What do I test to know if the ECM is switching from open to Closed loop?

90silverstang

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Jan 11, 2011

#1

• Jan 11, 2011

• #1

What do I test to know if the ECM is switching from open to Closed loop? Is ther anything that can be monitored with a DVM ?

 

ID89GT

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Jan 11, 2011

#2

• Jan 11, 2011

• #2

I would guess test if the ecm is getting a signal from the 02 sensors, but im sure Jrich will know for sure.

 

bmo37

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Jan 11, 2011

#3

• Jan 11, 2011

• #3

0.423v is the default o2 reading above it means rich lower means lean. I personally don't know what you could monitor without datalogging to tell you your actually in CL. And I would assume you would get a signal from the o2's regardless even during the warm up process. Feedback sensors dont guarantee your actually in the mode just that you meet the criteria to be in that mode. I don't know but maybe someone with more knowledge of the eec does.

 

shotsy242

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Jan 13, 2011

#4

• Jan 13, 2011

• #4

Sorry to hijack the thread, but could you fake out the computer and just send it 0.423 v all the time and delete the 02 sensors?

 

HISSIN50

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#5

• Jan 13, 2011

• #5

shotsy242 said:

Sorry to hijack the thread, but could you fake out the computer and just send it 0.423 v all the time and delete the 02 sensors?

Click to expand...

You'd probably just end up in FMEM.

Why do you want to remove the sensors?

EDIT: I see you have LT's. Forcing an OL idle via a tune is a more practical solution.

 

shotsy242

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#6

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HISSIN50 said:

You'd probably just end up in FMEM.

Why do you want to remove the sensors?

EDIT: I see you have LT's. Forcing an OL idle via a tune is a more practical solution.

Click to expand...

What is FMEM?

 

HISSIN50

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#7

• Jan 13, 2011

• #7

shotsy242 said:

What is FMEM?

Click to expand...

Failure Mode. More commonly known as limp-home mode.

 

C

crickifur

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#8

• Jan 18, 2011

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The O2 sensors don't keep you in open loop, they aren't even a factor til the engine is warm. Your coolant temp sensor keeps you in open loop til the engine is warm (it gives time for the O2 sensors to heat up as well). Once the engine reaches a pre programmed temp, the system goes to closed loop, then the O2 sensors are used. Basically your engine is programmed to run rich til warm up. Check your coolant temp sensor. Theoretically you could test it with a DVOM by removing it and sticking it in hot water. When in hot water it should have continuity across the leads. That isn't an exact formula though because they are bimetal switches and they wear over time so they don't open properly anyway....

 

347STROKER50

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Jan 18, 2011

#9

• Jan 18, 2011

• #9

the ecm ignores o2 sensor feedback until you go into closed loop so if your stuck in open loop you will be running rich if your coolant temp sensor is faulty you will stay in open loop cause ecm thinks the car is cold and adds more fuel also note that when you at wot the ecm also goes into open loop

 

347STROKER50

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Jan 18, 2011

#10

• Jan 18, 2011

• #10

you could test the coolant temp sensor remove connector use an ohm meter connect leads to sensor and watch the resistance drop as the motor warms up

 

HISSIN50

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#11

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The EEC goes into closed loop when the O2's heat enough (it takes 30-120 seconds). At that point, O2 feedback is used, even if the car is in a warm-up strategy. It is true that the trim does change based upon ECT's, but the car is still in CL.

The use of the O2's as quickly as possible (they need to be warm to give accurate feedback) helps the adaptive control, driveability, and reduces emissions. The desire to have this occur quickly is one reason that HEGO's are used instead of (cheaper) EGO's.

 

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crickifur

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#12

• Jan 19, 2011

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True, but till the engine reaches a pre programmed temp, not running temp. The computer has to receive multiple signals before switching to closed loop, the O2 sensor is just one of them, coolant temp is another, they all have to be reached before fuel trim is adjusted.....

 

Noobz347

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Jan 19, 2011

#13

• Jan 19, 2011

• #13

90silverstang said:

What do I test to know if the ECM is switching from open to Closed loop? Is ther anything that can be monitored with a DVM ?

Click to expand...

You need something to log EEC data with while the car is runnin. The cheapest would probably be a TwEECer and a laptop.

Their may be cheaper stuff out there. To me, it was all the TwEECer was really good for. hehe I found it difficult to actually tune with it.

 

D

DonMaximo

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Jan 19, 2011

#14

• Jan 19, 2011

• #14

I prefer and use the Moates quarterhorse, but you don't want to part with the $$$ for one of these unless you want to know more than when you're in CL v.s. OL.

The voltage check on the O2 sensors will oscillate Above -AND- Below 0.423V when working correctly.

If you find that your voltage "sits" below or above this setting, then your AFR is probably going to be screwed up on one or both banks of the engine.

As noted in prior replies, the ECT does play a significant role in when the EEC goes into OL.
When ECT reaches the configured temp within the EEC, the EEC will begin using O2 input for adjusting injector pulse widths...adjusting them + or - so the O2 sensors are constantly oscillating Above and Below 0.423Volts.

As an aside, the correct HEGO for a typical gas engine exahaust will produce 0.423volts when the stoichiometric AFR of 14.64 runs across the O2 sensor.

Is there a problem you're attempting to resolve ??? If so, the additional info would be helpful.

Have a good day !

-D

P.S. Sorry for being verbose - I tend to babylon

 

B

BYRDPE

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Jan 21, 2011

#15

• Jan 21, 2011

• #15

good info in this thread...