May have dead cylinder..help

[adrenaline_nsx]

So ive been getting a misfire that started last week. I can definitely hear it at idle and there's a loss of power through the whole rpm band. Ive replaced plugs, disconnected o2 sensors, tried different coil packs, new gas but it didnt go away. Yesterday I had the car idling and started disconnecting coil pack sensors one at a time, each would make the car sound different except coil 5, so that told me there was something wrong with that cylinder..either fuel injector, coil pack, or bad valves. I switched coil pack and fuel injector on that cylinder and the test result was the same. I havent performed a compression test that next on the list guess. I dont believe has ever had a valve adjustment done, could adjustments get so bad to cause the car to misfire?? Any ideas fellas????

 

[EdinKali]

So ive been getting a misfire that started last week. I can definitely hear it at idle and there's a loss of power through the whole rpm band. Ive replaced plugs, disconnected o2 sensors, tried different coil packs, new gas but it didnt go away. Yesterday I had the car idling and started disconnecting coil pack sensors one at a time, each would make the car sound different except coil 5, so that told me there was something wrong with that cylinder..either fuel injector, coil pack, or bad valves. I switched coil pack and fuel injector on that cylinder and the test result was the same. I havent performed a compression test that next on the list guess. I dont believe has ever had a valve adjustment done, could adjustments get so bad to cause the car to misfire?? Any ideas fellas????

How many miles are on the car? If a valve gets too tight it won't close fully
and you will lose compression in that cylinder and might even get some blow back/backfire into the intake tract.

 

[adrenaline_nsx]

How many miles are on the car? If a valve gets too tight it won't close fully
and you will lose compression in that cylinder and might even get some blow back/backfire into the intake tract.

there is currently 75k on the engine and there is no smoke or fumes...the car does smell like its burning rich though but then again I have no cats.

 

[Thanhnsx]

Are you running on stock springs and retainers? Maybe a slightly bent valve but I can be wrong. You're on the right track with compression testing.

I've never seen adjustments get that bad. If anything, it would be tapping loud.

 

[adrenaline_nsx]

Are you running on stock springs and retainers? Maybe a slightly bent valve but I can be wrong. You're on the right track with compression testing.

I've never seen adjustments get that bad. If anything, it would be tapping loud.

yes still on stock valves and retainers. bent valve doesnt look to far off :frown:

 

[Thanhnsx]

yes still on stock valves and retainers. bent valve doesnt look to far off :frown:

12.4 quarter mile on stock springs and retainers. That is pretty fast for stock springs and retainers. But then again you have a rev limiter but that still doesn't mean it can't float. But you never know. Might get lucky and it can be something else. You'll find out when you do your test.

Esp. going F.I. it's safe to have stronger springs and retainers.

 

[Larry Bastanza]

Next step is simple, compression test.

That will tell all. Let's hope for the best.

Regards,
LarryB

 

[Aircooled]

Put a little bit of oil in each cylinder and do that compression test. I mention the oil just in case cylinder 5 is a little dry. If your results are a little skewed then you might want to do a leakdown test which involves actually pressurizing the cylinder up to 100psi and monitoring how much air is being lost and where's it's being lost (It will tell you if it actually is a valve, and if it is, if it's the intake or exhaust side).

Personally I'd remove the spark plug in cylinder 5, disconnect the fuel pump (you can pull a fuse for that) and have somebody crank it over. If you ground the spark plug against a metal object on the car it should spark. This will obviously confirm or eliminate the ignition side. If it is sparking, reinstall the plug, start the car for about 10-15 seconds and if it's still misfiring, remove the plug again and see if you can smell fuel on the plug. If not then you could be looking at a faulty fuel injector, if you do then it could be a valve hanging open. Take the fuel rail off and switch number 5 fuel injector with one of the other two on the rail, if the misfire follows the injector then we've got our answer, if it doesn't then I would do that compression and leakdown.

 

[ScienceofSpeed]

Make sure that when the compression test is done that the throttle body is kept open. In addition, pull the fuse for the fuel pump. This is often missed by techs, and the restriction of the throttle will produce artificially low numbers.

regards,
-- Chris

 

[Larry Bastanza]

BTW, you can avoid pulling the fuel pump fuse by disconnecting the fuel injector resistor pack on the passenger side of the engine bay. Typically when I do this I am on that side of the engine bay working anyway, so it is easy.

As Chris has mentioned, do make sure the throttle is open. If you have no air to compress, your readings will be off.

Also I would do the test first WITHOUT the oil, if it comes up bad or low, add the oil, repeat the test, which will help you determine if the leak(if there is one) is ring related or valve related.

HTH,
LarryB

 

[Aircooled]

Also I would do the test first WITHOUT the oil, if it comes up bad or low, add the oil, repeat the test, which will help you determine if the leak(if there is one) is ring related or valve related.

HTH,
LarryB

Yeah you're right, for some reason I had cylinder wash stuck in my head when I wrote that (which would dry the cylinder walls out giving a horrible compression reading in a cylinder that may not be that bad). Either way I don't think it'll matter considering we're diagnosing a misfiring cylinder.

 

[FLA NSX FIXER]

Just for the record we have seen SEVERAL NSX'S in the shop with missfires that were caused by tight valves it is a very good posibility and the most welcome one

good luck

 

[adrenaline_nsx]

Just for the record we have seen SEVERAL NSX'S in the shop with missfires that were caused by tight valves it is a very good posibility and the most welcome one

good luck

im get a feel like this also, car idles well, drives well, just has a loss of power. So what was your fix..new valves/head work??

 

[adrenaline_nsx]

compression test done 160-170 for all cylinders, when cranked for 2-3 seconds. i was able to get in the 180s when it cranked for about 5 seconds. i assume this is a bit low??

 

[EdinKali]

Sounds about right and all are within 10% of each other. Might be worth hooking up a vacuum gauge to it in order to help with diagnosis.

If you aren't familiar with using one for diagnosis, this page will help you out:

http://www.secondchancegarage.com/public/186.cfm

 

[Aircooled]

compression test done 160-170 for all cylinders, when cranked for 2-3 seconds. i was able to get in the 180s when it cranked for about 5 seconds. i assume this is a bit low??

Sounds pretty good, now check the spark on that cylinder, and check the fuel injectors.

 

[Daedalus]

180 psi is well within spec (142 psi minimum), but not as close as I would expect to the 199 psi nominal. Even my sedan with 223k miles on it gets within 10psi on 7 of 8 cylinders. My guess is that even with the throttle plate open, the turbo might be acting as a restriction. Anyone know for sure?

 

[Aircooled]

Turbo wont act as too much of a restriction normally. I believe the 200psi spec is with the engine being warm, correct me if I'm wrong here.

 

[adrenaline_nsx]

got a chance to mess around with the nsx today..there is good news though I guess. Two of the spark plugs are NOT receiving any spark, causing the misfire and loss of power. So where should i go from here? damaged harness??

 

[Larry Bastanza]

BTW, you say "turbo setup in progress" in your sig. Are we talking about a stock setup or otherwise?

The next question is do you really not have spark, or are the plugs fouled, possibly some fuel management issue.

Regards,
LarryB

 

[angus]

Igniter.

 

[adrenaline_nsx]

BTW, you say "turbo setup in progress" in your sig. Are we talking about a stock setup or otherwise?

The next question is do you really not have spark, or are the plugs fouled, possibly some fuel management issue.

Regards,
LarryB

Larry, the spark test was done from pulling the coils actually so the spark plugs were left inside. So the problem is from the ignition system somewhere. the turbo setup is pretty much done but i want to get all the kinks out of the car before i boost on her. this was the last photo that i took, its completed now.

angus i shall try the ignitor tomorrow. thanks

 

[adrenaline_nsx]

Went to a fellow primers house yesterday and tried on his igniter box and....BINGO firing on all cylinders again! thanks Zishan! thanks fellas for the help..time for boost!

 

[swerve2007]

good deal

 

[angus]

I have seen this happen a few times before , glad to hear it is solved!