This is so aggravating. I swapped a 350tbi from a 305tbi (92RS). Got it started tonight and it ran very well. 20min drive and no problems.
My son takes it out right after that and says the car wants to stall and runs very rough, tach needle jumping around, etc.
I try it and this is what it does. If you put the a/c on it will usually provoke the problem, very rough and almost stalls. You can sometimes get through it by giving it more throttle. If you turn off the a/c it will go away but it may still come back. Mostly happens at very light throttle.
1st thing, I had 2 codes, 24 and 44. Turns out I had not reconnected the VSS sensor to the trans. The other one, 02 sensor I did not see any problem, sensor connected. Also, the 02 sensor was working, no codes, on the previous engine.
One thing I did when doing the swap was take the CTS sensor from the 350 as I had broken my original one. Are they different sensor maybe?
I also disabled the air pump system, the pump is still run by the belt but that's it.
I bypassed the fan temp sensor, grounded the wire so the fan is on all the time.
Only other thing I can think of is I changed the fuel pump a few weeks ago, maybe failing?
Also transfered the injectors from the 350 motor to my 305 tbi.
That's all I can think of, any ideas?
Bob

 

Did you go from a 305 to a 350? If you did you will need 350 injectors, ECS module, knock sensor and chip work. If you just have the 305 now the 350 injectors are overkill.

 

Yes, I went from a 305 -350. I took the injectors from the 350 and knock sensor but did not change the ECS module. Would that cause it to run so bad after having run very well for at least 20minutes? Also, would having the VSS disconnected have caused this? I reattached it afterwards but the symptoms are still there.
Bob

 

Sorry, by reading my orig. post I see I made it confusing. I had a 305tbi in the car, got a 350tbi and installed it. I took the intake from the 305 complete with tbi unit and put it on the 350 for convenience. Used the cts sensor from the 350 engine also.
Hope that makes more sense. Took the injectors from the 350tbi and put it on the 305 tbi unit.
Bob

 

You will need an 350 ECS module. You can get one from a 350 TBI caprice car. Your main problem lies with the chip. You will need a new chip. Your best option is to learn how to burn them yourself. Your new motor has new fueling and timing requirements that are not going to be met with the stock chip parameters.

 

Ok, not trying to beat a dead horse but why did it run fine for the 1st 20minutes or so?
As far as a chip goes, can I just get a computer from a junkyard as well as the esc module? What year Caprice do I need to look for?
Thanks again,
Bob

 

I found the problem
Measured the sensor voltages, tps, etc. Noticed that the 5 volt supply was 5.7v. Measured the ground terminal to battery ground, found .7 volts. I never found the missing ground wire, I just ran a new one to one of the sensor grounds and that did it. Car runs fine now with or without a/c.
Thanks for the help though, I really appreciate it.
Bob