Samurai_Of_Dawn

I've had a question since the first few weeks I owned the car (it's now 8 months I've had it so far).

I own a 87 IROC Z, and it originally came with a 305 TPI. That got swapped to a 350 TPI. Here's the question:

The original 305 ECM was left in the car with the 350 and it runs alright. I bought the 350 ECM for it, but I'm wondering, is it really mandatory to swap out the ECMs?

Also, if I plan to swap out the 305 ECM with the 350 ECM, what kind of steps/precautions do I take when I put it in? What can I expect of doing such thing?

All help is greatly appreciated on this as well. Thanks

Viprklr

iTrader: (5)

Depends.
350's have 22lb injectors and 305's have 19. Were the injectors changed in the engine swap?
Is the 350 ECM that you bought a MAF ECM like the 305 should be?

If everything was done correctly, your car will run more like it should.

Samurai_Of_Dawn

I did replace the injectors with 21lb venom injectors.

I beleive it's the correct ECM, but now that I think about it, what do I do about the proper prom that's supposed to go with it? All I have is the 305 ECM with the stock prom that's inside. I highly doubt it, but would the stock 305 prom swap into the 350 ECM with no problems, or would I have to buy a new prom? Arizona is a crap place for looking for parts. What's your thoughts?

Viprklr

iTrader: (5)

The ECM is usually the same between 305's and 350's. It's the prom that's different. The 305 prom will fit no problem.
Getting a 350 prom is usually as simple as hitting the classifieds boards here. Just make sure you do your homework and get the right one for your car. MAF vs. SD. Vats vs. no Vats. etc....

OR you could invest in prom burning equipment, keep the prom you have, and get more out of your setup then GM ever intended.

Samurai_Of_Dawn

Heh, that last part does sound quite nice, but I know for one that that stuff is not cheap. I'm aware of what MAF is, but what's SD?

If you can, could you point me in a direction on what those terms mean? I'm not looking for much of a modified prom, as all I'm really looking for is a stock prom that fits to the 350.

Also looking for any sites that may have this as well.

Samurai_Of_Dawn

If the 305 Prom fits in with the 350 ECM, would it give the car the performance of the 305 instead of the 350? Also, what are Vats vs no Vats?

Quick_Trans_Am

iTrader: (2)

Since you have a MAF car, there should be a long number on your ECM that should end in 165. The 305 and 350 both used this ECM. The problem with the PROM chip is that your 350's cam is more than likely a lot different in terms of lift, duration, etc., not to mention the extra cubic inches and larger cylinder bore your 350 has. The ECM can adapt to some modifications, but with the swap you have there, the 305 PROM is going to be far from optimal. For example: The 305 PROM is pulsing what it "thinks" are 19lb/hr injectors, so the Pulsewidth is going to be different than what your new 350, with 21lb/hr injectors needs. This isn't taking in to consideration your spark timing and a lot of other factors. Your engine will not function optimally with that PROM running it.

As far as VATS:

Vehicle Anti Theft System.

This was used to prevent vehicle theft by a module that would send a signal to your ECM, if the PROM has it programmed.
If you have a "chip" in your ignition key, you have VATS.
If the ECM got a bad signal from the VATS module, it would prevent the vehicle from starting, assuming that someone is trying to start it without a key, or with an incorrect key.
The VATS system can be enabled/disabled in your PROM.

Samurai_Of_Dawn

Ahhh, that helps very very much. Ok, now I know what vats is, and my key does not have the chip (my friend had one on his 91). My key is just a regular key.


On a slightly different subject, do I have to replace my IACV? I put a post up re about that, and nobody got back to me on that, and I was wondering if it could be the IACV, prom chip issue (I have the stock ECM with stock prom, but I DO have the 350 ECM but no chip), or a combination of both? I don't want to give up on this project, and I would really really hate to come down to the conclusion of just selling the car.

If need be, I can post the link to what I was asking about on the IACV subj. I'm just trying to figure out if it's just 1 problem, or a combination of 2 that I don't quite know about just yet.

All help is greatly appreciated!