1992 runs better in warm weather

[willabeest]

1992 NSX 108K miles Comptech headers and clutch otherwise stock engine.
the hotter the ambient air temp, the better it runs.
when cooler temps (60 F or less) throttle response is uneven - seems to have a variable flat spot around 2800 to 3500 RPM then surges forward.
when temp is above 85 F runs perfectly.
i am thinking the vehicle is running a little lean? cold air makes it leaner?
what do you all think?

 

[goldNSX]

My car showed exactly the same symptoms. A long time and many parts thrown at the car later I've found out that the fuel pump was on it's way out and showed it's weakness in colder temps. Not sure why in colder temps but it was exactly like you describe.

 

[docjohn]

well if it could be fueling related are your injectors original? On my obd2 car I was tripping lean condition cels...my fuel pump was fine,so we sent my injectors to RC for a cleaning and tune.....at the very least you could throw in some techron injector cleaner and run through the tank..Larry B swears by this.

 

[goldNSX]

I've had my injectors cleaned with no benefit.
I finally found that the 'flat spot' before 4k rpm went away when I short-cutted the fuel pump resistor. Cheap and simple test without throwing any money at the car at all.
First I've changed the FPR, rear coils, plugs, ignitor unit, cleaned injectors (Money, Money, Money). It was the fuel pump itself in my 91.

 

[willabeest]

My car showed exactly the same symptoms. A long time and many parts thrown at the car later I've found out that the fuel pump was on it's way out and showed it's weakness in colder temps. Not sure why in colder temps but it was exactly like you describe.

the car has the original fuel pump. bad pump = less fuel = more lean? more lean means cold air makes it leaner = runs bad . i will run it by my mechanic next time i get the oil changed. thank you for the tip.

 

[goldNSX]

the car has the original fuel pump. bad pump = less fuel = more lean? more lean means cold air makes it leaner = runs bad . i will run it by my mechanic next time i get the oil changed. thank you for the tip.

This might be a good explanation.
The problem is that it's not detectable as long as it's not very pronounced. I fell out of all clouds when I compared the low end torque of my car (with the bad pump) to another one (with a good one). The other one was pulling much stronger. The reason is that the ECU corrects for lower fuel or leaner condition up to the point where hesitation and so on occurs.

I've never read about someone here on prime who recognized this behaviour this way. That's why I think it's your car's problem but of course it can be something else.

Good luck!

 

[davidf]

Fuel pumps are a PITA to change. Please don't be talked into any aftermarket noname Autozone pump. Keep it OEM and don't worry, be happy!:wink: I would replace the FP relay at the same time. Cheap investment.

 

[goldNSX]

Let's find willabeest out if it's the fuel pump first...

 

[willabeest]

Let's find willabeest out if it's the fuel pump first...

new development. i changed my gasoline from costco premium to chevron premium. flat spot is now gone, even in cold weather. no idea why, but i am much happier with performance. perfect actually
now i have to pass smog...
costco premium 10 years ago was excellent. i guess they are not anymore.

 

[goldNSX]

Interesting. We seem to have fuel with lower quality differences in Europe. But I still think it's not related to the fuel unless your gas station is cheating you. Temporary my car ran better. Did you have a chance to compare the low-end torque to another car? Or did you bypass the fuel pump resistor as a (easy) test?

 

[d_prada1]

Mine is the complete opposite. My car runs crazy hard in the cold. All motor too.

 

[BATMANs]

My NSX runs great in ALL weather conditions but with the SOS SC it runs stupid power right now with this winter weather.

With double~ the power there are a few times where the NSX wanted to warp itself the side of a building or send me sailing off a cliff.

Yes, I can actually drive the NSX and NOT use all of the gas pedal - now that's a nice feeling to have; knowing that u have more power on tap......

 

[G III]

yep,,better in cold

 

[Rope]

Costco gas in CA is not a top tier gas so it would be the same as putting Arco gas in. My car starts to have idle and hot start issues if I use anything but the top tier gas. I suspect if you run a fuel system cleaner like the Techron injector cleaner along with using a top tier gas you will also find that the car's fuel efficiency will increase by about 2 mpg

 

[BATMANs]

Costco gas in CA is not a top tier gas so it would be the same as putting Arco gas in. My car starts to have idle and hot start issues if I use anything but the top tier gas. I suspect if you run a fuel system cleaner like the Techron injector cleaner along with using a top tier gas you will also find that the car's fuel efficiency will increase by about 2 mpg

When I had my GTO and NSX engine rebuild projects I had the injectors an valves inspected and there were no indication of abject quality gasoline (deposits, etc.).

http://www.costco.com/gasoline-clean-power.html

Personally, I would use Redline SI-1 about 2 weeks before I got an oil change, as the cleaned up deposits will wash into your oil—not necessarily a bad thing as the oil can probably absorb and neutralize the deposits, but there will be peace of mind from having clean oil in the engine (every 10k miles with the NSX & S10 and whenever the GTO automatic oil change light alerts me).

A fuel system cleaner that contains PEA (polyether amine). Alternatively, you can pay your dealer for a fuel injection cleaning service (around $250). Nonetheless, I’m always the one to try a cheaper alternative before I buck up.

Chevron Techron Concentrate (32% PEA, based on an older published MSDS spec sheet) has been the leading fuel system cleaner since its development sometime in the 1970’s (it's also a touted leading detergent in gas, albeit in MUCH lower concentrations than the stand-alone concentrate formulation). The main active cleaning ingredient is PEA. Other known fuel system products containing PEA include the following:

* Gumout Regane (30-40% PEA content based on published MSDS data)
* Redline SI-1 (30-50% PEA based on MSDS data)
* Amsoil Performance Improver (28-37% PEA based on MSDS data)

Other than the active-cleaning PEA, each product has variable fillers/detergents (i.e. Gumout has kerosene, Redline seems to have an octane booster, Chevron and Amsoil have naptha among other ingredients). I’m sure that there are other PEA-containing fuel system cleaners, but the previously listed products (with the possible exception of BG 44K) are known, sure-fire products (so I can not recommend any other products). Also, as an FYI, the cheaper Chevron Fuel Injector cleaner is NOT the same as Chevron Techron Concentrate—it’s just a watered down version of it from what I’ve read.

 

[willabeest]

chevron gas solved the hesitation problem low RPM but i failed smog which meant a lot more diagnostics.
what was found was an intermittent O2 sensor problem. sometimes they would work great, sometimes not. when they were first tested, they passed. they are "erratic". when replaced with OEM O2 sensors, engine ran much cleaner. this probably explains why my emissions numbers were bouncing around so much.
also noted (but may not be relevant) was a dirty fuel filter, a lot of carbon in the combustion chamber. i am happy, car runs GREAT!
now i can stop looking for an AWD porsche.

1992 NSX

 

[Rope]

Costco is not a top tier gasoline. Here is where you get the highest quality gas:

http://www.toptiergas.com/retailers.html

There gas is probably not the worse gas but it is not the best gas.