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week 3 quiz

  • Jonathan Haffer
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18 Feb 2020 18:38 #37623 by Jonathan Haffer
week 3 quiz was created by Jonathan Haffer
12.Tech A says stft command is retained in pcm memory. Tech b says st is looked at first to know were to start injector pulse.
_ i know tech B is wrong ,but is tech A wrong to ?

9. a no start condition, you notice the mil light doesn't light,you cannot communicate with the pcm,no injector pulse,no spark,no blown fuse ,good pcm,good power and grounds , What could cause this condition?

12. When is the only time you will see a substituted value on a scan tool?

5.A short to ground on a o2 sensor on a Chrysler may cause the signal voltage to read over 4 volts. True or False?

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19 Feb 2020 18:47 #37659 by Noah
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12. I believe tech A is also wrong. STFT is right now, based on the report from the O2 sensor. Although I am curious to know what the official answer is though. I could be wrong.

9. A shorted 5v reference will cause these symptoms.

12. In enhanced mode. Meaning, generic OBD II data will not substitute values (In therory... They DO substitute oxygen sensor voltages when a wide band afr is used).
Example: a disconnected coolant temp sensor will result in a reading of -40°f on generic data where as enhanced data may substitute a temperature of maybe 100°.

5. I say false, but kind of feel like this could be a trick???

Curious to see what others are thinking.

Thanks Johnathan! Great to have some discussion here concerning the material.

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20 Feb 2020 06:21 #37674 by Jonathan Haffer
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12.Thanks Noah for your input, one question though, I need to get my terminology right, on generic do you mean global and on enhanced do you mean oem data ?

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20 Feb 2020 06:51 - 20 Feb 2020 07:07 #37676 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic week 3 quiz
On the engines I work on STF is an exact mirror of the O2 sensor signal. When in closed the LTF is within normal range the computer wants to have LTF to tend towards an average of zero. At start up iniitial in open loop there is no useable respnse from the O2 sensor so the computer uses a fixed default fuel map --- the same as it does with igntion timing. At a cold start below closed loop coolant temperature the computer will apply up to 25% enrichment anyway, engines usually cold start if over rich (withi reasonable limits) but not when over lean.
Having said that some manufacturers are going to have different strategies ---

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Last edit: 20 Feb 2020 07:07 by Andy.MacFadyen.
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20 Feb 2020 07:03 #37677 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic week 3 quiz
Generic is plain vanilla OBD-II ---- a global standardised list of basic PIDs that have to be proven to provide data in a standard format.

Manufacturers extended PIDs aren't standardised the same PID number can mean something completely different between different manufacturers or even models and also the units format they are presented in can be completely different.

Basic OBD-II data though is pretty reliable think of it as a sanity check on what you are seeing in manufacuers mode.

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20 Feb 2020 07:09 #37678 by Noah
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Jonathan Haffer wrote: 12.Thanks Noah for your input, one question though, I need to get my terminology right, on generic do you mean global and on enhanced do you mean oem data ?


Yes, you are correct on both counts. The terms are widely interchanged.

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