Rebuilding a 350 for my 1989 c2500. Old engine is a 305 w/ roller cam, has the standard throttle body injection atop the intake. Wondering if the throttle bodies are the same for the 305 as for the 350? And then the computer... I doubt I can use the same computer? I've got an old throttle body that the person I got it from claimed it was off a 350... it looks identical, but maybe it's port size is different? The same guy also gave me 3 different computers, saying he knows 1 is for a 350, but wasn't sure which so he just gave me all 3. Any idea how I can find out which one is for a 350? (If any...)

Thanks in advance

It`s been years since we`ve did this swap, so I can tell you what I remember, the throttle body is the same, but you`ll need 350 injectors. the computer will work, but will need a 350`s chip, you`ll also need a knock sensor for a 350 since the bore sizes are different between the 2 engines. there may have been more, but it`s been so long since we did the swap I can`t recall.

Hmmm... about the nock sensor, glad you said so... cuz the one off my 305 is in better shape than one off a 350 so I was gunna use the 305 one. Why would it make a difference? They look identical, but obviously looks arn't everything.

Knock sensors work off frequencey, since the 305`s bore is smaller, when detonation sets in, it gives a certain frequencey for that bore size, and the 305`s knock sensor picks up knocks only in that frequencey range, since a 350 has a bigger bore, it`s frequencey range isn`t the same.

You can easy tell if they are different. Take your ohmmeter measure resistance the 350 should be 3900 ohms.

sorry to bring up a old post but I'm going to do the chip swap meself and I have a couple of questions, 1 is that all you need is the chip or do you need the comp also? 2 where is it? and 3 if you dont need the comp do I have to reprogram the 305 one?

Thanks!

if you open the little compartment on the computer you will find the eprom chip. each chip has a 4 letter code.
each code has a different set built for each engine / tranny /air /whatever option combo
my 90 stock 1500 truck had AZUL as its chipset.

i spent a lot of painful time amping up my tbi system, and had to learn more than i ever want to regurgitate on tbi efi!

look up the code /serial and i can usually tell the combo

later,
31

The computer is usually under the dash... in my 89' 2500 it is under the dash, to the right of the glove box. All I had to to is take out the glove box and I was able to get at it. Once you disconnect and remove the computer, there is a cover on it with a couple screws... under that is the eprom chip... it's the one that is removable. the CALPACK (I think it's called) is the other chip under there, and at least in the computers i've cracked open, are not removable. Get the serial number off the eprom chip, and there should also be a number on the computer itself... these will tell you what they are from. Find the right computer and EPROM chip and no re-programming is needed. In my case, I had a relative that had like 5 computers laying around... didn't know what they where from. I found some resources on the internet (it's been a while now though, and don't remember what the webpage was) and looked up what they all where designed for. I ended up with two that seemed it would fit my application, so I tried them both, and went with the one that seemed to work the best. Just a note... the truck ran for ***** the first hour or so... but after a few miles the computer adjusted itself. I also had a bad ESC, the computer was throwing code forty something, for bad nock sensor and/or ESC module. Swapped out the ESC with another one I had laying around and that fixed that! I knew it was the ESC because I hooked up a timming light, and the timing was ALL OVER THE PLACE... after I swapped it out, the timing was advanced or retarded much more smoothly, instead of jumping all over. Just a note, incase it might help.

I just wanted to say thanks! the truck runs allright now, I just need to do some tweeking tomorrow. every1 has been such a big help,


Thanks

just remember... run it for a while before you do any major tweeking like replacing the EPROM chip or anything. The computer can actually "learn" quite a bit and adjust accordingly. But this takes some time I guess...