Info:
I have swapped a 350 hydraulic cam for my 305 TPI. I am currently running stock MAF, injectors, and fuel pressure, and custom cam Lift 477 480 Duration 224 231 Lobe Separation 114 Intake Center Line 110. The compression is about 8:1 for a future forced air application. I have talked to both Howell Engine Developments and TpiSpecialties, which believe that the stock computer should have no problem handling these specs.

Symptoms:
The car idles pretty strong, but slightly rich. If I throttle it really hard and fast I get a lean backfire through the intake. Upon driving it will fall on its face with anything past a ¼ or 1/3 throttle, but will eventually catch up and run. Also, the air/fuel ratio gauge goes lean, but eventually reads normal. Again, if I hit the throttle too hard a backfire occurs through the intake and the car just sits there.

What I know so far:
The computer will not allow me to pull any codes from it (not even the 12 code that tells you that you are in the computer check mode), which leads me to believe the computer is bad. The timing sits mostly at about 0 BTDC until a certain RPM is reached and then jumps to 8 BTDC, and never goes above it. Also I am having a low and steady vacuum reading, about 13 in-Hg, which could be caused by the incorrect ignition timing according to the Chilton’s manual.

 

What Chip are you using????

 

stock chip

 

If you have a 350 now and are using the 305 TPI parts, I would
suggest getting a late GM 1988 MAF chip to try getting a baseline.
That is the chip I used when I made my 350 engine swap. I later changed to a Fastchip.

 

I am currenlty using the stock 305 chip.

Since most of the parts are the same should I get a stock 350 chip? (Is that what you were referring to?)

Don't you think that since I can't pull any codes from the computer (could in the past) that the computer might be bad now?

Thanks

 

I would first get a stock Gm chip for $60 then try the computer for $400. You can always use the chip but not two computers.

 

What year is it? If you change chips you also have to change your injectors. That would be the best solution for it to run correctly(not necisarily your problem but help it run better in long run) and depending on the year the computer may be the same as used in a 350 so if you need a new one you should be able to use yours as a core. Do you have the 350 knock sensor and esc module? That can cause you to get false knock and knock retard. I would think that if you are not even getting a code 12 that you probably need a new computer. It is probably running in open loop all of the time and since it has the 305 chip it is runing it leaner than it should. Since you are using the stock chip did you at least use an adjustable fuel pressure regulator and turn up the fuel pressure to compensate. Well my best guess would be the computer is bad but some of these other things will help it run its best if you get the problem fixed. I would at the very least change the knock sensor.

Ben