7747 Won't Enter Closed Loop At Idle

[In-Tech]

Have a look at the ASDZ idle closed loop settings. There are many GM files that go open loop at idle and none with any mileage have a prayer of passing emissions until that is fixed. I fix this quite often here in California, Dave W has you on the correct path, keep in mind all variables have to be "set" for closed loop to enable and stay enabled. Always convert to a heated sensor. As for the junk ass AC-Delco o2 sensors, I have thrown plenty away and always use Bosch or NTK, so, each to his own.

[tayto]

As for the junk ass AC-Delco o2 sensors, I have thrown plenty away and always use Bosch or NTK, so, each to his own.

i found the complete opposite. i do use NTK and bosch where the OEM uses them though (jeep and subaru)

[SBAdam]

Thanks. I am leaning toward manually setting the idle above 900rpm for the emissions test. I have confirmed that this forces CL idle due to the "RPM above which open loop idle is forced off" = 825.
Another option would be to fake the VSS to show >4mph at idle... From an emissions/engine operation perspective that would be better (ECM will manage idle to 650). Not sure how faking the ECM into thinking the vehicle is moving would affect anything (this is a manual transmission). Anyone have thoughts on this?
I am trying to avoid tuning (kinda strange to say in this forum, I know) since I am seeing the referee and don't want the risk of him flagging the cal file somehow, but that might be the better solution.
Thanks again
-Adam

[In-Tech]

If you are located in California they won't let you raise the idle speed :(

[Six_Shooter]

When's the last time you did a tune up?

There's really no reason that a stock engine (assuming, since there's no indication otherwise), shouldn't pass emissions with a stock bin, though the lack of AIR system might be the culprit here and I'm surprised you haven't failed on that alone.

[In-Tech]

When's the last time you did a tune up?

There's really no reason that a stock engine (assuming, since there's no indication otherwise), shouldn't pass emissions with a stock bin, though the lack of AIR system might be the culprit here and I'm surprised you haven't failed on that alone.

Plenty of tired engines don't pass smog in open loop. I have fixed quite a few of these over the years just getting them back in closed loop alone. Fixing the tune on tired engines helps even more.

[tayto]

AIR system should only be required on on old cats. my old caprice had the cat replaced and air system was hooked up. when I removed it the air pipe to the cat was present and hooked up but blocked inside from manufacturer

[SBAdam]

When's the last time you did a tune up?

There's really no reason that a stock engine (assuming, since there's no indication otherwise), shouldn't pass emissions with a stock bin, though the lack of AIR system might be the culprit here and I'm surprised you haven't failed on that alone.

The AIR system was removed due to failed pump and the emissions system is being certified compliant to 1991 model which eliminated the AIR system. Interestingly, the AIR solenoid valve was defective and likely never actually operated.
With respect to tune up, it is a good point, but since the vehicle passed the 2500rpm test I have assumed (perhaps incorrectly) that the engine is operating nominally. I am replacing the plugs with the recommended AC Delco parts, but not planning on replacing distributor parts. Timing is set at 0deg when EST is disconnected.

Anyone have feedback on my idea to force closed loop idle by feeding a VSS signal above 4mph? Not convinced that is a good solution... I would only use this in the short term (I am convinced the right long term solution is to tune the calibration file per In-Tech’s experience).
thanks!
-Adam

[1project2many]

Problem: Failed smog due to high CO at idle (0% CO at 2500rpm). I think my problem is that the ECM is not staying in Closed Loop at idle

In order to get right exhaust mix you need right mix of fuel and air and good combustion. Combustion is helped by heat in combustion chamber. Tailpipe emissions are also aided by hot exhaust manifolds. The heat encourages unreacted HC, CO, O2 to party together.

Do you have report with HC / CO / CO2 / O2? This report can be helpful.

At 2500 RPM factors like leaking valves or rings and even worn cams have a lower effect. Passing emissions at 2500 rpm does not indicate the plugs and wires are at their best.

First advice might be to look at a '91 calibration if engine is being certified as a '91. Later calibrations are less likely to be open loop at idle.
Make sure you have plenty of heat in engine. New T-stat? ThermAC / hot air tube connected? 94 deg F minimum intake air and 195 deg F minimum coolant temp is basis for stock emissions readings.
It won't hurt to bump timing by a degree or two on a high mileage engine.
Fuel quality OK? Introducing alcohol is a cheat but it can displace HC with O2 which can lower tailpipe readings.
Plugs, wires, tune-up should already have been done.
Fresh oil can help. Old oil accumulates HC waste which can be introduced into intake through PCV system.
I would not play with VSS signal. Better to have a calibration with the correct values in it.

[dave w]

I'm wondering if the idle minimum air needs adjustment? This website has good general information: https://www.gmcmi.com/wp-content/upl...alibration.pdf

I'm wondering if the injectors are in need of service? https://www.gbreman.com/


dave w