Spixer85

I have a 1998 z71 that had a blown up 5.0. I swapped it out with a 1996 5.7 vortec.it had 44 psi fuel pressure. I swapped the fuel pump out for a 80 to 140 psi pump. Still had 44 psi on the fuel rail. swapped out the fuel regulator with a 66 psi. Still 44 psi. So I put an adjustable regulator in and set it at 62 psi . Now I have good fuel pressure. It starts easy after idels down it gets rough and almost died. It will not accelerate. I've replaced everything in the ignition system 2 times making no difference.replaced fuel filter. The engine that was in the truck was blown up when I get it. And they lost the keys and didn't put the right columb back in it but I got the stuff I needed to fix what they messed up and I done a return on the system before I could ever get it to try to run I've done everything I know to do I'm a 35 year mechanic but got out of it right as fuel injection was getting popular. Oh and it has the updated spider system in it also. Any help would be greatly appreciated.

Thanks in advance.

Gumby22

Does it smell like it’s running rich?

If so, Verify its holding fuel pressure KOEO - if it’s bleeding off, the replacement assembly could be leaking.

Even the updated spider injector assemblies are prone to problems, regardless of how new it may be.

Spixer85

It is holding pressure but acts like it drops 3 to 5 cylinders after it comes down to the idle point. Turn it off and restart it and it does the very same thing. Not running rich if anything it is running a little lean. Can't figure this thing out it's driving me nuts.

Spixer85

It's holding fuel pressure and the injectors are not showing any leaks. How ever the guy I got the motor from was having trouble with it running. I have replaced the fuel pump, filter pressure regulator distributor plugs wires. It starts easy when it comes back to a idle it's like it drops 3 or 4 cylinders and no throttle response.

Spixer85

Sorry for the late response. I've been in the hospital.

Gumby22

There’s a lot of possibilities.

Try disconnecting all exterior vacuum connections (booster, EVAP, etc) and see if it changes.

Check for diagnostic codes - even if the CEL isn’t lit, codes could be stored.

Gumby22

Also, did you just swap the engines or did you also swap the ECM’s and wiring harnesses?

Although they’re technically the same generation of truck, and OBD2, there were some wiring and programming changes between those years.

Spixer85

No I just changed the motor and used all the stuff off of the motor that came out of the truck it ran good just blew a rod. So I used all the electronics off of the old motor that came out of the truck . I put a new distributor plugs and wires and the fuel pump and filter and now I have good fuel pressure but still won't run.

Spixer85

Follow up on my post I put the spider injection from the old motor in it today it's running like a new motor.

Thanks for all the help and advice.