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Tech Talk Technical Discussion About The Nissan 240SX and Nissan Z Cars |
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#1 |
Leaky Injector
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Bad valve seals = Bad O2 Sensor
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 |
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#4 |
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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
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#5 |
Leaky Injector
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#6 |
Zilvia FREAK!
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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. |
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#7 |
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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?
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#9 |
Zilvia Member
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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.
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The thing is, it’s a gearbox, okay? It has one job to do! One job! Pull the lever… ‘Am I a pencil? Am I a cauliflower? Am I a nuclear power sta– I’m a gearbox! Oh, heavens, I’m gonna swap some cogs around!’ Jeremy Clarkson on Automatics |
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#11 |
Leaky Injector
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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. |
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#12 | |
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Quote:
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
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#14 | |
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#15 |
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#16 |
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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.
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#17 |
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#18 | |
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Quote:
Post cat.should maintain a more consistent reading with minor switching
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#19 |
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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. |
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#20 | |
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02 does cause loss in power, poor gas milage, and a horrible idle among other things. What makes you think it doesnt??
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#21 |
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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? |
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#22 | |
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Plz show me a bike thats not car'bd that does not run an 02 sensor. This is interesting info.
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#23 |
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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. |
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#24 | |
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OP: What engine do you have? and what modifications?
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#25 | |
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#26 |
Zilvia FREAK!
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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. |
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#27 | |
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