head gasket probably ok, (its a low mileage car isnt it?) i replaced mine b/c i wanted to rebuild the heads. the old head gaskets looked pretty "soggy" bloated looking aroudn the cooling passages.
pressure check? on cooling system? assume you not talking about compression pressure check. it will probably tell you what you already know... leaky LIM gasket. they will just tell you have a slight pressure loss, not where it's at.
ECM/PCM
i use both terms. same thing, almost. PCM is really only for automatic transmissions (PCM = ECM + TCM). If you have a manual transmission then it's basically an ECM since there is no tranmission controller.
other confusing terms, not all apply to the lumina, or at least i havent run across them yet thankfully:
wss - wheel speed sensor - probably term used in conjunction with 4 wheel abs? Anyway, measure wheel rotation.
vss - vehicle speed sensor - sensor at TAIL shaft of transmission, basically how fast you are moving
tss - turbine shaft/speed sensor (measures the transmission INPUT shaft speed to determine amount of slippage from the torque converter. not sure if we have one of these on the lumina. remember torque converter always slips a little until TCC engages. NOT used to determine vehicle speed.
tcc - torque converter clutch. locks up torque converter at cruise for better mpg.
long time ago. i was in that "i hate all these fancy computer crap on cars" but have embraced it and fairly understand it. i was into hobby electronics before computers were the in-thing, made it that much easier.
not a fan of these side mount engines either, it just seems WRONG. no space to work, have to remove 5 unrelated parts to get to the part you need to replace. my dodge ram on the otherhand, i could fit a couple of bodies under the hood..
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to address the seepage.
cant have coolant seepage from side of engine unless its coming from head gasket.
there are 6 seals on each lower intake gasket:
see pic
http://www.automotiveforums.com/vbul...5&postcount=56
see pic of old intake gasket with arrows. the 3 big openings are INTAKE. the two edge openings are COOLANT.
3 orange seals between each intake runner and the crankcase oil. impossible for these intake seals to pull in coolant unless coolant is in the oil
2 orange seals for the coolant passages that goe into the intake. leak causes oil/coolant to intermix (oil leaks in cooling system on engine cooldown, while engine running, coolant forces itself into engine crankcase and mixes with oil) also cause external coolant leak and definitely air leak INTO cooling system.
1 black plastic all around generally seals the crankcase from open air.
if you look at the LIM gasket pic with the 2 arrows - that arrow on left shows where i had coolant almost POURING out onto the ground (external leak) AND some leaking into crankcase. middle arrow pointing at intake runner, shows where i probably had oil (and crankcase air) sucked into the combustion chamber of #3 or #4 cylinder (vacuum leak)
lower intake gasket failure causes one or more of the following:
1) external coolant seepage at front or back of engine.
2) internal coolant seepage into lifter valley and into engine oil. slight chance to suck in oil into cooling system during engine cooldown.
head gasket leak:
1) leak coolant into combustion chamber, and lots of air (fuel/air/combustion gas) into the cooling system
2) oil into combustion chamber
3) oil/coolant intermix
4) air leak between adjacent cylinders (low compression on 2 adjacent cylinders )
engine running, engine hot: oil is 40psi, coolant is 15psi. this is when oil can get into cooling system
engine off, engine cooling: oil is 0psi, coolant goes from 15psi to a "slight vacuum". this is when coolant can get into oil when cooling system is still pressurized, and suck in oil into cooling system when engine is cool and slight vacuum in cooling system
bubbles - since you dont have the steady stream of bubbles [indicating head gasket leak] then you are getting your air when the car cools - when there is a slight suction in the cooling system, leaky intake gasket sucks in air - instead of the rad cap sucking in coolant from coolant reservior. this air causes dexcool to sludge.