I installed a new distributor (Spectra Premium part GM17) on my Firebird (1988 2.8 v6) yesterday. The old one died (no spark) while driving down the highway. With the new distributor installed it fired right up, so I warmed it up to properly set the timing.

With a warmed up engine, I separated the connector for the tan wire with black stripe. I connected the timing light and started the engine. The timing was high so I brought it down to 10 degrees like it says on the hood decal. It idled at about 600 RPM. With the tan wire still disconnected, I gave it a little throttle and noticed that the timing dropped briefly and then advanced. Strange. I seems like the timing should not advance with the wire disconnected.

I turned off the engine and reconnected the tan wire (normal mode) and started it again and the timing still showed 10 degrees. And when I gave it a little throttle it dropped and advanced just like it did with the tan wire disconnected.

The timing adjustment seems to be doing the same thing in normal mode and timing mode. I would think that normal mode would show the timing more advanced at idle. The engine power while driving is not as good as when the old dizzy was working.

Am I missing something? What else do I need to do to set the timing properly?

 

Are the connectors in place on the distributor, how old is the balancer ? The outer could have moved showing incorrect timing. Could be a bad new distributor.??

 

Thanks for the list of items to check. The 2 connectors are in place. The balancer is only 29 years old and the outer ring does not move. It was off last week to reseal the timing chain cover and it is in real good shape. A bad distributor is a possibility.

Late last night I noticed the timing varies between 9 and 11 for short times.

 

It may not have been the EST/BYPASS connector that you opened. It is located over the HVAC box on the firewall. Comes out of the large harness, connector, then back into the harness.

If that is the one you opened then the ICM is bad. Either way I would replace it with a GM (AC Delco) ICM, better now then when the aftermarket ICM dies.

When the EST/BYPASS is open the ICM does have a self advance once above a particular RPM. This is a limp mode feature.

RBob.

 

This morning I changed the timing to about 18 instead of 10. I did not separate any connectors to make the change. It ran much better with good response and power.

At lunch I checked the wiring based on the RBob post. Surprise. I was disconnecting the wrong tan wire. The wire I disconnected was close to the coil and it looks tan and has a black stripe. (I am amazed that is caused no problems to disconnect the wrong one.) The correct one over the HVAC box looks real brown with a black stripe. I will correctly set the timing tonight after work.

I plan to rebuild the old dizzy with the proper parts and then use it. The parts are easily available and moderately priced but the full AC Delco dizzy is hard to find and pricey.

Thanks for all your help. This should resolve my issues.

 

The rebuilt dizzy works great. It runs good and I was able to set the timing properly. The bad one that was purchased new would fluctuate when the timing was being set and would allow automatic timing advance with a little throttle when the timing was being set and ran with low power at the "correct" timing level.

I will be returning the bad new one this evening.

 

Awesome 😀