Running lean help

NSXRAY1 · 7 May 2016

Hello Prime

My NSX seems to be running lean after 5 minutes of idling after a cold start up. It will stay there until I push on the gas. When I drive it will move between 12 to 17 AFR. Whenever my car sits idle for a while or sitting at a stop light it moves to 16 or 18 reading.

I have a 98 NSX with CT engineering supercharger, AEM EMS series 2, with injector dynamics 725, walboro fuel pump. Anyone have an idea of the issue?

Thanks

docjohn · 7 May 2016

how old are your fuel injectors

NSXRAY1 · 7 May 2016

docjohn said:
how old are your fuel injectors

The injectors are a year old but I had the injectors and Supercharger installed last November 2015.

The car was tuned in Nov and was running between 12 and 14 AFR.

docjohn · 7 May 2016

I'm no expert but my 96 had been throwing lean codes and after I had my injectors cleaned and bench tested my car has been great.Since you have new injectors it could be fuel pump...

NSXRAY1 · 7 May 2016

docjohn said:
I'm no expert but my 96 had been throwing lean codes and after I had my injectors cleaned and bench tested my car has been great.Since you have new injectors it could be fuel pump...

Thanks for the info. I hope I am able to figure it out. Fuel pump, I hope not.

Maybe the tune? Much to think about.

- - - Updated - - -

Should I have it retuned?

jwmelvin · 7 May 2016

NSXRAY1 said:
Should I have it retuned?

If the tune was correct then something has changed and I wouldn't just adjust the tune to accommodate the change. It will get worse. Fuel pump seems like the likely candidate. Check fuel pressure if possible. When was the fuel filter last replaced?

Old Guy · 7 May 2016

Definitely do as jwmelvin suggests and check the fuel pressure first. Unless you have modified something on the car since completion of the tune, also do as jwmelvin states and do not fiddle with the tune (this presumes that the tune after the supercharger install was correct).

If the fuel pressure checks out OK, check out your IAT sensor. Normally an IAT sensor with surface contamination will cause the air temp to read lower than actual resulting in the AFRs being low. If on a hot restart your AFRs start out high and then gradually return to normal, your IAT may be suffering from heat soak which fools the IAT into measuring air temperatures that are higher than the actual air temperatures. This causes the ECU to reduce the fuel PW resulting in the engine running with a higher than targeted AFR. As air flows through the intake manifold, the IAT temp eventually drops to the actual air temp and the AFRs return to their target values. The IAT sensor heat soak problem may become more pronounced if you are driving the car in ambient air temperatures that are significantly higher than the conditions under which it was tuned.

I know squat about AEM systems; but, some aftermarket ECUs come with a feature that allows you to deviate from the ideal gas law equation at high air temperatures. It may be called something like an air density correction curve. This feature allows you to add some correction to the fuel pulse width for very high air temperatures. Something to check out if the fuel pressure turns out to be OK.

As a final note, are you using a wide band O2 sensor with a configurable controller? Make sure that the controller and the sensor are working OK.

NSXRAY1 · 16 May 2016

Old Guy said:
Definitely do as jwmelvin suggests and check the fuel pressure first. Unless you have modified something on the car since completion of the tune, also do as jwmelvin states and do not fiddle with the tune (this presumes that the tune after the supercharger install was correct).

If the fuel pressure checks out OK, check out your IAT sensor. Normally an IAT sensor with surface contamination will cause the air temp to read lower than actual resulting in the AFRs being low. If on a hot restart your AFRs start out high and then gradually return to normal, your IAT may be suffering from heat soak which fools the IAT into measuring air temperatures that are higher than the actual air temperatures. This causes the ECU to reduce the fuel PW resulting in the engine running with a higher than targeted AFR. As air flows through the intake manifold, the IAT temp eventually drops to the actual air temp and the AFRs return to their target values. The IAT sensor heat soak problem may become more pronounced if you are driving the car in ambient air temperatures that are significantly higher than the conditions under which it was tuned.

I know squat about AEM systems; but, some aftermarket ECUs come with a feature that allows you to deviate from the ideal gas law equation at high air temperatures. It may be called something like an air density correction curve. This feature allows you to add some correction to the fuel pulse width for very high air temperatures. Something to check out if the fuel pressure turns out to be OK.

As a final note, are you using a wide band O2 sensor with a configurable controller? Make sure that the controller and the sensor are working OK.

Thanks for the advice. I will not mess with the tune. Since I do not know much about having a Supercharger sounds like I will need Acura look at it again for the fuel pump.

I have a Stackpro gauge reading fuel pressure and AEM Failsafe. What should fuel pressure be running at?

Thanks again

NSXRAY1 · 17 May 2016

jwmelvin said:
If the tune was correct then something has changed and I wouldn't just adjust the tune to accommodate the change. It will get worse. Fuel pump seems like the likely candidate. Check fuel pressure if possible. When was the fuel filter last replaced?

The fuel filter was changed when the supercharger was installed. Sounds like I must have the installer look at the fuel pump. Is that correct?

thanks

- - - Updated - - -

Anyone know how to download a video? I have a video of what is happening with the gauge readings.

Thanks

jwmelvin · 17 May 2016

NSXRAY1 said:
Anyone know how to download a video? I have a video of what is happening with the gauge readings.

Upload to YouTube and put a link here, generated by the "share" button in YouTube.

NSXRAY1 · 18 May 2016

jwmelvin said:
Upload to YouTube and put a link here, generated by the "share" button in YouTube.

Thanks. I'll load up tonight. I spoke with a local motorsports business about my issue. They agree with jwmelvin that it could be a fuel pump issue but not entirely sure.

NSXRAY1 · 21 August 2016

Update. The NSX was brought to a local mechanic that works on the NSX. Also has their own Dyno. The issue was the original tune. I will find out more next week when I pick up the NSX and share the resolution. Final results was 340hp.

yipiokayyay · 1 September 2016

Hi

Wondering if you had any updates on your experience

NSXRAY1 said:
Update. The NSX was brought to a local mechanic that works on the NSX. Also has their own Dyno. The issue was the original tune. I will find out more next week when I pick up the NSX and share the resolution. Final results was 340hp.

NSXRAY1 · 3 September 2016

yipiokayyay said:
Hi

Wondering if you had any updates on your experience

New update. Picked up the NSX last weekend and Rich from Richtuned Motorsports was able to figure out that the problem was the original tune. The business that tuned my NSX initially did not configure the AEM Series 2 correctly. Rich had to redo the entire tune to bring it within specs. My engine is running between 12 and 14 and operating well.

All is good to go now. I am taking the NSX out tomorrow for a full run.

Running lean help

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