Timing adjustement for a '92 3.1 Pontiac TS

[Meridivs]

We have a 92 Pontiac Trans Sport SE with the 3.1 TBI engine in it.

I need to know how to set the timing on this thing since it has the computer controlled advance. Any help is greatly appreciated!

[pocket-rocket]

Normally on a computer controlled advance dizzy there will be a plug with something resembling a blank plugged into it. Unplugging the "blank" will bypass the advancing and allow you to set your base timing. Where this dealy (normally only has 2 wires in it) is at in the bay of a 92 TranSport is, I've no clue

[robertisaar]

this should help

http://i.imgur.com/VOpQH.png

[Meridivs]

Thank you for the useful answers!

This weekend we completed the adjustment by the book - now the engine runs absolutely great

There's something new now:
- from time to time the idle rpm drops (usually at a stop light) and the engine struggles to stay running - usually after the engine reached the operating temperature
- most of the time the rpm stays where it should be and the engine pulls great at higher rpm's

Do you know what would cause this issue (note that most of the time it idles good but once in a while it runs really rough/struggles to keep it running and starts to run really rich)?

[Meridivs]

ALDL Cable

We finally got the ALDL OBD I to USB cable and diagnosis software to go with it.

Fortunately we have two Pontiacs TS with the same 3.1 TBI engine setup to compare so here are the readings:
1. the good Pontiac sensor data
http://www.pieseamerica.com/GOOD_LOG.htm

2. the bad Pontiac data
http://www.pieseamerica.com/BAD_LOG.htm

I have marked in orange the times when the engine died completely (usually when coming to a stop at a traffic light).

Can anyone make out some useful hints from this data?

[robertisaar]

being a 3.1, it has to have the TH125 trans... it's possible the TCC solenoid is getting stuck on when it's commanded off, and when you coast down, instead of it unlocking and allowing the engine to operate independently of the transmission, it bogs it down until it dies.

to test this theory, you could disconnect the wire that controls the TCC and drive around, see if you can cause it to happen.

also, in the "Bad" log, there are sections where the BLM and INT go VERY lean (170/150), the BLM/INT pop back towards 128 then a couple of samples later, it dies out.

[Meridivs]

Thank you for the input!

What is BLM/INT?

The TCC engages speeds above the usual speed we get in town driving. These two readings were done at speeds below 37 MPH where the TCC shouldn't engage.

Also, if it helps, this problem doesn't feel like a transmission/engine load problem. It's too light to be that - more like a bad sensor/Idle air control.

[robertisaar]

BLM and INT are how the ECM adjusts for fueling inaccuracies, BLM being a long-term value and INT being a short-term value.

assuming the O2 sensor is accurate, there were some VERY lean sections in the bad log.

[Meridivs]

Any idea how this can be corrected (change O2 sensor, adjust timing, TPS)?