Installed new MPI injection, replaced old spider poppet type, idle is lower than before. Doesn't start as easy. MPG went from about 20 to 17 highway. Checked for vacuum leaks, fuel leaks. No codes come up. Thought I'd see better performance and MPG. Waste of money, will probably put old spider inj back in. Any ideas?

Update: Removed baffle in my MAF sensor and cleaned sensor with MAF sensor cleaner, starts good, idle is up, more responsive, will wait and see what my MPG is.

 

If you replaced it for more power and mpgs that was a wrong reason to do it, you will get same power and some have got 1/2 more mpgs.
I just replaced mine with the newer style and I noticed it does start harder, sometime needing a bit of gas. Have not came up with mpgs yet, but I did also do plugs, cap, rotor o2, fuel filter.

 

im not sure what you issue is, because you have already said there is no fuel/vac leaks, but i have put the updated injectors in all of my trucks & have never had any of those problems, my thought would be if there really is no vac or fuel leaks did you place the new injectors in the right holes...and did you push the injectors down into the lower intake all the way?

 

Did you install it correctly; as in all of the injectors in their proper ports on the lower intake?

 

Yes, the injectors are in the proper ports and they are in solid. My Jimmy was running fine when I changed the injection. A friend told me he replaced the old poppet injection with the new style MFI injection in a 2000 chevy pickup with a 4.3, and gained about 3 mpg and engine was more responsive. I'm always looking for any upgrades that will pay for themselves over time. I am a fairly competent mechanic. I've rebuilt 4 or 5 engines, do all of my maintenance and repairs, and luckily I haven't had to take an outfit in to a mechanic in the last 20 years.
Prior to replacing the injection I had an intake manifold leak and replaced the gasket. I marked the distributor timing before I removed the distributor, put everything back together, including the old style injection, and it ran fine, so I don't think timing is an issue. I know the PCM takes care of the ignition timing, would the the cam sensor be effected if the distributor was off a couple of degrees? I appreciate the responses thus far. Thanks.................

 

Hey, man... did you ever get this sorted? I'm doing the intake manifold gaskets on my '98 Silverado and was thinking of doing the MPI conversion. My truck was running ok prior to the gaskets crapping out and a bad distributor gear. Thought I might do the conversion while I had it apart. Read good reviews on this conversion elsewhere. But, if I can't expect better mpg's and and performance I don't think I'll spend the money. Just curious on how your experience is going.