code 0340

my jimmy has been running real bad for a while now. i finally got a code reader and i keep coming up with codes that tell me to check the crankshaft position sensor. where do i start??

The crankshaft sensor has a Hall Effect device in it. It is essentially a solid state magnetic switch, that senses the position of the crankshaft and provides a pulse to the computer as each piston approaches top dead center. The computer takes this timing pulse along with other data and determines when and which spark plug to fire, and which fuel injector to open, ect.
The sensors fail in two modes, I've had both. One, the sensor fail outright and you don't go anywhere. It's the only sensor that does not have a limp home mode in the computer. Or they just get tired and start providing the pulse later and later in the crankshaft rotation., This has the effect of retarding the ignition timing among other things. Retarded timing causes poor engine performance, poor fuel milage and unburned fuel in the exhaust which will destroy your Cat and exhaust system if not corrected
What you neet to do is:
First, go to the book store and buy the Haynes manual for your truck, if you had told us the year I could give you the exact manual #. But I think it's Haynes #:
"24071 - S-10 & GMC Sonoma Pick-ups '94 thru '01 Models covered: All Chevrolet S-10 and GMC Sonoma pick-up '94 thru '01, Chevrolet Blazer & GMC Jimmy '95 thru '01, Olds Bravada & Isuzu Hombre '96 thru '01".
They cost about $20 and are worth every penny, or you can go to the dealer and get the GM Shop Manual for $150, I have both and the Haynes is my favorite.

Second, read the manual, determin the problem, then if necessary buy a crankshaft sensor and change it. If your going to take it to a mechanic to do the work, see if he will accept parts you bring in, he'll triple the cost you pay for the part, just for having it delivered for free.

Let us know what happens.
94

P0340 is for the camshaft position sensor circuit....not the crankshaft position circuit.

the jimmy is a 96. i do have aq chilton book but as usual most of the diagrams and detailed fixes are for engines other than mine. this misfireing happens iether hot or cold. i still can keep running even if it misfires. as far as poor milage i am still getting 20 mpg just as i did when it was new. i drive like an old man so performance isnt a real factor.

Although there is a possibility there is a problem with the circuit, it is not causing your misfire. The sole purpose of the camshaft position circuit is to collect information on misfires to store in the ECM, it has nothing to do with changing engine performance.

When was the last time you did a full tune-up?


Plugs
Wires
Cap
Rotor
Air Filter
Fuel Filter
PCV valve

the last full tune up was about 200 miles ago. that was the reason for the tune up. even with all of the new plugs, cap, rotor, wires, pcv valve, and mibile 1 oil change it didnt clear up. the wires and plugs (platinum) are delco oem. since thEen i have changed the plug wires one at a time thinking that it might be a bad wire.

Sounds like you have the tune-up covered other than the fuel filter and air filter.

The camshaft position sensor is part of the distributor, inspect the harness near there for damage, loose connections, etc... What ever is causing the camshaft position sensor circuit problem may also be causing your misfire.

[the fuel filter was also changed 2 weeks ago. air cleaner was replaced about 500 miles ago. i will look at the wiring on the distributer tonight.