Green89IROC305

My Iroc is always running rich and always has since I bought it a year and a half ago. It often backfires during deceleration. It is throwing no codes of any kind.

About the car:
It was a 305 car. The previous owner dropped a 350 GM Crate motor in it. He left the 305 injectors and eprom in the car. He apparently thought it was originally a 350 car.

I put some flowtech headers on it. Fuel pressure is 35-42 depending on load.
It has a new o2 sensor on it. Installed when I put the headers on.
I removed the Air Injection system as my headers were not equipped for it and the pipes were not salvageable. It has new coil/ICM/rotor/cap/plugs/wires. The only sensors that are not new are the TPS/MAF/IAC(I have a new IAC but still need to install it)

The EGR valve no longer seals properly so I plugged the valve with Red RTV. Shitty fix I know but but I do not have 80 bucks to blow on this valve.
I do have a 350 eprom but I cannot get it to work as it is out of an 88GTA and requires VATS. I have a module and its key but I could not wire it in and get it to work, even using the proper resistance values and resistors/potentiometer.

My suspicion on what may be causing it is this. Since the eprom and injectors are for a 305, it is doing fuel calculations based on 305 values. Since a 305 is a smaller displacement it would require less fuel. But the computer sees that this value of fuel is not proper so it doubles the injector pulse causing extra unneeded fuel to be delivered causing the rich condition.

If my suspicion is correct than probable the only fix would be bigger injectors and the proper eprom. I will get these eventually but in the mean time, if there are any ideas/suggestions I would appreciate it.

vetteoz

iTrader: (13)

I suspect having the correct prom and injectors would be the only solution , there is nothing shadetree you can do to bypass the programming you have

You could get TP to burn a custom prom with VATS deleted
https://www.thirdgen.org/forums/post...781-post4.html

If you got the '88 prom to work it would still be wrong because it is programmed for 22lb injectors and you have 19lb.

Green89IROC305

I suspected this would be the case. Perhaps next year I will get one burned.

vetteoz

iTrader: (13)

The amount you will waste on gas would pay for the new chip,
not withstanding the ill effects on your engine from dumping too much fuel in

Green89IROC305

You are not wrong on that at all. Question though. Can a custom eprom be burned taking into account 19lb injectors instead of 22? I do not want to be intentionally cheap but I am in college and don't work much because of it.

vetteoz

iTrader: (13)

Contact the member I linked above , he will set you straight.

If the injectors are too small for a engine they can't be opened and closed fast enough to work properly ( they have to stay open longer to spray the right amount of fuel )
Some reading
http://www.hywell.org/plhelp/injdutycycle.html

Green89IROC305

Appreciate the assist.

EDIT: Is there a way to confirm the size of the injectors. I am assuming they are still 19's. My only proof is in the chip and that he said "Oh I thought it had a 350 originally"

DAVECS1

iTrader: (2)

How did you diagnose the rich problem. Was this confirmed with a wideband O2 sensor and gauge. A car without functional cats and an air pump still attached can smell pretty bad, but it s NOX fumes not rich.

Green89IROC305

I diagnosed this with observations only. Being within 8 feet of the car can tell you it is running real rich. That and while decelerating/coasting foot off the throttle with torque converter locked or unlocked up it back fires considerably, which tells me unburned fuel in the exhaust. Beyond the NOX fumes there is a distinct fuel smell. That and 10-12 mpg tells me that extra gas is being used.
I get maybe 175-200 per 15 gallons. It varies a lot. My car seems to respond best to plus for fuel economy, and worst to premium.

It got worse mileage before I put headers on, removed the smog pump and removed the cat(legal or not on this part). The cat was destroyed by an exhaust shop welding too many adapters to it to compensate for the wrong y-pipe they ordered. This was before I put the headers on. They ordered the VIN E y-pipe which has a smaller outlet than the VIN F or 8 pipe. Despite me telling them the right size to order. They never did own up to this.