7747 Won't Enter Closed Loop At Idle

[SBAdam]

[QUOTE=1project2many;86776]

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

4E949A42-09A4-487B-BC2B-8A94B70EDA1D.jpg

“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.”

Yes, that is just what I was thinking. Will look this evening.

“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.”

Tstat is 205. Fans come on at 192/195, basically as soon as tstat opens. Might need to tune this let the engine get hotter.
Will pick up a new cap and wires to go with the new plugs.
Fuel is good. ThermAC is in place. Oil is new.

[PlayingWithTBI]

Just a silly question - what Cat do you have and how old is it?

[SBAdam]

Cat is brand new CARB certified.

[1project2many]

Thanks for posting that.

I believe higher HC and O2 readings show incomplete combustion more than incorrect AFR. Forcing closed loop with higher O2 ratio will cause ecm to respond with more fuel. I'm thinking that will only make high HC reading higher.

Tstat is 205. Fans come on at 192/195, basically as soon as tstat opens. Might need to tune this let the engine get hotter.
Will pick up a new cap and wires to go with the new plugs.
Fuel is good. ThermAC is in place. Oil is new.

Record average O2 reading now (should show slightly lean) and again with higher temps. Can always unplug a fan for a short time and monitor O2 reading as engine temp climbs. I'm thinking around 215 or so you'll see lower average O2 reading. This indicates better combustion.

It looks like ARJX is the right bin: 1991 manual for *California Emissions* vehicles. I compared to my current ASDW and there are a number of differences, though I didn’t see anything obvious that would solve my problem (don’t really know what the root of the problem is). I might switch to this calibration just to see if having a better match for the engine (no AIR), a later model year, and a California specific file will allow/enable closed loop idle.
I welcome other suggestions and questions.
thanks everyone for the guidance

There is considerably more spark advance at idle in ARJX. This alone may be enough to see an O2 sensor signal difference and to pass idle emissions. I have copied the first five rows of the main spark tables from both calibrations for comparison:

ASDW:
16.17	16.17	16.17	16.17	16.17	14.06	12.3	9.14	6.33	4.22	2.11	0	-1.76	-2.81	-3.87
16.17	16.17	16.17	16.17	16.17	16.17	16.17	9.14	6.33	4.22	2.11	0	0	0	0
16.17	17.23	17.23	17.23	16.17	14.06	12.3	9.14	7.03	4.22	2.11	1.05	0	0	0
15.12	16.17	18.28	18.28	16.17	14.06	12.3	9.14	7.03	4.22	2.11	2.11	2.11	-0.7	-0.7
14.06	17.23	18.98	18.28	16.17	14.06	12.3	10.2	9.14	7.03	5.27	5.27	4.22	2.11	2.11


ARJX:
20.04	20.04	20.04	20.04	17.23	14.06	12.3	9.14	6.33	4.22	2.11	0	-1.76	-2.81	-3.87
20.04	20.04	20.04	20.04	20.04	18.28	16.17	9.14	6.33	4.22	2.11	0	0	0	0
20.04	20.04	20.04	20.04	17.23	14.06	12.3	9.14	7.03	4.22	2.11	1.05	0	0	0
15.12	16.17	18.28	18.28	16.17	14.06	12.3	9.14	7.03	4.22	2.11	2.11	2.11	-0.7	-0.7
14.06	17.23	18.98	18.28	16.17	14.06	12.3	10.2	9.14	7.03	5.27	5.27	4.22	2.11	2.11

HTH

[SBAdam]

Thanks! That is really helpful. I will post O2 sensor data for current operation and with higher CTS temp.
Definitely going to change to ARJX.

[dave w]

As an experiment, the base timing could be advanced 4 degrees BTDC instead of ZERO degrees BTDC to see what happens to emissions.

dave w

[SBAdam]

As an experiment, the base timing could be advanced 4 degrees BTDC instead of ZERO degrees BTDC to see what happens to emissions.

dave w

True - though I can't get that feedback without a smog test, right? I think we are on the right track, I am going to examine the main spark tables more closely. The fact that they are significantly different is telling.

[brian617]

Your thermostat and fan temps seem backwards to me. Original T-stat should be a 195* and fan on off temps should be 200-215ish or higher.

I agree with Dave's suggestion on getting the injectors cleaned, Mr Injector does really good work cheap. Noticeable difference when I had mine done.

I also agree the California .bin you found is good place to start. Might even be able to find an original GM prom chip. Or Dave can flash that CAL .bin onto an original prom for you.

[PlayingWithTBI]

It's been a few years but doesn't your NOx go up with too far advanced timing? I didn't see what you NOx was on the slip.

[1project2many]

True - though I can't get that feedback without a smog test, right? I think we are on the right track, I am going to examine the main spark tables more closely. The fact that they are significantly different is telling.

You can't get detailed feedback, no. But you can look at the average O2 voltage to see if the amount of free oxygen (O2) in the exhaust is decreasing. With decreasing oxugen, the O2 signal voltage should increase slightly.

Your thermostat and fan temps seem backwards to me.

Agreed. With the reported temps the fan is likely to be on all the time.

It's been a few years but doesn't your NOx go up with too far advanced timing? I didn't see what you NOx was on the slip.

Indirectly, yes. NOx increases with higher temperature combustion. Advancing timing too far causes combustion temp to increase. But the numbers suggest that combustion temp is not yet hot enough...

[SBAdam]

Ok, with the fan temp sensor unplugged I let the CTS get to 215-220 for a few minutes. O2 mV average is around 750. At 189F the average is about the same, maybe slightly higher. It wasn’t a tightly controlled test (should have run for 20 minutes or so!instead of ~5), I think the point is still valid that the engine should be running with hotter combustion. I will look for a temp switch closer to 205/210
I am questioning the recommendation for a lower temp tstat, though. I thought this would bring the radiator into the loop at a lower temp and, at least on the highway or when fans are running, keep the engine temp lower.