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

[zff]

I'd never even ridden in an NSX before, so I really had no idea what to expect when I got my car a week and a half ago. Now that I've replaced the fuel filter, it's obvious that it wasn't running right when I got it.

The car would buck when I gave it a lot of throttle at low RPMs, the engine idled at a rough 1000-1200rpm, and the AC compressor made the idle go as high as 1800rpm... and of course, there was that 4000rpm surge. The car was still easily driveable, and I didn't think any of this was that bad. I figured it was just the ornery nature of the NSX's high strung engine.

With the new fuel filter, the bottom end feels much more refined. Smooth 900rpm or so idle, no surge at 4000rpm.. just a smooth, powerful pull right up to redline. I tried it a couple of times just to be sure

Now, though, less than 24 hours and about 20 miles later, some of that roughness is coming back. There's a tiny bit of bucking when I dip into the throttle at low RPM. It's not nearly as bad as it was before, but I'm pretty sure it wasn't happening last night during my test drive. There's no odd surges and the idle is still silky smooth.

I'm going to try a can of carb cleaner and keep an eye on the engine's behavior. In the meantime, though, can any of you think of what it could be or what I may want to look for?

Thanks again everyone, for all your help.

- Ken

 

[DanO]

Oxygen Sensor Test
After the engine is warmed up, try putting it in 3rd gear and accelerate from 5mph to about 45mph then let off the gas and let the car decelerate back to idle speed while still in gear. Do it again in 2nd gear, up to 35mph and back to idle speed. Look for a yellow check light.

Good luck,
DanO

 

[mickeylex]

I've been following this thread and decided to try this throttle body cleaning. I did the throttle body cleaning last night and noticed an immediate difference in acceleration when I took the car out. The idle is smoother now too. My TB had a healthy coating of black sludge in it which, after the cleaning, was gone. Thirty minutes, a couple of bucks and dirty fingernails were well worth the effort. I need to do this on my GSR now.

 

[Hapa88]

I've been following this thread and decided to try this throttle body cleaning. I did the throttle body cleaning last night and noticed an immediate difference in acceleration when I took the car out. The idle is smoother now too. My TB had a healthy coating of black sludge in it which, after the cleaning, was gone. Thirty minutes, a couple of bucks and dirty fingernails were well worth the effort. I need to do this on my GSR now.

Awesome, I picked up a can too, and also have the fuel filter on order. I hope to finally get to fix it this weekend. Unfortunately for me, I live in LA and my N stays in SD, so I don't get a chance to work on it every week. :frown:

 

[mrbone]

after working on hondas for fifteen years at honda dealers and then 6 more at my own shop what i found out about the throttle plate was that when the crud got in there what it was doing was causing the throttle plate to hang open slightly at idle letting air around the plate instead of sealing the bore. Idle is supposed to be controled by air bypase circuit in the throttle body and electronic idle control valve or its related counterpart depending on which type of vehicle you are working on. When the plate hangs open slightly the sensors detect this and try to compensate for it by turning down or up the injector pulse. (more or less fuel or even more or less air via the eacv valve.) When this occurs it throws the whole system out of wack and causes terrible idle as well as poor performance at all speeds but more so low end trouble. The fuel filter clogged problem is just that. Fuel starvation. When you change a fuel filter catch/pour fuel from the filter into somthing clean and inspect the fuel coming out of it. That will tell you more of what is going on. ie water or crud problems.
Since im fairly new to nsx ownership/maintance that is about all i can tell you about the nsx but hondas with blackish powder looking substance in the fuel in the fuel filter is an indication that the fuel pump is not long for this world.

Hope this helps

David

 

[mrbone]

after reading my prevous responce i realized i was sort of rambling. it is alittle more technical than that but that explains the throttle plate problem and fuel filter problem in a nut shell. To correctly fix any problem you need to do a series
of diagnostic procedures in certain order to zero in on the problem.

 

[Larry Bastanza]

mrbone,

Nice tip. I had never examined the fuel in the old filter with the intentions of checking for signs of a tired pump. Your explanation makes total sense. This could save someone a flatbed charge in the future.

Thanks,
LarryB

 

[TigerNSX]

So, if I do not have any rough idle problem (my idle is very smooth and consistent), but only experience the power surge around 4200 rpm, is the problem more likely to be related to the fuel filter or fuel pump or both?

I have been trying to fix this problem ever since I have acquired the car, and I really want to fix this.

Any comments would be helpful.

 

[mrbone]

if i suspected a fuel pump problem i would take a fuel pressure reading and rig the gauge so i could see it while driving the car. The manuel tells exactly where
to take the reading and what it should read under what conditions.
i prefer to diagnose problems rather than throw parts at them. If pressure is within specs after the filter then fuel delivery is ok. If that is ok i will think about this and try to direct you to the next step in the diagnosis process.

 

[TigerNSX]

Thank you.

 

[mrbone]

tigernsx
Did you or are you going to take a fuel pressure check? Lets see what the pressure is. You may want to also take a fuel pump volume test. Let me know what you are going to do. I hear people talk about a two speed fuel pump system on the nsx and i really dont see that it has anything but a common honda pump set up. do all test per the service manuel. By the way what year do you have? By the way check all simple stuff. air filter, plugs and their gap. I wish i could drive it as i can usually tell by the seat of the pants feel as where to look so bear with me as this may be a little difficult over the net.

 

[Larry Bastanza]

mrbone,

There is an item called the "Fuel Pump Resistor" in the NSX. This limits fuel pump flow if placed in the fuel pump curcuit(in series with the pump). I recall about 4800rpm this resistor is shorted out to increase voltage to the the fuel pump. It is also shorted out during the "Start" phase to enrichen the mixture.

HTH,
LarryB

 

[mrbone]

larry

Please list any info/page number of service manuel or any reference material and where i can find info about this resister. I find this interesting. Is this different from any other honda car? ie nsx specific. i regularly talked with tech line at honda when i worked for honda and never heard of this resister. But only worked on very few nsx's.

David

 

[NSX-Racer]

Please list any info/page number of service manuel or any reference material and where i can find info about this resister.

You may start here . And if you do further searches on this awesome online manual be sure to write "resistor" and not "resister".

 

[mrbone]

nsx racer and larry

Thanks for pointing me to this info. After looking at that and then getting the etm out i see it does have a seperate high speed circut. Pretty cool. it looks like that, as you said, the pump operates or gets it voltage through the resister and at a pre determined time (rpm) the ecu grounds the fuel pump relay that energizes the coil in the relay that kicks the contacts and send battery voltage straight to the pump instead of having to go through the resistor.

 

[Larry Bastanza]

Yes exactly,

It is also left out of the curciut my the main realy during starting. A classic sign of this resistor being open is that the car will start, then immediately die once you take the ignition switch out of the start position. Once out of the start position the resistor is in the curciut to power to fuel pump, so if it is open, your fuel pressure goes away.

HTH,
LarryB

 

[Hapa88]

Ok, so I changed the fuel filter (Big thanks to Nick at Applied Motorsport), and cleaned out the Throttle body and I am still having the same issues. The fuel filter was in fact dirty, but the new one didn't seem to fix the problem.

So here's a little more details as to the problem:
1) The car seems to pull fine as you start to slowly mash the throttle down to WOT. However you seem to reach an "equilibrium" point (at around ~80% of WOT) and if you add more gas after that point (to WOT) the car seem to bog down a little and acceleration seems to suffer.

2) At around 4200 RPM there seems to be a kick and the car really starts to pick up all the way to redline, which seems to be normal.

Anyone have any other ideas? Maybe I can meet up with one of the SoCal guys and see if you might know?

 

[Briank]

Have you checked the fuel presure, I would lean towards a bad fuel pump or a bad FPR

 

[DanO]

Did you do the O2 sensor test I mentioned above? My car had similar symptoms and I spent the better part of last spring/summer diagnosing. Turned out to be a bad O2 sensor. Thread: www.nsxprime.com/forums/showthread.php?t=31821

DanO

 

[TigerNSX]

Have you checked the fuel presure, I would lean towards a bad fuel pump or a bad FPR

What is FPR?

Thank you.

[EDIT] FPR probably means Fuel Pump Relay, I suppose? :biggrin:

 

[Briank]

Fuel Pressure Regulator

 

[TigerNSX]

Fuel Pressure Regulator

Oh, thank you! What does it exactly do? What are some of the symptoms if it goes bad?

Thanks again.

 

[Briank]

The FPR controls the relative fuel pressure in the fuel rails. By relative I mean the pressure difference across the fuel injectors. The difference changes with the amount of vacuum in the intake manifold. Thats why the FPR has a vacuum connection to the manifold. If it is bad you could see a rich condition or if stuck open a very lean condition.

 

[TigerNSX]

Thank you, sir.

 

[Onsoku]

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.

Would that I explain why it take about 3 seconds to start up & why I don't get a check engine light during a cold start? My happens after the car has warmed up and very light throttle. I i go WOT and then back off...and then lightly tip in, the CEL will show again.