MAF readings logged.... confused!!

[markymark1984]

Hi guys, i could really do with some help and advise.....please read!:icon_thumright:

I have hooked the car up to VAG COM and recorded the MAF with a run in 4th gear (private strip) and got the graph below. Max g/s reading was around 200 which seems good. There is a spike just below 3000 rpm, any ideas on what that is? Other than that seems quite smooth doesn't it?

I decided to do this data logging after putting the car on a dyno, the resulting power and torque graphs were quite worrying, they were all over the place (looked like a heatbeat monitor, spikes and dips all over the place!). And more worrying max power was around 220, even though the previous owner claims it has been Revo'd (i dont have the dyno graph unfortunately). Can anyone suggest why this might be? I thought it may be a crap MAF but from looking at the graph below it does seem the be fine....very confusing.

Is there a calculation i can do from knowing the g/s to work out the power my car has? I can then compare that to the dyno output, maybe the dyno wasn't set up right? I must admit though my car doesn't feel like a 260bhp remapped machine, its pretty much identical to me friends Fiat Coupe which has 225bhp.

Cheers for any help!

Mark

 

[enda1]

Marky.
In my A6 1.8T the MAF is in the air box. It measures the amount of air coming into the engine before the turbo. You could have a perfectly acceptable MAF figure but your turbo set up could be at falut with leaks or dumping boost and this is why you're getting a poor bhp figure. You need to check that you have no leaks in any of your piping post turbo and then stat checking the boost control gear such as the n75 valce to ensure this is working properly

 

[markymark1984]

OK, how would i go about checking for leaks? Visual inspection (pipework, DV, what else??) or hook it up to VAGCOM and check the requested boost vs the actual boost? I dont know if i would be better off taking it to a garage and getting someone to look at it for me, i'd rather diagnose it myself as it would save a lot of £££ no doubt!!

 

[enda1]

i'm no expert but a visual inspection first then as you say check requested vs actual boost.
Send me your engine type and email via pm and i'll try to get you a schematic of the boost plumbing from elsawin

 

[Longman]

Hi Mark

To my knowledge, Torque and BHP calculations from VAG-COM are of no use on a remapped car. There is a std Torque figure, saved to the ECU, that VAG-COM refers to when calculating actual torque while logging. This is not updated when the car is remapped so VAG-COM will always be refering to the original figure, instead of the new, remapped value.

In terms of the spike on your graph. (And this could be checked if you were to plot boost at the same time) Might be where your turbo is spooling up to meet requested boost and overboosts slightly. I have seen this before, mine does it a bit. It then settles down to follow the requested boost values throughout the range.

To check for boost leaks, I tend to measure block 114 and look at the 4th column. This is the N75 duty cycle. It will show you how hard the turbo is working to meet requested boost. Anything in the 90s would be ok at full throttle. You should never see 100%. If you do, you probably have a leak.

I hope this helps mate.

 

[markymark1984]

Righty, i've done a bit more research into working out if my car has been mapped or not.

From looking at my boost and MAF readings i thought it was likely it had been mapped (fairly high readings?) but after logging group 005 and plugging the values into the 'Butt Dyno', which is suposed to be fairly accurate, the max power comes out 218 bhp @ ~6000rpm and 208 ft lbs @ ~4500rpm.

What does everyone make of this? I've read on these forums that if you know you MAF reading, dividing it by 0.8 gives you a very rough power estimate. If thats the case my max MAF reading of 210 g/s equates to a max power of approx 260 bhp (which sounds about right for a remapped car). However the Butt dyno estimates a figure much less!?!

i think i will be taking it to VAGtech in the near future to get their opinion and get it remapped if their analysis proves it hasn't been already but i would quite like some peoples views on here if poss!!

The first graph shows requested and actual boost, MAF and N75. The second graph shows power and torque.

Cheers

Mark

 

[Longman]

Hi Mark.

N75 Duty looks good to me, as do your MAF readings. 210g/s on a remapped car is about what is should be.

The Actual and Specified boost look very similar to a Leon Cupra R I have worked on. The owner of this has had pretty much identical log results to you and was told the car was remapped with revo. It just was not making the expected BHP on 2 seperate Rolling Roads.

Your boost curves show the turbo spooling up to meet the requested boost, overboosting a little and then coming down to match, this is normal.

As the Leon and your S3 both show, the boost tails off from specified towards the end of the rev range, not meeting what is requested.

The Leon had also had revo, so it looks like a feature that is common to that map. I just don't know why this tailing off of boost happens or whether it points to the problem??

Looking at the BHP/Torque graph, I was told that the Torque and BHP should always cross at 5252 revs. So far this has been the case on the cars i have done it with. As does the example on the Butt Dyno. I am not sure if this is relevant though??

Maybe someone else has had some more experience??