96 Blazer - camshaft sensor?

[Big Zack]

A few weeks ago my 96 Blazer (4.3L V6 with 120,000 miles) would not start. Towed it to a local repair shop and they replaced the fuel pump assembly. While they were in there I had them tune it up with new plugs, wires, and distributor along with a new fuel filter.

The following week and all was fine. Truck was running better than it ever had.

And then...

It started out as a little hick-up misfire. Cruise control set @ 65 heading down the highway. Then another hick-up... and another... until it felt like I was on one of those high speed washboard test tracks they show on Auto-Week. When I got in the gas hard it would ramp up smooth, then as the RPM fell it got rough again.

After finding a safe spot to stop the thing finally stalled out and lit the check engine lamp. After checking under the hood (like I knew what I was doing?!) I started it back up and drove it to a repair shop that read the OBDII code for me. P0341-camshaft sensor. No problem, they had it replaced in a few hours and I was off again.

The following night I watched my Blazer ride off on the back of a flat-bed tow truck after it completely died while doing 60 down a very dark country road. Seems the repair shop didn't snug that ignition coil wire on very well - it had popped off. No big deal... that was a fix-it-for-free problem. (AAA worth every $)

The next few days and all was fine.

And then...

Same as before, only different. A little hick-up one day at highway speeds. Then a few more the next day. Then more the next, until I was back on the wash-board express. Finally it threw a code so I stopped by the local discount auto supply store for a quick code read and got P0300-misfire and P0342-camshaft sensor error... again!

So, what now? Could it be the camshaft sensor again? Could there be something causing the camshaft sensor to go bad? ECM problem? I have also read that the ECM could be wrong in reporting the cam sensor and that it could be the air flow sensor, the crank sensor, or tps (whatever that is). How do I figure this out? Could any of this be related to the tune up done with the fuel pump replacement?

Thanks!

-BZ

[amac209]

P0342 Camshaft Position Sensor Circuit Low Input
check the wiring to the cam sensor there may be a loose conection somewhere or the wires could be pinched somewhere and grounding out, i don't remember how the wires are routed but on some vehicles they get too close to the exhaust manifold and burn the insulation. it's also possible you bought a defective sensor did you get it from gm? theres nothing more frustrating than replacing a bad part with a bad part. it's possible the problem is in the computer but not very likely. i would take a close look at the wiring and if no problems are found get a new sensor from GM. if metal particles are on the sensor the signal gets screwed up.

[Big Zack]

Originally Posted by amac209

check the wiring to the cam sensor...

I pulled the connector off and checked all the contacts and the few inches of wire that I could get to... they go down behind the engine up against the firewall and into a bundle with a few dozen other wires - next to impossible to trace end-to-end. From what I could see, the wiring looks fine.

Originally Posted by amac209

it's also possible you bought a defective sensor did you get it from gm?

Yes, a new unit from my local GM dealer. (~$50) Does GM warranty electrical parts? I was wondering if I gave them the situation if they would trade me for another sensor.

Originally Posted by amac209

if metal particles are on the sensor the signal gets screwed up.

I pulled the cap off and hit the entire area with some compressed air to try and get any loose junk out that may be causing problems. No luck. I guess I will get a new cam sensor and try that - doesn't look too difficult to install.

Thanks for the info...

-BZ

[ttabuu99]

Did you ever figure out what the misfire was? I am having similar problems. I have replaced the fuel pump, plugs, wires, distributor cap, and fuel injection harness at this point, and the car will run fine for days and then for no reason misfire again! Mine reads a misfire in a different cylinder each time, but all of the plugs and wires have been triple checked, so we know that thats not it. Just hoping that you could shed a little light on my problem! I'm getting tired of replacing everything!

[Jeremy-WI]

I'd try a new distributor cap with brass contacts

[Big Zack]

Originally Posted by ttabuu99

Did you ever figure out what the misfire was? I am having similar problems. I have replaced the fuel pump, plugs, wires, distributor cap, and fuel injection harness at this point, and the car will run fine for days and then for no reason misfire again! Mine reads a misfire in a different cylinder each time, but all of the plugs and wires have been triple checked, so we know that thats not it. Just hoping that you could shed a little light on my problem! I'm getting tired of replacing everything!

I sold the vehicle shortly after my last trip to the repair shop. They ended up replacing the camshaft sensor (again), flashing the ECM, and installed a new distributor, cap, and rotor. I had no more problems for the next week, and then traded it in, so I am unsure if they really fixed it or not.

Sorry I couldn't be more help. Good luck!

-BZ