MIL light when coasting.

[Skeith]

My lumina with the 3.1L MPFI and a 5 speed auto transmission has a strange bug I cant put my finger on.

When I coast for longer durations the engine will feel like it hiccups (only sometimes) and the MIL light will come on. If I stop the engine and immediately restart it the light is off. This only happens with prolonged coasting such as coasting down a bridge etc. I cant check codes because I need to shut off the engine so I can bridge the AB terminals and then turn on the accessory to get the MIL to flash the codes.

However when I shit off the engine whatever malfunction there was is forgotten by the computer so this is useless.

Are there any common problems that can cause this.

sometimes the engine hiccups when it happens other times it doesn't.

[robertisaar]

sounds like the "hiccup" is the ECM doing the EGR test, and it sounds like it's failing regularly...

do you know if you have the digi or EVRV EGR? if digi, i have a cleaning guide in text here, and a quick video on youtube.

[Skeith]

I believe its the digital EGR. (the valve is composed of 3 valves, one slightly larger than the next, actuated by solenoids.) I did test the EGR and disassemble and clean it during the summer. (engine is a transplant so I did quite a bit of cleaning/replacing parts) I guess I could give it another shot.

Is there a way to check OBDI codes while the engine is running?

[robertisaar]

yeah, the 3 solenoid setup is the digi...

do you know what the ECM is expecting? if you can get a look at the silver sticker on the MEMCAL, i can take an educated guess at what it is expecting.

and did you mean 4 speed auto or 5 speed manual?

as for checking codes, if you try to do the paperclip trick while the engine is running, you'll throw it into field service mode, and the SES will blink on and off according to O2 sensor voltage, not the actual DTC blinkout. the only way to check codes while the engine is running is with a scanner....

however, if you could manage to stall the engine after the SES gets lit up without turning the key off, that MIGHT allow you to get the code to blink out... pulling the injector or ICM fuses would do it.

[pocket-rocket]

Or coming to a stop with the clutch out in gear and dog it out.

[Skeith]

Its an auto, so clutch method is a no go. I may try stalling it to pull the code when I have some time.

I had a spare EGR from the old engine, I stripped it down and cleaned it out real good. Put it back together and tested the valves on my bench with a power supply. Coil resistance is good as well.
No sticking valves, so I swapped em. Same problem, except it doesn't seem to hiccup anymore when the MIL comes on.

[pocket-rocket]

I read coast, so I tend to think manual transmission in neutral, lol. Ok, How about hotwire the TCC solenoid to a switch so you can get it to go into lockup and come to a stop. That will kill the engine. That or wire in a switch and fuse in place of the fuse for the ICM so you can kill the spark to the engine once the light trips.

[bszopi]

Did you check the EGR passages into the manifold, as well as the stove pipe from the exhaust? No matter how well the EGR works, if you have blockages anywhere, you will still get an error.

[robertisaar]

Did you check the EGR passages into the manifold, as well as the stove pipe from the exhaust? No matter how well the EGR works, if you have blockages anywhere, you will still get an error.

X2

luckily, the EGR passage on the LH0 intake is REALLY easy to clean and fairly straightforward compared to the passge in the 3x00 intakes. i had a solid chunk of carbon i pulled out of a 3.1 intake the size of my pinky, just try not to drop it into the motor, it's brittle, but i wouldn't take the chance.