So I blew a rod in my 305 and took my car in to this local mechanic. He built a 350, bored to a 357, and swapped out the engines. I'm trying to get it done for cheap as possible so I have somethin to drive so I didn't have him change out a few things such as the fuel injectors. (which i plan on doing later) So we are trying to run it with the stock 305 ecm and chip and stock 305 injectors. It has a 350 knock sensor. We had a problem for a while where only 4 chambers were firing. Now he has all chambers firing but there is a strong gas smell and the plugs keep getting flooded with gas. He thinks it could be the MAF sensor. Any suggestions? also should I be using a 305 or 350 esc? we have both but he said there's no change when he switches them out.

 

Welcome aboard thirdgen.org.

The 305 injectors aren't going to cause a problem with a 350 until you get to the higher power levels. If you're talking about just running it in the shop, no issues. Certainly wouldn't be causing it to run rich.

Is the SES light coming on? If so, it should tell you at least something about what's not right.

What was causing only 4 cylinders to run? How was that fixed?

You should be using a 350 knock sensor and module. Again, wouldn't cause it to run rich, but that's what's needed eventually for it to operate properly.

Easy way to know if the MAF is causing problems is to unplug it - if it starts running better, the MAF is causing the problem. If it doesn't start running better, the MAF is not causing the problem.

 

I'm not sure what was causing only 4 cylinders to work. I know he changed some magnet that was in the distributor, and spent a few days following all the wires. Thanx a lot for the advice, i should be getting the MAF in tomorrow around 3pm so I am going to have him disconnect it first and see if that's the problem...

 

Ok so I changed out the MAF and nothing happened so I took it back. It starts up fine but it's running really rough and after running for about 3 minutes it cuts out if you don't stay on the gas. The spark plugs keep getting flooded out with gas, so we are on like our third set of plugs. I just got a new esc for it from an 85 corvette, haven't tried that yet. Also, just purchased "another" set of plugs and new wires. Any ideas as to why this thing could be running so rough? it has a new new knock sensor and coolant sensor... no ses or any other lights on, code reader is giving us nothing

 

my 91 was doing the same crap with the gas on the plugs and starting and running like crap then dying. So I changed the TPS and disconnected the knock sensor and now it runs good. 305-350 swap tpi

 

First off thank you both for the replies, I really appreciate it. My mechanic has been workin on this car for 3 months and I'm tired of waiting for him to figure it out!

So here's where I'm at..

Everything is running good except the engine is still running rich. He hooked it up to his snap on computer and found that the IAC wasn't working right so we changed that out. We are using the stock 305 computer and chip since we are using the injectors from the 305. The 305 esc. The 350 knock sensor that was already in the block. According to the computer the MAF, TPS, and everything else is running fine. We changed the module to a 350 module. He says the injectors are good.... I've been reading posts for 3 weeks now and I'm completely stumped.. any suggestions? plz and thanx

 

A weak O2 sensor can cause the ECM to run rich without setting a code.

Is one bank rich and the other okay?

Ignition problem will not show up through the ECM. Make sure that is up to snuff. Swapped spark plug wires on the passenger side can raise havoc without the computer knowing a thing.

 

OK, I am going to try the 02 sensor today and I will post results. Both banks are running rich, so rich in fact he says gas was going thru the exhaust... thank u!!!

 

I changed out the O2 sensor today and nothing changed. Not sure what to do now. He's been checking over the distributor and that's good. We've been switching between two computers... the one that was in the car when i got it with no labels that ran the 305 good, and a new stock computer that is made for an 85 camaro with a 305. We are leaving the 305 prom chip in it because we have the same injectors in from the 305 and the 305 esc. when we put in the new stock computer it runs rich. When we put in the mystery computer that was in the car it doesn't run rich but it back fires, stutters, and runs all around bad. Any suggestions?