noise at higher rpm

[96altimagxe]

I have a question. I own a 96 altima automatic transmission with 144k on it. It seems to lose power the longer i drive it during the day. It's also been getting terrible gas mileage (sometimes under 20 mpg). After the engine warms up there is a rattling noise that comes jus before the transmission shifts. I'm not sure if it is detonation or excessive valve clearance. I got a trouble code for the knock sensor a few months ago. I bought a new sensor and sub harness and relocated the sensor on the firewall and grounded it out, to trick the ecm so it didnt retard my timing. I havent had the time or funds to pull the intake off and put it in properly. It runs alot better than it was, but not good. I dropped the timing back to 18 degrees btdc and run 93 octane and add octane booster for prevention. My question is could the problem be from excessive valve clearance or is it time to start looking for a new ride?

[NISTECH]

possible chain noise???

[96altimagxe]

The chain is noisy at idle. Could that be the noise that appears only before the transmission shifts gears after the car warms up? Could chain stretch be my performance problem?

[NISTECH]

not typically. how is your idle is it rough? those are known to suck the intake gasket in at the bottom of the #4 intake port. this could be the cause of your fuel consumption problem.

[96altimagxe]

It idles ok. It hesitates at higher rpms before it shifts, almost feels like it misfires, but not that severe. The pinging noise only starts to come after about a half an hour of driving. I do hear an air leak, but im pretty sure its from my exhaust manifold when checking for cat backup when looking for a knocking problem.

[96altimagxe]

The gas consumption problem started occuring after changing plugs and wires. I've changed them twice since and went back to factory plugs, but I'm still getting crappy gas mileage.

[NISTECH]

how bout the wires? factory?

[96altimagxe]

right now i have xact brand. I tried MacPherson (i think thats what they were) and the ones that were on there originally werent factory.

[96altimagxe]

I've heard about distributor problems on first generation altimas, could a weak secondary ignition coil cause this problem. The primary and transisters resistances are all in specs.

[NISTECH]

the distr probs I have seen with early alts was oil contamination of the cam position sensor inside the distr.

[96altimagxe]

Another thing ive seen when i pulled off the distributer was that the turning mechanism on the shaft seemed loose. I could actually pivot it a few milimeters each way. It doesnt look worn out though. I havent found a chance to compare this to a new one, but is this normal? And if this isn't could this cause detonation?