changing prom from 305 to 350, options?

[munroe]

im going ot need to change my computers prom from 305 to 350 in my 87 c10. the reason is im replacing the 350 carb motor that replaced the 305 tbi origional motor with a 350 tbi.the wiring harness and computer were left in the truck when the po did the swap. what im wondering is besides getting a stock prom from gm, could i replace the 305 prom with one from an outfit likr jet or one of the other chip makers? it might be easier to upgrade now as opposed to later. any ideas?

[Captkaos]

You can upgrade, but they would want the specs of the state of engine build first.

[rfmaster]

Munroe

There are couple of things you need to be aware about 305 to 350 TBI swaps.

First - did the previous PO swapped 305 Injectors to a larger 350 injectors? 350 injectors can be identified by black-orange color coding or by a common part number 5235206. The 305 injector can be identified by green-white marking or by a common part number 5235279.

Second - Your truck is probably equipped with 1227747 ECM. '7747 ECM was used by GM in numerous applications including I-4, V6, and V8 trucks. Depending on application the broadcast code which is identification of the EPROM used in ECM will be different for each application. Broadcast code is unique identifier for each engine-transmission-vehicle combination. This was done to attain best emission-performance for each application. For a typical 350 with automatic AKAL BCC was used. However, there were many other variations depending on optional equipment, axle ratios, etc used.

Third - Regarding mail order EPROMs. You will have to go back and forth before you'll get it dial in. The only way to achieve the best performance possible is to do it yourself. This requires investing in EPROM burning equipment and getting very familiar with how EFI works. It is doable, but not for the faint of hart. There are many DIY resources.

Forth - limp back mode requires calpack swap - but it is not as critical as getting fuelling and spark tables dialed in.

Fifth - do you know your engine specs - cam, compression, etc. What is the idle quality, vacuum (in-Hg) ??


//I hope this helps

//RF

[munroe]

sounds like it might be easier to get a 350 gomputer from a newer truck. the engine is a 93 or 94 350, i cant remember which

[rfmaster]

Munroe

Newer computer PCM (93-95) is required if you are planning to keep 4L60E tranny with your 350. If you have 700R4 or THM350 there is no need to keep this PCM. Also, you may need to check 93-95 PCM harness connector interface - it might be different from your '87!! Old 1227747 is by far the most common ECM that has been hacked, modified and used in applications ranging from 2002 BMW, IH 345 scouts, Jeeps of various flavors, slant six dodges, or stationery gas powered equipment. '7747 is easy to find and cheap. The same can not be said about 93-95 PCM which is an oddball PCM since in 96 all automakers had to switch to OBD-II capable PCMs.


305 to 350 swap is very easy and straight forward - check out thirdgen.org. They have a complete sticky.

The 93-95 350 is probably is equipped with a Vortech heads which do not need as much timing as old style wedge (76cc) heads. There are EPROMS for this combo as well.

//RF

[munroe]

thanks for the info and link, theres alot of good info there.