4.3 Engine Swap

[FXDWG1340]

I Want To Remove The Factory 4.3 From My 1994 Gmc Seirra And Replace It With A 350 Either With A Carb Or Tbi. I Would Prefer The Carb But Will My Factory Dash Gauges Work?? If Not I Would Have To Put A Tbi For Them To Work Correctly?? If I Have To Go With The Tbi Would A 1994 5.7 Work With The Computer From The 4.3?

[wally91vhevrolet]

theres a chip in the cpu called a PROM and this has to stay with the motor its made for, if u get one for a 350 it SHOULD make ur cpu work on the 350, not POSITIVE tho, also im not sure if ur gauges would work with the carb, the ECM mostly controls the TBI and if u pull this theres no use for the ECM because most of the other sensors tell the cpu whats goin on and it changed the TBI, i dont know a whole lot about this stuff but basically if u put on a carb your ECM becomes ineffective, the easiest thing to do would be find a 350 out of a truck of about the same year and get the ECM also

[lacarman]

If you are replacing the 4.3 engine with a 5.7 you will need to replace the complete wiring harness as well, might as well get the computer that goes with it.

Many times if the truck wont start, or run correctly, the computer can be reprogrammed by the dealer if you have a matching ecu.

Ive been down this road several times. Im changing out a 97 350 5 spd to a 350 auto right now and going through this mess.

Good luck.

[Kevin45]

If you are replacing the 4.3 engine with a 5.7 you will need to replace the complete wiring harness as well, might as well get the computer that goes with it.

Many times if the truck wont start, or run correctly, the computer can be reprogrammed by the dealer if you have a matching ecu.

Ive been down this road several times. Im changing out a 97 350 5 spd to a 350 auto right now and going through this mess.

If you have been down this road several times you should know that the wiring harness of the 4.3 and the 5.7 are both the same and do not have to be swapped out. The PROM will need to be changed but what you will need to do is look at Service Manual to see what exact PROM will work. If the engine that you are putting in is also out of the same year of truck then get the ECM and PROM for that engine. If it is out of the same year. If not, then use your ECM. The computer cannot be reprogrammed. The PROM can but they will more than likely sell you a new one for around $80.00. Also one thing you will need to do is replace the exhaust. The 4.3 exhaust will be too restrictive and will code out the MAP sensor. You may also have to change a few other sensors also. The reason I know this is that I just swapped out a 4.3 for a 5.7 which was an older block. I had to redrill a Throttle Body intake to go on to the older heads. The center 4 bolts go in at a different angle on older heads than on the newer heads. You will also have to swap motor mounts which is an undertaking in itself, change radiators, and fan shroud. Your '94 tranny will work fine with the swap. Also if you are thinking of headers, go with Edelbrock "shorties" as this will let you bolt up the factory pipes without any fabrication. Have fun. It's not the piece of cake swap everyone leads on it is. I have heard everything from "it's a piece of cake" to it's "only a 6 hour job to swap a 4.3 to a 5.7, to "I've done this swap many a times and there is nothing to it". It is not a piece of cake and without donor parts as in fan shroud, radiator, etc, the cast can rapidly rise to get it done. If you have any more questions I will help you all I can. After 2 months I finally have mine running pretty decent.

Kevin