boost dropped off (assume the computer avoids going lean)

    The car is at the dealer getting the LPFP changed and they will also do some other diagnostics like checking the fuel line is not plugged up, the low pressure sensor is not faulty etc....

  6. #6
    Senior Tuner Mep_q8's Avatar
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    For a stock vehicle or any modded LT engine for that matter, the hesitaton you're running into is the cylinder being flooded with fuel.

    Disable your COT enrichment and test it out again.

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    They changed the LPFP and crossover pipe. Car runs smoother and much stronger/responsive. Haven't taken it up to high speeds as it was rush hour will report back if its not solved.
    LPFP change1.PNG
    Last edited by C7LT4; 01-23-2019 at 07:20 PM. Reason: edited picture

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    Car bucks and stutters above 125MPH WOT. Happens when it is cold out. Am located in Houston TX (sea level)

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    Quote Originally Posted by C7LT4 View Post
    Car bucks and stutters above 125MPH WOT. Happens when it is cold out. Am located in Houston TX (sea level)
    these guys won't understand or agree what the problem is. We can do it to any stock z06 lt4 (and now you can as well since you know the secret process). I'm the one who already has my lemon ruling that GM must replace my car, and the other fellow you spoke to on the phone is about to go to battle on his this next week, but wanted to see how mine turned out first.

    If you have anymore questions, just hit me up here, they banned me on the other forum for explaining, or should i say, not explaining... what the problem is... as i know it will lead to a class action lawsuit, and call me selfish, but i wanted to lemon my car instead of start a class action and wait 3 years for GM to do nothing for me or any of us... instead, by lemoning the cars, it causes the GM accountants to realize, either way, they will be forking out money, so if enough of us lemon, it will start to make sense for them to just fix everyone's cars instead.

    Funny thing is, Mike explained it all to them over on CF, and people argued with him and told him he was lying and making it all up lol. One of those people is ironically in the other thread you have on this forum. His initials are HB here and CB in real life. The same guy argued with me as well when I was explaining it all before Mike did over on CF. The same guy got me banned over there and told the moderators i was wrong and was trolling.

    But, once all of our lemons are completed and we all have brand new 2019's and 2020's, then I might let the brilliant creatures on the other forum have their wish... and we will provide a step by step video of how to get the pre 2019 z06 to fail, and let all the know it all's and GM battle it out in a long drawn out class action court case, once it finally dawns on everyone what we can do on command to any pre 19 z06.

    I'll wait until your lemon is completed before I do this video Give HB time to reconsider his stance on the topic as well... he's a fast learner in all other aspects, but ive noticed... this topic is a real paradox for him to fathom.
    Last edited by irun4cops; 01-31-2019 at 01:50 AM.

  10. #10
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    Quote Originally Posted by Mep_q8 View Post
    For a stock vehicle or any modded LT engine for that matter, the hesitaton you're running into is the cylinder being flooded with fuel.

    Disable your COT enrichment and test it out again.
    ...aka... void your factory warranty, and tune your car... instead of make GM fix it under warranty?? Our opinions certainly differ.

    And no, its not the cylinder being flooded with fuel. It is the car running lean due to lack of fuel pressure due to the amount of air the MAF sees coming in and MAP, so it calls for huge amounts of fuel if COT is active (which it is, but cant be disabled on the stock tune), and the large fuel requests, which the high side pump can deliver, but in doing so, it outflows the low side pump, so the low side has a fuel pressure drop and in domino effect, so does the high side a moment later, and knock sensors going off and low fuel pressure sensors falling below critical thresholds of 60psi on the low side which cause the car to shut TB angle and pull timing, IF the car does not first go into limp mode for p228c or throw engine lights for p0089 aka high pressure side drop.
    Last edited by irun4cops; 01-31-2019 at 02:31 AM.

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    Any relationship in this chain of events to mid-throttle misfires?

    Capture1.PNG

    Capture2.PNGCapture3.jpg

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    Hello everyone,

    I have a 2015 C7 Z06 with the 7-speed manual transmission.
    I am having the EXACT same thing : huge hesitation in acceleration in 3rd or 4th or 5th gear (even sometimes in 2nd) around 4500/5000 rpm at WOT. If I keep pushing the car, it turns into limp mode, check engine like with the p228c code (high pressure fuel pump too low).
    Thus, I checked the log while running to analyse this and indeed it shows that I have a huge drop of fuel pressure at that specific rpm range (4500/5000 rpm), although the car doesn't seem to run lean according to my tuner it runs rich. Passed that 5000 rpm it seems to come back to the normal fuel pressure level where it should be.

    I have no idea what to do and I don't want to sell the car because that is really my dream come true car. Can somebody help because I see many topics but 0 conclusion on WHAT EXACTLY CAN FIX this issue ?

    ps : I just have an E85 flexfuel tune, no performance related, just to have the ability to run E85 because it's 0.7€/L instead of 1.8€/L at the gas station (I'm living in Paris). The car does the same in both E85 fuel or regular gas (SP98 in Paris, octane number being 98).

    Thank you so much for the help

  13. #13
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    Quote Originally Posted by C7LT4 View Post
    Car bucks and stutters above 125MPH WOT. Happens when it is cold out. Am located in Houston TX (sea level)
    Hello Sir,

    Did you find a solution to fix the issue ? I am having the exact same thing and I panic because I am living in France and I don't trust anyone working on my car here… So if you could tell me exactly what solved the problem so I can tell them directly.

    Thank you

  14. #14
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    Quote Originally Posted by victor_2111 View Post
    Hello everyone,

    I have a 2015 C7 Z06 with the 7-speed manual transmission.
    I am having the EXACT same thing : huge hesitation in acceleration in 3rd or 4th or 5th gear (even sometimes in 2nd) around 4500/5000 rpm at WOT. If I keep pushing the car, it turns into limp mode, check engine like with the p228c code (high pressure fuel pump too low).
    Thus, I checked the log while running to analyse this and indeed it shows that I have a huge drop of fuel pressure at that specific rpm range (4500/5000 rpm), although the car doesn't seem to run lean according to my tuner it runs rich. Passed that 5000 rpm it seems to come back to the normal fuel pressure level where it should be.

    I have no idea what to do and I don't want to sell the car because that is really my dream come true car. Can somebody help because I see many topics but 0 conclusion on WHAT EXACTLY CAN FIX this issue ?

    ps : I just have an E85 flexfuel tune, no performance related, just to have the ability to run E85 because it's 0.7€/L instead of 1.8€/L at the gas station (I'm living in Paris). The car does the same in both E85 fuel or regular gas (SP98 in Paris, octane number being 98).

    Thank you so much for the help
    You are requesting more of your fuel system than it can deliver, hence the fuel pressure drop. If this goes on long enough, the ECM will go into limp mode to protect your engine from damage. P228C

    Have your fuel system fully inspected and tested. If your fuel system checks out (low pressure pump, high pressure pump, flow, etc.) then you will need to either reduce airflow (lower boost levels), adjust fuel mixture appropriately, or upgrade your fuel system components to solve this. Using E85 definitely won't help since this increase the demands on your fuel system even more.

  15. #15
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    These cars can be fixed with a JMS fuel system voltage booster and custom calibration which I can provide remotely.

    The stock calibration is rich enough it is over whelming the low side fuel pump.

    The JMS will enhance the low side output with no down side.

    The custom calibration will dial in the AFR, Keep COT working and Not ask for more fuel than the system can supply.

    But like it was eluded to you will void your warranty, I don't know how much warranty you would have left on a 2015 so not really a big deal.

    Let me know If I can be of assistance.

    Ted

  16. #16
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    Quote Originally Posted by tunerpro View Post
    You are requesting more of your fuel system than it can deliver, hence the fuel pressure drop. If this goes on long enough, the ECM will go into limp mode to protect your engine from damage. P228C

    Have your fuel system fully inspected and tested. If your fuel system checks out (low pressure pump, high pressure pump, flow, etc.) then you will need to either reduce airflow (lower boost levels), adjust fuel mixture appropriately, or upgrade your fuel system components to solve this. Using E85 definitely won't help since this increase the demands on your fuel system even more.

    Thank you for your reply.

    I don't think the car request more fuel Under WOT than the fuel system can deliver because :
    1) It's a simple Flexfuel tune so I have exactly the same hp/torque as stock. No performance related, and the High fuel pump can handle injecting 15% more for the E85. It's litterally a tune that takes information from lambda sensor to recalculate the proper quantity of fuel that needs to be injected (depending on my E85 content, thus a flexfuel tune).
    2) The car does the same thing even when I run regular gas (SP98 in France, which is 98 octane number). And with regular gas, the fuel pump should be able to deliver without any issue (ps : when I run 98 number WITH my E85 Flexfuel tune. I don't remember if the car did this with the OEM tune, because as soon as I got the car, I did the tune like 600km after so I didn't push the car really hard).

    I will still try to go back to my OEM tune and run the car with 98 octane (regular gas) just to check if the issue is related to my E85 tune, but for these reasons, I think the problem is somewhere else, don't you think so ?

    To answer the rest of your message, why would I reduce airflow (lower my boost level) as the car is 100% stock performance wise ? Couldn't the problem be related to a defective MAF ? Or a loose spark plug or anything else ?

    Thank you so much for your help. I really love this car and I want to fix it not to sell it

  17. #17
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    Quote Originally Posted by JANNETTYRACING View Post
    These cars can be fixed with a JMS fuel system voltage booster and custom calibration which I can provide remotely.

    The stock calibration is rich enough it is over whelming the low side fuel pump.

    The JMS will enhance the low side output with no down side.

    The custom calibration will dial in the AFR, Keep COT working and Not ask for more fuel than the system can supply.

    But like it was eluded to you will void your warranty, I don't know how much warranty you would have left on a 2015 so not really a big deal.

    Let me know If I can be of assistance.

    Ted
    Thank you but I would like to first fix this without any upgraded parts. I don't understand why my Z06 wouldn't run nicely all of a sudden. If one day I want a performance upgrade, I will look further into details your Fuel system voltage booster

  18. #18
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    Quote Originally Posted by victor_2111 View Post
    Thank you for your reply.

    I don't think the car request more fuel Under WOT than the fuel system can deliver because :
    1) It's a simple Flexfuel tune so I have exactly the same hp/torque as stock. No performance related, and the High fuel pump can handle injecting 15% more for the E85. It's litterally a tune that takes information from lambda sensor to recalculate the proper quantity of fuel that needs to be injected (depending on my E85 content, thus a flexfuel tune).
    2) The car does the same thing even when I run regular gas (SP98 in France, which is 98 octane number). And with regular gas, the fuel pump should be able to deliver without any issue (ps : when I run 98 number WITH my E85 Flexfuel tune. I don't remember if the car did this with the OEM tune, because as soon as I got the car, I did the tune like 600km after so I didn't push the car really hard).

    I will still try to go back to my OEM tune and run the car with 98 octane (regular gas) just to check if the issue is related to my E85 tune, but for these reasons, I think the problem is somewhere else, don't you think so ?

    To answer the rest of your message, why would I reduce airflow (lower my boost level) as the car is 100% stock performance wise ? Couldn't the problem be related to a defective MAF ? Or a loose spark plug or anything else ?

    Thank you so much for your help. I really love this car and I want to fix it not to sell it

    On E85 the car can certainly request more fuel than the fuel system can provide. Depending on the blend you will need more than 15% increase in volume. 85% ethanol requires nearly 35-40% more fuel volume over stock. A bone stock Z06 cannot handle 85% ethanol.

    Bottom line is, a datalog would help shed some light on this. I often fix flex fuel tunes for guys who's tuner doesnt blend the table properly which causes large changes in spark during throttle roll on events which is perceived as a stumble.

    Depending on the year, it could be the fuel hose issue where the check valves causes a fuel pressure drop. Get some datalogs and dive in.
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    Quote Originally Posted by TriPinTaZ View Post
    On E85 the car can certainly request more fuel than the fuel system can provide. Depending on the blend you will need more than 15% increase in volume. 85% ethanol requires nearly 35-40% more fuel volume over stock. A bone stock Z06 cannot handle 85% ethanol.

    Bottom line is, a datalog would help shed some light on this. I often fix flex fuel tunes for guys who's tuner doesnt blend the table properly which causes large changes in spark during throttle roll on events which is perceived as a stumble.

    Depending on the year, it could be the fuel hose issue where the check valves causes a fuel pressure drop. Get some datalogs and dive in.
    Thank you the reply.
    I didn't know the car couldn't handle 85% ethanol... I'm really into american cars and all of the previous cars I had could handle without any issue (I don't mod the cars for perf, only to run E85).

    So I actually see me tuner 3 weeks ago and we saw on the datalogs that at around 4,5k rpm and up until 5k rpm (so exactly where the hesitation occurs) there is a huge drop in fuel pressure and the car keeps "enriching" the mixture at the same time. I don't know why this occurs at that specific rpm range and only at WOT, I'm guessing it's the pic power of the car. I don't understand why this occurs. I hope it's only because I run E85 and the High Pressure Pump can't handle that much volume of E85 to inject. The thing is I tried to put 98 octane (so my base regular fuel) and it did the same (I was on my tuner's E85 map, but it should adjust quantity as it's a flexfuel tune, which takes info at the lambda sensor). To sum up, I can't tell if the problem comes from the E85 with the car being bone stock, or if there is definitely a problem as it does the same with regular gas (but still with my E85 flexfuel map). I think I will ask the tuner to put my stock ECU map back on and try a couple of pulls in 3rd gear, checking the datalogs at the same time.
    I should see him soon. He told me he has a solution but didn't explain much on the phone. Remember guys I'm living in Paris and having a Z06 is litterally super exotic here. So not a lot of people have knowledge about this car in France. There must be like 20 of them in the country and people never actually drive the cars, aside from me, which is why I run E85 because it's super cheap and I drive a lot throughout the year

    Thank you guys for the help you provide. I really hope we can find a solution to this because I want to go full send with the car, and for now it's really frustrating...

  20. #20
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    The Gen V cars are Direct Injection. There is a much smaller window to inject fuel into. There are some tricks and ways to get more out of the system if you bump the low side but you need a tuner that knows what they are doing. If high side is dropping that is a tell tale sign you're asking for more fuel that the system can provide in its current configuration. A JMS booster and a proper recalibration of the FPCM will get you further on these cars when it comes to running E85.
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