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.

 

[e9coupe]

Finally drove the car (with a dealer plate). Drove in first gear up and down the street fine, flat spotted tires made it harder to tell how the motor was running but it seemed close to normal smoothness but not quite. Got on it fairly hard and shifted into second and motor started running really badly. Slowed down and it died at idle, restarted with the clutch while still moving and it ran horrible afterwards. Limped it into my garage and shut it off. No check engine light.

I had checked the fuel filter before and checked it again now and it shows no signs of debris and blows through with compressed air easily. The misfire now seems to be multiple cylinders and just worse than before.

Plan on testing fuel pressure next but don't have the right gauge. More to come...

 

[Old Guy]

That does sound a little bit like a fuel starvation problem. However, if you stop the engine and then do a restart, even a compromised pump will usually allow the engine to run unless the pump has really taken a nose dive. The fuel pressure test would be the first step in checking for fuel starvation.

When you did the test run, did you allow the engine to come up to operating temperature before the test? If so, the ECU should have been in closed loop control and if you had fuel supply issues you might have codes 43 -46 stored which would confirm a fuel issue - unless you cleared the codes by cutting the keep alive power (clock fuse reset) to the ECU. Use the service check connector to retrieve any codes that might be stored.

 

[e9coupe]

Okay, I'll check for codes. It was up to temp or close when I pulled out of the shop. Not sure.

 

[Honcho]

I'm strongly suspecting those injectors. You can't tell their condition by looking at the screens, you need to have them serviced.

 

[e9coupe]

I'm strongly suspecting those injectors. You can't tell their condition by looking at the screens, you need to have them serviced.

I am in 100% agreement. I already checked out RC to see how it works and will pull the injectors this week if I get time. I've been putting in 1000sqft of flooring in my house and it's been brutal on me. Anyway, I started the motor just now at lunch and it started but acted like it was out of time when it turned over so I only ran it for a couple seconds. I'm hoping it's leaking injectors loading up on fuel when cranking but I may check the valve timing just to know. I'm getting really good at taking the valve covers off. I don't think it's timing but I'm second guessing everything I do now. Bah.

Edit: out of time, meaning, it was hard to turn over in a couple spots like when a distributor is too advanced. No popping, backfiring, etc.

 

[drew]

Might start with a compression test...don't have to take off the valve covers and will let you know the internal timing.

I'm not sure there is any second-guessing on doing a timing belt that would be unwarranted.

 

[Old Guy]

Given the latest update on rough running following start up, I am kind of lining up with Drew. Sending your injectors out for cleaning will never be a bad thing; but,

Got on it fairly hard and shifted into second and motor started running really badly. Slowed down and it died at idle, restarted with the clutch while still moving and it ran horrible afterwards.

a sudden change like what you described would not be a typical dirty injector symptom. The effects of dirty injectors creeps up with masked effects (cylinder unbalance) until you run into the limits of fuel trim compensation. If the engine is running badly, you probably do not want to do the running pressure test as described in the service manual. However, you can do a static test with the engine off. Power up the fuel pump (maybe a couple of times) to get the pressure to spec (46-53 psi). With the return line on the fuel pressure regulator clamped off (to eliminate the effect of regulator leakage) observe the resting pressure in the fuel system. If the fuel pump check valve is good the pressure should drop a little bit on pump shut down and then decay very slowly (hours or not at all). If the pressure decays quickly that would be a sign of drooling injectors.

Rule out the fuel system problems first because they are easier to do; but, I am thinking next step is back in for a timing check.

 

[e9coupe]

Injectors are being sent out today so I guess I'll do a leakdown test in the meantime. I'd be shocked if the timing belt slipped. I know the tension was correct and I didn't accelerate/shift really hard, just "spirited".

 

[Honcho]

Injectors are being sent out today so I guess I'll do a compression test in the meantime. I'd be shocked if the timing belt slipped. I know the tension was correct and I didn't accelerate/shift really hard, just "spirited". But ya never know...

Your warm compression numbers are decent for a NA NSX. Generally (assuming sea level):

220+ = Perfectly maintained, brand-new spec
200 - 220 = Healthy
180-199 = Tired, but ok
<180 = Not great. Will run fine but could use a hone and new rings. Usually a history of NOS or FI, or heavy track use

The service manual says anything below 142 requires a rebuild.