Cranks but won't start

[Miner]

As long as it is running! And smoothly, I’d say everything is alright. Do double check the belt tension, but I think correcting the alignment was what the problem was

I haven’t done a TB on C30, but did it on my C27 years ago and numerous K series. The old spring tensioner was simple, almost primitive compared to what are on most modern engines. The whole turn the engine anti-clockwise to get rid of any slack seems to work fine as long as all the steps are followed.

 

[e9coupe]

As long as it is running! And smoothly

"Smoothly" is questionable but I'm just not sure. It starts immediately, revs quickly, but seems rougher then I remember but that was 12 years ago. I had a friend come over who had an NSX up till a few years ago and he said it definitely doesn't have a misfire but did seem rougher than normal. That's when I remembered I put the lighter flywheel on with the SOS 275. How much different is it with that lighter flywheel? I can't drive it yet so it's only without a load.

 

[drew]

Get a vacuum gauge.

Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

 

[e9coupe]

Get a vacuum gauge.

Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

I always forget about checking vacuum for internal problems. I use a smoke machine all the time though.

 

[Old Guy]

Despite the off-set crank pins, the 90 deg V6 is not a perfectly even firing engine. My C32 has always had a slightly rough sounding idle that is most noticeable when in the car probably because the noise / vibration is transferred through the front motor mount to the firewall which makes a good sounding board. A lighter flywheel will definitely make this worse. Manifold vacuum is steady. If your manifold vacuum is fluctuating then you have another issue.

 

[e9coupe]

Put a vacuum gauge on it and it was rock steady. Made my day. All that's left now is taking the covers off and setting the TB belt tension one last time.

The interior is still gutted but I'm ready to paint the top so it shouldn't take long now.

 

[Old Guy]

Put a vacuum gauge on it and it was rock steady. Made my day. All that's left now is taking the covers off and setting the TB belt tension one last time.

Steady vacuum is the correct answer! You didn't mention this in the previous posts; but, if the valve covers are coming off you might want to check valve clearances.

 

[e9coupe]

Steady vacuum is the correct answer! You didn't mention this in the previous posts; but, if the valve covers are coming off you might want to check valve clearances.

I didn't mention it, but I did check them and they were all within spec to my surprise. The car/motor has 180k on it and I only put 4k on it before it was parked so I don't know the maintenance history. I belive it was maintained by Shad at Driving Ambition. I bought the car from a coworker and know he took very good care of it based on how he operates. I parked next to it for years before I bought it from him. It wasn't going to anyone else. ;-)

 

[Honcho]

Funny, I had my first hot start failure last night. Had to feather the gas to get it to fire. Car was warm, outside temp was 40F.

I feel like the NSX just does this every few hundred starts.

 

[e9coupe]

It's been a minute... I finally found some time to mess with the car. The timing marks are dead on. Pulley mark and all the cam marks. Fuel injector screens are perfectly clean but I did not have the injectors rebuilt (yet). No signs of fuel issues as far as contamination. New plugs and gapped at factory spec. Coils look original but not sure (180k). Vacuum gauge is steady. Compression is 190-215. It's not registered so I can't drive it but I made a video of the exhaust so you can hear the popping. My gut says ignition but I don't have any tools to check it. A mechanic friend says with good compression I don't need to do a leak down test but I have a gauge.

 

[Old Guy]

I don't know. That doesn't sound that much different than my 2000; but, I only hear it from the outside when the engine is idling.

When the engine is in closed loop operation it is trying to run right at an AFR of 14.7. The thing is it doesn't stay steady at 14.7. If you look at the up stream sensor voltages the AFR is moving up and down which is part of the normal process of O2 replenishment for the 3 way catalyst. Perhaps when it swings high you get a mild misfire which creates that erratic exhaust pop.

At idle, the injector pulse widths are short. If you have one slightly dirty injector that particular cylinder may be getting a slightly lean fuel mix which could cause a lean misfire on that cylinder. A small fuel error on one cylinder will not generate a DTC or result in much fuel trim correction because the O2 sensor measures a blend of three cylinders. If the exhaust noise bothers you, send the injectors out for cleaning. If the noise persists after injector cleaning that is just the way it is.

The important part is are you getting misfires with the engine under load? Those will be noticeable while driving. If you are not getting misfires with the engine under load then you need to stop obsessing about the erratic exhaust noise.

 

[e9coupe]

I don't know. That doesn't sound that much different than my 2000; but, I only hear it from the outside when the engine is idling.

When the engine is in closed loop operation it is trying to run right at an AFR of 14.7. The thing is it doesn't stay steady at 14.7. If you look at the up stream sensor voltages the AFR is moving up and down which is part of the normal process of O2 replenishment for the 3 way catalyst. Perhaps when it swings high you get a mild misfire which creates that erratic exhaust pop.

At idle, the injector pulse widths are short. If you have one slightly dirty injector that particular cylinder may be getting a slightly lean fuel mix which could cause a lean misfire on that cylinder. A small fuel error on one cylinder will not generate a DTC or result in much fuel trim correction because the O2 sensor measures a blend of three cylinders. If the exhaust noise bothers you, send the injectors out for cleaning. If the noise persists after injector cleaning that is just the way it is.

The important part is are you getting misfires with the engine under load? Those will be noticeable while driving. If you are not getting misfires with the engine under load then you need to stop obsessing about the erratic exhaust noise.

The noise is to show the rough running. The noise doesn't bother me, and the exhaust is loud anyway, just trying to show the misfiring. It vibrates the car. It's not normal compared to how it ran in the past but since it's not registered yet I can't put it under load to see how bad it is. No obsessing, something is wrong.

 

[Miner]

I don’t really see or hear a misfire. There is a little bit of sputter, but it doesn’t seem to be a misfire to me. I remember when my TL has a misfire (under load) it was a very noticeable jerk.

 

[e9coupe]

Right, it's more running rough than a misfire in the sense that there's no rhythm to it like one cylinder not working like the rest. Maybe there's more than one problem, but it feels like the rough running is related to the vibration it makes throughout the car. An exhaust video doesn't help other than the noise it makes.