I know this is a really long post but I wanted to be very detailed in my
explanation so someone out there may be able to pinpoint my problem. I
really need someone's help figuring out what the problem is with my car!


I got a '96 Maxima back on Feb. 02, it seemed in good shape except for noisy
brakes which I figured I could fix easily enough (I paid $10,500 for the
car, fully loaded, with 70K miles; I think a good deal).

Anyway, after a week or two, the heater core blew and I had a floorboard
full of antifreeze (could the dealer have seen this coming?) Also it felt
like the tire was about to wobble off. So I griped to the people that sold
me the car, they agreed to pay half, and I took the car to a Nissan Dealer
to fix the problems. And they said I needed to replace my front brakes.

I picked the car up and the brakes were much quieter. But as I drove from
the lot, the check engine light began to flash on intermittently. I ignored
it at first but before long it was on all the time.

Now the car has gotten to where when I push the gas, it actually feels like
it is losing power. So I changed the spark plugs thinking that might be the
cause. It ran fine for a while, then started back, so I changed the fuel
filter, thinking it may not be geting enough gas through.

Now I notice white smoke coming from the exhaust which smells like unused
gas. I questioned a mechanic who thought it may be the O2 sensor, so I went
to another place to have the computer read.

It came up with the a Vacuum valve problem and a knock sensor problem (I
could post the exact codes if that would help). The mechanic said the vacuum
valve could be something the Nissan dealer broke while servicing the heater
core (could this be?). He really couldn't offer any info on why the car
wasn't getting power.

OK, so I went to get the oil changed because it's one of the only user
serviceable things I didn't do, at the EasyLube they told me they had a new
fuel injector cleaner that had helped quite a few people whose cars had been
"missing". So I let them do that, and drove the car back to the town where I
go to college an hour and a half away. It seemed great for the first 45 min.
or so, then it started to feel like it was less and less responsive. Anyway,
it got me home, and I was thankful.

So the next day I went out to drive the car and it would barely go at all. I
could get it up around 40 mph then it didn't want to do much else. If I gave
it much more gas, the RPMs would just go up to around 4000 like the car was
in neutral but it would never shift into the next gear. If you got over 4000
rpms it would make a horrible knocking sound.

So now here I sit, broke and afraid to take the car in and hear how much
this is gonna cost me.

I was hoping that someone may recognize some of these symptoms and be able
to point me in the right direction so the dealer doesn't eat me alive.

Could it be something that I knocked loose changing the spark plugs or the
fuel filter, or something the dealer messed up working on the heater?

Someone with some expertise please help me! I've got quite a few
mechanically inclined friends, and I'm learning some myself, so if this
sounds like something I might could fix, I'd appreciate your help!

Thanks
Dom

 

Obviously diagnosis is always difficult, especially from a remote location but here are some thoughts.

I don't know what the vacuum valve is, but a bad knock sensor may (guessing) retard the timing enough to cause the symptoms you describe. Other things to check would be a clogged air filter, clogged catalytic converter, or clogged muffler.

You may just have to bite the bullet and take it back to the dealer.

 

In all liklihood your car has multiple problems and this produces a confusing welter of symtoms.

White smoke in the exhaust is normal for the first ten or fifteen minutes of engine operation. If the white smoke persists beyond that time you may be "burning" coolant as a consequence of a failed head gasket. Have you had to replenish the coolant reservoir? Does the white smoke exhaust have a sweet sort of odor? Check the engine oil dipstick and oil filler cap. If you see brown or black oil, that is normal. If you see something that looks like an unappetizing chocolate milkshake, that is a bad sign.

Yes, it would help to post the specific Diagnostic Trouble Codes.

The lack of engine power is an ominous symptom and could be caused by a variety of problems.

- obstructed fuel filter (even though you already replaced it, there could be a load of dirt in your fuel tank)
- weak fuel pump
- bad fuel injectors
- bad fuel pressure regulator
- "tired" oxygen sensors (a "tired" sensor still works, but not well)
- obstructed air intake system (especially the air filter)
- obstructed exhaust system (especially the catalytic converter)
- bad Mass Air Flow Sensor

There are so many possible problems that estimating repair costs is a pointless guessing game. One thing is certain: someone (you, your friends, or your paid service professional) will have to spend 3-4 hours doing some serious diagnostic work. This would include
- a careful visual examination of the engine compartment wiring and vacuum hoses
- a careful visual examination of the exhaust system (look for a crushed pipe)
- a compression test
- an intake manifold vacuum test
- a fuel pressure test
- an exhaust back-pressure test