nasty04GT

i have a 2004 GT with 71k miles and my check engine light turned on recently. i took it to autozone to get the computer scanned for the problem code and the guy told me that it was the camshaft position sensor. i bought the new sensor ($15) and installed it in two minutes. i figured the light would turn off by now, but it just hasn't shown any difference at all whatsoever. also, my car has been backfiring every other time i start it up. it usually takes 2x to start up the car, but once the car is on, it performs normal. the alternator has been charging up the optima battery good. any advise or experiences?

SilvrStang

I would also replace the crank sensor man its about 15 bucks it doesnt hurt. Crank sensor going south will also cause this. I was in the same boat and replaced the cam sensor and it all worked out.

uberstang1

+1 on the crankshaft sensor, also discconnect the batter to reset the CEL and see fi it comes back on.

02TrueBlueGT

Change the alternator. Your sensor will always go bad even replacing it. There's a diode in the alternator that gives off energy (might have described it wrong) to the cms. Happened to me last year. Replaced alternator and then I was good.

nasty04GT

I disconnected the battery to clear the CEL and drove around for a while. The light appeared after about 30 mins of driving. I went back to autozone to check the code. The guy said it was still the cam position sensor. There wasnt a code for the crank sensor tho....

cliffyk

What was the exact code, there are four codes related to the CMP each with a different set (though overlapping) of possible causes ?

nasty04GT

the guy gave me a receipt of the problem code. this is what it says: "Troubleshooting code: P0340. probable cause: cam sensor defective. engine mechanical condition-timing belt/chain out of time. check connector and wiring to sensor".... and the same code poped up after i changed the cam pos. sensor

cliffyk

Here are possible causes and diagnostic tips for P0340. Note that one tip is "electrical interference from other improperly functioning systems may have intermittent impact on the CMP signal".

Many have found that a failing generator can create sufficient EMI/RFI to upset the cam sensor. The only way to definitively test for this would be to use an oscilloscope to monitor the generator output, without such a tool swapping out the generator is the only practical "test".

Check out all of the battery and ground connections to the block first...

nasty04GT

thanks for the advice. I guess im just stuck buying a new alternator. Do you know if the autozone 110 amp alt is much different from a PA alt. Rated at 130 amp? Im probably gonna buy the PA amp anyways since its only like 30 dollar difference. But should I expect any performance gains?

cliffyk

None, however if you actually need 130A it will take an additional 0.6HP from the engine to run the 130A unit.

110A * 14.6V = 1606W = 2.15HP (1600 / 746);
2.15HP @ 60% efficiency = 3.6HP required from the engine.

130A * 14.6V = 1900W = 2.5HP (1900 / 746)
2.5HP @ 60% efficiency = 4.2HP required from the engine.

where:
1HP = 746W
60% is a reasonable expectation of efficiency for an automotive generator.