What Exactly is IQ (Injection Quantity)?

Having just replaced the quantity adjuster seals, performed the Hammer procedure to adjust IQ and having read a lot here about it, I am still wondering just what Injection Quantity is. The units are mg/stk which I assume is milligrams of fuel injected to a cylinder per pump plunger stroke(?). However, I have read here in several places that lower values or IQ equate to "more fuel", and vice versa, which seems contradictory. Also, it appears that installation of larger injectors requires a higher setting of IQ for some reason.

Can anyone please give a tutorial on what IQ actually means and does or point me to a source of further info (my attempts of searching here did not provide much detail).

Subscribed.
I've never heard a good explanation for this.

Correction value that converts quantity position (voltage) into assumed injected quantity (mg/s) for ECU mapping and other corrections.

Spec range: 2.8-9.0

Drivbiwire said:

Correction value that converts quantity position (voltage) into assumed injected quantity (mg/s) for ECU mapping and other corrections.

Spec range: 2.8-9.0

Click to expand...

OK, it's a conversion factor that converts voltage (which in turn is a measure of the position of the quantity adjuster?) to an assumed injection quantity. But why then does the IQ value change when the QA body is moved left or right? And why is the spec range so wide (I thought the recommended range was 3 to 5)?

Thanks Powerslave, coincidentally I found the same article and I think I get part of it now. By saying moving the QA left or right "increases" or "decreases" fueling, it is meant that rather than increasing or decreasing fueling per sec, we are increasing or decreasing fueling at any given accelerator pedal position i.e a smaller IQ makes the ECU ask for more movement of the QA towards more actual fuel delivery as it thinks the amount per pump stroke has decreased(?).

I'm still not clear though on how the ECU knows the QA body has been adjusted (right or left), and by what IQ amount.

The 2.8-9.0 spec is the "official" range per VW and Bentley. The 3.0-5.0 range is based on practical experience as an average "sweet spot" for most cars.

NoSmoke said:

OK, it's a conversion factor that converts voltage (which in turn is a measure of the position of the quantity adjuster?) to an assumed injection quantity. But why then does the IQ value change when the QA body is moved left or right? And why is the spec range so wide (I thought the recommended range was 3 to 5)?

Click to expand...

Because quantity is not measured, and you are relocating the control collar over the shaft, this range cannot be measured or sensed, so it senses these changes by differences in crank acceleration and voltage required to maintain a specific rpm in respect to the power required to overcome the controllers internal spring.

What is the accepted IQ for BEW?

5.0-9.0 for a BEW

Thanks for the explanation Drivbiwire. Pretty clever way of doing it w/o additional sensors.

A lot of good info in this thread:
http://forums.tdiclub.com/showthread.php?t=431640

adaptation number change vs hammer mod IQ adjustment

Hi I'm not sure this will appear in the correct location - it's not a reply but a question. Is there any reason to adjust the injection quantity (IQ) with the hammer mod instead of simply changing values in the adaptation portion of VCDS? My 03 was idling very rough with an IQ of 1.2 so I changed the adaptation value from 32768 to 32675 bringing IQ to 2.2 and smoothing the idle. Should I raise the IQ number more? which method? Thanks

Hammer mod is used when you can go no further with vcds. You are at the rich end of the range and went leaner with your adjustment. When I adjust mine, I work toward lean and minimal smoke under hard acceleration and then riches it to where I like to suit my driving habits

Thanks so much that makes sense! I'll try to lean it a bit more though it's driving clean and smooth and strong right now.

I know this is pretty much a settled discussion in several other threads, but I've never been convinced that lower is more and higher is less.

A cold engine requires more fueling to maintain RPMs. If more (higher number) is less, I ask this one question. Why does the number drop as the engine warms up?

AndyBees said:

I know this is pretty much a settled discussion in several other threads, but I've never been convinced that lower is more and higher is less.

A cold engine requires more fueling to maintain RPMs. If more (higher number) is less, I ask this one question. Why does the number drop as the engine warms up?

Click to expand...

A cold Diesel engine has a more difficult time combusting fuel

AndyBees said:

I know this is pretty much a settled discussion in several other threads, but I've never been convinced that lower is more and higher is less.

A cold engine requires more fueling to maintain RPMs. If more (higher number) is less, I ask this one question. Why does the number drop as the engine warms up?

Click to expand...

jmodge said:

A cold Diesel engine has a more difficult time combusting fuel

Click to expand...

And ............

Sure, I know how a diesel engine fires the fuel. The colder the engine (and ambient) the more fuel it takes to start it and maintain idle RPMs without dying. Gasser engines from almost the beginning come equipped with a means to increase fueling when starting, especially a cold engine. .... choke, high idle cam on the carburetor, fuel pressure regulator, etc., come to mind. The simple 3-cylinder diesel Yanmar engine in my very old mini-excavator only has a manual throttle for increasing fuel... same as my uncle's 1944 army surplus dozer. If I don't increase the fueling on a cold day start, it will not start or is difficult to get started.

During a cold-start the ECU increases fuel on an ALH TDI engine based on engine temp, fuel temp, ambient air temp and crankshaft RPMs to maintain the programmed 903 idle RPM. When I start the engine on any of my TDIs, with VCDS connected, I see a high IQ number. As the engine warms up, that number drops and drops until the engine is fully warmed up.

So, is the lower number more or less fuel? If it is more fuel, why does the number get smaller as the engine warms up?

Lower IQ providing more fuel only applies when comparing a before hammer mod condition to an after condition.

When the engine is running a higher IQ always means more fuel than a lower. Turn on the AC. The IQ goes up due to the higher load.

On a properly calibrated pump the IQ is presumably pretty close to reality.

Take as a baseline a warmed up engine with a properly calibrated pump. Say it idles at 930 with an IQ of 5.0. That is really 5.0 since it's calibrated.

Say you hammer it to an IQ of 4.0. It still idles at 930, load on engine is the same so the actual IQ is still 5.0. The ECU ignores the feedback it's getting from the pump since it is maintaining the programmed idle speed.

Now when you step on the accelerator its programming takes over. It uses the feedback from the pump which was recalibrated with an offset. What it thinks is 4.0 is actually 5.0. Presumably 5.0 is actually 6.0, etc. It's providing more fuel. I assume it is an offset rather than some curvy function.

The hammer mod is a mechanical recalibration of the pump.

At least that's my understanding of what's going on. Never seen any other splanation. Only the often repeated "lower IQ means more fuel" with no qualification. Obviously that statement is incorrect for a running engine as you have observed.

jmodge said:

Hammer mod is used when you can go no further with vcds. You are at the rich end of the range and went leaner with your adjustment. When I adjust mine, I work toward lean and minimal smoke under hard acceleration and then riches it to where I like to suit my driving habits

Click to expand...

I was wondering this exact thing myself today!!

I poked around my ECU via VCDS and I was considering the hammer mod, but mostly wanted to learn more.
I did the 12233 Login on VCDS, and checked my 'adaptation value'. The thread I was reading said 32768 is the stock value.
I was a little surprised to see mine had been set at 32660.

Interesting...

I changed it to 32768 (per the thread's instructions) and immediately something..happened. Severely choppy idle, whole car shaking. Like a scary movie's drastic change of music when the bad guy shows up. My engine went from a symphony of cute sewing machines to a dirty DUB...DUB...DUB...DUB...
Sounded like someone threw a lopey cam in a farm tractor.

I adjusted it back to 32740 (I believe) to get my IQ right into the 3.0-3.2 range. Not sure what to think of my car responding so poorly to the stock value...

Stomachbuzz, I think just through wearing of components the IQ "migrates" slowly and at some point, in my experience, seems to move toward the rich end of the scale. Thus a hammer mod will "center" the "stock value" to the IQ "scale".

Andy, I have noticed those IQ changes with temperature. I understand where you are coming from on cold start fuel richness. I am thinking in terms of acceleration, such as the barf of black smoke and stumble coming from an ALH with a bad thermostat. I stood on mine in second gear when it was cold the other day jumping on M57 from a slow roll and it did that, doesn't do it when it is warmed up.