Okay, so the Maxima isn't exactly the fastest thing on four wheels, but it still has enough grunt to put a smile on my face when I plant the skinny pedal... That being said, it has developed a quirk (or perhaps it was always there and I just failed to notice it): when cold, the car has very snappy throttle response, and pulls very hard. When the car warms up to operating temperature, it's like I'm driving another car. I don't think that the difference in underhood temps would be responsible for this difference, but perhaps I'm wrong.

Keeping a close eye on the oil pressure guage, it seems that when the oil pressure is high, it's good to go, but once the car warms up, the oil pressure drops quite significantly, and the power also tapers off. I've kept pretty meticulous track of oil levels, and they're right where they should be. I did check the ATF level, and it seems a little low - that wouldn't cause the sort of problems I've described would it?

Thanks,
Nick  

actually all cars do that its because of a couple of things, one they run richer, the egr valve not get activated, and the engine is cold, as you know colder means more power. when the car warms up, the egr valve starts working, the ecu cuts back fuel, and the engine is warm. technically that's how its supposed to run. try doing a tune up, change the fuel filter, plugs, wires, cap/rotor, change the egr valve and clean the ports, new ignition coil, adjust your valve lash if you can, they type of stuff, but my old Honda did that too and everything else was perfect on it. the at fi really doubt that would do it, and yes the oil pressure will drop as it gets warm because the oil get thinner when its hot, it has to drop off, the rule is that you need 10psi of oil pressure for every 1000rpm, so at 1000 you need 10 and at 7000 you need 70, that's the lowest you can have.  

Gee, now if only I could figure out how to keep the EGR from tripping on at all. I replaced the fuel filter and plugs when I bought the car, but I haven't done the rest of what you're suggesting. What do replacement EGR valves cost?  

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the rule is that you need 10psi of oil pressure for every 1000rpm, so at 1000 you need 10 and at 7000 you need 70, that's the lowest you can have.

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well they depend on the car they can range from 50 to 400, you can test it, if its got a vacuum hose, take the hose off and get a vacuum gun, pump some vacuum on it ( no more than 20 inches) the car should stall, if not then the passages might be restricted or the valve might have gone bad, also it should hold vacuum, try this, at night when you get home park the car shut it off, and pull 15 inches of vacuum and leave it on there, go to bed and come back in the morning it should still be at 15 inches if it has dropped at all even 1 inch you have a leak and you need to replace the value, your valve costs about 140 from napa, so make sure that's its bad and not plugged before you go replacing it. next don't take it off, it does a lot of good things first its for emissions it reduces NoX, next it cools the combustion process, that's especially important on the highway, my truck had a bad egr valve and it did not open up, so what was happening is that the engine was pinging and the ecu was seeing it through the knock sensor, so it was retarding ignition and adding fuel, by doing that i lost of ton of power and had pretty bad gas mileage, once i replaced it it fixed the problem. i tested it with the vacuum gun and it was not holding vacuum. and as add on, some cars had egr valves called a positive pressure valve that means that when the engine is idling and has full vacuum the valve will not open, it does not matter how much vacuum you put on it, it will not hold the vacuum so what you have to do is keep the engine revved up at about 2000rpm and then try pumping it.  

really, yeah that's in all of the engine builder books, and the rule is as a minimum more is better but only to a point.  

What you are saying is very interesting.  I had a humvee in the army that would run fine in the winter time but not at all in the summer.  How did we get it to start in the summer time?  Untill we got a new fuel injector system we had to put a bag of ice on top of the fuel injector system.  Why?  It has to do with swelling rubber rings in the F.I.'s housing.  

Civicking I give you 5 Cheezy Stars...

Ahh wait. We don't have those anymore...


There we go. 5 Cheezy Grins.  

Believe it or not my mother's van does the same thing.  

Try 20w50 motor oil, change all the vacuum hoses and re adjust the ignition timing, change your fuel filter and check your computer for codes, also inpect all of your emmissions systems, and check your transmission oil/fluid ( even though auto tranny fluid is oil...) inpect your ignition system ( spark plugs, wires, distributor, etc.) and replace what needs replacing. check your coolant too and the cooling and heating hoses. check the belts and make sure they are okay. also make sure your brake pad are good and that you are not binding. Inspect your tires as well. when all of that is good your good to go.  

Thanks to everyone who commented on this - I'm going to check the EGR and PCV thoroughly on the weekend when I have enough time and light to make any necessary changes. Fortunately, I scored a FSM, so it lists all steps that should be taken in the event of driveability issues, including lack of power, and they were pretty consistent with what you all were sugggesting.  

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Try 20w50 motor oil, change all the vacuum hoses and re adjust the ignition timing, change your fuel filter and check your computer for codes, also inpect all of your emmissions systems, and check your transmission oil/fluid ( even though auto tranny fluid is oil...) inpect your ignition system ( spark plugs, wires, distributor, etc.) and replace what needs replacing. check your coolant too and the cooling and heating hoses. check the belts and make sure they are okay. also make sure your brake pad are good and that you are not binding. Inspect your tires as well. when all of that is good your good to go.

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first of all, check your codes:
http://www.sr20forum.com/archive/index.php/t-96214.html

all you need is a screwdriver...  

answer to your HMMWV problem.  The reason you need to do thet is simple.  The fuel injection pump sits in the valley between the cylinders.  It gets really hot in there.  Especially in the summer, and you have just driven somewhere and shut it off.  There is no more air blowing through there to cool it off, and the engine is hot.  That warms up the fuel in the pump, making it thinner or even boiling a little bit to cause a vapor lock.  The worn injection pump can not build enough pressure to open the spring loaded valve in each injector to sqiurt the fuel in the cylinders because the thin fuel seeps by the little pistons in the pump.  A new pump is then in order.

In Iraq I built aluminum heat sheilds to sit in the valley under the injector pump to reflect a little bit of the heat.  That was my little way to prolong the life of the injector pumps.  When the fuel gets thin or boils it hurts the little pistons and bores in the injector pump.  No lubrication for them, which causes the pump to wear out even faster than normal.  

Which is why some tuners get an In-tank pump.