Car runs lean and Check Engine Light at WOT

[TigerNSX]

Hello,

I am planning to take my car to mechanics, but wanted to see if anyone else had similar problems previously in order to better explain my situation to the mechanics.

Situation:
-The car runs lean from 0K rpm all the way to ~ 4.5K rpm.
-If the car is in higher gear, such as 4th or 5th, in the low speed, and if I go WOT, then the check engine comes out. Check engine light is for O2 sensor. Restarting the car gets rid of the check engine light.
-Replaced all O2 sensors, but the problem has not disappeared.

Mod:
DC Headers

Service and Maitenance:
Up to date

Any advice or help?

 

[hlweyl]

How do you know the car is running lean, are you detonating? Also, going WOT at anything less than 2500 rpm in higher gears is not very good for your engine, serious lugging there.

 

[Briank]

TigerNSX

Need more info, what year is your car, what code are you getting?

 

[TigerNSX]

How do you know the car is running lean, are you detonating? Also, going WOT at anything less than 2500 rpm in higher gears is not very good for your engine, serious lugging there.

I was informed by the previous owner regarding the car running lean.
I only went WOT to replicate the check engine light..

TigerNSX

Need more info, what year is your car, what code are you getting?

It's 91 with 58k miles. Prior to when O2 sensors were replaced, the code that we were getting was the O2 sensor code (two on the headers).

Thanks for your time, guys.

 

[TigerNSX]

How do you know the car is running lean, are you detonating? Also, going WOT at anything less than 2500 rpm in higher gears is not very good for your engine, serious lugging there.

Oh, one more thing.. I feel the sudden surge of power from ~4.5k rpm which is not when the VTEC kicks in. So I am assuming that the car runs lean before 4.5k rpm, and rich or normal after 4.5k rpm.. Does this make sense? The power delivery is not very smooth throughout the rpm range. It feels a bit sluggish before 4.5k rpm, and normal after 4.5k rpm.

 

[Briank]

There are seprate codes for both the front and rear O2 and O2 heaters. If you are getting codes from both then you have a fuel delivery problem. Filter, pump or regulator. You need to reset the ecu, cause a CEL and re-read the code.

 

[TigerNSX]

Thank you, Brian.

I will look into this. Hopefully, this won't be too costly

 

[hlweyl]

I wouldn't think you have a lean/rich condition. The computer controls air/fuel/timing automatically. Running lean and rich is pretty much a thing of the past i.e. carbuerators unless you have an ECU problem.

Brian gives good advice here (as usual )

Good luck

 

[ScienceofSpeed]

Common problem is the wires in the DC extension harnesses being switched (two grounds). Check the code, and report back.

Cheers,
-- Chris

 

[jgtcnsx]

to see if your running rich or lean check your spark plugs. if they are like a yellowish color you runnin rich. if you they are like a birght bleach white and showing signs of detonation you are running lean. if its running lean you wont be gettin enough fuel if it is rich you are geting to much fuel. could be a filter pump, reg,or inejector(hope not). so check it out. if all the spark plugs have the same problem it would be more likely the pump, reg or the filter. if it is one cylinder then its probably an injector.

 

[TigerNSX]

This problem still has not been solved even after new o2 sensors.

After replacing o2 sensors, I could not replicate the problem when I was with the mechanic. We tried every single scenario - going WOT in all gears from low to high rpm and etc. No check engine light. I, then, thought that the problem went away.

A few months later from that day (today), I was driving and went WOT in 3k rpm (going 30mph) in the 4th gear all the way, then there it was the check engine light with the same codes - fauty o2 sensors.

I am going crazy... :frown:

 

[Briank]

CODE 1 - 2 ????

It's unlikelly you have a bad o2 since you replaced them and they very seldom fail at the same time. I would look real hard at the wiring from the o2's to ECU. Also have you changed your fuel filter and done a fuel pressure check?

 

[Viper Driver]

CODE 1 - 2 ????
Also have you changed your fuel filter and done a fuel pressure check?

I think that Briank's advice is pretty good.

I don't know how it would tie into O2 sensor fault codes, but your symptoms outside of that sound like your motor might not be getting enough fuel. Because you get a "surge" around the time the fuel pump kicks into high speed, I'd really take a hard look at your fuel pressure and delivery.

Have you had your car on a dyno to see what your air-fuel is? That will tell you a lot about what's going on. Also, have you checked the wiring harness extension to ensure the wires aren't crossed between your O2 sensors and the stock wiring harness?

 

[SaberX]

Do you have an NSX factory service manual? If not, look at the one online. Apparently, if you get the O2 sensor codes there is a flow chart that can help you determine if its a fuel system issue (which it sounds like it is). All this information is in Chapter 11 of the service manual. Since you know its not the O2 sensors I think this will put you on the right track.

 

[dang]

I'm not an NSX guy (yet), but could these symptoms be related to a vacuum leak? I know the system can adjust for different air/fuel mixtures, but it depends on where and how bad the vacuum leak is. Not convinced that this is the problem by any means, just throwing out an idea...

Dan
(in line to buy a coworker's NSX someday)

 

[hondatech_v1.0]

If he's getting both codes assuming it's running lean it's a fuel delivery problem. I'd like to add to the possible faulty parts as well since nobody mentioned injector resistance pack. I've seen it before.

 

[GreyHoundSteve]

Back from the dead.

After searching prime i have seen several of these "car runs weak below 4,500 rpm and cel codes 1 and 2" and i have yet to see a definitive answer about the solution to this problem.

So code 1 & 2 are the o2 sensors, i have replaced both. I have also tested the voltage to the sensors and that is fine too.

I replaced my spark plugs, fuel pressure regulator and fuel filter. So now the mechanics are guessing bad fuel pump.

If anyone has solved this problem and it was not the fuel pump then please speak up and tell me what it was?

It is also possible that i have a bad extension harness from my Cantrell headers so i am going to test this first and then if that checks out get a new fuel pump.

My main relay is also new.

Any other guesses before i buy a new fuel pump?

 

[GreyHoundSteve]

My problem was indeed a bad fuel pump. Car runs great now.