96 jimmy 4.3 4X4 144k miles, I rebuilt the upper end both heads machined a 1000 miles ago, bought ebay used injector spider was clean and listed as tested good, all new cap, rotor, wires, and plugs. Started and ran good with no codes for about a 1000 miles now throws P0303 every time you drive it a while 20 miles or so. I can't believe the compression has changed it test good after the rebuild and the electric parts are 2 months old hard to believe they are failing so it leaves the injector spider
anyone tell me how to test the injector without having to pay for dealer visit. Any help would be great!

 

I wouldn't assume anything. I would pull the plug for inspection and to test the compression, comparing it to the previously taken value. Ohm out the spark plug wire. Check the distributor cap.

 

Thanks I put some gas and the chevron injector cleaner in it and drove it all day MIL light came on P0303 turned it off and it has not come back the rest of the day and no codes pending, holding my breath

 

If injector cleaner helped, the poppet nozzles in the spider may be gummed up. This is an issue with pretty much all CPI & SCFI engines and is why GM redesigned the spider for the SCFI engines to move the injectors out to the poppet nozzle locations, thereby alleviating the issue.

I would run a double dose of Chevron Techron Fuel System Treatment Plus (20 gal treatments) in the next tank to try to really get the injectors & poppet nozzles clean. See if that helps. If it doesn't, then your next step may be to replace the SCFI spider with the updated MFI spider. For further details on the upgrade, search "MFI+spider" or "MFI+upgrade".

 

Thanks Again, we are on the same page, filled the tank and added the 2nd 20gal Chevron injector cleaner drove most of the day yesterday and no problem, no lights, no active or pending codes.
Thanks Again