New owner - getting a power surge @ 4,000 rpm

[Hapa88]

So I drove a few NSXs before this one and never noticed it on those. My friend Vince also has a 1993 NSX but doesn't have this issue.

Its most noticeable in 2nd and 3rd gears. If you shift into second at around 2000 rpm and slowly get on the gas until you hit WOT before the 4000rpm mark, you'll feel the car accelerate hard, then reach a point and it feels like its starting to fall on its face. But once it hits ~4000-4250 rpm it takes off again, kind of like when VTEC kicks in on an Integra.

If you're WOT at 2000rpm, the car accelerates fine but theres quite a noticable jump in power at ~4200rpm. I've kind of experimented and kind of held the throttle steady at around 3700 rpm and gunned it. Same thing happens, get a power surge at 4200rpm. So I'm assuming something with the ECU or maybe the fuel is happening. Anyone have any suggestions or ideas?

 

[zff]

I'm also a new NSX owner, and the same thing happens in my car. I've never had a car with this kind of sophisticated valvetrain, so I've always assumed it was the VTEC. I'd be mighty interested if it's something else.

 

[nsxtasy]

I've always assumed it was the VTEC.

It's not VTEC, since the VTEC crossover point is 5800 RPM.

 

[MJK]

Disclaimer: I am not a mechanic, I don't play one on TV and I did not stay at a Holiday Inn last night. But, depending on the maintenance history and your DIY aptitude, I would probably change the fuel filter, change the spark plugs and check the coil packs.

 

[caz-nsx]

Clean the throttle body. I had power problems on mine last summer. A little spray in the throttle body solved the problem.

 

[NSXT]

Isn't 3800~4000 rpm when the fuel pump switches to high speed mode? You may have a nearly clogged filter.

 

[Hapa88]

Isn't 3800~4000 rpm when the fuel pump switches to high speed mode? You may have a nearly clogged filter.

I'll look into the Fuel filter issue. Anyone have a link on a "How-To" fix for this? As in removal and replacement. Thanks!

 

[NSXT]

Page 11-97 of the online Service Manual

 

[TigerNSX]

Wow.. I thought that I was the only one who experienced this.

Please give us an update with what you find!!

 

[Larry Bastanza]

Listen to caz-nsx.

LarryB

 

[AU_NSX]

Clean the throttle body. I had power problems on mine last summer. A little spray in the throttle body solved the problem.

Sorry to sound stupid... A spray of what?

 

[MJK]

Listen to caz-nsx.

LarryB

Larry is the man, and I would certainly put his advice before mine BUT if that doesn't work do what I suggested. It fixed similar symptoms in mine 2 years ago.

 

[rjp]

i believe the guys are referring to an air intake cleaner spray...these sprays are avail in several brands at most auto stores (Pep Boys in my case)...just an aerosol can that'll cost you a few bucks.

 

[caz-nsx]

It's called throttle body cleaner. There is also carborator cleaner which is most likely the same thing. As rjp mentioned you can get it Pep Buys, Auto Zone, etc.

All you have to do is open the air intake and remove the air filter. Then pull off the rubber piece that goes to the throttle body. Once you get to the throttle body open up the butterfly valve by pushing on the throttle cable. I also put a towel under the opening because some of the cleaner will run back out. Spray the cleaner in behind the butterfly valve. If you see a bunch of black carbon running back out you may be on to your problem. I spray inside as much as I can with the tip of the cleaner to get good coverage. Then I put everything back together and start up the engine and take it for a nice ride.

Acura told me you can spray the cleaner into the throttle body while the engine is running. That probably would work better and get the cleaner further into the throttle body. Maybe someone here can comment on this.

This is an interesting problem because it doesn't give a check engine light or anything. In my case it was intermitent and sometimes I couldn't even tell there was a problem. I asked LarryB to take my NSX for a drive and he knew within the first 100 yards that my NSX was down on power.

I took it to Acura the next week and told them that something was definately wrong. I got a call later that day telling me that they cleaner the throttle body and it was back to new.

When I picked it up I took off out the parking lot and spun the tires. I couldn't believe the difference. I had been so use to it not being right that it felt like they installed a supercharger or something.

 

[TigerNSX]

It's called throttle body cleaner. There is also carborator cleaner which is most likely the same thing. As rjp mentioned you can get it Pep Buys, Auto Zone, etc.

All you have to do is open the air intake and remove the air filter. Then pull off the rubber piece that goes to the throttle body. Once you get to the throttle body open up the butterfly valve by pushing on the throttle cable. I also put a towel under the opening because some of the cleaner will run back out. Spray the cleaner in behind the butterfly valve. If you see a bunch of black carbon running back out you may be on to your problem. I spray inside as much as I can with the tip of the cleaner to get good coverage. Then I put everything back together and start up the engine and take it for a nice ride.

Acura told me you can spray the cleaner into the throttle body while the engine is running. That probably would work better and get the cleaner further into the throttle body. Maybe someone here can comment on this.

This is an interesting problem because it doesn't give a check engine light or anything. In my case it was intermitent and sometimes I couldn't even tell there was a problem. I asked LarryB to take my NSX for a drive and he knew within the first 100 yards that my NSX was down on power.

I took it to Acura the next week and told them that something was definately wrong. I got a call later that day telling me that they cleaner the throttle body and it was back to new.

When I picked it up I took off out the parking lot and spun the tires. I couldn't believe the difference. I had been so use to it not being right that it felt like they installed a supercharger or something.

Thanks, John. So, it is absolutely okay for the cleaner to go behind the butterfly valve? And you do not have to make sure that the cleaner is completely dried out? Is it basically spray and leave it on kind of thing?

Everyone told me that 91-94 coupes were faster than 95-96 coupe, but when I picked up my 91 coupe, I felt that it was slower than my 95 T before 4200rpm. I am now excited that this may be the reason.

Thanks!!

 

[TigerNSX]

Then pull off the rubber piece that goes to the throttle body.

What exactly does it look like? Does it need to be replaced once you take it out?

 

[caz-nsx]

The cleaner basiscally softens the grime that has accumulated over time. You want to get everything back together and start the engine before it evaporates. Like I said, I believe you can run the engine and adjust the throttle while you are spraying into the opening. All the crud gets blown through the engine and out the exhaust. The engine will run rough at first and you may see more smoke from the exhaust than usual, but it goes back to normal after a minute or so.

Hopefully, someone while reply with more detail about this process.

You will see the rubber piece once you get in there. It is about 4" diameter with fins that make it flexible. It is also 5-6" long, and connects between the air box and throttle body. There are a couple of small hoses that have be unclipped as you go, but nothing major.

 

[TigerNSX]

Thanks, John! :biggrin:

 

[Hapa88]

Awesome guys. Looks like I'm on my way to PepBoys to get some of this cleaner. If that doesnt' work, I'll try the fuelfilter deal. And if that doesn't work, look for another post by me! Thank again for all your help!

 

[zff]

Running the engine while opening the throttle enough to get the cleaner to spray back behind the butterfly sounds, uh, noisy.

 

[zff]

Wow, THANK YOU to everyone who posted in this thread. I just replaced my fuel filter and my NSX runs silky smooth. Not knowing what VTEC is supposed to feel like, I thought the surges were typical NSX orneriness. I would never have known had it not been for NSX Prime.

Thanks again.

 

[TigerNSX]

Now I am confused... is it because of the fuel filter or the dirty throttle body? Could someone please explain to me why this (surge of power after 4200rpm - or loss of power before 4200 rpm) happens when either fuel filter is bad or throttle body is dirty?

Thank you.

 

[NSX-Racer]

Now I am confused... is it because of the fuel filter or the dirty throttle body? Could someone please explain to me why this (surge of power after 4200rpm - or loss of power before 4200 rpm) happens when either fuel filter is bad or throttle body is dirty?

First, it was not the original thread starter that said he solved the problem (although zff wrote he had the same problems).

2nd: It may have to do something with the VVIS . Maybe the intake pressure conditions change slightly in the range below 4,800 rpm - affecting air/fuel ratio or intake speed. Aren't there also resonance effects in the intake that may lead to a power loss when something with the throttle body or fuel supply is wrong? Just a guess, I'm no techie.

 

[NSXT]

Both can have this effect. In the case of a dirty TB, various ports would not open properly and various sensors would be reading incorrectly with a buildup of sludge, therefore giving bad info to the ECU. Just not bad enough to trigger a sensor failure detection.

In the case of clogged fuel filter, at 4000 rpm, the fuel pump switches to higher flow mode, and pressure in the line will increase ahead of the restricted filter, forcing more fuel through the restriction.

What I believe was occuring was that below 4000 rpm, there was little fuel due to a clogged filter. This was starving the engine and therefore low on power. When the fuel pump kicked into high flow mode, he got better fueling and felt the surge. With a clean filter, fuel is now available throughout the range. His power should be much better everywhere and smooth through the range.

 

[TigerNSX]

That makes sense. Thanks so much!