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Thread: 17 ZL1 FSCM tweak with JMS voltage booster

  1. #1
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    17 ZL1 FSCM tweak with JMS voltage booster

    Hey guys, I have a 2017 ZL1 Camaro with a 2650 Maggie and cam and all the other stuff. My question is whether or not I have to tune the FSCM to allow the 17.5 volts from the JMS to get to the low side fuel pump? Right now my low side is tanking at 5700 rpm running e40. I lowered the e to 13, essentially running 92 pump gas, and the low side held strong at 74psi through 6700. A tech at JMS said he doesn't thing the voltage is getting to the low side even though the booster is pushing out 17.5 volts at WOT.

    Any help would be greatly apprediated.

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    You have to tune the pressures and a couple other things to take advantage of the JMS's additional voltage to the fuel pump. Additionally the JMS needs to be set up properly as well. If you don't get either one of these right, you won't get any additional low side fuel.

    Also, seeing as you have a 2650, there is a chance your asking more from the stock low side and JMS than it can provide. It is not a replacement for the DSX low side kit but it will bump up your stock low side quite a bit.
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    Quote Originally Posted by TriPinTaZ View Post
    You have to tune the pressures and a couple other things to take advantage of the JMS's additional voltage to the fuel pump. Additionally the JMS needs to be set up properly as well. If you don't get either one of these right, you won't get any additional low side fuel.

    Also, seeing as you have a 2650, there is a chance your asking more from the stock low side and JMS than it can provide. It is not a replacement for the DSX low side kit but it will bump up your stock low side quite a bit.
    The JMS is outputting 17.5 volts at WOT. I am reasonable certain it is installed and setup properly. But here is the weird thing: I made multiple low to midrange pulls without issue to gather info for the final tune. After installing the final tune, the low side held a 70psi at 7K rpm for one pull w/15# of boost @e51. I lowered the e to 40 and the low side dropped to 46psi at 5700 rpm. Do you think that the FSCM/ECU learn and then pull the voltage?

    Thanks for you help.

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    Quote Originally Posted by Martinle View Post
    The JMS is outputting 17.5 volts at WOT. I am reasonable certain it is installed and setup properly. But here is the weird thing: I made multiple low to midrange pulls without issue to gather info for the final tune. After installing the final tune, the low side held a 70psi at 7K rpm for one pull w/15# of boost @e51. I lowered the e to 40 and the low side dropped to 46psi at 5700 rpm. Do you think that the FSCM/ECU learn and then pull the voltage?

    Thanks for you help.

    I've seen this happen when you turn the JMS voltage up too high and it either a) overdrives the pump too much and cavitates, or b) damages the pump and it fails to hold pressure, eventually tanking and causing the car to go dangerously lean. So keep an eye on your low side.

    The FSCM will not learn to pull voltage. But your tune may not be correct to extract the most out of the JMS. Try turning the JMS down to 17.25 volts. Having inconsistent low side pressures under the same conditions (boost and fuel consumption) is not the norm with the JMS.

    Having said all of this above, its really just a guess based on experience. You haven't posted a log or a tune file. I would look at your two logs described above and see if there are any differences in airmass. You could just be on the edge of pump ability and a slight increase in airmass sends it over the edge and pressure tanks.
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    Quote Originally Posted by TriPinTaZ View Post
    I've seen this happen when you turn the JMS voltage up too high and it either a) overdrives the pump too much and cavitates, or b) damages the pump and it fails to hold pressure, eventually tanking and causing the car to go dangerously lean. So keep an eye on your low side.

    The FSCM will not learn to pull voltage. But your tune may not be correct to extract the most out of the JMS. Try turning the JMS down to 17.25 volts. Having inconsistent low side pressures under the same conditions (boost and fuel consumption) is not the norm with the JMS.

    Having said all of this above, its really just a guess based on experience. You haven't posted a log or a tune file. I would look at your two logs described above and see if there are any differences in airmass. You could just be on the edge of pump ability and a slight increase in airmass sends it over the edge and pressure tanks.
    When I get home, I will send you the logs. Can I send them through this site or do I have to email them? Thank you very much for your time and knowledge.

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    Quote Originally Posted by Martinle View Post
    When I get home, I will send you the logs. Can I send them through this site or do I have to email them? Thank you very much for your time and knowledge.
    Here is fine
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    e50 log.hple41 log.hpl7000noJMS.hpl

    The log named e50 is the log I sent to JRE after final tune. The e41 was the next pull I did after they suggested that I only run e40. The 7000noJMS is self explanatory. I have logs with the JMS working and with the e13 all logs are fine. I will add the last log I did with the JMS still enabled. It is 6800-4-13 which is 6800rpm, fourth gear pull and at e13.6800-4-13.hpl

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    As the Ethanol % goes up, more and more duty cycle is commanded by the fpcm to maintain the commanded pressure. So if the pump is is trying to hold 76PSI on e13 vs E50, then the pump is going to be cycled on much more often on E50 than E13 due to the volume requirement. If the pump is holding pressure on E13 that would support the theory that the pump isn't faulty/bad. But I do find it odd that on E50 the pressure was fine, then on E41 the pressure fell off up top. That supports the theory that the pump is failing or cavitating. The air temps were similar so that is odd. Were the pulls in the same gear?

    I can only offer that we had a ZL1 with a similar issue. The car would run E60 and the pressure would start falling as demand went up in higher gears . Then we would run E76 and the low side pressure would hold. Well after enough testing, the ethanol content didn't matter much between E60-E76, it turned out that the low side pump was failing and intermittently dropping pressure. Since I didn't install the JMS on that particular car, there is no telling if the owner over volted it with the JMS. These low side pump DO NOT like anything over 17.5 volts. I always settle for 17.35-17.45 volts on these. Overvolting can cause damage to the pump or cavitation where fuel pressure drops. If pump duty cycle is too high and there is enough voltage the pump will cavitate and/or overheat. So while the JMS is a great solution to the low side, you cannot push it past 17.5 volts, or run it to run the low side pump to the very edge, while maintaining reliability.

    Honestly, at your mod level, I would install the DSX low side. It's all a guess from my end here on if you're actually at the limit of the JMS + low side, or if the low side pump is starting to fail, or if the pump is cavitating, or maybe something else?

    I know its a long winded answer without much clarity. I'm only throwing out logical ideas, based on my experience with the JMS, to consider as possibilities. This all assuming the JMS is working properly as well. Might want to test the output voltage on it just in case.
    Last edited by TriPinTaZ; 1 Week Ago at 08:09 AM.
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    Thank you for your time. I will turn down the voltage and check how much is getting to the pump. The e41, e50 and the 7000noJMS were done in second gear (m/t).

    So, my take on your thoughts is that with the bigger injectors the car is surely out of pressure (with pump gas)without the JMS which the 7000noJMS log supports. With the booster I'm ok running pump gas as the 6800-4-e13 supports. Any appreciable e content over-works the pump and pressures drop which the e41 log supports. Maybe the pump is failing (I just replaced the thing). Maybe I'm over-volting the pump. Therefore, I think my first order of business is to make reasonable sure the pump is good. As I said, I will lower the voltage to 17.25 volts, just to be sure, and log some runs and see what happens. Maybe I will luck out and find that just those extra couple of tenths are the problem. You are not the first experienced tuner that has said I really need the DSX low side. I have no problem with that if I only knew for sure that would solve the problem.

    I will run the lower voltage logs tonight and see what happens. I will let you know. And once again, thank you very much for all your help.

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    Oh, I am running a 15% (9.34) lower and a 90mm upper.

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    FWIW, when I was running the JMS I originally had it set to 17.5 or 17.6 volts and I kept getting fuel pressure error codes. I lowered it to 17.25 and the codes went away. But if you’re going to keep cranking up the power, just rip the band aid off and install the Fore system. It’s the only solution that just fixes the problem once and for all.
    2017 Camaro SS, Kong-ported Whipple supercharger, Mast LT Black Label heads, custom CamMotion cam, Katech 112mm TB, LPE BB HPFP & LT4+52% injectors, Fore Innovations triple in-tank pump setup, 5" CAI, etc.
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    Quote Originally Posted by Joshinator99 View Post
    FWIW, when I was running the JMS I originally had it set to 17.5 or 17.6 volts and I kept getting fuel pressure error codes. I lowered it to 17.25 and the codes went away. But if you?re going to keep cranking up the power, just rip the band aid off and install the Fore system. It?s the only solution that just fixes the problem once and for all.
    Hey Joshinator99,

    I follow you on the Camaro forum. My power goals are met for the long run. If I ever find the money tree, who know what might happen? I am thinking that the DSX aux pump would suffice for my application? I am certainly taking the advice from those smarter than me - and like you - who have spent way more money than me and their car still runs.

    I lowered the JMS to 17.37 (from 17.57) and ran an e40 pull e40.hpl. I think the car is ok with it. (With the booster set at 17.57, my low side dropped to 46psi.) I'm not sure I need the double pump Fore and the warnings on the Fore sight about heat build up and having to be very cognizant of your fuel level and the price have me a little shy of it. But, if it would be the "be all and end all" of my fueling needs, who knows. And wouldn't I need to upgrade my high side to really utilize it?

    So, all in all, don't you think half of a band aide would work?

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    Quote Originally Posted by TriPinTaZ View Post
    As the Ethanol % goes up, more and more duty cycle is commanded by the fpcm to maintain the commanded pressure. So if the pump is is trying to hold 76PSI on e13 vs E50, then the pump is going to be cycled on much more often on E50 than E13 due to the volume requirement. If the pump is holding pressure on E13 that would support the theory that the pump isn't faulty/bad. But I do find it odd that on E50 the pressure was fine, then on E41 the pressure fell off up top. That supports the theory that the pump is failing or cavitating. The air temps were similar so that is odd. Were the pulls in the same gear?

    I can only offer that we had a ZL1 with a similar issue. The car would run E60 and the pressure would start falling as demand went up in higher gears . Then we would run E76 and the low side pressure would hold. Well after enough testing, the ethanol content didn't matter much between E60-E76, it turned out that the low side pump was failing and intermittently dropping pressure. Since I didn't install the JMS on that particular car, there is no telling if the owner over volted it with the JMS. These low side pump DO NOT like anything over 17.5 volts. I always settle for 17.35-17.45 volts on these. Overvolting can cause damage to the pump or cavitation where fuel pressure drops. If pump duty cycle is too high and there is enough voltage the pump will cavitate and/or overheat. So while the JMS is a great solution to the low side, you cannot push it past 17.5 volts, or run it to run the low side pump to the very edge, while maintaining reliability.

    Honestly, at your mod level, I would install the DSX low side. It's all a guess from my end here on if you're actually at the limit of the JMS + low side, or if the low side pump is starting to fail, or if the pump is cavitating, or maybe something else?

    I know its a long winded answer without much clarity. I'm only throwing out logical ideas, based on my experience with the JMS, to consider as possibilities. This all assuming the JMS is working properly as well. Might want to test the output voltage on it just in case.
    I lowered the JMS to 17.37 and this is the loge40.hpl. What do you think. Again, it was pretty cool this morning, 70 degrees.

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    Quote Originally Posted by Martinle View Post
    I lowered the JMS to 17.37 and this is the loge40.hpl. What do you think. Again, it was pretty cool this morning, 70 degrees.
    It looks better. The low side pressure is dropping just a bit on a more linear line but still safe. I think you're just maxing out the fuel past 6500 RPMs and the high and low side drop a bit but nothing dangerous yet.

    17.57v is too high for the FPCM. 17.4v is actually the recommended maximum. Anything past that and you can get weird behavior. Perhaps that is all that was happening to you. My personal car is running 17.42v and has zero issues.
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    Quote Originally Posted by TriPinTaZ View Post
    It looks better. The low side pressure is dropping just a bit on a more linear line but still safe. I think you're just maxing out the fuel past 6500 RPMs and the high and low side drop a bit but nothing dangerous yet.

    17.57v is too high for the FPCM. 17.4v is actually the recommended maximum. Anything past that and you can get weird behavior. Perhaps that is all that was happening to you. My personal car is running 17.42v and has zero issues.
    Thank you for your time, I very much appreciate it. I am going to install a DSX aux pump and call it good for the mean time.
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    Quote Originally Posted by Martinle View Post
    Hey Joshinator99,

    I follow you on the Camaro forum. My power goals are met for the long run. If I ever find the money tree, who know what might happen? I am thinking that the DSX aux pump would suffice for my application? I am certainly taking the advice from those smarter than me - and like you - who have spent way more money than me and their car still runs.

    I lowered the JMS to 17.37 (from 17.57) and ran an e40 pull e40.hpl. I think the car is ok with it. (With the booster set at 17.57, my low side dropped to 46psi.) I'm not sure I need the double pump Fore and the warnings on the Fore sight about heat build up and having to be very cognizant of your fuel level and the price have me a little shy of it. But, if it would be the "be all and end all" of my fueling needs, who knows. And wouldn't I need to upgrade my high side to really utilize it?

    So, all in all, don't you think half of a band aide would work?
    I’m sure the DSX would be fine if you’re going to stay in the general power range you’re in. It would give you more headroom than you have now for sure.
    2017 Camaro SS, Kong-ported Whipple supercharger, Mast LT Black Label heads, custom CamMotion cam, Katech 112mm TB, LPE BB HPFP & LT4+52% injectors, Fore Innovations triple in-tank pump setup, 5" CAI, etc.
    955 WHP, 842 WTQ, 9.65@146

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    Thank you.
    JRE Terminator Rough Idle Cam
    Magnusun 2650 - 9.34 lower / 90mm upper
    Ethanol 40%
    FIC +30%
    JMS
    NW 103mm TB - Roto Fab CAI
    2" TSP LTs