Mark, what truck year are you using for parts? The OBS 94.5 - 95 utilizes a check valve in the oil cooler filter area that was only staked in and had the issue of falling out with an oil change. This caused long start and sometimes no start issues. The 96 - 97 models had that check valve secured with an e-ring which prevented it from falling out.

My understanding is the purpose of that valve is to supply unfiltered oil directly to the HPOP for starting purposes only, it's a spring loaded thing. To see if it's still there you would need to remove the oil filter and see if there is a nickel size hole inside the housing where the oil filter assembly screws into. If you can stick your finger in the hole then that part is missing.

 

The truck I'm picking at with the long start is an '01 former municipal plow truck with 73,000 miles on it. I expect it has some idle hours on it.

 

Mark, any update on this issue? Now that I've learned how to read these graphs correctly, thanks to you, I'm very curious why it's happening. I agree, it sure seems like the PCM is giving a HP oil signal to the IPR % but for some reason the HPOP is not responding very quickly, weird.

I do believe you, now, that the truck does start quicker with scanner connected while monitoring ICP pressure, at least on cold starts in my case. More on that issue at a later time.

 

Nope, no progress. Except that I have pulled the rear off of it and I want to swap it into my DD. Now that it's gotten colder it chug, chug, chugs with no smoke at start up so I'm figuring that an injector or two needs shimming. I'm wondering if there's something internal to the injectors that causing a late buildup of HPO pressure.