***Fuel pressure tester accuracy needs to be taken into account here.***

The fuel pump pressures are within spec. Technically, regulated fuel pressure is too low, and a new regulator should take care of it, (provided it's adjusted properly). Check pressure again after you replace it, just to make sure Needs to be 60psi to 66psi. Low regulated pressure will cause the fuel mixture to be on the lean side, and fuel trims should indicate slightly positive.

Usually if there's a problem with dirty injector nozzles, they tend to run rich, but it might not be a bad idea to dump a bottle of Chevron Techron fuel injector cleaner in the fuel tank with ~12 gallons of fuel. Then run it down almost empty before refueling.

 

I was able to check my gauge and it is accurate, but...

I bought a BWD Regulator from Advance Auto. Installed it. Got everything buttoned back up. 55psi and it would leak down 20psi in 10 min. Boy I was pissed. It did state on the website it is a 65psi regulator and it has good reviews, but regardless it was leaking down quickly. Garbage. So I took it out and reinstalled the stock regulator. Since this was reading a bit low, before I put the plenum back on, I hooked up the fuel lines and adjusted the regulated pressure on this one because it had a security Torx adjusting screw on it. Less than a full turn later I was at 65psi so I put it all back together. The ends of the injectors were so gummed up. I should have taken a picture. The poppets were recessed below all the carbon build up with just enough room for fuel to get by. I scraped it all out and cleaned with brake clean. I thought for sure I had found my issue with KR and misfires. Not. But I did fix a problem that was going to cause issues down the road and I feel good about getting to know this engine a bit more. I will say though after a couple maf tunes to compensate to the added fuel pressure the truck absolutely ran better than before. Also I was chuckling at myself for running injector cleaner through it to breakdown the deposits. LOL after seeing it I realized there was no way that was going to break down as I was basically chipping it out of the nozzle . I will run inj cleaner through as regular maintenance though so hopefully it won't build up as quickly.

Do you have any last ideas where to go next to figure out the kr/misfires? It is not something that I can tune out so I believe it is a mechanical issue. I will look into one more part thinking the ignition side, then just saying good enough until it gets to the point it causes drive ability issues or it throws a cel. Only thing I can think of is the distributor. I did cap and rotor, but I wonder if that smidgen of shaft play and small amount of lash can cause random misfires on all cylinders. The s10/blazer forums are full of people experiencing similar issues and a distributor solved it, but I wanted to tackle the fuel thing first.

 

Are you still running the original poppet style injectors? It would probably be well worth it to do the MPI upgrade to eliminate any of the possibilities of a bad poppet or future regulator problem. If i had to pull the upper plenum for any reason and found the original injector system i would replace it even if it is a slightly expensive part. just not having to worry and deal with it later makes it worth it. you can get an upgraded AC Delco or Delphi MPI unit for under 200 dollars. worth it to me.

 

Yeah, I believe it to be the original injector. It is clean and operating properly as far as I can tell so I will keep it for now.

I think I may have narrowed it down to the distributor. I was not logging the cam position because it did not seem relevant to the basic tuning I was doing to this truck and no VVT. I logged the cam position this morning and it is -9. I also had no idea the cam sensor was tripped at the distributor. I think this points towards worn gears. I will update after I dig into this issue.

 

Pulled the distributor. I believe it was replaced right before I bought it. The gear looks brand new like its just slight wear marks more like scuffs and there is no play side to side.

The cam reading would deviate from -9--10. I notched the bracket slightly to bring it to zero. I had to move it about 4mm counter clockwise, which is a lot I think, but it is dead on now. That woke the truck up too. It is very clear this directly affects ignition timing as well. This did not solve any issues though, sadly. I will fish a little longer and see what I get. If you have any other suggestions let me know.

Part of me thinks the misfires and little kr I am getting are a load of BS from the controller.

 

Adjusting camshaft retard does not affect ignition timing. It aligns the camshaft position sensor with the camshaft, hence the name of the sensor At the same time, it aligns the terminals in the cap so there is minimal distance between the rotor segment and the cap terminal when the ignition coil fires, which keeps crossfire inside the cap to a minimum. Camshaft retard off by 10 degrees will definitely cause crossfire which means misfires.

I agree with the injector upgrade, absolutely worth doing. What you were able to clean out certainly helped, but the crud on the backside of the poppets is a problem too. The difference in performance with the upgrade is noticeable, even if the old style is working fine, but don't expect HP or MPG to change

 

I know it is a cam sensor, but I looking at it like this(and I could be totally wrong):

Since this vehicle has pcm controlled ignition timing it needs to have a reference or a trip. The crank and cam are rotating in a fixed position. So the cam, if everything is right mechanically, is at 0 degrees. The cam sensor must be set up to report based off the cam angle because the feedback is not actual, but rather where the sensor "thinks" the cam is(because we already know cam angle is 0). It is not actual if I can change it without moving the cam. So if my cam sensor says -10, and the ignition timing starts from that reference point, I will be getting less ignition timing than what is being reported. The pcm does not appear to adjust for cam angle in the ignition timing.

This is a repeatable adjustment as well. I positively felt more power after the first adjustment at +4-5. Second adjustment was to -.5 -0 and on the second drive I felt a loss of power. In all 3 instances(-10,+5,0), the idle ignition advance stayed the same at around 19.5-20 degrees, but the idle airflow was greater at -10 than +5.

 

All my cars/trucks have been coil on plug before this Blazer. Are you aware of a diagram or info on how the ignition timing works with a distributor and spark tables as well? I am not getting this completely, nor do I get my results otherwise. Especially considering somehow the crank sensor attributes to the ignition timing as well and I found a bulletin on how they can contact the crank so I will check that tonight...that should be obvious if it is occurring when I look at the sensor. As you can tell...I took this one to work with me so I am not being very productive this morning lol.

 

The sole purpose of the camshaft position sensor is to tell the PCM exactly where the camshaft is in its rotation. It is adjusted by rotating the distributor, and viewed on a capable scanner as CMP retard, or camshaft retard. Data from the camshaft position sensor, along with data from the crankshaft position sensor, is what enables the PCM to detect, and accurately identify, cylinder misfire. You can unplug the camshaft position sensor and the engine will still start and run exactly the same as when it's connected. The check engine light will come on, a DTC for the CMP sensor will be set in memory, and misfires will not be detected.

There is a 3X tone ring behind the timing cover on the front of the crankshaft. The crankshaft position sensor generates a magnetic field. When the tone ring passes through the magnetic field, the field is interrupted, and the sensor sends a pulse to the PCM. The PCM uses the pulse for ignition timing, injector timing, etc, etc. The PCM calculates ignition timing and sends a ground pulse to the ignition control module which sends a pulse to the ignition coil, and it fires. Without reprogramming, ignition timing is not adjustable on this engine.

If/when the timing cover and/or crankshaft position sensor are moved, removed, replaced, or disturbed in any way, the crankshaft position sensor relearn MUST be performed using a scanner capable of initiating it. If it is not performed, the engine will still start and run, but injector & ignition timing will be incorrect.

Hope this helps, any questions, just ask