What is your peak MAF reading?

[Mik]

360....maxed out

[KayGee]

I agree however most dyno tuning isn't done as an "absolute measurement". It is a tuning aid, if I change this parameter this happens. With a dyno what you are measuring is wheel torque or engine output, if you so wanted you could do exactly the same thing with air flow, it is after all what you want an engine to do, ingest air. The more air an engine ingests the better it is performing. The more air you can get into an engine the more power it will make. Instead of looking at the power output at the wheels you are measuring the engines ability to swallow air.

Essentially an engines power output is a maths equation, massively simplified "more power out=more air in". I know a car can be tuned just as easily by monitoring the air mass input as it can by the wheel torque output as the two are directly related. No tuner worth talking to would consider tuning a modern car without accurate AFR, EGT and IATs values, fortunately modern ECUs provide nearly all of this information. Narrow band AFR sensors suck for tuning, latest genration modern cars are now shipping with wideband lambda sensors.

The tuner will typically manipulate two variables, timing and AFR (putting boost and wastegate duty aside). Whilst watching IAT, knock and EGT to make sure the engine is operating safely. Hope that makes sense.

AFR is what a lot of tuners use to tune a car, they choose a target AFR and manipulate the fuel injector cycle so the car runs the target AFR. 14.7 typically for light/medium throttle and 11-13:1 (typ 12.5) at WOT. This is measured by a wideband lamda sensor. They then manipulate the timing maps.

Timing is essentially a function of engine design and rpm, you ignite the fuel air mix so the max flame front occurs just before TDC, so the explosion drives the piston back down with the maximum force.

During all of this the tuner will be watching IATs, especially on turbo cars to make sure the ingested air isn't getting too hot and also monitor EGT too make sure the cars exhaust gases aren't getting too hot indicting an imminent engine failure (melted pistons). These can be combatted by altering AFR (using petrol as a coolant or washing as it is sometimes called), changing the timing (this is what our ECU will typically do) or reducing boost (ECU can do this as well).

So the tuner looks for the best balance of timing and AFR, whilst controlling IAT, knock and EGT levels.

When looking at MAF figures they are actually real world, since they occur when the car is moving through the air. Part throttle wide open throttle all can be measured. You do the same thing as you would with a dyno, do a run, make a change, look a the output, did it improve or get worse. Same principle as a dyno but using input (mass of air) rather than output (wheel torque).

There are lots of ways of tuning cars, a dyno is just one way to measure the results of the tuners work. Some people tune by spark plug colour, others tune by EGTs or AFR. Its all the personal choice of the tuner concerned and what works for them.

[tartan_rob]

Okay guys, I did a run yesterday. Uneven surface, 14deg c, full tank of fuel.....I was getting a peak of about 230....that is lower than before, I was expecting to see 260/270 odd. I have noticed over the last few days that the car has been a little bit slower than normal.

So I think boost leak - but I'm getting good boost figures !.2 approx peaking at 1.4 (as I got MRC to set-up). So the only other thing may be the MAF, it was changed 18 months ago approx so I'm going to hoof it out later on and do that alchohol thing and give it a clean along with the K&N element too. Fingers crossed, that'll be my problem...

[ZeroK66]

A STANDARD mapped car should read 250ish, so think you have a dodgy MAF. My original MAF was reading 210 - which they replaced and I got 257 (Before pre-cats).

Sorry to hear that... the anticipation increases...

[DavidT]

360....maxed out

Cool

[DavidT]

Okay guys, I did a run yesterday. Uneven surface, 14deg c, full tank of fuel.....I was getting a peak of about 230....that is lower than before, I was expecting to see 260/270 odd. I have noticed over the last few days that the car has been a little bit slower than normal.

So I think boost leak - but I'm getting good boost figures !.2 approx peaking at 1.4 (as I got MRC to set-up). So the only other thing may be the MAF, it was changed 18 months ago approx so I'm going to hoof it out later on and do that alchohol thing and give it a clean along with the K&N element too. Fingers crossed, that'll be my problem...

Could be, an air leak after maf but before the turbos, causing the maf to read low (as its not measuring all the air the turbos are compressing) and therefore the engine will run lean as it fuels based on the amount of air the maf says its getting.

[DavidT]

K&N element

Eeek, that might be it you know, K&N filters with too much oil on them have a big effect on maf life.

[tartan_rob]

There looked like that was a lot of trace oil on the maf so all cleaned now and going to re-assemble and see what happens.

[tartan_rob]

No luck, I have not taken a MAF reading but she still feels down on power. Time to start looking for leaks.

[JonnyX]

Did you log blk 115 as well Rob? A plot of requested vs. actual would be useful.
Also, try clearing your fault codes, going for a blast and then checking your
long term fuel trim (032 I think). I would imagine if you have a leak you will
be having to do some lambda regulation which should show up there.

I would still bet your MAF is fubar

[KayGee]

If after a reset, still iffy, disconnect your MAF, do a throttle body re-align, take it out for a spin. If it feels OK, duff MAF. I agree with comments about K&N filters and oil, I'm back to a paper filter, same g/s readings and no risk of oil contamination.

[ash318]

does a rs4 maf fit straight in place of standard s4 maf and does it offer any advantages over standard cheers ash

[KayGee]

Need to modify the airbox as housing is larger, basically gives you ability to measure more g/s. Stage 3 or above.

[tartan_rob]

Ash - the RS4 MAF is bigger, you need the airbox and the plastic pipe that joins the maf to the Y pipe. You'll also need some re-mapping afterwards.

Kaygee - I'll try that and see what happens. I appear to have no major air leaks either. Could well be MAF on its way out.

[buzzard]

kaygee , your write up is very interesting and informative on tuning and air intake readings
explanations are valuable to us for future .
things have changed since tuning my HC Viva...