Acura nsx na1 I need help!!

[Na1_george]

hello,
First time being in a forum so please be patient, I'll do my best to keep this short.
1991 acura nsx 149k supercharged
(don't know if that needs to be said)
Had the car for a couple of years and never had an issue with it, I took the car to the track. First lap was fine, second lap 3 gear at 8000 rpm, biggest black cloud of smoke I seen in a car, car shuts off, I get off the road, I can't see shit because the whole Rear window is covered with oil, when I go check, a part of the valve cover gasket is hanging out, crazy spill of oil everywhere, I towed the car home, when I get home. I start to take everything apart, I have oil in the intake manifold, I have oil, running through the sideskirt, I remove the valve cover, it was the one toward the rear end of the car, I replace the gasket, turned the car on.
Car is running fine, no problem, when I drive the car at low rpm, everything seems fine, if I pass 6000 rpm black smoke will come from the exhaust, only from.the left side, and I have a little oil leak somewhere that I haven't been able to find, it sits on the headers, but it's little, All this happened 2 years ago, i was away and couldn't get into it, when I came back home, I Been using the car like twice a month, not passing 65 MPH and shifting below 4500 rpm, the car doesn't feel like it has lost power, a couple mechanics have checked the car out, but there's a lot of theories, pvc valve, blown piston, bad piston rings, one told me I need to buy a whole engine, one of them said the car just need to be tuned, another said it was the head gasket. So question is (sorry for the whole story) does anyone have a clue? On what is going on? I just don't Want to bring the car to a shop and get charged an arm, if there is a way I can figure this out myself.
Hope this makes sense. Thanks.

 

[Old Guy]

What did the mechanics do when they 'checked the car out'? Did you pay for these mechanics to actually check and test things or did you try to get a free diagnosis because it seems like you are just getting a bunch of knee jerk 'could be this' responses.

Have you done a compression test? That would give you a good indication as to whether its "blown piston, bad piston rings, one told me I need to buy a whole engine". If you discharged as much oil as you described with the engine continuing to run I would be inclined to think that there might be some secondary damage from oil loss. Did the low oil pressure light come on or the oil pressure gauge indicate low oil pressure when any of this occurred?

The supercharger may be material to this problem. Since there are different supercharger systems for the NSX you would need to specify the type of supercharger and the connection for the PCV system. Based upon your description it almost seems like the supercharger might have pressurized the crankcase. The NSX does have some oil pooling issues that can materialize during high G turns on the track and the supercharger PCV arrangement may make that a bigger problem. Since my NA2 is NA, I will let somebody who tracks their car with a supercharger system advise on that.

If you have not carried out any actual tests / measurements on the engine and you are not able to do this yourself, then its time to suck it up and pay some money to have someone do this for you. That will provide you with an indication as to whether the engine assembly has been damaged. If the engine is OK, then you can move on to figuring out why you have what appears to be a crankcase pressurization issue.

 

[Honcho]

I think you need to do the following:

Compression Test
Leak Down Test

These two tests will tell you if there are any ring seal issues and also potentially signal a head gasket leak. Any decent mechanics shop can perform these tests if you don't want to buy the gauges. I would ask for a cylinder-by-cylinder report in writing on each test. You will have two data points for each cylinder- cylinder pressure and leakdown %.

For compression, ~200 psi is considered "nominal" for the NSX. Anything above 142 psi is considered within service limits, but generally anything below 180 psi (assuming you are sea level) is considered to be not great. Max variation between cylinders is 28 psi, but again, anything more than around 5 psi can indicate a potential issue.

For leakdown, you're looking for less than 5%. Again, variation between cylinders is the most important. If it's like 5 6 4 8 27 6, that indicates a problem.

Block Gas Test

This will tell you definitively if you have a blown head gasket because it can detect even the smallest amount of combustion gas in the coolant system. You can buy the kit on Amazon and DIY.

PCV Valve Test

If the PCV hoses are routed in the OEM pattern, this can be an issue with supercharged cars because, like Old Guy mentioned, it will pressurize the crankcase. The PCV valve is supposed to open under engine vacuum and close when manifold pressure goes positive up to 1 ATM. The NSX PCV system is designed to accommodate 1 ATM of crankcase pressure- it will ventilate out through the rear head and into the throttle body (the black metal pipe that sticks into the side of the throttle bellows).

A supercharger will make things worse because under high load there is a lot more crankcase pressure than 1 ATM-, it will blast all that crankcase gas and oil through the throttle body to be burned, hence the black smoke. If the PCV valve is failing closed, it will make the problem much worse- the crankcase will be constantly pressurized and venting through the intake manifold. Not all of the oil is burned- it ends up collecting in the reservoir at the bottom of the manifold. It's possible you have been filling the reservoir full of engine oil because your PCV valve is stuck closed and whenever you hit the throttle hard, it gets sucked up and burned. The high crankcase pressure would also explain why it's blowing oil out of the valve cover gaskets and all over the car. Those gaskets are designed to just contain drip pressure, not 1 ATM+ from a supercharger.

From the symptoms, my educated guess is that it's a PCV issue. To solve the black smoke, you'll need to replace the PCV valve and clean the oil out of the intake manifold. Long term, you may want to consider a ventilated catch can like the SOS version here.

 

[Na1_george]

What did the mechanics do when they 'checked the car out'? Did you pay for these mechanics to actually check and test things or did you try to get a free diagnosis because it seems like you are just getting a bunch of knee jerk 'could be this' responses.

Have you done a compression test? That would give you a good indication as to whether its "blown piston, bad piston rings, one told me I need to buy a whole engine". If you discharged as much oil as you described with the engine continuing to run I would be inclined to think that there might be some secondary damage from oil loss. Did the low oil pressure light come on or the oil pressure gauge indicate low oil pressure when any of this occurred?

The supercharger may be material to this problem. Since there are different supercharger systems for the NSX you would need to specify the type of supercharger and the connection for the PCV system. Based upon your description it almost seems like the supercharger might have pressurized the crankcase. The NSX does have some oil pooling issues that can materialize during high G turns on the track and the supercharger PCV arrangement may make that a bigger problem. Since my NA2 is NA, I will let somebody who tracks their car with a supercharger system advise on that.

If you have not carried out any actual tests / measurements on the engine and you are not able to do this yourself, then its time to suck it up and pay some money to have someone do this for you. That will provide you with an indication as to whether the engine assembly has been damaged. If the engine is OK, then you can move on to figuring out why you have what appears to be a crankcase pressurization issue.

I have not done any test, the mechanics didn't mentioned any of this, I'm so glad there's people like you and all the ones that have reply. I will get to that, just ordered all the kits. The pressure light did not come on.
The oil pressure wasn't reading the same though, it is lower at idle than before.
The car is in dominican republic, unfortunately I don't know of any certified mechanic here that I can trust to bring the car. Don't know how to reply to each of you specifically, but really, THANK YOU SO MUCH. Will keep you guys up to date on the car.

 

[Old Guy]

If you are slightly mechanically inclined, it is fairly easy to carry out your own compression test. A reasonably accurate engine compression tester can be had for less than $50. A remote starter switch is useful; but, not necessary. If you search the Prime web site, you should be able to find links to .pdf copies of the 1991 service manual which will set out the procedure for carrying out a compression test. Or go here for a copy of the manual

Acura NSX 1991 Service Manual : Honda Motor Co : Free Download, Borrow, and Streaming : Internet Archive

Service manual for the 1991 model year Acura NSX

archive.org

If you don't want to carry out the compression test yourself, there are Honda dealerships in the Dominican Republic and one of them should have the mechanical skills to carry out a compression test.

Carry out the compression test or get it done and then compare the test results with the specifications that @Honcho mentioned. That will fairly quickly indicate whether you have valve / piston / piston ring damage and will likely point out a head gasket problem (but, not always). If the engine fails any of the compression test parameters I would stop there because its pretty much guaranteed that the engine is coming out of the car for a tear-down. As Honcho notes, the block gas test is fairly easy to carry out yourself.

Some people like leak-down tests. I am not sold on their value. Leak down tests are a Federal Aviation Administration thing for piston engine aircraft with a very specific test equipment requirement. None of the leak down testers for sale that I have seen indicate FAA compliance with the results that % leakage values are generally not comparable between different testers. If you don't like the % numbers with one tester you can switch to a different tester and get different numbers. For a mechanic using a consistent same leak down tester who has experience with multiple NSX engines the test can provide useful additional information. Since you don't appear to have access to a mechanic with multiple NSX experience I would not bother. The leak down test requires a fairly large air compressor so if you don't have one that definitely eliminates it as a home garage option.

Since you report a change in oil pressure, you might want to arrange for an oil pressure check to confirm that it is acceptable. The NSX oil pressure sender units can go out of spec / fail with age.

As Honcho notes, check out the PVC system. However, without knowing the specifics of your supercharger system I don't know that the PCV tests in the factory service manual will apply. Does your car still have a PVC system - perhaps its just venting into a tank vented to atmosphere?