89 350 backfiring problem

have an 89 that backfires when the timing connector is connected but runs fine when disconnected. The timing is dead on 0 btdc. I am getting a code for lean exhaust. Here is what I have done

Relpaced the Distrubitor, Dist cap and rotor, New plugs and wires.
Replaced the fuel pump and filter as the tank had alot of water in it.
New knock sensor
Compression check 150psi avg on all 8
The throttle body came from a 305 but I put 350 inj in it along with cleaning everything out inside and replacing all filters, diaphram and gaskets.
Timing set and with the timimg connector connected it is reading 17 deg advanced as my light will tell me how much it is advancing it.

Thank you Ken :banghead:

might be a problem with the ignition module or ecm. does the service engine light come on when it does this? does it advance further when it's reved up? try unhooking the neg battery for 15 minutes and see what it does

When the engine is first started there is no check engine light and seems to backfire the most when its cold. After warming up the check engine light comes on and stays on but only giving a lean O2 reading. As for the timing advancing more when reved up I do not know. If it does or doesnt what would that mean to me?

Do you think it can be the throttle body running lean due to some internal problem from injectors/idle air control causing the the O2 to read lean thus causing the computer to adjust the timing to correct to the point of backfiring?


Thanks Ken

try the timing you must bypass the electronic control (tan wire with black stripe by blower motor) unplug this and set you're timing also could be an 02 sensor or egr valve

I replaced the IAC and it smoothed out alot but still have to unplug the timing plug to get it first started up but can plug it back in after a few min and it runs fine, and still getting an occasional check engine light when warm. The only code being lean exhaust. I will replace the O2 sensor next