420A 2GNT Can I run a AFPR and a FMU?

[DumbtruckDSM]

I have a turbo Eclipse (420a) and it doesn’t run great. The AFR is reading lean and someone told me it’s cuz I don’t have an FMU but I have a AFPR (and a 255 Walbro fuel pump). Can I just put on the FMU with the AFPR or do I have to go back to a stock FPR?

 

[Mello]

This would depend on how your fuel system is set up. Usually the FMU is used when your fuel injectors are not properly sized (too small) for your fuel needs. FMU will increase fuel pressure non-linearly (6:1, 8:1) to force more fuel through the injectors. An FPR tries to hold the fuel pressure constant (1:1) to a set differential across the injector's input & output so the ECU can determine the proper amount of fuel to achieve the target AFR. FMU's are band-aides for improper fuel systems setups (mainly injector sizing). Too small fuel lines can cause restrictions and can be a problem in the fuel system setup too.

You have no car profile so specific recommendations are only guesses & a shot in the dark.

 

[99dsmer4g63]

I seen your other thread. If your car is running lean at idle and at light throttle(no boost) the turbo has nothing to do with it. You have a vacuum leak or a fuel problem.

I believe what you are trying to do is use an fmu for a stock ecu 420a. Most people are going to tell how trash your setup is and buy mega squirt or just a 4g63 car so don’t be surprised or butt hurt when that happens .

You should fill out a profile because 420a’s fuel rails and fpr locations are different based off the year of the car.

We put a turbo on my dads 420a using a fmu as a budget fun build for us together. I forget if we used a 10 or 12 fmu ratio but at 8 psi the car runs flawlessly with it installed. Just a 255 walbro. Stock injectors and fpr. Wot his wideband says the car is happy. Are the injector duties high? I’m going to guess absolutely as I have no way to monitor it with a stock ecu.

The car runs and drives like factory at idle and cruise. It also performs well at wot and the wideband readings agree.

-Daniel

 

[DumbtruckDSM]

This would depend on how your fuel system is set up. Usually the FMU is used when your fuel injectors are not properly sized (too small) for your fuel needs. FMU will increase fuel pressure non-linearly (6:1, 8:1) to force more fuel through the injectors. An FPR tries to hold the fuel pressure constant (1:1) to a set differential across the injector's input & output so the ECU can determine the proper amount of fuel to achieve the target AFR. FMU's are band-aides for improper fuel systems setups (mainly injector sizing). Too small fuel lines can cause restrictions and can be a problem in the fuel system setup too.

You have no car profile so specific recommendations are only guesses & a shot in the dark.

What

I seen your other thread. If your car is running lean at idle and at light throttle(no boost) the turbo has nothing to do with it. You have a vacuum leak or a fuel problem.

I believe what you are trying to do is use an fmu for a stock ecu 420a. Most people are going to tell how trash your setup is and buy mega squirt or just a 4g63 car so don’t be surprised or butt hurt when that happens .

You should fill out a profile because 420a’s fuel rails and fpr locations are different based off the year of the car.

We put a turbo on my dads 420a using a fmu as a budget fun build for us together. I forget if we used a 10 or 12 fmu ratio but at 8 psi the car runs flawlessly with it installed. Just a 255 walbro. Stock injectors and fpr. Wot his wideband says the car is happy. Are the injector duties high? I’m going to guess absolutely as I have no way to monitor it with a stock ecu.

The car runs and drives like factory at idle and cruise. It also performs well at wot and the wideband readings agree.

-Daniel

yes I know what you mean by people coming at me I just wanted something fun and different, not really ideal but I already had a 420a and 4g63 cars where I live are definitely not cheap. Thank you, I’ll go by your dads setup

 

[Mello]

What

Sorry but what you're asking is fairly far up the ladder from a "tuner" perspective. Your trying to throw parts at your car without knowing how all these different individual pieces are engineered to working together.

 

[BLACK'98DSM]

Are the injector duties high? I’m going to guess absolutely as I have no way to monitor it with a stock ecu.

You actually can monitor this on the stock ecu if you have a fancy enough scanner to view charts & live data. In the past I used an Autel touchscreen unit to view mine. Now I definitely would not say it's as "live" as your view through Tuner Studio due to longer refresh periods, but can give you a general idea.

 

[DumbtruckDSM]

Sorry but what you're asking is fairly far up the ladder from a "tuner" perspective. Your trying to throw parts at your car without knowing how all these different individual pieces are engineered to working together.

Sorry I didn’t mean to type “what” idk why it says I said “what” but yes I understand what you’re saying and it’s very helpful thank you, I have no tune at the moment because I heard wiring the megasquirt was difficult and I need a car now to go to school and stuff so I’ll go with the fmu since it seems like the better option.

 

[chrisman287]

You run either a FPR with larger injectors or a FMU with stock injectors. You can look into an adjustable FMU also.

But a 12:1 FMU should be fine. You already have the 255 pump so you’re good there.

You need a FCD (Fuel Cut Defender). It’s basically a MAP clamp to keep the MAP sensor from seeing the full 5V. HKS and Turbosmart still sell them I believe.

 

[99dsmer4g63]

You need a FCD (Fuel Cut Defender). It’s basically a MAP clamp to keep the MAP sensor from seeing the full 5V. HKS and Turbosmart still sell them I believe.

There is no need for a FCD on this setup.

-Daniel

 

[DumbtruckDSM]

You run either a FPR with larger injectors or a FMU with stock injectors. You can look into an adjustable FMU also.

But a 12:1 FMU should be fine. You already have the 255 pump so you’re good there.

You need a FCD (Fuel Cut Defender). It’s basically a MAP clamp to keep the MAP sensor from seeing the full 5V. HKS and Turbosmart still sell them I believe.

Oohhh okay I see, thank you this helps a lot

 

[Canadian_CD9A]

There is no need for a FCD on this setup.

-Daniel

On a 420A, that's absolutely false. The ECU goes ballistic when if it gets a signal that positive boost has been reached, a MAP clamp is a necessity. I didn't want to get involved with this because this adventure is almost guaranteed to end in disaster, but I'll explain it in simple terms.

-The stock ECU is calibrated to work with stock injectors at stock fuel pressure. When below 90% (or so) of throttle, the ECU operates off of the stock o2 sensor, which is essentially a dumb device that tells you if you're leaner or richer than 14.7:1 AFR. This is called "closed loop". It can't tell you what your AFR is specifically. So, while the ECU is in "closed loop" at full temperature, it always shoots for 14.7:1 AFR by asking "are we leaner than 14.7:1? If so, add fuel!" and the inverse.

-When you are above 90% throttle, the ECU stops reading off of the o2 sensor and goes into "open loop" - a pre-programmed fuel map that shoots for richer AFRs to keep the engine safe.

-14.7:1 AFR with boost is incredibly dangerous for your engine. If you see boost at 14.7:1 AFR, there's a very good chance you're going to run into preignition, which can/will destroy your engine. This is why FMUs are so dangerous - they are only effective when the ECU isn't in closed loop. If you want to be boosting, you HAVE TO be at WOT, which is a stupid way to be driving.

-If you do not have stock fuel pressure or stock injectors, the ECU is very limited in its ability to hit target AFRs. It has short and long term fuel trims (25% either way) to help the ECU achieve 14.7:1 more frequently, but that's it. Adding more static fuel pressure on stock injectors does nothing but remove the ECU's ability to do its job in normal driving, it doesn't make the 'tune' any safer.

-A lot of FMUs are double adjustable: you can set the base fuel pressure at static atmosphere (43 psi), and then set the rate of fuel pressure gain for every pound of boost that the turbo produces. Tuning that ratio (from 4 psi fuel pressure per pound of boost, to 12 psi fuel pressure per pound of boost typically) is the only 'tuning' ability you have with it. This will not produce a consistent AFR across the entire RPM band, it can't.

-Fuel injectors are glorified on/off switches. They flow more by switching 'on' more - the rate at which they're open is called 'duty cycle'. Only the ECU can control when the injector is open & closed. When the injector is open 100% of the time, it cannot flow anymore without changing fuel pressure. Bigger fuel injectors are going to run like trash on the stock ECU, because it cannot compensate enough in normal conditions, and it will run poorly & rich. You can pull fuel pressure, but then you're right back at square one: you can't just throw bigger injectors on a stock ECU car to make it run properly in boost. Period.

-FMUs get around the fuel injector conundrum by shoving the fuel through at higher pressure, resulting in higher fuel flow through the injectors. The ECU doesn't know you're doing this, but this has limits. Fuel injectors do not like having 100 psi of fuel shoved through them, and fuel pumps don't like working against 100 psi of pressure. Flow drops off, and parts fail. Even a stock injector won't be able to keep up with a sizeable amount of boost at 100 psi, so you will need to go with bigger injectors.

-When you go with bigger injectors, your ECU loses its ability to hit its targets. This is when the adjustment of base fuel pressure is required. A set of 30# injectors on a 420A will likely need a base fuel pressure below 25 psi to let the ECU hit its targets. Fuel doesn't atomize well at those low pressures, and it won't run great.

-So basically when you add an FMU, you're removing the ECU's control over the WOT function, it is hijacked by the added fuel pressure.

-When you change the base fuel pressure or add bigger fuel injectors, you're removing the ECU's control when it's not in the WOT function.

-Turbo setups typically need reduced ignition timing to stay safe. Without a standalone ignition timing controller like a MSD BTM, you cannot pull ignition timing back from the stock ECU, and that's dangerous.

I bought my turbo Neon in 2008 with a 2.4L swap and a Hahn Racecraft 16G kit. It had an Aeromotive fuel pressure regulator, a separate FMU, and Accel 36# injectors. It operated at 22 psi of fuel pressure at idle, and around 82 psi of fuel pressure at 8 psi of boost (7.5:1 gain ratio on the FMU). I can't tell you how much trial/error & tuning that the builder required (I assume it was a lot), but the setup still wasn't ideal. In 2023, an FMU with different fuel injectors is an absolute hack way of turbocharging a car. It's not cheaper, it's not better. It's inexcusable.

If you want to do this PROPERLY, there's only one choice: a standalone ECU and appropriately sized fuel injectors. That's it.

 

[99dsmer4g63]

On a 420A, that's absolutely false. The ECU goes ballistic when if it gets a signal that positive boost has been reached, a MAP clamp is a necessity. I didn't want to get involved with this because this adventure is almost guaranteed to end in disaster, but I'll explain it in simple terms.

-The stock ECU is calibrated to work with stock injectors at stock fuel pressure. When below 90% (or so) of throttle, the ECU operates off of the stock o2 sensor, which is essentially a dumb device that tells you if you're leaner or richer than 14.7:1 AFR. This is called "closed loop". It can't tell you what your AFR is specifically. So, while the ECU is in "closed loop" at full temperature, it always shoots for 14.7:1 AFR by asking "are we leaner than 14.7:1? If so, add fuel!" and the inverse.

-When you are above 90% throttle, the ECU stops reading off of the o2 sensor and goes into "open loop" - a pre-programmed fuel map that shoots for richer AFRs to keep the engine safe.

-14.7:1 AFR with boost is incredibly dangerous for your engine. If you see boost at 14.7:1 AFR, there's a very good chance you're going to run into preignition, which can/will destroy your engine. This is why FMUs are so dangerous - they are only effective when the ECU isn't in closed loop. If you want to be boosting, you HAVE TO be at WOT, which is a stupid way to be driving.

-If you do not have stock fuel pressure or stock injectors, the ECU is very limited in its ability to hit target AFRs. It has short and long term fuel trims (25% either way) to help the ECU achieve 14.7:1 more frequently, but that's it. Adding more static fuel pressure on stock injectors does nothing but remove the ECU's ability to do its job in normal driving, it doesn't make the 'tune' any safer.

-A lot of FMUs are double adjustable: you can set the base fuel pressure at static atmosphere (43 psi), and then set the rate of fuel pressure gain for every pound of boost that the turbo produces. Tuning that ratio (from 4 psi fuel pressure per pound of boost, to 12 psi fuel pressure per pound of boost typically) is the only 'tuning' ability you have with it. This will not produce a consistent AFR across the entire RPM band, it can't.

-Fuel injectors are glorified on/off switches. They flow more by switching 'on' more - the rate at which they're open is called 'duty cycle'. Only the ECU can control when the injector is open & closed. When the injector is open 100% of the time, it cannot flow anymore without changing fuel pressure. Bigger fuel injectors are going to run like trash on the stock ECU, because it cannot compensate enough in normal conditions, and it will run poorly & rich. You can pull fuel pressure, but then you're right back at square one: you can't just throw bigger injectors on a stock ECU car to make it run properly in boost. Period.

-FMUs get around the fuel injector conundrum by shoving the fuel through at higher pressure, resulting in higher fuel flow through the injectors. The ECU doesn't know you're doing this, but this has limits. Fuel injectors do not like having 100 psi of fuel shoved through them, and fuel pumps don't like working against 100 psi of pressure. Flow drops off, and parts fail. Even a stock injector won't be able to keep up with a sizeable amount of boost at 100 psi, so you will need to go with bigger injectors.

-When you go with bigger injectors, your ECU loses its ability to hit its targets. This is when the adjustment of base fuel pressure is required. A set of 30# injectors on a 420A will likely need a base fuel pressure below 25 psi to let the ECU hit its targets. Fuel doesn't atomize well at those low pressures, and it won't run great.

-So basically when you add an FMU, you're removing the ECU's control over the WOT function, it is hijacked by the added fuel pressure.

-When you change the base fuel pressure or add bigger fuel injectors, you're removing the ECU's control when it's not in the WOT function.

-Turbo setups typically need reduced ignition timing to stay safe. Without a standalone ignition timing controller like a MSD BTM, you cannot pull ignition timing back from the stock ECU, and that's dangerous.

I bought my turbo Neon in 2008 with a 2.4L swap and a Hahn Racecraft 16G kit. It had an Aeromotive fuel pressure regulator, a separate FMU, and Accel 36# injectors. It operated at 22 psi of fuel pressure at idle, and around 82 psi of fuel pressure at 8 psi of boost (7.5:1 gain ratio on the FMU). I can't tell you how much trial/error & tuning that the builder required (I assume it was a lot), but the setup still wasn't ideal. In 2023, an FMU with different fuel injectors is an absolute hack way of turbocharging a car. It's not cheaper, it's not better. It's inexcusable.

If you want to do this PROPERLY, there's only one choice: a standalone ECU and appropriately sized fuel injectors. That's it.

I still stand by what I said. I never said this is ideal. I already explained to the OP everyone will tell him how trash his setup is. Thanks for proving my point on that.

Funny thing is I have no FCD on a 99 gs with a small turbo running 8 psi. A 255 walbro and an fmu. Never once has it had a problem under full boost.

Once again I stand by what I said a FCD is not needed on his setup unless I just have a unicorn of a gs. Not sure if your neon is different because I’ve never had one or have any experience with one.

For clarity this a 99 gs m/t. 255 walbro, stock injectors, fpr and an fmu. Still running a stock ecu. Only other thing I did was tapped a dedicated boost source to the fmu.

Have you personally done this on a 2g 420a? Or the neon needed a FCD so you assume a 2g needs one too?

-Daniel

 

[DumbtruckDSM]

On a 420A, that's absolutely false. The ECU goes ballistic when if it gets a signal that positive boost has been reached, a MAP clamp is a necessity. I didn't want to get involved with this because this adventure is almost guaranteed to end in disaster, but I'll explain it in simple terms.

-The stock ECU is calibrated to work with stock injectors at stock fuel pressure. When below 90% (or so) of throttle, the ECU operates off of the stock o2 sensor, which is essentially a dumb device that tells you if you're leaner or richer than 14.7:1 AFR. This is called "closed loop". It can't tell you what your AFR is specifically. So, while the ECU is in "closed loop" at full temperature, it always shoots for 14.7:1 AFR by asking "are we leaner than 14.7:1? If so, add fuel!" and the inverse.

-When you are above 90% throttle, the ECU stops reading off of the o2 sensor and goes into "open loop" - a pre-programmed fuel map that shoots for richer AFRs to keep the engine safe.

-14.7:1 AFR with boost is incredibly dangerous for your engine. If you see boost at 14.7:1 AFR, there's a very good chance you're going to run into preignition, which can/will destroy your engine. This is why FMUs are so dangerous - they are only effective when the ECU isn't in closed loop. If you want to be boosting, you HAVE TO be at WOT, which is a stupid way to be driving.

-If you do not have stock fuel pressure or stock injectors, the ECU is very limited in its ability to hit target AFRs. It has short and long term fuel trims (25% either way) to help the ECU achieve 14.7:1 more frequently, but that's it. Adding more static fuel pressure on stock injectors does nothing but remove the ECU's ability to do its job in normal driving, it doesn't make the 'tune' any safer.

-A lot of FMUs are double adjustable: you can set the base fuel pressure at static atmosphere (43 psi), and then set the rate of fuel pressure gain for every pound of boost that the turbo produces. Tuning that ratio (from 4 psi fuel pressure per pound of boost, to 12 psi fuel pressure per pound of boost typically) is the only 'tuning' ability you have with it. This will not produce a consistent AFR across the entire RPM band, it can't.

-Fuel injectors are glorified on/off switches. They flow more by switching 'on' more - the rate at which they're open is called 'duty cycle'. Only the ECU can control when the injector is open & closed. When the injector is open 100% of the time, it cannot flow anymore without changing fuel pressure. Bigger fuel injectors are going to run like trash on the stock ECU, because it cannot compensate enough in normal conditions, and it will run poorly & rich. You can pull fuel pressure, but then you're right back at square one: you can't just throw bigger injectors on a stock ECU car to make it run properly in boost. Period.

-FMUs get around the fuel injector conundrum by shoving the fuel through at higher pressure, resulting in higher fuel flow through the injectors. The ECU doesn't know you're doing this, but this has limits. Fuel injectors do not like having 100 psi of fuel shoved through them, and fuel pumps don't like working against 100 psi of pressure. Flow drops off, and parts fail. Even a stock injector won't be able to keep up with a sizeable amount of boost at 100 psi, so you will need to go with bigger injectors.

-When you go with bigger injectors, your ECU loses its ability to hit its targets. This is when the adjustment of base fuel pressure is required. A set of 30# injectors on a 420A will likely need a base fuel pressure below 25 psi to let the ECU hit its targets. Fuel doesn't atomize well at those low pressures, and it won't run great.

-So basically when you add an FMU, you're removing the ECU's control over the WOT function, it is hijacked by the added fuel pressure.

-When you change the base fuel pressure or add bigger fuel injectors, you're removing the ECU's control when it's not in the WOT function.

-Turbo setups typically need reduced ignition timing to stay safe. Without a standalone ignition timing controller like a MSD BTM, you cannot pull ignition timing back from the stock ECU, and that's dangerous.

I bought my turbo Neon in 2008 with a 2.4L swap and a Hahn Racecraft 16G kit. It had an Aeromotive fuel pressure regulator, a separate FMU, and Accel 36# injectors. It operated at 22 psi of fuel pressure at idle, and around 82 psi of fuel pressure at 8 psi of boost (7.5:1 gain ratio on the FMU). I can't tell you how much trial/error & tuning that the builder required (I assume it was a lot), but the setup still wasn't ideal. In 2023, an FMU with different fuel injectors is an absolute hack way of turbocharging a car. It's not cheaper, it's not better. It's inexcusable.

If you want to do this PROPERLY, there's only one choice: a standalone ECU and appropriately sized fuel injectors. That's it.

Thank you, I realize and know that the setup is not ideal but it’s what I see on YouTube and forums that the fmu is used more and seems to work fine. I will try the setup because I need my car running asap but later on hopefully I’ll buy and wire the megasquirt (or at least attempt)

 

[Canadian_CD9A]

I still stand by what I said. I never said this is ideal. I already explained to the OP everyone will tell him how trash his setup is. Thanks for proving my point on that.

Funny thing is I have no FCD on a 99 gs with a small turbo running 8 psi. A 255 walbro and an fmu. Never once has it had a problem under full boost.

Once again I stand by what I said a FCD is not needed on his setup unless I just have a unicorn of a gs. Not sure if your neon is different because I’ve never had one or have any experience with one.

For clarity this a 99 gs m/t. 255 walbro, stock injectors, fpr and an fmu. Still running a stock ecu. Only other thing I did was tapped a dedicated boost source to the fmu.

Have you personally done this on a 2g 420a? Or the neon needed a FCD so you assume a 2g needs one too?

-Daniel

My Neon needed the MAP clamp yes, I’ve never seen an exception to this in all my years in the community. Seems like it was a regular thing for the DSM based on posts here, too.

 

[99dsmer4g63]

My Neon needed the MAP clamp yes, I’ve never seen an exception to this in all my years in the community. Seems like it was a regular thing for the DSM based on posts here, too.

The car I speak of has been running like this for about 5-6 years. Technically it’s my dads car but it might as well be mine. (It was a replacement after my rs was stolen after it left him sitting on the interstate) The RS was in both of our names because I was 16 when we bought it and in Pa you can’t register it solely in your name until your 18. He bought me a gsx so he pretty much took the gs .

Anywhos as I stated I’ve never had issues after transitioning for vacuum to boost or full boost at wot. If the car did anything funny while my dad was driving it I would surely know as we talk almost everyday about cars or dirt bikes.

Driving around normally you wouldn’t even know anything was done. Idles rock solid and cruising is as normal when it was n/a. Just a 255 walbro and fmu ( pretty sure it’s 10 or 12 ratio.) Installed a wide band too. But no FCD for sure I promise.

-Daniel