Hey everyone, i know this question was probably asked alot but here goes.... i have an 85 z-28 now with a 400 and im trying to set the timing, it says in a chiltons manual that i need to unplug the 4 wire connector harness then set the timing, well i had it pluged in set at 42* total advance and then i unpluged it and it was at 31* so then we set it at 39* and then plugged it in, i didnt check the timing after but i went and tried it out and it ran about the same as it did when it was set differently(no spark knock). am i supposed to reset the computer or anything after? any advice is needed.

 

Chilton says NOT to disconnect the 4 wire plug, depending on how you read it. What does the underhood label say? There is usually a single tan wire with a weatherpack plug in front of the heater blower on the pass side all by it's lonesome. With the engine at temp unplug that connector and the timing should not change with rpm. That is the base timing adj. Normally with that single wire disconnected you will throw a code, after base timing is set replug the wire and clear the code.

 

"For 8-5.0L VIN H engines, disconnect the 4-wire connector at the distributor. For the 8-5.0L VIN S engine, disconnect the tan/black wire at the right valve cover to place the EST into the by-pass mode; DO NOT disconnect the 4-wire connector at the distributor." exact quote from my book. Vin S is TPI right? and Vin H is LG4, mines an LG4. so if this is true then i dont know.

 

Unplugging the connectors just takes the cpu out of the equation so you can set your base timing. Then the cpu advances it from there. Usually you set timing at idle and let the cpu take it from there.

 

So what danno says is incorrect? or just he was refering to the TPI cars?

 

You are correct, I missed that. So used to working with FI forgot about the carbs. Couldn't be the Southern and 807's with the motorcycle gang?

 

ok so i do unplug the 4 wire connector for the ecm? and im supposed to set the timing at idle am i correct ont his as well?

 

Yes, you want to make sure when the connector is off that if you raise the rpms the timing does not change, that tells you that any electronic advance is disabled. Then set base timing at idle speed when its hot, my 89 5.7 tpi calls for 6 deg btdc.