mysterious code 43 problem

Kevin Trowbridge · September 22, 2015

i have a 93 gmc sierra 4x4 with a 4l60e transmission and 5.7 engine. originally the truck came equipped with a 4.3 engine but that got swapped out to the present 5.7 engine. ever since ive owned the truck its always had the code 43 flashing on the trouble codes. ive done everything to the original engine to help solve the trouble code but it always came back mysteriously.it continued to do the same thing even after i swapped the engine to the 5.7 it has in it now. the problem that i have now is that the truck will run ok til the engine temperature reaches operational temp then it starts to stall and fumble and when i try to accelerate the engine rpm themotor stalls and eventually dies. at first i thought it wasnt getting fuel to the throttle body, but that wasnt the problem at all. in fact it looked as if it was dumping too much fuel into the throttle body assembly. my first attempt to fix it was to replace the engine coolant temperature sensor, this was a problem before and fixed the problem before so i thought what the hell give it a try. no luck that didnt help at all and now the engine wouldnt even run at all. ive replaced everything electronic that i can think of and the only thing that helped to get the motor was to replace the knock sensor. that got it running but just like ive stated before, itll run just fine til the motor starts to get warm then it starts to falter again. ive read a couple of books to see if i could figure it out that way but the books tell me to replace the ESC module but guess what THERE IS no ESC module where the books state its supposed to be at and some of the online articles ive read state that the ESC is integrated with the PCM. so how do i fix that? ive replace the PCM with another one thats designed to run with a V8. some of the articles have even stated that there could be a short in the wire that goes from the knock sensor to the pcm but tracking that wire has become a real difficult task by itself. it seems as if though the problem has something to do with the distributor, almost as if its not advancing its timing like its supposed to do under normal conditions. for some reason the timing will not advance when the engine reaches normal operating temperature like its supposed to. ive even adjusted the distributor while the motor was running and got it to accelerate normally, but as soon as i shut the engine off and re-start the engine, the same problem returns again. im really flustered with this problem and have asked everyone i know that has some mechanical expertise. nobody seems to know how to fix my problem. now its your turn. lol. just to let you know ive replaced every part that i replaced before just to help eliminate any faulty parts.............hope you can help me solve this problem............................Kevin

Duelin · September 22, 2015

The computer you are using did that come from the vehicle that the engine came from? If not how do you know what PROM to use? When you are adjusting the timing are you disconnecting the spark advance line? Is the computer compatible with your spark advance line? Do you know what kind of temperature the computer is seeing when it warms up. Have you disconnected the EGR valve or blocked it off to see what happens?

barry G · September 23, 2015

egr is a good idea to see if it is a problem.

advancing an engine from 1993..

is there a map sensor working?

I still use a 1 bar on an old subaru.. but it is with a very modern msd computer.

vacuum leaks can disrupt it.

grampadirt · September 23, 2015

Do you still have the original PCM? There will be a label with a long #,maybe seven or eight digits and there will be another label with four letters...can you post those for both PCMs.Duelin is right,you might have a PCM or PROM that won't work in your truck.If the PCMs are the same maybe a PROM swap will work