Autorotor CTSC Low Boos + Walbro 255LPH Fuel Pressure at idle

[MvM]

I have a '98 NSX with low-boost Comptech Autorotor Supercharger.
I recently had the Walbro 255LPH installed together with the heavier wiring kit from SoS.
Already installed was a Zeitronix wideband Lambda sensor and SoS Fuel pressure gauge in the engine compartment.
I also had the Zeitronix boost- and AIT sensors installed to be able to measure those values, just for safety.

I noticed that my fuel pressure at idle is higher than before. I am not sure, but before it was something like 43 PSI at idle with a warm engine.
Not it is sits there at a steady 50 PSI, even at 900 RPM. The engine is running rich, because I can smell the gas. When I go into full boost at high RPM and high speed, I noticed a cloud coming from my exhaust, feels like the engine is throwing out excess fuel (??).
My lowest recorded AFR is down to 9.6 at 0.49/0.50 Bar of boost (7.1-7.25 PSI).

Which fuel pressure should I be aiming at when the car is idling ??

 

[NSX-Files]

That happens bc the Walbro is pushing more pressure and maybe your current fuel pressure regulator can't bleed off enough fuel to get the pressure down to the stock level which is 36-43psi. Perhaps you can adjust the comptech rising rate fuel pressure regulator to compensate.

 

[MvM]

Ok, I was already planning to adjust the regulator back to around 40-43 PSI at idle.

I am still a little worried about the low AFR-readings at boost. I know lower is normally better, but IMHO, getting blow 10.0 in AFR at boost is overdoing it a little. I always thought around 10.5-11.0 is safe enough.

 

[E-Nough Logic]

Lowering the base pressure may bring that up to a reasonable level. Adjust and check again. To properly adjust base fuel pressure make sure to remove the vacuum line while it is idling so there is no vacuum on the regulator.

 

[NSX-Files]

Lowering the base pressure may bring that up to a reasonable level. Adjust and check again. To properly adjust base fuel pressure make sure to remove the vacuum line while it is idling so there is no vacuum on the regulator.

I would suggest follow both methods outlined in the manual and check for pressures both with vacuum line disconnected (and plugged) and also with it still connected to the FPR. Your pressure readings under both scenarios should be within the ranges outlined in the manual.

And yes, AFR of below 11 will likely damage your catalytic converters (if you have them) and could potentially wash the cylinder walls of the protective oil film, and smell god-awful too.

QUESTION: have you bypassed the fuel pump resistor in the engine compartment? Perhaps you have if you've installed the SOS wiring kit, which incidentally I don't think you need with that Walbro. Anyway if so, then your pressures will be very much higher than stock when below 4800 rpm. That's about when the relay kicks in to bypass the resistor. Given you have the CTSC kit, with presumably a Boost-a-Pump component, then maybe this doesn't apply. But thought I'd mention it.

 

[goldNSX]

Maarten

AFR < 10 is 'pig-rich' for a CTSC setup and is not necessary. CT says AFR should be between 11.2 and 11.7 at WOT. So the leanest condition should not exceed 11.7. That's the main value you should look at, regardless what the base fuel-pressure is. The problem is that AFR can vary as the parameters change. So you want to be sure it's correct for all conditons, hot or cold outside temps etc.

Your question about what fuel pressure should be at idle needs to be reformulated. What I did on mine: I reduced the fuel pressure to a value (individually per car, so not of interest) that AFR are ok under WOT. The resulting fuel pressure at idle will be in or near the range of the SM but don't concentrate on that. If you're a little bit off the ECU is compensating in part-load conditions as you will see AFR 14.7 for emissions. Only if the car sees (even light) boost AFR go to the boost mode.

Just as reference: my car is normally in the 11.2-11.7 window but under some conditions it's running richer, God knows why. The key is that it should never run leaner or it can go BOOM.

BTW: with the SoS wiring the fuel resistor has no effect at all on the pressure.
Don't fuss with the ramp rate of the fuel pressure regulator. Unless it's faulty it's fixed.

Good luck!

 

[MvM]

@NSX-Files

Thanks for your reply. I was looking for the FPR-manual, but couldn't find it.
Lucky enough, changing the adjustment on the FPR is not that difficult.

Hi Thomas,
Thank you for the reply. Was more or less expecting a reply from you anyway

I have adjusted the FPR now, so it runs at around 44-45 PSI at idle with a warm eninge.
In my NSX, I had installed a Zeitronics wideband AFR-sensor and just upgraded that with a IAT-sensor and boost-sensor.
I also had the AS Motorsports phenolic manifold gaskets installed to reduce the heatsoak-issue with the Autorotor.
So far, I have not seen any temps higher than 70 degrees Celsius (158 degrees Fahrenheit).
I also have the datalogger of the Zeitronix and am going to log my rations the coming days to see if it needs more adjustment.
Before the Walbro was installed I never had any troubles with pinging, and I don't remember getting any lower dan 10.5 at boost.

Will keep you guys posted

 

[goldNSX]

As a rule of thumb: if AFR are in 90% of the cases within 11.2-11.7 AND never leaner but sometimes a little richer your car is safely tuned. Don't worry about those 10% of cases when it's running a little richer for a second or two. I think at the VTEC point the mixture is 'richened' anyway, stock or boost.

NEVER boost it with a cold engine as the timing won't be retarded enough when cold. I drive it normally (no boost at all) for 15minutes/15 km before I step on it. I had to teach this to my friend too.

Have fun with it, the season's just started!

 

[MvM]

As a rule of thumb: if AFR are in 90% of the cases within 11.2-11.7 AND never leaner but sometimes a little richer your car is safely tuned. Don't worry about those 10% of cases when it's running a little richer for a second or two. I think at the VTEC point the mixture is 'richened' anyway, stock or boost.

NEVER boost it with a cold engine as the timing won't be retarded enough when cold. I drive it normally (no boost at all) for 15minutes/15 km before I step on it. I had to teach this to my friend too.

Have fun with it, the season's just started!

Thanks for the input(s)
Do you have any idea what your IATs are during driving or while in boost?
I can now see my boost going up to 0.5 bar max and so far, IAT temps getting around 70 degrees Celsius at that boost.
Unfortunately, I have no idea if that is ok or not.

 

[goldNSX]

I've no temp gauge for IAT. Temperature reading depend much on how you drive, esp. how long you boost and how hot the charger itself gets (short boost during cruising versus German Autobahn at top Speed, winter versus summer and so on). I think your reading is at the lower side of the range.