TBI ignition problem

[clstolten]

Is it normal for a TBI distributer to still advance some with it disconnected from the computer. While I was trying to set my timing to zero, I noticed that if I rev the motor the timing will advance about 6 degrees, and stay there until I return back to idle. Also I am getting huge knock counts. While reving the motor in neutral I have seen as many as 50 counts appear all at once. If I leave the knock sensor connected and try to drive the truck, it will hesitate and backfire under full throttle or heavy load. With the knock disconnected it drives much better with no hesitation, and rarely a backfire, but runs somewhat rough. I wonder if my spark control module is bad. Anybody have any ideas? Thanks.

 

[sweetk30]

pull the dist cap and rotor. then check to see if the center reluctor unit cover is loose fitting on it. when thay get junk and rust build up thay bind up and cause problems. i had one do this and swaped it out for good dist and good to go.

just a good starting point to check.

 

[clstolten]

are you talking about the copper cage looking thing? How loose should it be? Mine seemed to rotate a bit. Thanks.

 

[b-dogg]

The adavance should be vacumed controled on most chevy tbi ......right?
Its when they are tuned port that they add all the timing ecm icm crap I beleave
depend on the year and make you can proably just rebuild the hole thing for about $40 new pick coil controle module ect.Its pretty easy but you have to remove the distributor and pop the pin on the gear to rebuild it and then you also have to re-time the motor

 

[HarryH3]

The adavance should be vacumed controled on most chevy tbi ......right?
Its when they are tuned port that they add all the timing ecm icm crap I beleave

Nope. All of GM's factory EFI engines use the ECM to control timing, TBI included. No weights or vacuum lines required.

 

[Thunder]

It should have no advance.
I think you have a problem with the magnetic pick up coil as Sweet 30 said above. Also the bearings could be worn in the dist letting the shaft move around.
You have to pull the dist to repair the pick up coil and bearings. So mabe it is time for new dist.

 

[clstolten]

I found out that some advance when increasing the rpm is normal due to slack in the timing chain and backlash in the cam to distributor gear. I have completely rebuilt the distributer with new pick up coil and module. I am now pretty sure that the backfire is caused by the knock sensor giving false knocks and the ecm then retarding my timing.