I've seen variations on this thread throughout the site. I've done most of what folks have recommended and tried my best to follow the diagnostic tables, given my limited equipment. Still not working. So, here goes my own thread.

2001 Blazer starts and idles like a champ. As soon as RPMs get above about 2,000 it starts misfiring and the tach bounces all over the place. Under load it pings bad. Throwing one code P0335.

When the trouble started my future son in-law replaced the CKP sensor...no change. He did a complete (wires, cap, rotor, plugs) tune up...no change.

Since I've been playing with it:

I've checked the new CKP sensor for rub marks and found none. The gap doesn't appear to be adjustable except for using a shim, and since it's not rubbing I don't think it needs a shim. Am I missing something?

I've buzzed out the wiring between the CKP and the PCM and it checks...zero ohms. Yes I shook the wiring while testing and all looked fine. Read in another thread that if it starts and idles the CKP is getting power.

The TPS tested bad so I replaced it... no change

I replaced the PCM...no change.

I read somewhere that the distributor gear in the 4.3L tends to fail frequently so, I pulled the distributor and sure enough the gear was worn pretty badly. thinking I had finally found the problem I replaced the distributor. For good measure I used a new cap and rotor. Still failing.

The thing smells funky (like something's overheating) after taking it for a short jaunt around the block. Water temp is about 190. Could it be a clogged cat or maybe a head gasket? This motor has 100K plus miles on it so, I suppose it could also be a timing chain or a cam position sensor.

I don't have a fancy scan tool...just a basic code reader, a multimeter and a compression tester. I'm planning on doing a compression test next. Getting tired of throwing parts at this thing. Any advice is appreciated.

 

Nobody has any ideas?

 

I have been having the same problem lately. I have changed all the things that you have changed along with 2 out of 3 02 sensors anf the catalytic converter. Still have the same problems. Any suggestions from any experts would be greatly appreciated.
Thanks

 

The cam sensor is easy so I might try that first, but my intuition from the beginning is that it's probably the timing chain.

 

Sounds good. I hadn't thought about the timing chain. I've never replaced the timing chain before but it seems like a pretty good project. I am going to try and change my cam sensor first also.

 

I read somewhere that the P0335 is essentially saying that the crank and cam signals are out of sync. If the chain is stretched too far that could cause it, and in the case of the vehicle I'm working on, it has over 100K miles so, a stretched chain is likely. Timing chain is a pain in the neck though. Have to pull a lot of stuff off the front of the motor, including the fan and shroud, accessories, the harmonic balancer, the water pump and the timing chain cover. I'm guessing it's a good all day affair for someone who doesn't do them all the time.

 

Well, I bit the bullet and bought new Platinum tip ACDelco plugs, ACDelco wires, Oil filter, Oil, Fuel Filter, Cam Shaft Postion sensor, and Crankshaft Postion sensor. $350.00 total, Changed the plugs, wires, fuel filter,oil filter and oil yesterday with no change. Will change the two sensors this afternoon after work with hopefully a change. Will post results after i get some.

 

Did you guys do a CASE (re?)learn after replacing the crankshaft position sensor? AFAIK that requires a visit to the dealer with a TechII Scantool.

 

P0335 is a problem in the "A" circuit to the crankshaft position sensor. The "A" circuit is battery voltage to the sensor. It runs directly from the underhood fuse panel to the crank sensor, (there are no other connections between them). The DTC indicates that the pink wire is losing battery voltage to the CKP sensor. Could be a poor or loose connection at or in the fuse panel, in the pink wire itself, or the connection at the sensor, or a faulty sensor. The sensor is used for determining spark timing and detecting engine misfire. It must be calibrated to the pulse ring on the crankshaft before it will supply correct data to the PCM. If the sensor is disturbed in any way, which includes loosening it, replacing it, or moving or replacing the timing chain cover, a crankshaft position sensor relearn MUST be performed, (this requires a bidirectional scan tool). If the relearn is not performed, the PCM uses calibration data from the old sensor which is incorrect. The engine will usually run using the old data, but not correctly. The crankshaft position sensor and the camshaft position sensor are both used for ignition timing and misfire detection. If the cam sensor, or distributor, are disturbed in any way, camshaft retard must be checked and adjusted if necessary. Both sensors provide similar data to the PCM and must be in "sync" with the engine and each other to work properly. If the PCM is replaced, there is no data in the PCM for the crankshaft position sensor so the crankshaft position sensor relearn must be performed along with camshaft retard checked and adjusted if necessary.

The problem starting at 2,000 RPM could very well be a clue: the camshaft position sensor data is ignored below 2,000 RPM.

 

OK, so i have finally changed the Crankshaft pos. sensor and the Camshaft pos. sensor and did the relearn and it is running worse now then it did before. The odometer is erratic and jumping around, and it skips real bad. Need help please.