Voltage booster -> Walbro 255 -> too lean

[goldNSX]

I've a CTSC since one year. Till now I've used the OEM pump + voltage booster. Today we've installed a Walbro 255 to get wrid of the voltage booster. The voltage booster was by-passed, also the fuel-pump-resistor.

Before I had AFR = 11 or lower as soon as boost was building up, regardless of rpm and time of load.
Now with the Walbro 255, at lower rpms AFR is around 12 at higher revs around 13 and from 2k rpm to 6k rpm it goes up to freaking 13-13.5. It visually leans out.

There seems to be a bottle-neck but I don't know where. The Walbro 255 is said to deliver enough fuel for a low-boost CTSC but also consumes around doulbe the current of the OEM fuel-pump.

Any hints highly appreciated.

Thanks!

 

[Elite]

Something is wrong with the wiring. I'm stepping out of the house, but can try to remember what you need to do regarding the voltage step up, resistor etc if needed. The Walbro should supply more than enough fuel.

 

[goldNSX]

I just came back from a nightly test-drive and plugged the voltage-doubler back in et voila: pig-rich 10.5-11 AFR again. I guess my car is a candidate for the SoS power supply upgrade, right? I'm pretty sure it's the power supply. A Walbro 255 is capable to deliver the fuel as you've mentioned but it won't if the power supply is the weak point.

 

[DDozier]

I just came back from a nightly test-drive and plugged the voltage-doubler back in et voila: pig-rich 10.5-11 AFR again. I guess my car is a candidate for the SoS power supply upgrade, right? I'm pretty sure it's the power supply. A Walbro 255 is capable to deliver the fuel as you've mentioned but it won't if the power supply is the weak point.

What other mods to the fuel system and engine management have you made?

 

[comtec]

What injectors are you running?

Mike

 

[goldNSX]

What other mods to the fuel system and engine management have you made?

Just the stuff you do with a low-boost CTSC, no mods:
- stock injectors
- CT fuel pressure unit
- and so on
We've just installed the Walbro 255 today and disconnected the voltage-booster with the effect of running much too lean.

 

[comtec]

Nature of the comptech kit, think it will have to be boosted. This sort of thing is exactly why i am going a different route with my low boost install. With the comptech kit you boost the pump so you can boost the fuel volume so you can overdrive the injectors. Not for me.

Mike

 

[goldNSX]

For those who are not interested in my test results, here they are:

Walbro 255 in the fuel tank, resistor bypassed

voltage at the fuse box: 14.3 V
voltage at the voltage doubler incoming: 13.86 V
voltage at the voltage doubler to the pump: 13.68 V
now:
voltage at the pump with the voltage doubler inactivated (like OEM): 10.90 V

all measured at idle and 46 psi fuel pressure.

I don't want to know the voltage under load.

This is just is neglegiable warning to those who believe that the Walbro is a simple drop-in and needs no further adjustment (for current).

 

[RYU]

Gold - I'm running the Walbro 255 with the Voltage booster in place per SOS's recommendation. This made my system run pig rich as confirmed by DDozier at around the high 10s mid 11s. It took me more than a few attempts at adjusting the RRFPR 1/4 turn at a time to get to a more reasonable 11.7-12.4 AFR. My standing fuel pressure at idle is about 57lbs. It wasn't difficult.. just a pain in the butt because as you heatsoak the ECU will also run it rich after a few pulls. Kept on chasing my tail but ultimately I got it where I feel it's about as good as it's going to get.

I had wanted to experiment removing the Boost-a-pump and fooling around with the RRFPR again but I don't think the RRFPR has the proper spring in there to provide a linear curve (just a hunch on my part). I feel like it'll either be too rich on the low rpms and too lean on the upper RPMs or vice versa.

If I was simply street driving my NSX i'd be happy with where I have it now but with the planned meth and perhaps even full motor NA/ITB build I might just go straight to the EMS S2.

My recommendation is to keep the voltage booster in place and tweak the RRFPR.

 

[goldNSX]

RYU, thanks for sharing your experience. I know of people who deleted the voltage-booster and installed a Walbro 255. The Walbro 255 should be able to supply the fuel for a CTSC IF the voltage is strong. I guess that's the critical point. The voltage booster simply does the same thing the voltage supply kit of SOS does, it shortens the cables and offers less voltage drop for higher current fuel pumps. I've ordered a kit and will see if the stable voltage is bringing the Walbro 255 back to specs, so I can delete the voltage booster. Next week I'll know I hope.

For now I also have the voltage booster in series for the Walbro 255 and I', also running pig-rich (AFR 10.5-11) as I think that the voltage booster does too much for a Walbro 255. It already offers a stable 13.x voltage for the pump. A Walbro should not need more voltage for a low-boost CTSC I believe. I'll see.

Thanks.

 

[RYU]

Agreed. You should look into your voltage issues first. That seems like a big drop.

Fyi my voltage with the booster never falls below 13.9v at full boost. It's at 14.1v at cruising speeds. This is measured at the battery. I had to switch over to a Odyssey lightweight (645 model?) Which have a bigger cca reserve to support the increased current demands of the booster and Walbro, but did not have to upgrade any wiring. I did make sure the gauge wires I used are adequate, contact points are clean, relays are new, and proper soldered connections were used.

You have to keep in mind that those oem injectors operate at 100+psi at full boost to provide enough fuel. I believe the walbro are rated to flow 255 ltr/hr at 40 psi @ 13.5V?

I haven't done the math but I'm not sure it can supply the flow rate even at 14v w/o the booster. I would love for you to confirm the booster isn't required and simply the rrfpr only needs the adjustment. That would be great. My hunch tells me no, which is why I have not tried it myself. Again, would love to be proven wrong here.

 

[DDozier]

You have to keep in mind that those oem injectors operate at 100+psi at full boost to provide enough fuel. I believe the walbro are rated to flow 255 ltr/hr at 40 psi @ 13.5V?

I haven't done the math but I'm not sure it can supply the flow rate even at 14v w/o the booster. I would love for you to confirm the booster isn't required and simply the rrfpr only needs the adjustment. That would be great. My hunch tells me no, which is why I have not tried it myself. Again, would love to be proven wrong here.

This is the issue guys, the OEM injector needs the increased fuel pressure that the increased voltage to the pump provides. While the Walbro will provide a higher flow of fuel that a higher horse power application will need the stock injectors will not flow enough fuel at the lower fuel pressure. So it is not about volume it is about pressure with the OEM injectors. The BAP (voltage doubler) forces the pump to drive harder and produce more flow, the fuel pressure regulator is overwhelmed by the increased flow and the fuel pressure goes higher, and that is what allows the small OEM injectors to flow enough fuel.

So you have two choices, keep the BAP in place and adjust for the average fuel condition, or make larger changes to the fuel system to make things more adjustable.

One option that is more simple than the other is to use a programmable BAP. MSD makes a unit PN 2351, it is a pressure based voltage doubler. Unlike the Comptech unit this unit allow you to pick the amount of voltage increased based on the amount of boost. It uses simple software and a built in boost sensor to program the amount of voltage feed to the pump. You can pick when and how fast to ramp up the voltage to get the pressure you need. I consider the Comptech fuel system to be a bandaid for you fuel system with this one upgrade you get some tuning ability with the supply of fuel, but it is still just a better bandaid.

http://www.msdignition.com/WorkArea/DownloadAsset.aspx?id=15032386121

There are many other options that have been beat to death in many threads about the CTSC and all of them revolve around replacing the fuel injectors to larger units and getting control of the injector pulse width with some sort of engine management device.

And Gold remember that the CTSC fuel system is just that it deals with fuel alone and will not solve any issues related to ignition. I have read in other post that you are trying to reduce underhood and IAT's. This is in most aplications a very good idea but with the CTSC in its stock form may not be the best plan. The CTSC needs the higher IAT's to control timing from the OEM ECU. Cool those IAT's back down to NA levels and you are back at NA timing levels, not a good thing on a high compression boosted motor.

Dave

 

[goldNSX]

I've read the voltages just before the fuel pump, at the cable which been cut for a voltage booster. 10.9 Volt means that there's about an excessive drop of 3 V in the OEM wires with a Walbro 255 at 46 psi at idle. I don't have voltage with the OEM fuel pump installed. The Walbro draws 7 ampere at this pressure and goes up to 11 ampere at 90 psi. I would expect even lower values than 10 Volt. No wonder there's no fuel.

The FPR raises the fuel pressure due to it's vacuum hose. The fuel pump must deliver more fuel to meet the higher psi. The voltage booster overdrives the fuel pump therefore. There's no voltage booster needed if the fuel pump delivers enough fuel. So I have to make sure the voltage at the pump isn't reduced to below 10 volts under boost. This is the first thing I have to solve.

DDozier: yes, I already have an engine cabin cooling device but it just brings the temps down from 200 F to cool the cabin, not the IAT. This is to cool the belt (slipping) and electric components in the engine bay. The charger still gets hot and the IAT too.

 

[DDozier]

I've read the voltages just before the fuel pump, at the cable which been cut for a voltage booster. 10.9 Volt means that there's about an excessive drop of 3 V in the OEM wires with a Walbro 255 at 46 psi at idle. I don't have voltage with the OEM fuel pump installed. The Walbro draws 7 ampere at this pressure and goes up to 11 ampere at 90 psi. I would expect even lower values than 10 Volt. No wonder there's no fuel.

When you read the voltage you need to read and record them while you drive as the OEM fuel pump resistor (if installed) will drop the voltage when the car is not under load to reduce pump noise, you can bypass the fuel pump resistor then measure the voltage to know what the real pump voltage will be under load. The fuel pump wires are not that long and even with the higher current draw of the Walbro you should not have that much voltage drop, if the wires were that undersized you would likely have very hot wires when the pump goes under load. In the end running larger lines for any fuel pump is not a bad idea but there are a lot of Walbro fuel pumps running on OEM wires. I have had three in three different cars with no issues in supply.

The fuel pressure regulator is controlled by vacuum to increase the pressure but the volume of fluid is what dictates the pressure in the end. If you do not have the supply you do not get the pressure. Keep in mind all fuel pumps even the Walbro have a decrease in volume as the pressure increases making it harder to maintain the higher pressure without the help of the BAP.

Dave

 

[goldNSX]

When you read the voltage you need to read and record them while you drive as the OEM fuel pump resistor (if installed) will drop the voltage when the car is not under load to reduce pump noise, you can bypass the fuel pump resistor then measure the voltage to know what the real pump voltage will be under load. The fuel pump wires are not that long and even with the higher current draw of the Walbro you should not have that much voltage drop, if the wires were that undersized you would likely have very hot wires when the pump goes under load. In the end running larger lines for any fuel pump is not a bad idea but there are a lot of Walbro fuel pumps running on OEM wires. I have had three in three different cars with no issues in supply.

My reading above are with a bypassed resistor already. I don't have a voltage drop due to the resistor. It would be interesting to compare to voltages to similar car. My friend will do a test too.

 

[RYU]

Keep us posted with your results. This might sound like a dumb question but the BAP is wired properly, yes?

FWIW, i'm running fine on the OEM wires but I really do not like overdriving the Walbro 255 in general.

 

[goldNSX]

...but I really do not like overdriving the Walbro 255 in general.

My reason to install a Walbro 255 was to throw the voltage booster out of the car. The wiring is correct, of course.

The fuel pressure regulator is controlled by vacuum to increase the pressure but the volume of fluid is what dictates the pressure in the end. If you do not have the supply you do not get the pressure. Keep in mind all fuel pumps even the Walbro have a decrease in volume as the pressure increases making it harder to maintain the higher pressure without the help of the BAP.

Dave

Yes, I'm fully aware of the physical relations. At higher pressure the fuel pump also looses it's capability of delivery high amounts of fuel. But I still strongly think that the voltage drops even more than to 10.9 Volt when the pump is drawing more current at high psi.

The SOS kit is on it's way. I'll have know next week how it improves.

 

[DDozier]

My reason to install a Walbro 255 was to throw the voltage booster out of the car. The wiring is correct, of course.


Yes, I'm fully aware of the physical relations. At higher pressure the fuel pump also looses it's capability of delivery high amounts of fuel. But I still strongly think that the voltage drops even more than to 10.9 Volt when the pump is drawing more current at high psi.

The SOS kit is on it's way. I'll have know next week how it improves.

I hope everything works out, if you want to do some more testing to know what is going on you can try one of the Mityvac test tools to pressurize the FPR and measure your pump voltage as the pressure is increased. You can also patch in the larger piece of wire that was feeding 12v to the old BAP directly to the pump and see if you have the same voltage drop. Since you have the SOS kit on the way all this extra testing may not be worth the time but it would be nice to know and share the results for others with a similar issue.

http://www.mityvac.com/info_sheets/MV8255PIS.pdf

Dave

 

[goldNSX]

I've more and pleasant data. As the CT voltage booster is still mounted in the car and and attached to the fuel pump I've disconnected the boost switch to avoid that the voltage booster gets active/boosts the voltage. After deactivating the boost switch I still have 13.68 volts at the fuel pump due to the CT wiring from the fuse box in the engine bay (as expected).

Result:
In boost I've read AFR <11 up to the rpm limit, even in longer sequences. This prooved my suspicion that the wiring from the fuse box in the engine bay offers enough current for a Walbro 255 and the pump itself is capable to supply enough fuel for a low-boost CTSC BUT ONLY WITH A THICK WIRE FROM THE FUSE BOX IN THE ENGINE BAY. The OEM wiring is not capable to power a Walbro 255. You may not feel it in a non-boosted car but it's still not optimal.

So I'll definitly uninstall the CT voltage booster from the car to reduce complexity and install the SOS wiring kit. I'll have a dyno run on this (about 60 seconds WOT) to make sure I'm on the safe side.

I'm still running a little bit on the rich side with AFR 10.5-11.0. FP at idle is around 56 psi with the Walbro 255 at 13.68 volt. Is it advisable to adjust the CT FPR?

Thanks to all who helped!

 

[RYU]

Good findings gold. Replacing the factory wires leading to the Walbro makes complete sense and I never thought that would be the problem. I suppose if i had tried it I would have found out eventually too like you did.. but here's to teamwork! *cheers*

So it sounds like you're on your way to tuning for WOT without the BAP. Nice. Please also report back your AFRs at partial throttle and mid rpms. This is where i'm wondering if the RRFPR can also adapt properly. Are you able to log data?

Please also let us know what static idle fuel pressure you end up at.

btw.. yes, you'll need to adjust the RRFPR. It's the top allen bolt held in place with a locking nut. Take it from me.. adjust only 1/4 of a turn at a time. It's also best you not do a lot of the final tuning while the car is heatsoaked. I had to do this tuning over several hours and rechecked this a few days later a few more times. Generally a PITA.

 

[DDozier]

I'm still running a little bit on the rich side with AFR 10.5-11.0. FP at idle is around 56 psi with the Walbro 255 at 13.68 volt. Is it advisable to adjust the CT FPR?

Thanks to all who helped!

Sounds like you are making progress, now adjust static fuel pressure to the recommended level in the owners manual, 46-53PSI with vac line removed and 36-44PSI with the vac line connected and at idle, then test for AFR under boost.

Dave

 

[goldNSX]

So it sounds like you're on your way to tuning for WOT without the BAP. Nice. Please also report back your AFRs at partial throttle and mid rpms. This is where i'm wondering if the RRFPR can also adapt properly. Are you able to log data?

Thanks for your recommendations, I really appreciate it.

I'm able to log AFR but not throttle position. But from what I've seen is that at part throttle and mid rpms it's AFR = 11 too. It's reacting pretty fast but not as fast as with the voltage-booster. But I'll certainly report back as soon as the SOS wiring kit is installed and I did some adjustments.

Do I understand correctly? Less fuel pressure at idle results in higher AFR at WOT? I'd like to have it on the safe side and won't squeeze every little hp out of it. So I want to stay below AFR < 11.5 under all conditions.
I don't know how the CT piggy back works exactly. Does it have a fixed fuel and timing map? If I lean the mixture out are the injectors corrected to open more frequently or longer?

 

[DDozier]

Thanks for your recommendations, I really appreciate it.

I'm able to log AFR but not throttle position. But from what I've seen is that at part throttle and mid rpms it's AFR = 11 too. It's reacting pretty fast but not as fast as with the voltage-booster. But I'll certainly report back as soon as the SOS wiring kit is installed and I did some adjustments.

Do I understand correctly? Less fuel pressure at idle results in higher AFR at WOT? I'd like to have it on the safe side and won't squeeze every little hp out of it. So I want to stay below AFR < 11.5 under all conditions.
I don't know how the CT piggy back works exactly. Does it have a fixed fuel and timing map? If I lean the mixture out are the injectors corrected to open more frequently or longer?

You set the static fuel pressure at idle and when the car goes into boost the CT piggy back clamps the MAP sensor voltage that the ECU sees. This lets the ECU think the car is operating at WOT but without boost. That is all it does. No magic other than the actual clamp voltage that CTSC picked will have an effect on total timing, but since you can not adjust it you get what they gave you.

Your RRFPR is what is controlling the amount of fuel available to burn. If you raise your static fuel pressure you raise your peak pressure assuming the pump can deliver the fuel needed to reach the new peak pressure. This higher peak pressure will make the AFR's go richer. Lower the static fuel pressure and you lower leak pressure and raise the AFR to a leaner rate. With the RRFPR there is a correlation to the amount of fuel pressure increased for every PSI of boost you add but it is not linear so you would have to measure your fuel pressure at every PSI to map out the correlation. They offer different springs to go inside the FPR to change the ramp rate of the RRFPR. So the device is somewhat tunable. On the highboost model they also had a bleed screw that you could adjust to change the peak pressure as well as different springs to adjust the ramp rate.

Dave

 

[goldNSX]

I've reduced the fuel pressure from 56 psi to 50 psi and get AFR 11-11.5 now (was 10.5-11 before).

 

[DDozier]

I've reduced the fuel pressure from 56 psi to 50 psi and get AFR 11-11.5 now (was 10.5-11 before).

Great, with this type of fuel control you have to be very carefull and monitor your AFR over time, lots of things will effect the WOT AFR now more so than if you had larger injectors and ran more OEM fuel pressures. You should write down and keep track of the fuel PSI and its effect on WOT AFR. Hopefully you never have to change the FPR or the fuel pressure again but at least this way you will have a starting point on setting up a new one or adjusting the one you have.

Fuel filters, injector seat cushion and o-rings, fuel lines, fuel pump, vac leaks and FPR are all things that can cause fuel issues and can lead to everything from lean conditions to fuel leaks and fire. There are lots of systems out there running with elevated fuel pressure to add fuel to undersized injectors but you just need to be aware of the possible issues so you can stay on top of the maintenance needed to prevent a problem. Since you have a wideband your best indicator of a supply problem will be with your WOT AFR. The other issues will require visual inspection and should be done quite often to look for leaks around the injector fuel rails and fuel lines.

Dave