Tuned M20B25 throttle lag problems

[Sam8888]

Hi!

I have an M20B25 engine, with ported cylinder head. I bought the engine from a racecar, so it is possible that it have a little bigger comp ratio or may have a bigger cam in it too.

The problem is (i've heard it from other tuned M20 owners that they suffering from this kind of problem too), the engine has a little lag.
I mean if the engine is at the idle, and i add a little gas, it almost stalls, i can hear the air sucked in, then revs up. It's very annoying. :der:

Something like that in the video, but the symptoms a little bit harder:

http://www.youtube.com/watch?v=1wlJ13I5LZg

Above about 1100Rpm, it's just fine.

I changed kinda everything around the engine, there is 100% that it's not a vacuum leak, or an ignition problem. TPS checked, works fine, AFM too.

I think the ecu don't giving enough petrol to the engine.
I also have a ghetto O2 monitor, wich is a cheap digital voltage meter that shows the o2 sensor voltage, but it shows the correct values only at WOT.

So actually now i'm using Bosch 0 280 150 714 (M30B35) injectors, it's got a little better, my engine has more low-end torque, but it's still have that lag.

I guess the problem will be here:



I think the ecu don't give enough petrol at the low throttle map.
Now i don't have an eprom burner, but i will buy one soon, and will try to fix this problem.

Any other thoughts what causing this lag?

[TurboJake]

It's due to the VAF style AFM. Switch to a MAF or MAP and that will vanish.

[Sam8888]

Nope.
I had an m20b23 engine originally with L-Jetronic, that is swapped to m20b20's motronic 1.3
With the m20b20 ecu, it did the same symptoms, very laggy throttle response from idle.
When i changed the ecu to the m20b25 one, the problem solved... (Again, 2.3 litre engine with 2.0 ecu is not worked properly, but with the 2.5 one worked like a charm)

And it had the same VAF style AFM.

Also my friends factory m20b20 has much sharper throttle response...

Sorry but i think it's not the answer.

[BenjaminButtton]

I have the same issue with my m20 stroker running 19# injectors... Always kinda blamed it on the AFM as well.

Interested to see what people say/have done to counteract this.

[603Racing]

Same... Cam, headers, chip, 17# injectors... hesitation when first on the throttle.

[BenjaminButtton]

Can anyone with an MAF converted m20 chime in..?

[Sam8888]

If i can't solve this thing with the original AFM, i guess i will try with a MAP instead of MAF.
Or maybe i'll change to standalone like megasquirt, but it's costs hellofalot money here in Eastern Europe.

A friend of mine said, the engine needs bigger injectors, because the Fuel acceleration Enrichment map is the responsible for this, and at low rpm's the injectors fully open. So i guess it didn't solved with the 19# injectors, i should go bigger. Maybe from a 328i dunno.

I think the answer will be somewhere between the m20b20 and the m20b25 ecu's differences.