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Hesitation Mystery continues...replaced many parts

Joined
30 October 2000
Messages
4,249
Location
Houston, TX
I've been having this low RPM hesitation for a while now. It has been getting worse over time. I've replaced a number of parts, but no luck.

The hesitation occurs when I'm cruising at lower RPM's and give the car gas without down shifting. It will start hesitating and popping, and feels like it's running on 3 cylinders. If I down shift to get the RPM's up and then accelerate, it's fine. The problem was solved when I unpluged the 02 sensors, it seemed to run smooth and not hesitate, but it returned. It got so bad the car was back firing slightly under low RPM load.

Here is a list of replaced parts/services done:
  • 02 sensors(bosch)
  • spark plugs(ntk)
  • air filter (unifoam)
  • main relay (oem)
  • cleaned throttle body
  • fuel injector cleaner
  • fuel filter (oem)
  • coil packs (oem)
  • fuel pump (walbro 255)
  • installed a fuel pressure gauge...pressure normal
  • checked ground connections
  • "ignitor"/ICM (Ignition Control Module)
  • 02 sensors again (ntk)
  • injectors (rdx swap)
  • oil change
  • new battery

I just did the RDX/ECU Rom from Prospeed and it runs much better(I was hoping it was the injectors). But I noticed the hesitation is still there down low when I try accelerating at lower RPM's. It's not as bad, but it's still there.

My thoughts/research via "search" are to replace:

  • speed sensor
  • fuel pump resistor
  • throttle position sensor


SPECS:
1991 Acura NSX 5 speed
dc headers
test pipes
Pride V1 exhaust
intake/unifoam filter
RDX injectors with Prospeed ECU Rom
 
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Put a vacuum gauge and verify how much vacuum the car is making.If it is low look for a vacuum leak, after verifying that ,watch fuel pressure gauge and check fuel regulator. Pull off vacuum hose on pressure regulator and make sure pressure rises when you take the hose off. Do you have a a/f meter?
 
I think I have your answer. You said the problem was solved after unplugging the 02s, but also said it returned. Were the 02s still unplugged when the issue returned? If not, and it only came back after plugging them back, then this means your DCs (with flex bellows) have a crack somewhere near the 02 sensors and is letting outside air in. This air is throwing the 02s off which causes these issues.

Had the same issues like you and tracing this garbage was a long ass headache as the DCs showed no signs of leaks. Ended up putting back oem headers on just to rule out things and what do you know, the issue was fixed.
 
Put a vacuum gauge and verify how much vacuum the car is making.If it is low look for a vacuum leak, after verifying that ,watch fuel pressure gauge and check fuel regulator. Pull off vacuum hose on pressure regulator and make sure pressure rises when you take the hose off. Do you have a a/f meter?

I sure don't. I'm a garage mechanic that kinda learns as I go. I might end up taking it to the mechanic....as I've spent enough $. I will give him your suggestion! Thanks so much!


I think I have your answer. You said the problem was solved after unplugging the 02s, but also said it returned. Were the 02s still unplugged when the issue returned? If not, and it only came back after plugging them back, then this means your DCs (with flex bellows) have a crack somewhere near the 02 sensors and is letting outside air in. This air is throwing the 02s off which causes these issues.

Had the same issues like you and tracing this garbage was a long ass headache as the DCs showed no signs of leaks. Ended up putting back oem headers on just to rule out things and what do you know, the issue was fixed.

That actually makes sense. I think I've been hearing an exhaust leak as well. The problem did go away when I unplugged the 02's, but after driving for a few days like that, it returned with the 02's still unplugged.
 
Z, Look for CL65captains thread on here. Jim has done a lot of the same things you have looking for a hesitation.

He ( this weekend ) called me from the track about a possible small exhaust leak. This will cause this problem. He has top speed headers. I think He is bringing it in this week for us to inspect them and hopefully find the problem.
 
Z, Look for CL65captains thread on here. Jim has done a lot of the same things you have looking for a hesitation.

He ( this weekend ) called me from the track about a possible small exhaust leak. This will cause this problem. He has top speed headers. I think He is bringing it in this week for us to inspect them and hopefully find the problem.

I'm searching for it now...thanks!

I was looking for the leak yesterday as I was under the car, but nothing stood out. I didn't look thoroughly though.

Man, wish your shop was closer.... :biggrin:
 
Reading through another thread, I remember I also replaced the "ignitor"/ ICM (Ignition Control Module).

My problem is similar to CLS65 Captain's problem, except mine happens mostly on the highway or at a consistent speed, when trying to accelerate and the car is already warmed up.
 
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I'm searching for it now...thanks!

I was looking for the leak yesterday as I was under the car, but nothing stood out. I didn't look thoroughly though.

Man, wish your shop was closer.... :biggrin:

Yes I wish too!

It can be a hairline crack. We are going to smoke test his headers to locate it if it is not visible.
 
Too bad it eventually came back. Maybe you can try it a few times to see if the issue goes away every time you unplug the 02s. At least you will have an idea that the 02s does have a direct effect on the issue and you're getting somewhere. With that said, you threw allot of parts at the car already, might as well try the OEM headers if you're pulling your hair out by now.
 
Too bad it eventually came back. Maybe you can try it a few times to see if the issue goes away every time you unplug the 02s. At least you will have an idea that the 02s does have a direct effect on the issue and you're getting somewhere. With that said, you threw allot of parts at the car already, might as well try the OEM headers if you're pulling your hair out by now.

Ya I don't mind the parts, as I feel some are maintenance parts that need to be changed....it is a 91 after all. Thinking that way makes me feel a little better. I just want the problem resolved. :redface:
 
Those DC headers are prone to cracking around the flex joints, I bet thats your issue. What do you think of the RDX/ECU Rom from Prospeed?
 
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Those DC headers are prone to cracking around the flex joints, I bet thats your issue. What do you think of the RDX/ECU Rom from Prospeed?

Actually the flex joints have already been repaired about a year ago. I'm thinking they are leaking from somewhere else.

As far as the RDX injectors, I like them. The car feels smoother and has a hair more pull. I'm not pushing my car hard at all until this other issue is resolved....then I'll write a better review. :smile:
 
almost sound like my tps problem I had on my integra. With the hesitation when your just cruising and not opening up the throttle. I just replaced the tps and the car ran smooth. It is a very annoying problem, I hope you figure it out.
 
My Bmw used to do this.

It was the airflow sensor. (MAF)

Disconnect it and the car ran fine as the car ran off map defaults rather than the sensor.


With the nsx at higher RPM it might run off ecu values instead of the sensor like it does with the O2 sensor.



Out of curiousity, turn off the traction control and try it. (Seperate to the above suggestion)
 
almost sound like my tps problem I had on my integra. With the hesitation when your just cruising and not opening up the throttle. I just replaced the tps and the car ran smooth. It is a very annoying problem, I hope you figure it out.

I will look into this....thanks for the advice...I really appreciate it.


My Bmw used to do this.

It was the airflow sensor. (MAF)

Disconnect it and the car ran fine as the car ran off map defaults rather than the sensor.


With the nsx at higher RPM it might run off ecu values instead of the sensor like it does with the O2 sensor.



Out of curiousity, turn off the traction control and try it. (Seperate to the above suggestion)

Thanks for the suggestion, I will definitely give that a try. I did try running with the traction control off and it's the same. No change. :frown:

But thanks for the advice...I will report back.
 
I have lived, on and off with this condition, for 8 years now. Once or twice a year I throw a CEL code 43. I have replaced a ton of O2 sensors, and each time it seems to run better for a short time. I've ready every hesitation thread on Prime, and hope to one day resolve my issue.

I have not gone down the part replacement route just yet, because I don't really feel this is the cost effective solution. I've swapped around a few coils and mounted a fuel pressure gauge that I can see from inside the car while driving. Pressure never falls off when the hesitation is occurring. I always believed it was the TPS, because it always happens around the same spot, but if the TPS was bad, I think it would do it all the time and not just 90% of the time.

Something I wanted to add that I don't believe I have read before. A while back I had my car dyno'd. The operator said it was running very lean. I never thought much about this until recently. I believe a lean condition can cause hesitation? Maybe this has something to do with my O2 replacement history? I really don't know. I just wish I lived near SOS or Larry, so I can drop it off and just tell them to fix it. I'm ready to resolve this once and for all.


Sent from my EVO using Tapatalk 2
 
Just throwing in: what about EGR.

Just a comparison: my Insight I has lean-burn-mode. The EGR potentiometer was worn and let the whole engine shake under light-throttle-conditions, esp. in lean-burn (AFR 25:1) because the EGR potentiometer was giving the ECU wrong data. After replacing the EGR unit it runs like a champ again.

A bad EGR on older Hondas is every common, not sure about the NSX though.

For testing you could disconnect the EGR plug and see if it improves. It will throw a code but nothing to worry.
 
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