97 s10 4.3l missing bad(3 DTC's) HELP?

okay so a buddy of mine has a 97 s10 with the 4.3 in it, he just bought it about a month ago and in the past week it started to run really rough when he would drive for longer periods of time( after about 20-30 mins), but yesterday i met up with him to take a look at it and he gave me the codes that autozone had checked for him...

here are the codes:
1. p0300
2. p0340
3. p1345

anyway, i started working on it yesterday and i knew that the p0300 code was for random or multiple misfires, so i changed the plugs and coil so far and it hasnt gotten any better, but i wanted some advice on what to do or things i could do to find out whats wrong with it without him spending every dime he has... any info would be much appreciated

thnx
Devin

P0300 - Muti misfires
P0340 - Cam sensor
P1345 - Crank sensor

Do a visual inspection on sensors, and clean sensors with CRC electrical cleaner.

check and make sure it's not cat converter or have you already? and vaccumme hoses.

DTC's must be diagnosed and repaired in the order they were retrieved. Then clear all DTC's, perform a drive cycle and retest the OBDII system.


P0300 is in fact random cylinder misfire. It is almost always due to secondary ignition faults ie spark plugs, plug wires, distributor cap and rotor, and ignition coil. These engines are very fussy when it comes to ignition parts, if you use parts other than AC Delco/Delphi you can expect to have performance issues. If you don't diagnose the problem correctly and just throw parts at it in hopes of repairing it, you're wasting your money and time. So, if you insist on throwing parts at it, at least throw AC Delco or Delphi ;)

The P0340 indicates a problem with the camshaft position sensor circuit, (not necessarily the sensor itself). The P1345 is indicating a problem with camshaft and crankshaft correlation. Usually it's caused by the distributor being installed a tooth or more off from where it should be. It can also be set if the timing chain jumps a tooth or more. A quick check for the cam sensor is unplug the sensor, turn the ignition on but do not start the engine. The pink wire should show battery voltage and the pink with black tracer should show less than 5 ohms resistance to ground.

To check if the distributor is timed correctly, manually rotate the crankshaft clockwise until the rotor lines up with the "6" on the distributor housing.

http://i561.photobucket.com/albums/ss58/cwhook/Distributorrotoralignment43L.jpg

Then check the marks on the vibration dampener and make sure they are lined up.

http://i561.photobucket.com/albums/ss58/cwhook/43LVortecFinding1TDC-Copy.jpg
If all marks line up at the same time, and the distributor has not been removed since the engine ran ok, the timing chain and distributor are both ok.

we already changed the plugs, coil and also crank sensor, and the truck ran great for about a day and then started doing it all over again, so tomorrow im going to check the cam sensor i guess... i dont believe its the dizzy or timing because when you first start the truck it runs fine, actually really really smooth, but then after driving for a bit it starts missing real bad.... so ill check the cam sensor and see what codes come up this time and post back...

in the mean time feel free to disprove my theory :)

Have you checked fuel pressure and leakdown rate? If there's a problem with the camshaft position sensor, even an intermittent one, or the distributor alignment, it WILL set a DTC. After you replaced the crankshaft position sensor, did you perform a crankshaft variation learn? Gotta use a capable scan tool to do it. It must be done if the sensor is moved in its mount or replaced. You've already retrieved P0340 and P1345, clear the DTC's and perform a drive cycle and see what DTC's come back. http://www.obdii.com/drivecycle.html

okay so i got the codes checked again and this time the only codes that were thrown were:
1. P0300
2. P0145

so now the pcm isnt throwing a code for the cam sensor anymore.... im stuck guys, let me know what you think...

thanks again
Devin