flat spot about 3500 RPM

[willabeest]

1992 NSX 108,000 miles.
for about 3 weeks, noticed under moderate throttle a dead spot around 3000 to 3500 RPM. when it hits about 4000 it starts accelerating again.
only engine mods are comptech headers - these have been on car a long time.
exhaust by tubi - also old.

what is wrong?

thank you.

 

[goldNSX]

fuel pump or o2 sensors

 

[Pchpleno]

Lately mine has been doing the same thing. Also remember starting the car once or twice and it just stalled itself out beginning to think it may be a fuel pump

 

[A.S. Motorsport]

Indeed fuel pump and 02 Sensors would be likely causes on later DBW cars it can be the DBW system as it's occasionally less responsive at certain rpm ranges.

 

[FarEastGrappler]

Did your check engine light go on? I would guess O2 sensor.

 

[goldNSX]

Or it's the hot chick posing on the rear wing of your car.

 

[NSXCessive]

1992 NSX 108,000 miles.
for about 3 weeks, noticed under moderate throttle a dead spot around 3000 to 3500 RPM. when it hits about 4000 it starts accelerating again.
only engine mods are comptech headers - these have been on car a long time.
exhaust by tubi - also old.

what is wrong?

thank you.

Is your maintence up to date? Plugs, coils, air filter, fuel filter, o2 sensors in spec, check for carbon build up on tb & PCV & EGR valve, make sure the IAT is clean, and reseting the ECU by pulling the clock fuse.

I had similar hesitation issues with a '91 NSX years back with RM intake, comptech headers, and Ark exhaust. I decided to check the spark plugs and noticed water made it past the plastic covers on the valve covers, and worked its way down between the coil and sparkplugs on the rear bank. Took all the coils out dried out the water causing me hesitation, problem fixed

 

[willabeest]

Is your maintence up to date? Plugs, coils, air filter, fuel filter, o2 sensors in spec, check for carbon build up on tb & PCV & EGR valve, make sure the IAT is clean, and reseting the ECU by pulling the clock fuse.

I had similar hesitation issues with a '91 NSX years back with RM intake, comptech headers, and Ark exhaust. I decided to check the spark plugs and noticed water made it past the plastic covers on the valve covers, and worked its way down between the coil and sparkplugs on the rear bank. Took all the coils out dried out the water causing me hesitation, problem fixed

i think it might be the fuel pump. the O2 sensors are pretty new (thank you CARB) and when the weather turned cooler the problem got a lot worse, so i am thinking cold air means leaner mixture made it worse so fuel pump not pumping enough.

 

[docjohn]

nice thing about the obd2 cars is when the fuel delivery gets weak we get a cel for a temporary lean condition.which can help to take a look at the pump or injectors.

 

[Briank]

At 4000 rpm the fuel pump gets full power (the fuel pump resistor is bypassed). A fuel pressure check check would not be a bad thing to do along with making sure the vacuum line is connected to the fuel pressure regulator. Also has your fuel filter been changed?

 

[willabeest]

At 4000 rpm the fuel pump gets full power (the fuel pump resistor is bypassed). A fuel pressure check check would not be a bad thing to do along with making sure the vacuum line is connected to the fuel pressure regulator. Also has your fuel filter been changed?

good ideas. BTW that radio you fixed is still working great. Thank you Brian.

 

[willabeest]

Shad figured it out

1992 NSX 108,000 miles.
for about 3 weeks, noticed under moderate throttle a dead spot around 3000 to 3500 RPM. when it hits about 4000 it starts accelerating again.
only engine mods are comptech headers - these have been on car a long time.
exhaust by tubi - also old.

what is wrong?

thank you.

OK the check engine light went on this morning. i stopped. shut car off. restarted. light gone rest of commute.

 

[willabeest]

Re: Shad figured it out

OK the check engine light went on this morning. i stopped. shut car off. restarted. light gone rest of commute.

OK i have one tire with a leak. i have aftermarket rims. when my tire pressure gets to 29 pounds, the traction control slows the power to the wheels.
solution is to get the tire pressure up. thank you Shad.:smile:

 

[Lamini]

Re: Shad figured it out

do you think that if you turned of traction control, the car would operate as normal?

 

[AU_NSX]

1992 NSX 108,000 miles.
for about 3 weeks, noticed under moderate throttle a dead spot around 3000 to 3500 RPM. when it hits about 4000 it starts accelerating again.
only engine mods are comptech headers - these have been on car a long time.
exhaust by tubi - also old.

what is wrong?

thank you.

Clean your throttle body! It's gunked up... A spray can of carburettor cleaner should fix it.

 

[willabeest]

Re: Shad figured it out

do you think that if you turned of traction control, the car would operate as normal?

it operates fine with the tire pressure where it should be.

 

[gt_nfr]

I actually have similar issues. I recently changed my fuel filter and now car takes longer to start in the cold and I can feel this "flat spot" Brian, what were your methods for diagnosing this issue?

- Pressure test fuel system
- ??

Update, I just did a few 2nd and 3rd gear pulls from 2k-5k RPM. No hesitation as OP mentioned...I guess it was in my head. I still have this intermitten starting problem. I have a remote-start installed and last year around this time, the car would always start-up immediately. This year, after doing my T-belt, water pump, seals, etc [90k maintenance], I'm experiencing a much longer cranking time when the car is cold. To the point where my remote-start will no longer start the car on the first try.

My thoughts are: pressure test the fuel system tomorrow to see if I'm within spec. Other than fuel pressure tests, what else should be checked?

My car is a '93 and approaching 140k miles. Me thinks the fuel pump may need replacing but I'm waiting on the Prospeed injector mod so I can do all of this at the same time.