I have a 4bta in a chevy pickup the truck has recently been idleing strangly it shakes noticable at idle and will smooth out it you increase rpms a little. It was smoking at idle I decided to replace injectors because I wanted to up grade any way I put it back together and there is no more smoke at idle but still shaking, so I pull the injectores back out and swap the pump line around on #1 so that I can check the spray pattern. the injector will not fire with the engine idleing on three cylinders, but when you rev it up just slightly it will pop the injector, this happens the same with the old or new injectors> I am thinking that the injection pump is almost dead and not making enough pressure to fire at idle but when you rev it it starts working. The injectors were pop tested and are in the correct range so its the pump that cant generate enough pressure right? I checked the lift pump and have 7# and I also pulled the return line and checked for any air in the return and did not get any. The injectors and lines were bleed extensively.

 

Have u tried a OBDII scan yet? Mine threw a code but no SES light when my pump went. I had to check with a scanner.

 

this is a first generation rotary pump

 

sounds like the ip is on its way out.