tank1949

This is weird, but it may not be. I was checking the timing of my 5.7 by disconnecting the tan with black stripped wire near the heater. Using timing light, the distributor seemed to be adjusted to 0 correctly. Then I reconnected tan/black wire. Now, when I increase the throttle, my timing light does not show any advance. This is WEIRD! It is my understanding that the truck's brain next to heater is supposed to advance timing. What could be not working? Help!

geo1

Certain perameters have to be met,is the motor feeling sluggish?

tank1949

I tested again after my initial post. It has never really had power, considering that factory ratings were only about 200 HP. Having reconnected tan/black wires, at idle (700 rpms), it advances around 8 degrees from 0 on timing tab mark. However, if I raise rpms to 3000, then I would expect timing mark/light to advance considerably. It looks like it only advancing an additional 10 degrees(18 total) . If my memory serves me correctly, the older vacuum advance 350s would hit 30 degrees real fast at 3000 rpms and in neutral. Perhaps the computer is not sensing enough load and only advancing accordingly? It is my understanding that the motor's brain control advance. If not, perhaps I have a failing part?

kevinkpk

At higher rpm's the distributor wouldn't be on vacuum, but mechanical advance.

kevinkpk

Should say at least in the older cars.

geo1

The"failing part"is the ?,the advance is determined by many factors,if the motor is struggling,it is thinking it's under load, with a throttle blip,during the blip,retard,once stabilized,advance,how's the tune up parts?

tank1949

All parts are the same and good as best thet I can tell. Truck runs well. Gas millage sucks. Plugs only have about 10K on them. Computer is not issuing any codes.

geo1

Maybe a failing 02 sensor?many miles on it?how about some techron fuel injection cleaner

tank1949

Truck has Seafoam run through it on occasion. Last gas that I added, I also added prescribed amount of Seafoam/per gal. O2 sensor has about 40K miles on it, but it is not making computer throw a code. It is my understanding that 88-95 TBI Chevy Trucks didn't have much power due to EPA regs and technology hadn't bypassed the regs. to provide more power during those years. I believe Vortec heads in 1996 added more HP. By 2000, 350s were all generating 300+ HP

For the present time, I am more concerned about spark advancing correctly. Perhaps, unless under a load, and using a traditional timing light, these 1995 TBI computers will not advance spark like the older vacuum controlled advance distributors.

geo1

Can you get a scanner on it?might be helpful,just to see if sensors are behaving,or a vacuum gauge