p0340 and p0303 and low compression, Please Help!

[cwc1960]

I have a 1999 Altima with 174,000 mi on it. It has had a 3rd cylinder misfire for a good 6 months and would idle and run a little rough when below 1,000 rpm and was perfectly smooth idling or driving above 1,000 rpm. Fuel injector cleaner would clear up the misfire and come back once I stopped using the cleaner. After a few months of this I decided to replace the 3rd injector to see if it helps. I could not find any vacuum leaks, the plugs, wires, distributor cap and rotor are all new. All this time the only code present was a p0303. Changing the injector went smoothly, I lubed up the new o-rings on the new injector and it fit right it. Tightened it all up and started the engine and it idled similar to how it had in the past, maybe slightly better. However when I drove it, any acceleration above 1,500 rpm was very rough with a lot of shuttering until I let off the gas, not to mention very weak power but it does not stall or act like it will cut off. I now how a p0340 (camshaft position sensor circuit malfunction bank 1) and a p0303 (3rd cylinder misfire) code showing. Last of all, which I should have done first, was to do a compression test, cylinders 1,2 and 4 are all good at around 150, but the 3rd was a low 30. Leaking exhaust valve is what I thought but how could this happen at the exact same time i changed the injector? Or maybe low compression was the cause of my misfire all along, but what did changing an injector have to do with creating this new problem of very rough acceleration and low power? I used a noid light to check the injector wiring harnesses and all 4 tested fine. The new injector passed a multimeter ohm test as well. I am just hoping there is a somewhat cheap and practical fix to this and the car is starting to rust and show other wear that makes me not want to put too much money into it. I know the p0340 code can be caused by a wide range of problems but any suggestions would be greatly appreciated!

[ThunderDome]

what motor is in it? if it's the KA motor, it's an interference motor. meaning that if the timing chain snapped, there is a chance that the piston(s) could have come in contact with the valves of the cylinder(s). this could bend the valves and cause them not to seat right, therefore answering ur low compression in cylinder 3. which brings me to my next question. did your timing chain snap and did you have it replaced? another probable cause would be if your compression rings on piston number 3 failed and are allowing a leak past the piston and into the crankcase.

[cwc1960]

Motor is the KA24DE, no the chain has not snapped, I'm assuming I would know pretty quickly if it did. I did a wet compression check too, with a little oil down the spark plug well and that did not change the low reading for the third cylinder. Other than a valve job I am not sure what to do anymore. Thanks for your help!

[ThunderDome]

well being a valve issue doesn't seem to be the case but i guess check it out and see what comes up. only other thing i can think of is the compression rings on the piston have failed. and honestly, i'd rather have it be a valve issue lol. possibly a partially blown headgasket maybe. not sure on this one man. hope you can fix it