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Old 08-20-2016, 12:53 PM   #21
far2grumpy
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Join Date: Oct 2008
Location: Cedar Rapids, IA
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2005 VUE 3.5L
2007 VUE 3.5L
Default Re: Bad ECU or OBF Replacement Throttle Body

Quote:
Originally Posted by Vladymere View Post
When I start the vehicle up it runs fine until the ECU leaves closed loop operation and enters open loop operation then it runs like crap.
I'm just a bit confused about the described sequence ... engine should start in Open Loop and then move to Closed Loop when possible ...

Here's FSM extract:

Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The control module ignores the signal from the heated oxygen sensor (HO2S). The control module calculates the air/fuel ratio based on inputs from the ECT, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:

The HO2S has varying voltage output, showing that the HO2S is hot enough to operate properly.
The ECT sensor is above a specified temperature.
A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for this engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the control module calculates the air/fuel ratio, injector ON time, based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.


In any case it sounds like you found a really good bargain if dealer is going to repair for $115.

...
I try to visit forum often but suggest you use private messages if in a rush (comes to cell) and include email address for extracts. I seldom check visitor messages so please don't use.

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Old 08-22-2016, 11:26 AM   #22
Vladymere
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Join Date: Aug 2016
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2008 VUE Red Line
Default Re: Bad ECU or OBF Replacement Throttle Body

far2grumpy,

I have the terms closed loop and open loop confused (reversed). The vehicle when cold would start and run without issue for 2.5 to three minutes and then operation would go to hell. You could turn the vehicle off for a short duration (10 seconds, 30 seconds) restart the vehicle and it would again run well for a short duration.

I believe that while running in open loop (what I called closed loop) that it ran well as it was running on internal programming and ignoring some (or many) of the sensors. Once the ECU switched over to all external sensor input for operation performance would fail.

I do know that the original throttle body was bad as one of the throttle position sensors (which I no longer remember and would have to meter it again which I can do if requested) measured infinite ohms.

Now that the ECU has been replaced with the used 2008 Chevy Malibu ECU and programmed by the dealer all is well.

The dealer charged a total of $127.90. $115 for re-programing and $4.25 for shop supplies and $8.66 tax. I am not unhappy with the charges.

far2grumpy, Thank you so very much for the advice and documentation you provided. You help has been instrumental in the repairs being completed.

I would like to think that I have still, in the end, saved money over having the vehicle towed to a dealer for diagnosis and repair. Also, having made my living with my hands for all of my life ( and having been and automotive service technician by training and employment having the left the field over 37 years ago) I just don't trust the work of others. I don't always make the correct repairs the first time around but when it is still wrong I know in the end what I failed to do.

Vlad

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