I have a 90 350 TBI....when I set checked the timing....I noticed that the timing mark would stay at 0, then would suddenly jump to 20 degrees when reving engine. Back to idle, O degrees again...just jumps from 0 to 20 , no smooth movement at revup. Is this normal?????? Also, the reason I checked it to begin with, I have a bad knocking. I did replace the knock sensor, but didnt help. I tried 94 octane. Made very little difference. I tried a new computer. No better. Added new MAP, no better either....HELP!

 

Make sure that you have the Electronic Spark Timing module unplgged when you are checking the timing. I'd check the distributor components to make sure that they aren't worn out. Not just the cap and rotor but the module and the distributor mechanisms as well.

 

Can you explain the knock in a little more detail?

Steve

 

Sounds ok at idle and sounds good reving engine. It only happens under a load. Driving down road and accel. fast, etc.
Sounds like valvetrain noise.

 

Check your egr system. If it doesn't work properly it can't cause a bad knock problem.

Steve

 

Yep......I also installled new EGR.

 

Did you check to make sure the passages weren't blocked?

Steve

 

Everything looks ok, I just tore the engine down, valvetrain looks ok, going to pull the crank and rods today. 130,000 miles and the cylinders look good with very little ridge. I kinda hope I find a problem with the bottom end so at least I will know the problem.

 

dropped off the engine at my machinist today.....looks as though I had a piston slapping a little....so Im going .030 over with a new rv cam......hope she runs good.......thanks for your input!