Bad valve seals = Bad O2 Sensor

[S14mc]

The other day I noticed oil leaking from the exhaust manifold port (cylinder #1). It looks like its coming from a worn out/bad exhaust valve seal. Ran a compression and leakdown test, 147-150 across the board and 4%,7%, 7% and 25% on cylinder #1. Spark plugs confirm no oil being burnt in combustion chamber.

My question is this - Will it be okay to drive with my motor (cylinder #1) in this condition? Is the valve seal leak affecting my O2 Sensor erroneously changing the lean or rich reading? Just a guess, but it feels as though this may be the reason why my motor doesn't pull as hard as it used to. When my car is warmed up and goes closed loop it feels my car loses 50% of it power.

Any input would be great!

Thx
Jon

[Deviousjet]

TTT having the same issue but now my car is sputtering!!!

[S14mc]

TTT having the same issue but now my car is sputtering!!!

Could be your maf? Have you checked your ignition/coils?

[Deviousjet]

Yup swapped maf and replaced coil last year. The car sputters at idle. then when I turn the ac on the idle is fine, no missing or anything. Then turn the ac off and the car goes back to sputtering

[S14mc]

Yup swapped maf and replaced coil last year. The car sputters at idle. then when I turn the ac on the idle is fine, no missing or anything. Then turn the ac off and the car goes back to sputtering

Battery + Charging system??? Did you replace your O2 Sensor?

[VNG704]

s14mc, as far as I know, bad valve seals won't hurt performance. If anything, not 50% as you said.

deviousjet, I would check coil for good connection. Have you changed sparkplugs? I know a sparkplug with wrong gapping would cause sputter at idle. I can tell you that the ac being on raises the idle that's why the sputter is going away. A bandaid solution, but you can raise the idle by adjusting the IACV.

[Deviousjet]

recently changed spark plugs, pulled them out and spark plug electrode#4 was covered in soot or oil I'm guessing. ALso just recently replaced the alternator and starter. Running out of things to replace. Looking like the egr sensor possibly?

[VNG704]

I asked about the sparkplug replacement because some people just drop them in without checking the gap. /threadjack.

[yabeet]

If anything you will have crud on your valves [from oil dripping down them constantly] in cyl 1 that is preventing them from sealing good when closed.

[hiimgreg]

did you do a leak down test?
do all your valves seal?

[S14mc]

did you do a leak down test?
do all your valves seal?

I did do a leak down test. All percentage were good except 25% on cylinder #1. I'm now thinking, possibly because a worn valve seal, oil deposits built up where the valve sits, compromising the valve to fully close. Does this warrant pulling my head and replacing seats, valves, and guides? I do have a set of BC cams laying around. Maybe its time to put those in as well. So little time, too much to do.

Thx for your input so far guys.

[rex2sx]

I did do a leak down test. All percentage were good except 25% on cylinder #1. I'm now thinking, possibly because a worn valve seal, oil deposits built up where the valve sits, compromising the valve to fully close. Does this warrant pulling my head and replacing seats, valves, and guides? I do have a set of BC cams laying around. Maybe its time to put those in as well. So little time, too much to do.

Thx for your input so far guys.

Leakdown Test IS NOT for oil, its for compression leaks. Tell me, if your valve SEATS are sealing like they are supposed to. While the valves are CLOSED doing a leakdown test, how are bad umbrella (aka valve) seals going to show up? They ARE NOT

BTW it said that 20% cylinder leakage is still ok. Read the gauge, 20% is still green, anyway. I wouldnt bee too worried until it passes 30+

Honestly, i think they is something called a valve guide test but other than that, without tearing the motor apart, its hard to daig leaking valve seals.

Also, how is your 02 sensor responding? Are the PIDs jumping back on forth showing rich/lean?

Oil does ruin your 02 though..So if its not switching like it should be..it might need to be replaced after the leak is fixed

[VNG704]

How is your o2 mounted? If it's not at the bottom of piping, it might not even be affected by the oil. May unscrew to check for crud on the o2?

[S14mc]

Leakdown Test IS NOT for oil, its for compression leaks. Tell me, if your valve SEATS are sealing like they are supposed to. While the valves are CLOSED doing a leakdown test, how are bad umbrella (aka valve) seals going to show up? They ARE NOT

BTW it said that 20% cylinder leakage is still ok. Read the gauge, 20% is still green, anyway. I wouldnt bee too worried until it passes 30+

Honestly, i think they is something called a valve guide test but other than that, without tearing the motor apart, its hard to daig leaking valve seals.

Also, how is your 02 sensor responding? Are the PIDs jumping back on forth showing rich/lean?

Oil does ruin your 02 though..So if its not switching like it should be..it might need to be replaced after the leak is fixed

Good point. I'll see if I can borrow a wideband.

[S14mc]

How is your o2 mounted? If it's not at the bottom of piping, it might not even be affected by the oil. May unscrew to check for crud on the o2?

I have a bottom mount, so its right after the turbo on the o2 housing.

[rex2sx]

Good point. I'll see if I can borrow a wideband.
You dont necessarily need a wideband. Just test your factory 02 sensor with a Digit mulit meter, volt meter, or watch the PIDs on a scan tool.

[S14mc]

You dont necessarily need a wideband. Just test your factory 02 sensor with a Digit mulit meter, volt meter, or watch the PIDs on a scan tool.

I see. That's right. Should I be seeing oscillation between .9 to .2 volts? Or should it be at a particular voltage?

[rex2sx]

I see. That's right. Should I be seeing oscillation between .9 to .2 volts? Or should it be at a particular voltage?

Pre cat..should "bounce" back and forth, like you said

Post cat.should maintain a more consistent reading with minor switching

[Hashiriya415]

o2 has nothing to do with you loosing power, over 60% throttle ECU runs open loop and ignores any o2 readings.
Check your fuel pressure, ECT sens, and TPS.
Mechanical stuff would be a clogged cat, worn cam lobes, non sealing valve seats. Check with google on how to test for any of these if you need info.

[rex2sx]

o2 has nothing to do with you loosing power, over 60% throttle ECU runs open loop and ignores any o2 readings.
Check your fuel pressure, ECT sens, and TPS.
Mechanical stuff would be a clogged cat, worn cam lobes, non sealing valve seats. Check with google on how to test for any of these if you need info.

Do you know how the ECU reads WOT. At +4.9volt. At WOT your car is not using feedback form the O2. So if your ECU is reading WOT at only 60% of throttle, looks like YOU have a problem. 02 sensor feedback is not used either at WOT or cold starts

02 does cause loss in power, poor gas milage, and a horrible idle among other things. What makes you think it doesnt??

[Hashiriya415]

I don't have an o2 on both my tuned cars and my bike that run OPEN loop all time.
No power loss, better gas mileage since it runs leaner then factory, normal idle. Makes me think something wrong with your vehicle.
You want to be controlled by the government keep your o2 with factory tune for an efficient 14.7 clean burning combustion chamber and proper working cat. That's what your o2 is good for, making you stay in the 14.7 for maximum cat efficiency and clean air-fuel burning.
Why do bikes not have an o2, except Cali most do?

[rex2sx]

I don't have an o2 on both my tuned cars and my bike that run OPEN loop all time.
No power loss, better gas mileage since it runs leaner then factory, normal idle. Makes me think something wrong with your vehicle.
You want to be controlled by the government keep your o2 with factory tune for an efficient 14.7 clean burning combustion chamber and proper working cat. That's what your o2 is good for, making you stay in the 14.7 for maximum cat efficiency and clean air-fuel burning.
Why do bikes not have an o2, except Cali most do?

Ok..Where do i start...Your explanation was still not correct. Plus, you never stated you had a tuned vehicle in the beginning. How do you know he has a tuned ECU? You disbale 02 sensor feedback on TUNED vehicles..Some ECUs need to see feedback from an 02 to work properly. Im not sure if it is this way for nissans becuase i have never tuned on them, i will admit. From an average consumer standpoint (untuned), yes; gas mileage will decrease along with power and other problems.

Plz show me a bike thats not car'bd that does not run an 02 sensor. This is interesting info.

[Pacman]

If they were seals, you'd have a puff of blue smoke on initial start up, size of smoke depends on how worn they are. Let the car sit one night and on morning start, look for smoke. You wouldn't have an external visual leak of oil outside the engine. Not you problem.

What you're dealing with, high leak and rough runnng, low fuel mileage, no power, sounds like you have a burnt valve in number one. Do a leak down test again and listen for where the air is escaping. If you hear it in the exhaust, burnt exhaust valve. If you hear it in the intake, burned I take valve (highly unlikely since these run cooler than the exhaust valves). Lastly, if you hear air leaking in the engine (like through the oil fill cap), you have bad rings. Now, with this, you need to take the cylinder head off and regrind the valves at a machine shop or re-ring the pistons (depending on where the leak is).

Basically, you're talking about valve seats, not seals. The seats will cause sensor malfunction due to incomplete burn; fouling o2 sensors and such.

[rex2sx]

If they were seals, you'd have a puff of blue smoke on initial start up, size of smoke depends on how worn they are. Let the car sit one night and on morning start, look for smoke. You wouldn't have an external visual leak of oil outside the engine. Not you problem.

What you're dealing with, high leak and rough runnng, low fuel mileage, no power, sounds like you have a burnt valve in number one. Do a leak down test again and listen for where the air is escaping. If you hear it in the exhaust, burnt exhaust valve. If you hear it in the intake, burned I take valve (highly unlikely since these run cooler than the exhaust valves). Lastly, if you hear air leaking in the engine (like through the oil fill cap), you have bad rings. Now, with this, you need to take the cylinder head off and regrind the valves at a machine shop or re-ring the pistons (depending on where the leak is).

Basically, you're talking about valve seats, not seals. The seats will cause sensor malfunction due to incomplete burn; fouling o2 sensors and such.

the worst thing he got was 25%, which is still "good", well it is according to the gauge. So i dont think burned valves have that low of a percentage, but maybe?? I simply brought up the other symptoms dealing with an 02 senor so he might watch them to see if he experiences this, becuase the OP was worried about his 02. For all we know it could be fine.

OP: What engine do you have? and what modifications?

[S14mc]

the worst thing he got was 25%, which is still "good", well it is according to the gauge. So i dont think burned valves have that low of a percentage, but maybe?? I simply brought up the other symptoms dealing with an 02 senor so he might watch them to see if he experiences this, becuase the OP was worried about his 02. For all we know it could be fine.

OP: What engine do you have? and what modifications?

Its an S13 Blacktop. I'm running a JWT tuned ecu. Program is for 50# injs. and Z32 maf. Actually, my car idles and drives fine, with the exception of a noticeable power loss. No noticeable smoke when the car is fully warmed up, accel or decel. Only thing is I can "smell" the burnt oil when I pull up to a stop. That's why I was thinking that possibly the leaking oil may cause a disruption with the o2 sensor, hence affecting performance. I had a spare o2 sensor and tried that out but same result. The power loss is only noticeable once the car is fully warmed up and after about more or less 20 mins on the freeway. Should I try running without an o2 just to see if there's a difference?

[VNG704]

The burnt oil smell is the oil on the exh mani. Was it leaking out of the exh mani port 1 or on it? Can you see where the oil is leaking from? could be valve cover gasket, could be from that "T" for blow-by off the crankcase, loose hose.

The power loss could be anything. It could be stuck wastegate? I mean, I don't think the o2 has anything to do with your prob. I'd look elsewhere.

[S14mc]

The burnt oil smell is the oil on the exh mani. Was it leaking out of the exh mani port 1 or on it? Can you see where the oil is leaking from? could be valve cover gasket, could be from that "T" for blow-by off the crankcase, loose hose.

The power loss could be anything. It could be stuck wastegate? I mean, I don't think the o2 has anything to do with your prob. I'd look elsewhere.

Thx. The oil is coming from inside exhaust port #1. I'm assuming it has be a worn valve seal or blow-by.