Technical help/advice needed please

R

rave777

Registered Member
Joined
5 October 2004
Messages
45
Location
Victoria, Australia
Hi everyone,

I have a 1992 NSX, it is stock except for an NA2 exhaust system on it.

On a recent drive everything was going fine and normal. After some point during the drive I noticed a change. The intake sound had changed dramatically to a very deep drone when trying to accelerate, and at the same time the car would rev but not accelerate anywhere near what it should and did before. I did not try to rev it to much as I did not want to hurt it. Asking for any acceleration even from 4k would result in deep intake noise and hesitant revs.

I took the car home as soon as I noticed this. Driving it home it did not feel any different while cruising or driving in the low revs. But if you tried to get some acceleration the intake would get the deep drone again (kind of like it was being strangled) and the car would rev, but not deliver any real acceleration. Feels very hesitant if you ask for some acc, but ok in the normal range.

No warning lights have come on at all.

A light tapping noise can be heard while listening to the engine. By holding and/or slightly adjusting the screws at the side of the intake manifold it appeared to stop the tapping. I thought maybe some screws from the intake manifold could have come loose not allowing the butterfly valves to operate correctly, but upon inspection they are all there.

I have had my mechanic check the air box and intake manifold, but everything there looks normal.

Any advice would be greatly appreciated.
Thanks.
 
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I am suspecting the same thing.
Plugs or coils.
Its easy to check these.
There is a section in the manual on how to test the coils with a volt/ohm meter.
I did mine when I did the compression test just for fun.
Gentle with the plugs in and out.
Maybe since your in there, its time to change the plugs.
Careful attention to the torque of the plug and no cross stripping or dressing!!!
Trev
 
Just wondering what screws you are talking about???
Pictures speak hundreds of words.
Just a note to all, It has been reported that the two screws that hold each of the variable volume intake valves to their shafts, have come lose in some cars, and even fallen down into the belly of the intake. It sucks to suck one of these down the engine, I'm sure.
The screws where peened at the factory but still some come loose.
Trev
 
Thanks for the advice so far everyone. I will get the mechanic to check the coil packs and spark plugs on Monday (weekend here now) and see how we go.

ffffanman: The screws I thought may have come loose were the screws that hold each of the variable volume intake valves that you mentioned. On inspection though they are all there and still secure.
The adjustment screws I was referring to are on the exterior of the chamber, on the end of the shafts that have the variable volume intake valves attached.
 
wow, so you had him take off the intake manifold and split it, nice!
Trev
 
Ok, the spark plugs and coil packs have been checked. We replaced the spark plugs while we were in there as it can't hurt. My mechanic said that the coil packs looked ok.

Still doing the same thing. Really deep intake noise when trying to accelerate and no acceleration. It will rev, but not make anywhere near the power it should and has before. Feels really held back.

Any other thoughts as to what my car may be doing?
Thanks.
 
I'd check the timing on the timing belt.

But just as FYI... I've had once in my experience, a significant piece of the intake filter at come apart and then got lodged at the throttle plate creating a HUGE restriction, which cause the same symptoms you're describing.

So take off the intake pipe and take a look in there too. But like I said, I have a feeling it has to do with the timing belt it self (skipped a tooth), or ignition timing.

Does your check engine light work at all? ie: when you turn the key from OFF to ON position, does it turn on for 2secs and then shut off?
 
Do you mean a piece of the actual air filter itself has come off?

The engine check light does work. It comes on when the key is turned and then goes off.

I will mention the timing belt to the mechanic.

What would be the first things to check regarding the ignition system?
 
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rave777 said:
Do you mean a piece of the actual air filter itself has come off?
Click to expand...

Yes... unlikely, but it only take 5min to check.

The engine check light does work. It comes on when the key is turned and then goes off.
Click to expand...

ok.. so its most likely not the MAP or TPS sensor, those would cause similar symptoms too if one was unplugged or faulty.

I will mention the timing belt to the mechanic.

What would be the first things to check regarding the ignition system?
Click to expand...

Well, you mentioned your mechanic "looked" at the coil packs... they can "look" physically fine, but could be bad internally, there's no real way to check them other than swap them out with known good ones and try them.

You'll have to take the valve covers off to check the if the timing belt has slipped or not.
 
I would suggest doing the following things:

1. Get a vacuum gauge on the vacuum line #4 and see if you have a steady vacuum at idle. (Should be rock steady)

2. Check the fuel pressure.

3. Perform a compression test.

The results of these tests will tell us a lot.

BTW, If you have a problem with #1, skip #2, and do #3:).

Typically when I am working my way through a problem like this and it seems to be eluding me, I go back to basics and prove the engine is mechanically sound.

HTH,
LarryB
 
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this sounds like text book exhaust restriction, low speed ok ,accel no good, (with intake noise) hook up vacuum gauge as larry suggested, vac at idle should be steady (around 20 " ) increase rpm slowly , if the vac starts to fall as rpm increases you most likely have a exhaust restriction,(providing you have no timing issues) , vac gauge still one of the most important tools in the box
 
ok everybody, I finally have some news to post on this.

The car is finally back to normal now. Turns out it was a timing issue. It had skipped some teeth so I had the timing redone and now it is back in action.

Thanks everyone for your support, help and suggestions through this. I appreciate it. Just goes to show what a great community we all enjoy here on nsxprime.
 
This should be a lesson for those who question the necessity of timing belt service. You are very lucky, it could have been disasterous.
 
By the way, it was the 7th post not the 2nd, Your not that good buddy!!! lol
Trev
 
ffffanman said:
By the way, it was the 7th post not the 2nd, Your not that good buddy!!! lol
Trev
Click to expand...


Trev,
I think there's an old saying... Don't knock on someone if you something blah blah? how does it go? :P

I do believe I said in *MY* second post... not *THE* second post :P

C-speed said:
Didn't I say it was the timing belt that skipped some teeth in my second post?
Click to expand...


:biggrin::biggrin::biggrin:
 
davidf said:
This should be a lesson for those who question the necessity of timing belt service. You are very lucky, it could have been disasterous.
Click to expand...

You are beyond lucky. I have never seen a belt just jump one tooth, usually it is disaster.

Just an FYI, I did a timing belt last week on a 1992, 42K miles. It had the original belt. As I was getting the engine to TDC to set the cams prior to belt removal, guess what? I was able to rotate the crack pulley 4-6 degrees back and forth with NO movement of the cams:eek:. This belt was about the skip, and maybe be the cause of a very bad day for the owner.

I cannot stress enough how bad this is. It is sort of like high blood pressure, a silent killer. You get no indication, no early warning, it just fails.

Regards,
LarryB
 
Ah shucks, i thought i had you on that one.
Now I look like the fool, fool!
lol
Your the man.
Trev
 
So Larry, if it is a cog'd belt an its on all the pulleys, what is stopping the belt from turning the rest of the cogs?
Are you saying that there where no ridges on the belt or that the belt was so loose that it was slack and the cams take so much effort to turn that the grooves jump out of the cogs or what?
I need to know, cause I can't see it.
Trev
p.s. I just like saying cog cause I use to like the Jetsons.
 

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I'm going slightly off topic here, but someone {vendor} offered a blue HD timing belt I believe the name was "Toda" possibly. Any thoughts on it?:confused:
 

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