Timing Adjustment

[tmob2009]

I have a 91 Caprice w/ 305 TBI and I want to set the timing. I have read all of the threads that have to do with this and can't find one that shows or tells you were the bolt is that needs to be undone in order to move the distributor. I also am not sure where the connection is that I'm supposed to disconnect in order to set the timing. I know what you are thinking why don't I just buy a repair manual. I'm a student with no money but I want my car to be in tip top shape. Thank You for any help.

[Blue Bowtie]

If the timing has never been moved, it should still be at 0º. You might want to check this before moving the distributor, just to avoid opening a can of worms which can never be re-canned.

For most models, there should be a flat 4-wire connector on the distributor base, adjacent to a 2-wire connector. The 4-wire connector is the EST system. Disconnect that to bypass the EST to check or set the base timing.

If your engine does not have the 4-wire EST connector on the distributor, it would have a single brown/white wire along the firewall near the fuse/relay center on the right (passenger) side inner fender with a WeatherPack connector in it. Disconnect the connector to check or set the base timing as described below.

If the base timing is correct you have two choices:

• You can leave it alone and accept what the factory allowed for timing and total advance, and live with the fuel mileage and performance the factory intended (to some extent).
• You can advance the base timing to provide a bit more dynamic cylinder pressure and power. This is not only to increase the potential for power, but can also provide additional efficiency (power and efficiency usually go hand-in-hand), especially in an older engine with more cylinder leakage. You can maximize your fuel mileage by running the advanced timing, and this will be especially true if you are using ethanol blended fuels. The ethanol will not only help control detonation by its cooler, slower burning, but can produce more power if ignited earlier to provide peak pressure at the appropriate time.

If the base timing is incorrect, you need to decide where you want the timing to be, and adjust it accordingly.

The distributor clamp bolt is on the right (passenger) side of the distributor near the base of the distributor, and is threaded into the intake manifold.



It only needs to be loosened, not removed. Loosen it only enough to allow rotating the distributor, snug it slightly, then start the engine. With the EST in bypass, set the base timing to 0º BTDC or whatever you decide. Tighten the distributor hold down bolt and recheck the timing to be sure it didn't move. Reconnect the EST and the timing should be all good.

Bypassing the EST and running the engine to set timing should turn on the "Check Engine" lamp. You can disconnect the battery for five minutes (long enough to check/clean the connections), or remove the ECM/Fuel Pump fuse for five minutes, or wait for 50 engine start/run cycles for the code to clear.

[tmob2009]

Thank You for the help. I tried to set the timing today and followed the instructions provided. I disconnected the 4 wire harness on the right side at the base of the distributor, but the car would not start. I'm not sure what to do now. Any thoughts.

[463]

the timing for the 91 305 is computer controled. base timing like blue said is set at "0" deg and the computer takes care of the advance. to look at the base timing a timing light is needed. there is a brown or black wire on the pass side on the intake by the tbi. this is unpluged the car will run with 0 advance for the base timing check. there ia a bit of a relearn for the computer after this check. if the distributor has not been moved this is not required.

[tmob2009]

I checked it with the timing light and while the car is running it is between 4 and 8 degrees. Is that normal.

[463]

the obd 1 computer is moving the timing with relation to the eng load and rpm.

[silicon212]

There are two connectors on the distributor - one is a two conductor with a pink and a white wire. This is the power source and if this is disconnected, the engine won't start! The other is the EST connection and is 4 wires. This should not prevent the engine from starting, but it will set a DTC and light the MIL or "check engine" light while the engine is running.

[j cAT]

Originally Posted by tmob2009

I checked it with the timing light and while the car is running it is between 4 and 8 degrees. Is that normal.

the timing mark should be highlighted with white chaulk also the flywheel groove...this then will clearly show what the timing is at..

when you tighten the dist hold down bolt you may see the timing change...before starting this it is best to check timing so you can go back to what you had....sometimes it is very difficult on some engines to adjust this correctly..

[tmob2009]

Thank You for everyone's help. I finally got it to work, I had to use the brown wire with the white strip on the passenger side by the intake to get the time set to zero. It runs more smooth now with better acceleration. Thanks again.

[463]

Originally Posted by 463

the timing for the 91 305 is computer controled. base timing like blue said is set at "0" deg and the computer takes care of the advance. to look at the base timing a timing light is needed. there is a brown or black wire on the pass side on the intake by the tbi. this is unpluged the car will run with 0 advance for the base timing check. there ia a bit of a relearn for the computer after this check. if the distributor has not been moved this is not required.

i rest my case. good to see it worked out

[coupeboy]

so wen i get to like 25mph my car kinda jerks is that my timing

[463]

a bad plug wire that is burnt or is shorting to a ground will give that jerking sensation. a dirty fuel filter or water in the gas will also give the jerk you speak of.

[silicon212]

In my case, a fouled spark plug did the trick. Replacing it made the jerk go away.

[GreyGoose006]

Originally Posted by coupeboy

so wen i get to like 25mph my car kinda jerks is that my timing

depending on the year of your car and transmission, the torque convertor locks up in earlier cars at 27mph under light throttle.
this could be what you are feeling.

after a few years, GM changed it to 35mph lockup because of the jerkiness of the lockup at low speed.

[Blue Bowtie]

Originally Posted by silicon212

...a fouled spark plug did the trick. Replacing it made the jerk go away.

Please, don't let Mrs. Bowtie find this out. I'll be getting spark plug replacements every day...