Does your scanner read live data? If it does start it dead cold and watch the fuel trim readouts live and see if the truck starts acting up as soon as the fuel system transitions from open loop to closed loop.

What are your short and long term fuel trims.

Also if you have live data capability we can look at your MAF sensor signal to see if it makes any sense.

Do you ever get any misfire codes?

George

 

I by no means am an expert, but I can share with you somethings I’ve learned from the forum... It is always nice to know mileage and such when asking a question. Focus on the first code first. Other codes may be a result of the first one. Clear your codes and see what pops up first. You listed the P0341 first, so I will start there (but still clear your codes and tell us the first one) Have you removed your distributor at all? Typically that code means the dizzy is off. You need a scanner capable of showing CMP retard and the values you are looking for is +/- 2 degrees. I’m going to guess you are going to be way out or spec. Without looking I cannot remember how many degrees off each tooth equates to, it’s like 11 degrees or 13 somewhere in there.... if you haven’t distrurbed the dizzy then it’s possible the gear is worn and you might need a new dizzy. The skip white is a popular replacement dizzy and very affordable... Its my understanding timing chains rarely slip on this engine. Also, codes don’t tell you what sensors to replace, just what system is malfunctioning. I certainly would not put in a new camshaft position sensor, crankshaft position sensor, and MAF at this point. So I suggest check out the cam retard and the condition of the dizzy. Tons of info on this if you look around the forum... let us know what you find!

 

I am becoming fascinated with this problem. It is good to know that timing chains rarely slip though.

The above reply has many good points. I think the suggestion to look at the sequence the errors show up would be wise.

Had you had the distributor out? I know I had trouble putting mine back in when I did the intake manifold gaskets. I was surprised by how much it rotated when off by one tooth. Looking at parts pictures, there are 13 teeth on the distributor drive gear which translates to just under 28 degrees per tooth. That is almost halfway between the 60 degrees per cylinder spark. Can a 4.3 run with the distributor off by one tooth? I don't know enough to answer that.

For comparison, I also looked at the number of teeth on a cam timing gear sprocket (again by looking at pictures of parts) and found that they have 56 teeth (6.4 degrees per tooth).

If you data says you are off by bout 28 degrees, it could be the distributor that is off by one tooth. If you are off by about 6.4 or multiples of that I would contend that the problem could be the timing chain having slipped.

Would it be reasonable to also check if the distributor is correctly mechanically timed by setting the crank to TDC and then looking at the position of the rotor? Would this be a way to check if one of position sensors is bad?

BTW, my feelings will NOT be hurt by anyone else's suggestions or if I'm wrong. For some reason, as I said above, I find this issue fascinating and hope to learn from its resolution. I hope you figure it out soon!

Happy Thanksgiving!

Christine

 

I don’t have a live data reader unfortunately. I have not ever had a misfire code on it either. Now on another blazer I owned I had dizzy problem and got missfire codes? This seems to be different? I guess I’ll pick up the camshaft position sensor and try it first since it was first on list. From my understanding the camshaft position sensor sends a signal to the crankshaft position sensor?

 

If you are just going to buy a new sensor and install it, you are most likely wasting your time and money. I’m not trying to be rude here at all. The code is telling you there is a problem with that system, not that the sensor is bad necessarily.

If you want to buy something, buy a device to view live data and cam retard. There are blue tooth devices for phones available. Les Meyer has a thread on an Android application if you have an android phone. I do not....

If you don’t want to buy something yet, just pull the dizzy and check for wear. Make sure and set the engine to TDC first though to aid in reinstalling. Not sure what to look for? Pull it and post a pic...

Christine, yes, it is 13 teeth and 28 degrees.... I knew there was a thirteen in there somewhere! . And yep, it will start and run (although poorly) if the dizzy is installed a tooth off.

 

Howdy Silver Bullett,
As far as I understand, all is fine while You drive and the problem exists only, when engine is idle on low RPM.

On idle, the throttle is shut. However, still there is need for the air supply to the combustion chambers to keep the engine running on idle. In general engines are equipped with an actuator (commonly with a conical head) that is controlled by an ECU to keep the air flow and idle rpms constant. They are called idle air controller valves.

While You drive, the throttle is open supplying much more air in comparison to the air controller valve, so a faulty actuator may not be noted.

I would aim for testing the idle air controller valve. Never done that on Blazer, however I used to:
- remove it from a socket and
- adjust the air flow manually by partially covering the actuator socket with a hand
- see if there is a position that RPMs would go steady on idle (ECU will most probably indicate a fault with check engine lamp, as regulator parameters are not in a closed loop, but that's nothing to be worried about)

I would not expect that it is related to ignition coil, as the problem is gone while You drive.

This could be a slipped timing chain, but also I would recommend checking crank position and cam shaft position sensor and their wiring. A grounded or (occasionally) missing feedback signal may give similar results.

Anyway, I would start with air controller valve - easy access and immediate test results.

Just my 3 cents. Keep us updated.

Cheers, Mike

 

That's good advice above. The odds of three sensors failing at once is very low, diagnosis is your friend here. Buy a used scanner on eBay or get the Lesmyer solution which is a Bluetooth dongle on Amazon, a used Android tablet off eBay and car gauge pro.

How does it run when it's cold and first started? That's an important clue.

George

 

Runs much better when cold

 

I got a scanner/gauge system call Ultra gauge. It does all of the OBDII code reading and also reads data real-time as a configurable gauge system you can mount in your truck. I purchased it so I could monitor the transmission temperature in real time while towing my sailboat.

 

Walmart has a autel autolink AL319 live data reader for $35. I’m gonna go get it and hopefully u can help me do the test right or help guide me for what data we need to be looking at. Hopefully there AL319 is sufficient enough?