Timing All Messed Up

[THEFERMANATOR]

After reading this thread the EE in me comes out. I am thinking if I could take a oscilloscope and trigger off the crank sensor while looking at the IP OS and crank it over, measure the time, then do some math I could set the OS position like it should have been on the IP test stand. I realize not everyone has a scope handy, piggy backing into the connectors is a pain, but it should be doable. If you wanted to set the OS out of the truck, a cheap test stand to do this on could be made from a junk block with a crank, flex plate, starter, cam/IP drive, crank sensor, some wiring, a few parts to energize the sensors and nothing else. Yea I'm nuts.

The optic sensor timing has nothing to do with crank timing. The optic sensor reads a disc inside the injection pump. This disc tells it position and injected amount by how much of the disc and when it reads it. Without a test stand, the closest way to set an optic sensor is to install a #5 resistor, do a TDCO learn, and then check your idle fuel rate. If it is reading roughly 8-10 MM3 of fuel at a hot idle, it is pretty close. If it is reading high or low you will need to bump it slightly and then recheck it. The test stand checks for proper OS position in relation to the spinning disc with the pump at a specified timing position, and then it tells you how much fuel is being put out so you can put in the proper calibration resistor in the PMD.

 

[L98TPI]

The optic sensor timing has nothing to do with crank timing.

If the ECU does not compare the position of the pump to the position of the crank (TDC indication) how does it know any thing about where the injection events are occurring? Why have a crank sensor at all? :skep:

 

[THEFERMANATOR]

If the ECU does not compare the position of the pump to the position of the crank (TDC indication) how does it know any thing about where the injection events are occurring? Why have a crank sensor at all? :skep:

it uses teh crank sensor to tell it where the engine actually is at, but the optic sensor does ALOT of functions. It tells it where the stepper motor has the pump timed at, how much fuel is being injected, and wether or not the fuel solonoid is fucntioning properly. it's signal is dependant on where the pump itself is at, not where the crank is at.

 

[buddy]

So basically, you could figure out based on the crank and OS signals (if you can read them) how far from actual TDC it has stepped to. The PCM does compare the two, but they are different references as TheFerm pointed out. It obviously needs both sensors to set up an accurate TDCO so it can then operate somewhat accurately with only one of the two.

 

[orrum]

My brain hurts.......If yall dont mknd I am gonna stick with grounds, grounds, grounds, gotta check them grounds.

 

[allanh]

So I got around to doing the OS calibration this weekend. Set the two pieces of the sensor so that the right edge of the top piece was 1/3 width as the left edge, relative to the bottom piece. Also, just put the entire sensor about center between the inner walls of the pump. Re-assembled, started it up and bingo! Problem solved. Sounds normal again, no more "racing" or "choking" sound. Checked the scanner and fuel rate was down to 8-9mm from 16-17mm. Drives well now too.

That seems to have been the fix Buddy. Thanks for the tip.

-Hank

 

[buddy]

Glad its running right now. Thats one of the things to watch out for when getting a rebuilt pump, as I have seen it a handful of times in last couple years, and thats just the guys that post about the issue.