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Old 08-03-2017, 02:42 PM   #15
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I am back with a bit of news, I had the motorhome in a local shop getting the major fluids (coolant, oil, trans, diff as the motorhome hit 75,000 miles last month and I only have a maintenance history going back to 50,000) changed today before I leave on a big trip this weekend. On the drive over to the shop I started getting a mis-fire warning, as mentioned I just changed spark plugs and wires, so thought it was probably just a loose plug wire. It turns out 2 of the brand new AC Delco spark plugs were defective (Cyl 1 and 3) , 2 of the old moderately worn Auto-lite plugs are back in now and it is running smooth. On 10 mile drive home with all new fluids, I am now seeing LF1of 2 to7 and -2 to +3 on LF2. After getting home I installed a new starting battery so computer should be reset before the next drive.
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Old 08-03-2017, 04:10 PM   #16
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0 is the target but +\-10% is within specification.


Great, thanks. Mine are generally running -3 to +1, both long & short on both banks so I guess I am okay.
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Old 08-04-2017, 06:57 PM   #17
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Originally Posted by Isaac-1 View Post
I am back with a bit of news, I had the motorhome in a local shop getting the major fluids (coolant, oil, trans, diff as the motorhome hit 75,000 miles last month and I only have a maintenance history going back to 50,000) changed today before I leave on a big trip this weekend. On the drive over to the shop I started getting a mis-fire warning, as mentioned I just changed spark plugs and wires, so thought it was probably just a loose plug wire. It turns out 2 of the brand new AC Delco spark plugs were defective (Cyl 1 and 3) , 2 of the old moderately worn Auto-lite plugs are back in now and it is running smooth. On 10 mile drive home with all new fluids, I am now seeing LF1of 2 to7 and -2 to +3 on LF2. After getting home I installed a new starting battery so computer should be reset before the next drive.
Where did you buy the spark plugs?
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Old 08-04-2017, 09:30 PM   #18
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They came from an Amazon seller, Ice Auto Parts
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Old 08-04-2017, 09:53 PM   #19
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They came from an Amazon seller, Ice Auto Parts
Counterfeit Auto Parts & Fake Car Parts | ACDelco

https://www.corvetteforum.com/forums...parkplugs.html

General Motors Cracks Down On Counterfeit Parts | GM Authority


I buy all my parts from the local Chevrolet dealer just for this reason.
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Old 08-15-2017, 10:36 AM   #20
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0 is the target but +\-10% is within specification.
What does +/-10% mean in actual numbers? My long term is 5 and 7 and I have not driven it since I programmed the SG to display these numbers. Moving it around my driveway, the short term numbers were locked on 0.

I lost an engine years ago (before SG) with no codes being set and do not want to lose another.
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Old 08-15-2017, 11:13 AM   #21
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What does +/-10% mean in actual numbers? My long term is 5 and 7 and I have not driven it since I programmed the SG to display these numbers. Moving it around my driveway, the short term numbers were locked on 0.

I lost an engine years ago (before SG) with no codes being set and do not want to lose another.
+/- 10% means the ECM is being told to add or subtract 10% to the fuel that goes to the injector over or under what the Mass Airflow Sensor and other sensors are telling the ECM to send to the injectors.

The MAF measures air flow before the throttle body. MAF numbers go into the ECM. The ECM also takes info from the throttle position sensor, coolant temperature, inlet air temperature, manifold absolute pressure, knock sensor, as well as several other inputs and decides how much time the injectors should be pulsed open. The O2 sensors measure the percent of oxygen left in the exhaust after combustion. The system is trying to achieve the perfect Air Fuel Mixture of 14.7:1.

If the O2 sensors sense more oxygen in the exhaust than normal it sends a resistance to the ECM. The ECM senses this resistance and adjusts the pulse to the injector to richen up the mixture. +10% means the ECU is compensating for a lean condition by adding 10% to the fuel pulse through the injectors. -10% would be a rich condition where the ECM would be reducing the pulse through the injectors.

This is typically considered Closed Loop Mode and is achieved after the engine is up to normal operating temperatures and the ECM is getting proper feedback from all the applicable sensors.

Typically just idling or moving slowly and any time the TPS is at zero the short and long term fuel trim will trend toward zero.

Any time the TPS is 100% open the system goes into Open Loop mode where the ECM uses a preprogrammed set of parameters for fuel delivery and ignition timing.

I am no expert by far but this is my understanding of how a typical GM Engine Control Module works. There are plenty of way smarter guys here who can add clarity and correct some of my misunderstandings.

Hope this helps
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Old 08-15-2017, 11:32 AM   #22
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What does +/-10% mean in actual numbers? My long term is 5 and 7 and I have not driven it since I programmed the SG to display these numbers. Moving it around my driveway, the short term numbers were locked on 0.



I lost an engine years ago (before SG) with no codes being set and do not want to lose another.


The fuel trim percentage is a calculation of how much the ECM is having to compensate from stoich to maintain proper air fuel ratio. Positive fuel trims mean that it is keeping the injectors open slightly longer to "add" fuel for a lean condition and negative fuel trims are just the opposite. Anything under 10% is just fine.
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