? about timing and rough idle.

[Da Hapa]

Hi guys/gals -

After buying my NSX last year with about 43K miles on the odo. I took it to one of the more reputable shops in my area and had the timing belt, water pump, hoses, 60K mile service, gaskets, etc. done to the total tune of a few thousand dollars. My reasoning was that the car was then 7-years old, and the previous owner had spotty maintenance records on the car. I intended to (and have) enjoyed the car tremendously and I figured it was best to clean the slate and start from scratch.

In almost a year and about 8K miles (more than 2K of which were to and from NSXPO) the car has been really good to me. The original shop changed the oil at about 4K miles (Mobil 1), changed the tranny fluid (I tired GM synchromesh for some notchy cold shifting) and nothing more. As expected for a "refreshed car"... it's run like a champ.

This week, I took it into another highly reputable place to have some minor problems addressed (driver's window slow to roll up and the damned climate control fan noise). Nothing serious but little things that go wrong on an 8-year old car that I wanted fixed.

I have no reason to doubt the new shop, and what they're telling me (an admitted lay person when it comes to working on cars) makes sense. But my car is running a bit rough and they believe the timing is off. They investigated the plugs and coils to see if that was the problem and it wasn't. So they now think it's the timing.

I don't want to give out the names of either shop since my intent isn't to dispariage anyone. My hope is to get some feedback from you experts (Larry... Mark...) because something seems odd to me. I should state that the last time the car was at the original shop I got a funny feeling about them and that's the reason I'm now with the new place. But that's just my gut.

Any all feedback from you would be greatly appreciated.

 

[Daedalus]

Sounds a lot like they're guessing and throwing parts at the problem. First sign you should go somewhere else. Besides, between the timing and the plugs/coils, checking the timing is a lot cheaper. If they're going to guess, at least insist they guess at the cheaper things first. How did the plugs look?
Is it rough like it's a random misfire?

 

[Briank]

The timing on the NSX very seldom needs adjustment but it would not hurt to check it just to rule it out. A throttle body cleaning would not be a bad idea along with doing the re-centering the motor mount procedure. Also pulling the clock fuse to reset the ecu may also help and is easy to do.

 

[Jin1976]

Does it gives any CEL code? Mine read 12 and is going to a workshop this weekend to clean the EGR. Idle is slightly rough.

 

[Da Hapa]

Does it gives any CEL code? Mine read 12 and is going to a workshop this weekend to clean the EGR. Idle is slightly rough.

No... it does not give any CEL codes.

 

[Da Hapa]

Sounds a lot like they're guessing and throwing parts at the problem. First sign you should go somewhere else. Besides, between the timing and the plugs/coils, checking the timing is a lot cheaper. If they're going to guess, at least insist they guess at the cheaper things first. How did the plugs look?
Is it rough like it's a random misfire?

Sorry, I went back and edited my original post because my wording was misleading. They looked first at the coils and plugs because the head tech felt that I'm having a very slight misfire on the #6 cylinder. It wasn't that so they think it might be the timing.

There has been no charge to me thus far. But if I ok investigating the timing, that will end up costing me some $.

 

[PoohBEAR]

I would take it back to the shop that had done your timing belt and ask for their opinion. If they charge you a few more bucks, I would pay it so you can really find out. Your other option is to take to another shop and have a second opinion.

 

[Daedalus]

Sorry, I went back and edited my original post because my wording was misleading. They looked first at the coils and plugs because the head tech felt that I'm having a very slight misfire on the #6 cylinder. It wasn't that so they think it might be the timing.

There has been no charge to me thus far. But if I ok investigating the timing, that will end up costing me some $.

The problem is there's no easy way to diagnose a random arc in or under a coil. Ohm tests won't find it. You pretty much have to record the plug's time-trace and make sure there isn't a single fire missing. And do it for all 6 cylinders to be sure. If they've done this then they're all over it. If they've done this but aren't charging you for it, they're your biggest charity. Probably not, if they're going to charge you to check the timing. It would be quicker to just swap all 6 coils with 6 known good ones, but most shops don't have 6 good coils lying around. I'm wondering why they suspect #6, and how they verfied the coil and plug are good. Did they remove them both and look at the plug? The plug can carry a lot of info.
If it's a problem with a single cylinder, and if it isn't the fire, then it's almost certainly the fuel. Injector could be (partly) clogged. Or out of spec or OL (full misfire). Timing will affect overall power, but it won't cause an unbalanced roughness from a single cylinder.

Are you "hapa" as in "half"?

 

[Scin]

Also keep in mind that the NSX is known to idle rough, especially at fast idle while warming up. Take a look at:

http://www.nsxprime.com/FAQ/Troubleshooting/roughidle.htm

 

[Da Hapa]

The problem is there's no easy way to diagnose a random arc in or under a coil. Ohm tests won't find it. You pretty much have to record the plug's time-trace and make sure there isn't a single fire missing. And do it for all 6 cylinders to be sure. If they've done this then they're all over it. If they've done this but aren't charging you for it, they're your biggest charity. Probably not, if they're going to charge you to check the timing. It would be quicker to just swap all 6 coils with 6 known good ones, but most shops don't have 6 good coils lying around. I'm wondering why they suspect #6, and how they verfied the coil and plug are good. Did they remove them both and look at the plug? The plug can carry a lot of info.
If it's a problem with a single cylinder, and if it isn't the fire, then it's almost certainly the fuel. Injector could be (partly) clogged. Or out of spec or OL (full misfire). Timing will affect overall power, but it won't cause an unbalanced roughness from a single cylinder.

Are you "hapa" as in "half"?

It's my understanding that they did check the plugs and installed new coils to make sure that wasn't the issue. Their original thought was that one of the coils was bad and they asked me whether I had ever had the engine steam cleaned. My understanding is that the coils and plugs looked fine.

And yes... you've got the right hapa.

 

[Larry Bastanza]

Very Simple, remove the valve covers and check the cam timing. I am suspecting this is the "timing" they are refering to.

HTH,
LarryB

 

[dynomike]

The way to check if timing belt is off a tooth is hook a vacum gauge up to the motor if your vacum is 20 inches of vacum than your fine, anything lower than that your timing belt may have sliped a couple teeth. I have never seen a nsx go out of timing to where it makes the car run rough. Another thing I have seen is the fuel injectors get dirty and not work appropriatly.

 

[Daedalus]

Can you actually jump a tooth or 2 without causing an interference? I agree being off a whole tooth would be pretty darn noticeable--more than a little rough. One or both banks would be way off.

 

[ScienceofSpeed]

One tooth drops compression in the affected bank by about 75 psi per cylinder on a healthy motor. You will notice a little rough idle and performance decrease, but nothing I'd consider dramatic if the other cams are timed properly. As Mike notes, check with a vacuum gauge at idle. The fuel pressure regulator line is a good one to use. This shouldn't take a tech more than 15 minutes to do.

Cheers,
-- Chris

 

[Da Hapa]

Very Simple, remove the valve covers and check the cam timing. I am suspecting this is the "timing" they are refering to.

HTH,
LarryB

Correct.

That is exactly what they're going to do on Monday. I'll post the results at that time.

 

[Larry Bastanza]

Hi Mike and Chris,

Two great tips about vacuum gauge and compression. Thanks.

I have never seem a timing belt jump a tooth on an NSX, but I have had a few mis-installed that needed to be reset.

There is a distinctive V8 type rumble at idle if the rear exhaust cam is off as tooth, but I agree it is subtle.

Regards,
LarryB

 

[PaulL]

Maybe you could get that free emissions system check done (see other thread), and depending on the age, etc, they will replace plugs for free.

 

[Da Hapa]

Maybe you could get that free emissions system check done (see other thread), and depending on the age, etc, they will replace plugs for free.

Unfortunately, my car is a 1998 so I don't think it falls within the range of the emissions check.

 

[Da Hapa]

Hi Mike and Chris,

Two great tips about vacuum gauge and compression. Thanks.

I have never seem a timing belt jump a tooth on an NSX, but I have had a few mis-installed that needed to be reset.

There is a distinctive V8 type rumble at idle if the rear exhaust cam is off as tooth, but I agree it is subtle.

Regards,
LarryB

Essentially one year and 8,000 miles later it's basically impossible to tell whether the problem initiated at the timing belt change or if the timing belt "jumped" a tooth. I wasn't able to discern the slight rumble at idle primarily since I took my car to the first shop as soon as I purchased it and never really drove it before that. I recall asking about the slightly rough idle as it was rougher than the 3.2L V6 was in my old Legend coupe but I was told that it was completely normal for the NSX to have a slightly rough idle.

Overalll, I have a very good feeling about the shop that has the car now and I'm comfortable sharing with everyone that it is with John Marting at Cerritos Acura. John has called me every day to tell me exactly what he's thinking, what he's doing, and what he's found. While I'm not mechanic, it's all made sense to me and I'm glad to see that it jives with so much of what you guys/gals have pointed out.

John told me that car seems to be running very smoothly right now and he did do a vacuum test on the car and that a good motor should show 20 and mine is showing 20. He's recommended a fuel injector service as a double, secret probation style safety net just to clean out any carbon deposits that might have developed with the rear cam timing being off and I'm probably going to do that too while it's in. I might be pissing my money away but I'm a big fan of better safe than sorry.

Thanks to everyone who has offered input on this thread. I sincerely appreciate your time and consideration.

 

[Da Hapa]

One tooth drops compression in the affected bank by about 75 psi per cylinder on a healthy motor. You will notice a little rough idle and performance decrease, but nothing I'd consider dramatic if the other cams are timed properly. As Mike notes, check with a vacuum gauge at idle. The fuel pressure regulator line is a good one to use. This shouldn't take a tech more than 15 minutes to do.

Cheers,
-- Chris

Thanks Chris. This also jives with what John is telling me. I've always felt my 1998 runs strong to start with but John says that I've been "leaving a little something on the table" with the previous set up. I'm looking forward to having John install the Cantrell AIS on my properly set up car!

 

[Daedalus]

That's kind of the point of the vacuum reading--to see if the cam timing is off. If the gauge is reading a very steady 20"Hg that would be very good news.

 

[nis350]

That's kind of the point of the vacuum reading--to see if the cam timing is off. If the gauge is reading a very steady 20"Hg that would be very good news.

Can someone please explain why vacuum reading of 20"Hg indicate a good motor? Is that for all motors or just the NSX

What is the significant of the vacuum to timing and valves being too tight?



DA Hapa - was your motor idling rough when warm? As Chris stated that the motor would lose about 75lb of pressure/compression, I would think that your motor would lose quite a bit of power and lots of vibrations.

Just want to learn something. Thanks :wink:

 

[Daedalus]

Can someone please explain why vacuum reading of 20"Hg indicate a good motor? Is that for all motors or just the NSX

What is the significant of the vacuum to timing and valves being too tight?

Not sure what you mean by valves being too tight. The amount of vacuum will vary a bit from model to model, but generally it will be above 16"Hg for all cars (adjust for high elevations). The vacuum test is the quickest method of revealing most potential problems with the internals. The steadiness of the needle is just as important as the value itself. If it varies--and *how* it varies--give clues about what might be wrong. In the same way that bad valve timing reduces compression, it will also reduce vacuum. Much quicker to pull the booster hose for a vac test than all coils and plugs for compression/leak down testing. Low but steady vacuum might indicate a vacuum leak, mis-timed crank sprocket or a tired engine with leaking rings. A wiggling needle will indicate other things, depending on the motion/pattern of the wiggles...perhaps a single mis-timed cam (1/2 engine), or single burned valve or broken lifter (1/6 engine). It is by no means conclusive, but it catches a lot of the big ones ($$$). If the engine runs like crap but the vacuum is good, then you might sooner suspect a fuel/ignition problem.

 

[Da Hapa]

DA Hapa - was your motor idling rough when warm? As Chris stated that the motor would lose about 75lb of pressure/compression, I would think that your motor would lose quite a bit of power and lots of vibrations.

Just want to learn something. Thanks :wink:

After the first shop did the timing belt, I thought my car was idling a bit rough. Nothing bad with vibrations, etc. but rougher than the 3.2L V6 in my old Legend Coupe idled and certainly rougher than I would have expected. The original shop told me that was "normal" for a 3.2L NSX. So... not knowing any better I went about my merry way and never thought anything else about it.

As soon as John Martin started my car and I mean as soon, he said there was an issue. Take that for what it's worth.

I'm hopefully getting my car back this week so I'll be really interested to see how it idles now.

 

[Larry Bastanza]

I think it is very likely that the rear exhaust cam is retarded one tooth. I have seen it so many times. There is a specific method laid out in the service manual to get this right, you must follow it.

HTH,
LarryB