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Jstefans
New User
Dec 4, 2007, 11:45 AM
Post #1 of 2
(1630 views)
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Gas in engine oil
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I have a '92 Pathfinder SE, V6 VG30 motor, w/ abt 200k kms... I routinely have my engine oil sampled and tested (I use synthetic oil and extent my oil changes). Recent test came back indicating the presence of gas in the oil... What is the likely cause(s) and solution(s)?
PS- when accelerating after stopping, have noticed slight hesitation initially when engine is at normal temp.
Thanks, Jay
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DanD
Veteran
/ Moderator
Dec 5, 2007, 5:58 AM
Post #2 of 2
(1619 views)
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Re: Gas in engine oil
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Seems like a simple question to answer at first read BUT it’s not; there are so many variables; this could be caused by one thing or a combination of a number of things that could add up to this happening.
First thought the engine is running rich (being over fueled) due too excessive fuel pressure, leaking injector(s) or a sensor that’s out of range, sending inaccurate information to the computer. Not so far out of range that the computer can see this and set a check engine warning light.
Then there are ignition misfires, due to spark plugs, ignition wires not supplying an adequate spark to light the fuel mixture. Leaving unburnt fuel in the combustion chamber for the piston rings too drag down into the crankcase.
Next are lean misfires, due too the lack of fuel compared to the oxygen in the combustion chamber. Possible causes of this are insufficient fuel pressure, vacuum leaks, EGR opening too soon or too much, diluting the fuel mixture.
This lean mixture leaves pockets of air or void of fuel areas in the combustion camber. The flame front that starts after ignition, comes across the combustion chamber, hits one of these pockets and the flame goes out.
A single cylinder misfire regardless of which type can cause a chain reaction and the computer could add more fuel to all cylinders. This is caused for the fact that an oxygen sensor is just that, all it can report on is oxygen content in the exhaust; it doesn’t care about the hydrocarbon (raw fuel) that’s present. When a misfire occurs, it’s not only the fuel that doesn’t burn but the oxygen as well. This unburned oxygen is seen by the O2 sensor, in turn the O2 sends a lean indication to the computer. The computer reacts to this by adding fuel to all cylinders, in an attempt to get the O2 back to the proper “normal” signal.
I could go on too engine mechanical reasons for fuel getting into the crankcase but I’ll stop here because I only just scratch on the above reasons.
To find the root cause could be a long and diligent process of elimination not skipping any steps, starting with engine mechanical, basic fuel & ignition and then on too electronics.
Simple problem maybe, maybe not?
Note
To any of the other techs reading this; I’m talking about this person’s 1992 OBD1 vehicle, without misfire detection.
Dan.
Canadian "EH"
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