8625 Flash V6 to V8

[cordatta]

I have a question for you ECM guys. I have a 93 GMC with a tbi 4.3L in it but am going to swap to a tbi 350 V8 come Dec. I thought that the ECM was going to have to be changed to a 350 but I am being told that my ECM can just be programmed (flashed) with a 350 code and i should be good to go. MY ECM is the 16168625.

My question...is it necessary to buy a complete ECM with prom or can i just get a prom from a 8625 and have it burned with the 350 code and put it into my original ECM. I think that this would be the fastest approach here but not sure if it will work like i think. I am clueless when it comes to computer aspect with this thing. Help me out fellas.

[whitelightnin92]

you have alot of options. the simplest is to get a 350 prom and your good to go. as long as the engine is stock. if its modified then you will be better off with a custom tune

[cordatta]

No the 350 is stock performance wise its been bored out .030 but other than that no major upgrades. So any 350 prom will work or would it be best to stay within the 93-94 year since my trans is the 4l60E?

[jim_in_dorris]

The only other change that I know about it is that you will need to make sure that you install 2 4.3 knock sensors as the 350's only had one knock sensor. I am trying to find a v8 memcal for my 8625 ECM, but all I can find is the V6 ones, the difference being the knock sensor circuit.

[cordatta]

why do i need to install two knock sensors? my 4.3 only has one knock sensor on the driver side by the oil filter.

[Fierobsessed]

There is only one Knock sensor on either motor, last I checked.
Elaborating on what Jim in Dorris was saying:
There is a problem with using the MEMCAL from a 4.3. The EPROM which is inside the MEMCAL unit could be reprogrammed easily, but the knock sensor circuit (is also contained within the MEMCAL. specifically the jelly covered circuit board part) is tuned to be "# of cylinders" specific.

Best bet is to find a 93-95 truck with a 350 at a U-pull it, and take its MEMCAl out of the computer. It should set you straight. Just be sure that your rear end gearing is the same.
Like if you have a truck with a GU6 Code, which is a 3.42 rear, get one with the same code. Van's and Trucks are interchangeable.

[cordatta]

Ok this is making more sense to me now. It is nice to know that I will just have to get the Memcal or Prom from a donor computer. Next question is where will it tell me what rearend came with the vehicle? Is that found on the Vin? Thanks for all the help.

[SpankyCSW]

Originally Posted by cordatta

Ok this is making more sense to me now. It is nice to know that I will just have to get the Memcal or Prom from a donor computer. Next question is where will it tell me what rearend came with the vehicle? Is that found on the Vin? Thanks for all the help.

Should be in the list of codes in the glovebox.

[cordatta]

If i dont find one with the exact rearend that I have what will need to be done or what will happen?

[whitelightnin92]

the memcal in my truck was from a V6, it runs fine. but for him i would just get the whole 350 memcal and put in or heck even the whole ECM. theyre fairly cheap

[93V8S10]

A little more info on the knock sensors. The pre balance shaft 4.3's had one knock sensor just like the V8's. The latter balance shaft engines had two knock sensors. This occurred in 93 so some of the trucks got the older engine and some got the newer engine. Clear as mud :)

The 350 MEMCAL can come from either a 8625 or 6395 or 7427 PCM.

[Fierobsessed]

If the rear end doesn't match, you will want to re-burn the chip. It's not a big deal, but if you have your choice of proms, get the right one it should be plug and play.

[cordatta]

I appreciate all of your help fellas. I know now what to look for and have a better understanding of what I need.