lean area around 2500ish rpms-2014 ctsv

[GHuggins]

It might be a high flow switch over or pressure dance like you're talking about. I just looked over the log of one I did with a cai only trying to get to the root of something in a near stock car and it stayed right at 50psi until 3400 where it switched over to 60psi causing the injector pulsewidth to suddenly drop. No afr lean spikes anywhere on the dyno readout unless y'all see something, but I didn't' have the widebands hooked up in the log to see more instant info. Most of what I'm seeing in the tune even shows the opposite. Drops in airflow or fuel requirement through the 2500 rpm range. I don't see anything special about it, but maybe y'all will see something that stands out? The pulls were in manual mode, but it was an auto car. I know it looks like a lot of timing in this one, but the guy beat on it regularly racing and never had a problem. I wouldn't run this much timing now with today's fuels.... Just forewarning for anyone who may try to copy something. Even the MAF curve was smooth up till the 11300 hz area where it peaked out.

[L1FTD]

It might be a high flow switch over or pressure dance like you're talking about. I just looked over the log of one I did with a cai only trying to get to the root of something in a near stock car and it stayed right at 50psi until 3400 where it switched over to 60psi causing the injector pulsewidth to suddenly drop. No afr lean spikes anywhere on the dyno readout unless y'all see something, but I didn't' have the widebands hooked up in the log to see more instant info. Most of what I'm seeing in the tune even shows the opposite. Drops in airflow or fuel requirement through the 2500 rpm range. I don't see anything special about it, but maybe y'all will see something that stands out? The pulls were in manual mode, but it was an auto car. I know it looks like a lot of timing in this one, but the guy beat on it regularly racing and never had a problem. I wouldn't run this much timing now with today's fuels.... Just forewarning for anyone who may try to copy something. Even the MAF curve was smooth up till the 11300 hz area where it peaked out.

Cant see the tune right now, but AFR looks good. A small torque loss around 2500, then spiking up. Pretty much how the engine torque shows in the scanner, but this is on a dyno? Could be a sign of something, but the AFR doesnt show it.

Those fuel flow modes were a nuisance for a while, was sure it had something to do with that. Full throttle, I would always switch from low to normal around 2600rpm.

Turns out, the flow mode switch doesnt affect the problem. Annoying coincidence? Or GM knew there was something going on at that RPM and made the switch happen there? Who knows?

Ive run the car up with pressure locked at 300kPa, 350, 400, 450, 500. No flow mode changes, static pressure. Was doing this to better dial-in the fuel pump trims.

Lean spots are there at every pressure. They get richer with lower pressure, but not gone.

I still think its FSCM, or a physical fuel issue.

If its FSCM, may only be certain P/N?s affected.

Even in the threads on other forums (different cars) discussing a similar lean issue, its not every car experiencing the pressure/pulse resonance. Bigger injectors certainly highlight the problem though.

If I could get an FSCM code to trip and disable the pressure test, could at least rule that out.

[sgod1100]

It might be a high flow switch over or pressure dance like you're talking about. I just looked over the log of one I did with a cai only trying to get to the root of something in a near stock car and it stayed right at 50psi until 3400 where it switched over to 60psi causing the injector pulsewidth to suddenly drop. No afr lean spikes anywhere on the dyno readout unless y'all see something, but I didn't' have the widebands hooked up in the log to see more instant info. Most of what I'm seeing in the tune even shows the opposite. Drops in airflow or fuel requirement through the 2500 rpm range. I don't see anything special about it, but maybe y'all will see something that stands out? The pulls were in manual mode, but it was an auto car. I know it looks like a lot of timing in this one, but the guy beat on it regularly racing and never had a problem. I wouldn't run this much timing now with today's fuels.... Just forewarning for anyone who may try to copy something. Even the MAF curve was smooth up till the 11300 hz area where it peaked out.

It's so crazy that in that log there isn't any evidence of the lean spot in there. Has me scratching my head for sure

[sgod1100]

Cant see the tune right now, but AFR looks good. A small torque loss around 2500, then spiking up. Pretty much how the engine torque shows in the scanner, but this is on a dyno? Could be a sign of something, but the AFR doesnt show it.

Those fuel flow modes were a nuisance for a while, was sure it had something to do with that. Full throttle, I would always switch from low to normal around 2600rpm.

Turns out, the flow mode switch doesnt affect the problem. Annoying coincidence? Or GM knew there was something going on at that RPM and made the switch happen there? Who knows?

Ive run the car up with pressure locked at 300kPa, 350, 400, 450, 500. No flow mode changes, static pressure. Was doing this to better dial-in the fuel pump trims.

Lean spots are there at every pressure. They get richer with lower pressure, but not gone.

I still think its FSCM, or a physical fuel issue.

If its FSCM, may only be certain P/N?s affected.

Even in the threads on other forums (different cars) discussing a similar lean issue, its not every car experiencing the pressure/pulse resonance. Bigger injectors certainly highlight the problem though.

If I could get an FSCM code to trip and disable the pressure test, could at least rule that out.

I haven't looked the dtc's but could there be some FSCM tests that we should possibly disable? Just throwing out random ideas at this point?

[L1FTD]

I haven't looked the dtc's but could there be some FSCM tests that we should possibly disable? Just throwing out random ideas at this point?

Good idea! But doesnt look possible, through HPT anyway.

Theres not that much we can modify in the FSCM. Thankful enough that HPT provide what they have, but theres no option for disabling any diagnostics. Cant add any user-defined to it either.

In the fuel system tab, theres another set of DTC for the FSCM.

In the pic I attached of the pressure test diagnostic, if any of the DTCs listed are active, the test shouldnt run. Like failing the MAF, needs to see the code, cant be no error.

Problem is getting one of those DTC to trip, and still keep the car running.

Fine if youre running aftermarket fuel system, but for us running fuel through the FSCM, could be an issue.

Might not be this test anyway. Just one more thing Im trying to rule out. Very long list so far.

[Cringer]

Cant see the tune right now, but AFR looks good. A small torque loss around 2500, then spiking up. Pretty much how the engine torque shows in the scanner, but this is on a dyno? Could be a sign of something, but the AFR doesnt show it.

Those fuel flow modes were a nuisance for a while, was sure it had something to do with that. Full throttle, I would always switch from low to normal around 2600rpm.

Turns out, the flow mode switch doesnt affect the problem. Annoying coincidence? Or GM knew there was something going on at that RPM and made the switch happen there? Who knows?

Ive run the car up with pressure locked at 300kPa, 350, 400, 450, 500. No flow mode changes, static pressure. Was doing this to better dial-in the fuel pump trims.

Lean spots are there at every pressure. They get richer with lower pressure, but not gone.

I still think its FSCM, or a physical fuel issue.

If its FSCM, may only be certain P/N?s affected.

Even in the threads on other forums (different cars) discussing a similar lean issue, its not every car experiencing the pressure/pulse resonance. Bigger injectors certainly highlight the problem though.

If I could get an FSCM code to trip and disable the pressure test, could at least rule that out.

Seems like a good way to test this would be to poke around on the fuel tab and tweak the Low/Med/High flow definitions and possibly the Fuel Pressure Transition Rate values.

Also, has anyone driven around with a physical fuel pressure gauge hooked up to see what is going on?

[sgod1100]

Seems like a good way to test this would be to poke around on the fuel tab and tweak the Low/Med/High flow definitions and possibly the Fuel Pressure Transition Rate values.

Also, has anyone driven around with a physical fuel pressure gauge hooked up to see what is going on?

I've never driven with a mechanical gauge hooked up, but when you increase the resolution in the scanner of the FP you will see it gets extremely chopping going through that 2600 and even the 1600 rpm areas. Now I'm not sure if that's a result of something else or the cause

choppy FP.JPG

[L1FTD]

Seems like a good way to test this would be to poke around on the fuel tab and tweak the Low/Med/High flow definitions and possibly the Fuel Pressure Transition Rate values.

Also, has anyone driven around with a physical fuel pressure gauge hooked up to see what is going on?

Unfortunately tried all that, many times over.

Can set the pressure to 300kPa, 500kPa, high flow full time, 100% pump DC full time, and anything in between.

Shows up the same every time.

Same as sgod, ive only looked at pressure as PID in scanner, and a math transform for pressure sensor volts.

I've never driven with a mechanical gauge hooked up, but when you increase the resolution in the scanner of the FP you will see it gets extremely chopping going through that 2600 and even the 1600 rpm areas. Now I'm not sure if that's a result of something else or the cause

choppy FP.JPG

Thats those nasty pulses im talking about!

At a minimum theyd be throwing off the injector delta pressure, albeit briefly.

If you sit around that RPM, >50kPa MAP, the leanness hangs around as long as youre there.

[sgod1100]

Unfortunately tried all that, many times over.

Can set the pressure to 300kPa, 500kPa, high flow full time, 100% pump DC full time, and anything in between.

Shows up the same every time.

Same as sgod, ive only looked at pressure as PID in scanner, and a math transform for pressure sensor volts.



Thats those nasty pulses im talking about!

At a minimum theyd be throwing off the injector delta pressure, albeit briefly.

If you sit around that RPM, >50kPa MAP, the leanness hangs around as long as youre there.

yyup, I remember you posting something about how your FP got jagged throughout those rpms...same exact thing for me as well

[GHuggins]

It's so crazy that in that log there isn't any evidence of the lean spot in there. Has me scratching my head for sure

I only had that one car where it was horrible after going back through the different ones I did. Think I might have sent you the log for it at one point? It was going super lean at those rpm spots and I'm pretty sure it was very lightly modified like the above posted ctsv. I've looked closer at some since this thread started and a lot did have the lean spots but only very slightly, which I fixed via fueling. In the above car it was actually rich in that rpm area as you can tell by the VE mods. Really makes me wonder if it's just air entering through the TB causing the fuel issues. The lsa blowers were sensitive to airflow. I honestly don't remember what brand cai that particular ctsv had on it in the above. It was several several years ago.

[sgod1100]

I only had that one car where it was horrible after going back through the different ones I did. Think I might have sent you the log for it at one point? It was going super lean at those rpm spots and I'm pretty sure it was very lightly modified like the above posted ctsv. I've looked closer at some since this thread started and a lot did have the lean spots but only very slightly, which I fixed via fueling. In the above car it was actually rich in that rpm area as you can tell by the VE mods. Really makes me wonder if it's just air entering through the TB causing the fuel issues. The lsa blowers were sensitive to airflow. I honestly don't remember what brand cai that particular ctsv had on it in the above. It was several several years ago.

Yeah, I believe you did send me that log a little while ago. Mine has does it consistently with the stock TB with an airaid, with a 90mm TB with an airaid, and with a NW103 TB with a DDP (my current setup). I also wondered if maybe it could have something to do with the bypass valve causing some goofy air pulses or something? I've been half tempted to dis-connect it and see if the lean spots are still there.

[L1FTD]

Yeah, I believe you did send me that log a little while ago. Mine has does it consistently with the stock TB with an airaid, with a 90mm TB with an airaid, and with a NW103 TB with a DDP (my current setup). I also wondered if maybe it could have something to do with the bypass valve causing some goofy air pulses or something? I've been half tempted to dis-connect it and see if the lean spots are still there.

I thought same as you.

Mine is now fully disconnected from the boost protection, and electrical.

Re-routed the vacuum side to run from the SC boost reference port. Still gets vacuum at light throttle, but slams shut a lot quicker for boost, and is forced closed when in boost.

Sadly, no change to lean spots

[sgod1100]

I thought same as you.

Mine is now fully disconnected from the boost protection, and electrical.

Re-routed the vacuum side to run from the SC boost reference port. Still gets vacuum at light throttle, but slams shut a lot quicker for boost, and is forced closed when in boost.

Sadly, no change to lean spots

Dang, have to take the wind out of my sails with that one huh....lol. Glad you did it though, saved me some time messing with it..lol

I always wondered about re-routing mine like that but is that bypass valve designed to be able to handle that positive pressure on the back side of it? I know in the stock config it doesn't see boost (At least I don't think it does, just going from my memory here)

[L1FTD]

Dang, have to take the wind out of my sails with that one huh....lol. Glad you did it though, saved me some time messing with it..lol

Sorry man haha. Theres not much I havent tried at this point.

I did try it fully closed, air through rotors all the time.

Same result, no change to lean spots, just dramatically increased IAT lol

[sgod1100]

Sorry man haha. Theres not much I havent tried at this point.

I did try it fully closed, air through rotors all the time.

Same result, no change to lean spots, just dramatically increased IAT lol

Back to the drawing board unfortunately

[L1FTD]

Dang, have to take the wind out of my sails with that one huh....lol. Glad you did it though, saved me some time messing with it..lol

I always wondered about re-routing mine like that but is that bypass valve designed to be able to handle that positive pressure on the back side of it? I know in the stock config it doesn't see boost (At least I don't think it does, just going from my memory here)

Not sure about the pressure on the other side. I guess the internal diaphragm is seeing -80kPa of vacuum regularly, sucking it out.

Once I hit boost, its only going to see +110kPa pressure pushing back the other way for a short period.

If it starts leaking, Ill be able to tell. The two chambers should always stay separate/sealed.

Im making a little more peak boost this way. The protection line of the bypass can leak a little I think, just looking at the design.

Stock form, boost pressure can push back on the diaphragm (through the P line) and open a touch. Also minor boost leak through the breather port on the protection assembly (foam covered).

Ideally there would be no leak, but theres potential for a small loss.

With no P line into the bypass, no boost can push on the diaphragm (opposite now with mine, boost pushing it closed). No boost pressure to protection assembly, no loss through breather.

Very smooth, definitely comes in earlier, more torque.

Might be too soon for some, i.e. daily driver or auto or likes to lug around low rpm higher load.

Anyway, ive gone off topic lol

[sgod1100]

Not sure about the pressure on the other side. I guess the internal diaphragm is seeing -80kPa of vacuum regularly, sucking it out.

Once I hit boost, its only going to see +110kPa pressure pushing back the other way for a short period.

If it starts leaking, Ill be able to tell. The two chambers should always stay separate/sealed.

Im making a little more peak boost this way. The protection line of the bypass can leak a little I think, just looking at the design.

Stock form, boost pressure can push back on the diaphragm (through the P line) and open a touch. Also minor boost leak through the breather port on the protection assembly (foam covered).

Ideally there would be no leak, but theres potential for a small loss.

With no P line into the bypass, no boost can push on the diaphragm (opposite now with mine, boost pushing it closed). No boost pressure to protection assembly, no loss through breather.

Very smooth, definitely comes in earlier, more torque.

Might be too soon for some, i.e. daily driver or auto or likes to lug around low rpm higher load.

Anyway, ive gone off topic lol

Nah, it's all good...may need to try that out that with mine then. Drivability pretty much the same then routing it that way or is the gas pedal much more "touchy"?

[L1FTD]

Nah, it's all good...may need to try that out that with mine then. Drivability pretty much the same then routing it that way or is the gas pedal much more "touchy"?

Yeah not much change to general drivability, just takes less pedal to get all the air going through the rotors. The vacuum drops a lot quicker at the SC port.

Still operates the same, idle and cruise fully open.

Boost climbs almost vertical when you stomp it, and nice to know youre getting all the boost.

I only did it to try and eliminate another cause for lean spots. Liked it so ended up keeping it.

[sgod1100]

Yeah not much change to general drivability, just takes less pedal to get all the air going through the rotors. The vacuum drops a lot quicker at the SC port.

Still operates the same, idle and cruise fully open.

Boost climbs almost vertical when you stomp it, and nice to know youre getting all the boost.

I only did it to try and eliminate another cause for lean spots. Liked it so ended up keeping it.

cool..did you remove the boost solenoid assembly and have to get rid of a dtc in the tune from unplugging it?

[L1FTD]

cool..did you remove the boost solenoid assembly and have to get rid of a dtc in the tune from unplugging it?

Yeah I removed the whole solenoid assembly, left the electrical tied out of the way.

Needed better access around that area to run some hose, and thought it?s better sitting in a box than gathering dust in the engine bay. Can always go back. I used some bigger silicone hose too, took the tiny factory ones off.

Youre running the MAF, so youll need to disable the DTC for the bypass, code 0033 I think. If the MAF is failed, the bypass code wont set regardless.