Hi. When the 'paperclip' has been applied to the diagnostic port, and the car is being driven, the SES light will indicate wether the ECM is in open or closed loop mode.

Does anyone know off the top of their head what blink rate corresponds to each mode? I have 4: OFF while coasting, ON while at WOT, and 2 different blink rates for holding my current speed.

Thanks!

 

Nobody wants to touch this one?

(TTT)

 

Here's the lowdown on the field service mode:

1. Light flashing once per second: closed loop
2. Light flashes 2.5 times/second: open loop
3. Light off all/most of the time- lean exhaust
4. Light steady on, rich exhaust

So you're normal for accelerating (light on, ECM enters PE - power enrichment mode) and slowing down (light off). You should hit closed loop (slow blink) as soon as the car warms up.

 

Great, thanks! I guess this proves that my new O2 sensor is functional... maybe...

 

(laughs) Yeah, right? I suppose you could always throw a meter on it. Should be a constant voltage when the exhaust is cold, and then a varying voltage when the exhaust gets warm.

 

Well, I replaced the O2 sensor a few weeks ago, so I'm *assuming* that it works correctly. I've finally got my idle thing nailed down. I needed to re-adjust the throttle blade for minimum idle speed. Then I set my TPS to .552vdc, and it idled GREAT. A little high, but nice and smooth nonetheless. Deciding that the idle was too high, I set my TPS to .500vdc, and it appears to be about the same.

With the idle set to .500vdc, what should my WOT voltage be at or above?

 

The GM book says TPS at WOT should read 4.50 volts, but that's impossible to reach. To get 4.50 at WOT, idle voltage gets cranked up to .8x, and you get a crappy idle. So I found out thru Glenn (one of the prom burners) that the ECM enters PE (power enrichment mode, aka "WOT") at 80% above the idle voltage. He approximated this to 4 volts or above. So as long as your meter shows 4.00 or above at WOT, it'll be fine.

Kinda sounds like a self-adjusting TPS, like on the 90-92 3.1's, but the 90-92 3.1's TPS will self-adjust for idle voltage. We have to set our idle voltage. The 3.1 speed density ECM grabs the mininum voltage of the TPS at startup, and uses that voltage as a reference for "car is idling".

And if in doubt, throw a meter on the oxy sensor. You could also double check to make sure the sensor wire, at the car's "harness side" (not the stubby 5" wire attached directly to the sensor), hasn't melted on the y-pipe. Happened to me once. The whole connector actually melted onto the y-pipe. I lucked out, and just had to buy the outer black plastic "snap" part of the connector from Pep Boys. The center pin was okay. But the car threw a code... code 45, I think, as soon as the engine warmed up. Oxy sensor voltage is constant when the exhaust is cold because the sensor doesn't "work" unless it's hot. So when the exhaust warms up, the oxy sensor outputs a varying voltage to the ECM. If the ECM knows the car has warmed up (CTS) and the engine's running time is for a certain length (like 5 minutes), it knows there Should be a varying oxy sensor voltage- and if it still sees a constant voltage (oxy sensor wire melted to exhaust), it throws the code.