ignition module

[larrym]

got into it a bit and noticed some knock let off and chalked it up to not priming the Alky pump. Down the road about 30min later I roll to a stop give it some gas it jumps and dies. No start, check and change the CCCI fuse fires up and drives fine under normal cruising conditions decided to change the ignition module with a known good one.

Put it in tonight and something sure changed! It went very rich on start up but settled down after a bit. Drove it around and my block learns dropped by about 8 cells decided to go WOT and see what happened had the boost set to 18 PSI 02s went 10.0 and it bogged way down. So obviously its getting to much fuel but how does the ignition module affect fueling?

 

[mgmshar]

If your old ignition module was causing misfires, then unburnt fuel and air was going out of you exhaust. Your oxygen sensor was seeing the unburnt air (which is full of oxygen) and assumed that you were running lean. Over time, your BLM's went up to compensate, meaning the ECU was adding more fuel to compensate for the false lean condition being caused by the misfires.

When you put in your known good ignition module, you presumably cured all of the misfires. So, there was no longer unburnt air and fuel going out your exhaust. Your oxygen sensor didn't see nearly as much oxygen, so the ECU interpretted that as a rich condition (which, in fact, it was). Thus, it compensated by starting to drop your BLMs, which resulted in less fuel being delivered to the engine.

You can either drive the car for a while to let the BLM's settle down to the new values, or you can disconnect power from the ECU to reset all of the BLM's to 128 and then drive the car for a little while to see where the BLM's eventually settle.

This is why misfires are bad - they cause a false lean condition due to the unburnt air full of oxygen fooling the oxygen sensor. The ECU responds by adding more fuel in an attempt to "cure" the false lean condition. More modern ECU's have technology to detect misfires, but our 1987 ECU's don't have such a thing.

Hope this helps.

 

[kidglok]

If your old ignition module was causing misfires, then unburnt fuel and air was going out of you exhaust. Your oxygen sensor was seeing the unburnt air (which is full of oxygen) and assumed that you were running lean. Over time, your BLM's went up to compensate, meaning the ECU was adding more fuel to compensate for the false lean condition being caused by the misfires.

When you put in your known good ignition module, you presumably cured all of the misfires. So, there was no longer unburnt air and fuel going out your exhaust. Your oxygen sensor didn't see nearly as much oxygen, so the ECU interpretted that as a rich condition (which, in fact, it was). Thus, it compensated by starting to drop your BLMs, which resulted in less fuel being delivered to the engine.

You can either drive the car for a while to let the BLM's settle down to the new values, or you can disconnect power from the ECU to reset all of the BLM's to 128 and then drive the car for a little while to see where the BLM's eventually settle.

This is why misfires are bad - they cause a false lean condition due to the unburnt air full of oxygen fooling the oxygen sensor. The ECU responds by adding more fuel in an attempt to "cure" the false lean condition. More modern ECU's have technology to detect misfires, but our 1987 ECU's don't have such a thing.

Hope this helps.

^x2

 

[larrym]

thanks now it all makes sense!