Fuel Trim Thread

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Jef

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Figured I'd start a fuel trim thread since it is such a common issue. One of the things I've noticed is a lot of people, including professional techs, don't grasp what fuel trim is.

Here is a pretty simple video that give you a foundation on it this topic:

Youtube user "realfixesrealfast" has no connection with Ross-Tech. I just point people to this since it give a simple explanation on the concept of fuel trim.

Take in this video, wrap your head around it... the next video will I'll be posting (not a Ross Tech video) will really kick you down the rabbit hole.
 
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Jack@European_Parts

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A good dumbed down video, however........

An important thing this video negates and I consider an ultimate basic is ( FOD ) Foreign object damage and manipulation through modification or QC.

Since VW-Audi are huge for modification........ and VCDS is used for logging abilities for modified calibrations, or detection.

Things to note.

If ( OXS ) is placed in a path other than OEM location........ this will change the outcome of fuel trim.
This is a very common problem.

If the ECU is modified such as with tools like Uni-settings, etc....... changing the offset of Adaption, or other blocks and including the flash.
Especially field 009 for BASE timing!

It is recommended in ME 5>7 series cars to investigate the ADP values in 0x01-10-001-016
Are monitors turned right off and set at a static target.....? Better check in VCDS...... looking if basic settings tests, are they already ready and set to OK or test complete?

Is the air intake correct with proper MAF size, and quality part #....... not a cheap knock off........ and this includes the OXS sensors?

Altered size injectors....... is a big issue I see........
Turbo charger size change......

Waste-gate modifications on turbo cars......physical...... and the N75 itself, with different units sold as half ass enhancement.

FPR size correct? Is FP correct size for to little or to much fuel?

Plug gap and heat range alteration.....

On and on the curve balls will come. It can get really stupid......... that's why you should listen and learn basics dead cold before playing.
 
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Jef

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Sorry Jack, I couldn't find your video on this topic, so I posted that one instead. Please provide the like and I'll update the original post. The first post is just to help people get their minds around the concept of fuel trim, not be the end all be all on the topic. Lets not complicate the subject mater just yet.
 
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Jack@European_Parts

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I am no trying to complicate things......and apologize if you think I am trying to do so.
What I am saying is....... after watching the video to explain the basic concept .......is that considerations for modification are a very important basic.

It doesn't take a rocket scientist to take a look visually, and compare pictures or part #s......
This is hardly complicated, nor meant to pooh pooh the post......merely additional information.

Like this link I think you should of put in the post to further the discussion or understanding.

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

If I find a better video in my travels, I will send it to you.

I like this video in comparison to the seesaw.

http://www.automotive-emissions-troubleshooting.com/Fuel-Trim.html

You should make a video Jef........ using VCDS doing something similar........ showing what happens when specific situations exist like the wrong/bad MAF, vacuum leak......etc. Especially explaining bank 1 from 2 and what side is what on the car.

http://www.automotive-emissions-troubleshooting.com/Scan-Tool-Monitor.html
 
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Jef

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I'll be making a video showing a simple example of short term/long term fuel trim using my 2012 R or 2004 R32, something that most people will be able to duplicate. That will be in the next week or 2 for it to get done though.

This next video now goes into a lot of detail on fuel trim. It is a training video and I suspect it is geared toward GM/Ford type vehicles, but the bulk of the concepts here apply to VW and Audi.

Youtube user "ScannerDanner" has no connection with Ross-Tech. I just point people to this since it goes into pretty good detail about fuel trim.

Note that the term "Stoichiometric" is used often. VW/Audi use the term "Lambda" instead. Lambda 1.0 and Stoichiometric mean the air:fuel ratio is 14.7:1. Something else that is different with VW/Audi vehicles, Long Term Fuel Trim will have 2 values on our cars. One for Long Term Fuel Trim at idle, and another Long Term Fuel Trim under load.

As noted, in the near future I'll post a video using VCDS to get live readings and some testing that most people will be able to duplicate.
 
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Jack@European_Parts

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Great video Jef as usual.....

A couple things to add to video or post I believe.......
Maybe even VCDS to be helpful for the enthusiasts....... that don't understand the basics.

One.....

Incorrect exhaust ( FOD ) or an exhaust leak/incorrect placement of OXS sensor/diluted readings( No fouler ) can cause faulty trim values.

Two.....
In addition to OXS,MAF,FP, plugs, Injectors........

Sensors of reference at end of video should include the intake air, Fuel PSI sensor for rail/HPP, The MAP sensor since some cars have no MAF.
Incorrect coils or improper dwell from faulty grounds.....( China issue )

Three.....
When referencing Banks in VCDS.....like as the one you ref in video.
I think it would be a good idea to state which side is the right and left side of car...... because this is always a thing I see people don't know........they screw it up big time!

BANK 1 = RIGHT PASSENGER SIDE

BANK 2 = LEFT DRIVERS SIDE

Second integer means its the front or back of CAT.
Example : So if bank 2 sensor 2 .........this would mean = left side rear OXS sensor.

Four.....
I think non flammable fluids for intake fault finding spray......... are also to be considered for inverse display in VCDS.
Especially for warm-up transition........ to help find multiplicative faults for trim. ( The ones that hide under crap plastic intakes or from broken down/folded gaskets )

Diesels require it so run away isn't induced......! Don't forget we have trim in TDI's to contend with..... so better to retrain, verse a dumb mistake happening.
See...... when you spray no flammable gas carbon in........ it will miss and store DTC typically for the port which is the leak!
This lets VCDS tell you what ZYL........ verse just a higher idle and rich trim to observe.....
They are also not as dangerous to combust and cause a fire potentially in bay or noxious.

Five.....
Remember....... when Jef is pulling the dipstick and inducing the air leak getting a lean code.
The actual function of the ecu is to dump fuel to compensate.
This is what causes the serious issue for carbon build up, and oil dilution with gasoline....ultimately!...... getting you the misfire and rings wiped out along with CAT destroyed.

Overall I think this is a great thread and again great job on the video..........

I am just bias on the seesaw........ because when I was young someone jumped off and let me fall.......The hell with that dam seesaw.....
 
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Jef

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Tons of content could of been added to the video, but left out, this is why it is a 7 minute video and not a +3 day class.

Carb spray is not the best way to do the test I did, but at the same time, it is a lot cheaper than the correct stuff... "G 001 800 A1". As I recall, that stuff is flames in a can like carb spray. :D But at over $30 per can for that stuff, it would of put the video over budget at least $30.
 
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Jack@European_Parts

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I would also like to add the curve ball.........might as well right?

Don't forget when getting lean conditions such as this.............. that air can leak hidden/ghost as false to cause such problems.
Anything that attaches to the intake and or has a valve that is switched should be suspect......... and isolated with plugs or crimps to see if trim is altered.

examples....

N80
LDP circuit
Booster lines or booster itself.
Noids for SAI or diverters.....
VC diaphragm or crank case PCV fire gates
All these may never see a difference with a spray flammable or non.....
 
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