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305 to 350.. original 305 memcal still in car!

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Old 04-04-2014, 07:27 PM
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Car: 1991 Z28
Engine: 350 tpi
Transmission: auto/stock
Axle/Gears: stock
305 to 350.. original 305 memcal still in car!

so like the topic says I just found out why the car I bought not long ago is running rich and has somewhat of a rough idle.

whoever did the engine swap never changed the memcal in the ecm.. wtf moment, right?

however, finding it certainly relieves some of the stress of these symptoms.. my question is, how bad is this for the car? is it possible the timing, iac, tps or other could have been set wrong in order to compensate for this bone headed mistake?

I had nothing what so ever to do with this and that's why it's a relief to at least have nailed down one major issue.. now I'm afraid I opened pandoras box and there could be some other major issue because of it..

anyone had experience with this before? concerns, comments etc..?
Old 04-13-2014, 07:07 PM
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Re: 305 to 350.. original 305 memcal still in car!

I too have the same set up and symptoms as you how do you tell what what nemcal is what? thanks len
Old 04-13-2014, 07:50 PM
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Re: 305 to 350.. original 305 memcal still in car!

There's a lot of permutations possible. If it's a 305 TPI setup (using 19 lb injectors) with a 305 chip (which expects 19 lb injectors), it's not gonna run quite right on a larger 350. If it's got the bigger 22 lb (350 TPI) injectors with a 305 chip (expectng them to be 19 lb.) it's also bad, but in different ways. Get the right chip matched for the proper injectors on the proper sized motor, and it works much better.

Can't say I've actually DAMAGED any motors (at least not stock motors with modest power capability) by having things like this mismatched, but you're certainly leaving some significant drivability and power on the table.
Old 04-13-2014, 08:11 PM
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Car: 1991 Z28
Engine: 350 tpi
Transmission: auto/stock
Axle/Gears: stock
Re: 305 to 350.. original 305 memcal still in car!

pull the ecm out and open the small trap door that has two screws on it..

then look for the code below and see if you have the right one..

http://www.3rdgenformula.com/91/promcodes.htm
Old 04-13-2014, 09:02 PM
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Car: 1991 Z28
Engine: 350 tpi
Transmission: auto/stock
Axle/Gears: stock
Re: 305 to 350.. original 305 memcal still in car!

Originally Posted by Damon
There's a lot of permutations possible. If it's a 305 TPI setup (using 19 lb injectors) with a 305 chip (which expects 19 lb injectors), it's not gonna run quite right on a larger 350. If it's got the bigger 22 lb (350 TPI) injectors with a 305 chip (expectng them to be 19 lb.) it's also bad, but in different ways. Get the right chip matched for the proper injectors on the proper sized motor, and it works much better.

Can't say I've actually DAMAGED any motors (at least not stock motors with modest power capability) by having things like this mismatched, but you're certainly leaving some significant drivability and power on the table.
I figured.. I'm 99% sure I have a 350 with the 22lb injectors however the 305 memcal calling for 19lb.. I should have a fix soon.. car still runs but pretty sure not optimal like you said..
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