IQ Adjustment – Hammer mod vs VAG settings to get there???

I adjusted the IQ recently, and realized there are 3 routes to setting the SAME mg/str value (regardless of the value that you chose).

To help you visualize what I’m asking, I’ll arbitrarily use 3.4 – 3.6 mg/str for the examples below. Can anyone tell me (or direct me to URL’s or club threads that will tell me) the difference in fueling, economy, and power characteristics that will be obtained at different rpm and load requests by:

1) leaving the VAG-COM adaptation parameter defaulted at 32768, and adjusting the head to read 3.4 – 3.6 mg./str.
2) adjusting the VAG-COM adaptation parameter DOWN as far as it will go (raising IQ), and then hammering the head back to the to the driver’s side (lowering IQ) to read 3.4 – 3.6 mg/str.
3) adjusting the VAG-COM adaptation parameter UP as far as it will go (lowering IQ), and then hammering the head back to the to the passenger’s side (raising IQ) to read 3.4 – 3.6 mg/str.

IQ is measured at idle, and as you know, it changes as you drive. At a high (out of recommended range) value, my car smoked. At a lower (within recommended range) value via method #2, the smoke decreased, mpg has gone up a bit, and the car is more responsive. Because of the foregoing, I have a feeling that this question is deeper than it appears, and that fueling across the load and rpm ranges are affected by the method used.

Help, anybody?

Hi,

Set the metric at 32768 and hammer the QA to read 3.5mg/stroke (engine hot, AC/defroster must be off, idle at 903). If QA is not adjusted correctly (hi or low), it throws off the max duty cycle for Q-adjustor (QA collar position - analogous to TBA adjustment with throttle body on gas cars). ie. when asked for 4v, it it has to make up 0.1 volt given by adaptation, it will only give 3.9v final position. This is no problem for part throttle, but full throttle will be cheated by incorrect full stroke/position. See the wot QA voltage in vagcom field 1, ie. 4.0v at 45mg/R, vs 3.9v at 40mg/R. Flip side is lowering IQ too much will give too much voltage, and can shut down (limp mode if more than 4.3v, like tuning boxes and evry mods, etc.) Just like gas injectors if you pull too much pulse witdth/voltage, it will kill ecu drivers from too much voltage/current. When the QA moves the collar and uncovers the piston fuel delivery hole, there is no way more voltage can uncover a hole more then it is already fully uncovered.

Please don't hammer mod unless you know what you are doing. I often have to fix this cuz some unknowing mechanic decided it was necessary to fix smoke. This doesn't fix smoke, it only detunes your car. Smoke is usually clogged intake/exhaust or boost/vaccume problems, unless someone has obviously mismatched heavy fueling mods to turbo's capability.

This is also true for timing and start of injection duty cycle.

You can see the duty cycles in vagcom.

Jeff

jsrmonster said:

<SNIPITY, SNIP, SNIP>
Please don't hammer mod unless you know what you are doing. I often have to fix this cuz some unknowing mechanic decided it was necessary to fix smoke. This doesn't fix smoke, it only detunes your car.
<MORE SNIPITY, SNIP, SNIP>

Jeff

Click to expand...

Excellent answer -- just the type of info I was looking for. I'll make a minor adjustment in the next few days to make it read the correct value at the default parameter. FWIW, you and I know exactly who hammered my car in the first place. All I did was wait a year to start adjusting it back.