I guess one reason is that this engine has 187k on it. What is required to go to MPFI?

 

its an update made by GM. no mods needed. replacement part.

 

Well, I finally got around to testing the fuel pressure. I bought an Actron CP7838 Professional Fuel Pressure Tester from Amazon for about $46. Hopefully it's somewhat accurate.

The fuel pressure reads fairly steadily at 54psi when at idle. When it begins to surge, the psi will go up to 60 as the rpms drop, and then the psi will drop to about 54 when the rpms go back up. After turning the engine off, the fuel pressure gauge read 58/59 psi. I waited ten minutes, and the psi didn't change at all. (I also did this test before starting the car, and the pressure dropped from about 58 down to 49 within ten minutes, but it's possible that it was because and I hadn't bled the gauge and it was full of air). I released the fuel pressure until it was about 7psi (it's hard to get it to 10 exactly!). I let it sit, and the pressure didn't drop any more; instead, it actually went up to about 11psi.

What I did notice about the surging while doing this testing is that it'll be idling somewhat smoothly, but then if you open the throttle, the engine will almost stall before it revs up (and then it seems to over rev). It will do this even if you barely move the throttle at all. Also, sometimes it will be idling fairly smoothly and then out of nowhere the idle will drop off and then rev up. Like I said before, it doesn't seem to do this when the engine is warm. It seems to run fairly well when the engine is warm, but it does seem to run a little rough when going up a hill without accelerating (it kind of acts like the timing is too far retarded).