This information is about changing the crappy CSFI spider to the much better MP spider.
We've all seen them from different companies. GM, AC Delco, BWD etc. They are all manufactured by Standard Motor Products.
Here's an example.
MP replacement
But 2 things I bet you did NOT know is: What pressure they should achieve and that they can NOT achieve that pressure.
Since I rebuilt my engine a 1 1/2 yrs ago, I never checked the pressure of system. It has always idled crappy (lets say crappier then before). Last month I installed a gauge and confirmed it's reading with a Snap-on gauge. The unit from the build could not achieve 45 pounds. Now first remember the OEM spec is 60 to 66 pounds.
So I first changed the FPR no change. Then changed the fuel pump, no change.
So I surmised the only thing it could be was the central fuel block. I ordered a new injector unit and returned the old one for credit. The pressure now was higher but still not spec. New one was still only 48 pounds.
I also figured that due to the fact that both units had low pressure, the specification must have changed. Contacted Standard in Virginia and found out the MP spec was 55 to 62 pounds. But these units still could not get there. So an easy mod to the return line and it runs 100 percent better.
So if you don't like the way the vehicle idles after the install of the MP unit, pressure is the problem. Now that I've upped the pressure to spec, it idles smooth as silk.
Summary for those searching on the internet for information regarding the Vortec MP injector unit.
The new pressure spec is 55 to 62 pounds. Chances are good the unit you get can't achieve it. Modification to the return line is the only way to ensure you get the pressure correct.
You can either slightly crimp the return line (near the schrader valve is easiest). Or Try this to correct it.
fastenal no.68779 since the return line is 5/16 and most do it centers don't carry that size. Fastenal ships to your door in 3 days.
I hope this information helps someone.