85irocinjected

So I got the 4.8/5.3 in my rock buggy going....kinda...the injectors where bad (junk yard motor for 3+ years.) so put new injectors and they work but the motor is doing something weird...first start with new injectors it fired and ran fine for a minute or two then died. Now it will not start with the injectors fully seated unless the throttle is WIDE OPEN. When we unseat the injectors from the engine then try to start it fires right up but then goes full throttle (obviously sucking ALOT of air).

Can anyone help?
Problem: new injectors from gm and motor wont run unless WOT even then it just sputters, but runs.

12thstreetjunkman

iTrader: (16)

is the coolant temp sensor, and air intake sensor hooked up, if not and it is warm outside, it will start the first time while the engine is cold, but you will have to pretty much floorboard it to get it to start again. The pcm thinks it is -38 or something and will be sending it way too much fuel. Might be something to check.

85irocinjected

All the sensors are hooked up and even if the ect was not hooked up it would still run fine. Did that with my camaro and the pcm read -38. It should not dump enough fuel to flood...but again all the sensors have been double checked and are hooked up properly.

12thstreetjunkman

iTrader: (16)

If the ect is not hooked up it WILL give it too much fuel and flood once the if the engine is warm, I have seen it first hand several times, once you get it started it will lean up enough to stay running, but will have trouble starting, unless you give it a lot of pedal. Whats your fuel pressure?

85irocinjected

61# before start then 57 while trying to run.

The computer is setup for an auto tranny but there is not a computer controlled trans hooked up to the vehicle (th350). How can I change it to where it does not need the auto tranny. If Im not mistaken without the trans all plugged in the vehicle will not run correct? I think I had that issue with a '98 454 and 4l80e combo I had. I just did some work and tried to start the truck without the tranny installed but it would start then die after 5-10 seconds or so.

Thanks for your thoughts/help 12thstreetjunkman, I have never had any issues with a Gen III motor till this dang 4.8

Old Geezer

iTrader: (3)

What are you seeing on the scanner?

85irocinjected

That I will have to post later tonight. I dont have any of my logs with me and was extremely tired so I dont remember off hand.

12thstreetjunkman

iTrader: (16)

the fuel pressure seems kind of high, but I don't think too high to cause a problem, or at least that much of one. It should still do fine if the trans is not connected, There are several swaps running around here with th350's, a4 harness/pcms, with the codes just disabled for the trans and nothing else hooked up. They say they won't run right without a vss, but everyone is happy as far as I know with the way they run.