I just purchased a vechicle that originally had a 4.3TBI and was swapped out to a jasper 5.7TBI. It will start and run, but not smoothly. Ive had this car since last season and would really like to get it up to daily driver status. I began trouble shooting but am at a knowledge loss that has brought me to a stand still. The engine light will come on after a few minutes and if I remember correctly it is a o2 sensor and one other code. I have swapped computers to the correct one for the 5.7. The swap was not a professional swap, so I feel like there might be some type of wiring issue. If anyone is in the indy area and would be willing to come out to educate and help me, I would be more than willing to compensate them for their time, wether you want my help or prefer to work solo. Thanks in advance everyone.

 

Sounds like a standard tuning issue. 350 TBI with stock 305 tune. This combo equals nightmare. You are going to need to tune a new chip for your combo and or find a chip from a 350 TBI B-body car (no trucks, just impala's, caprice, roadmaster's etc). You should check to see what injectors are in the TBI unit. What color are the leads?

 

Check the following...
tune up parts & filters
fuel pressure
the egr valve might be stuck open or getting vacuum at idle, which it shouldn't
ignition timing
double check the connections, esp the ecm grounds, might be at the t stat area or back of the heads
vacuum leaks

 

did they sell you a complete engine? where did the tbi come from. did you change the spark control module to a 350 one? also the knock sensor needs to be changed as well. and what is the gm part number on the ecm that you are using.

 

of the computer that's in there


. That yellowish one Is white

Changed the knock sensor from the old 4.3 I believe it was

Sorry I'm not the most automotive knowledgeable person, but I like to learn

 

whats the number off the tag on the outside of the ecm. here is an example

1617427 or 1228746

and the knock sensor needs to be from a 350 as well as the spark control module

 

Now that I think about it we left the knock sensor from the donor vehicle which was an 88 suburban with a replacement Jasper crate motor. So the engine is fresh and it ripped *** when it was in the suburban.

The story behind the car is It was a buddies of mine car that I "helped" him do the swap. It was my first and he has done a few before, never a tbi tho. I was more the extra hand and tried to do all the correct research on what was going to be changed over. After he lost interest in it not running right he sold it to me because I loved the car and thought I could figure it out.


EDIT: fyi I know the chips have been swapped. I paid this electrical shop to "fix" it once and thats what they determined it was, but after leaving the shop with my car they didnt latch the cowl hood all the way down. needless to say first time i hit the gas the cowl ended up thru my windshield. so after i finally replaced the windshield it still wasnt running "right" and has been sitting neglected since