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Huge Flat Spot above idle

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Hi everyone, major lurker here finally admitting to requiring help from people far more intelligent than myself haha.

Long story: I am tuning my Audi S3 8L with a 1.8t, using the brilliant Motorsport Electronics ME442. This is one of the first times this ecu has been used on this engine, so there really isn't much base info on the subject, hence needing to ask the experts.

As it stands, the engine is mechanically uprated internally and ready for turbo and injector upgrades, but I am currently making a map for the standard engine running the standard K04 turbo. I regularly plug in the standard Bosch ECU to use the car, and there are no issues with it at all.

With regards to the engine running on the new ECU, I have got cranking and idling quite well sorted (more fettling to get it perfect will be needed later on), with lambda around 0.9 at idle. The current problem I have is that with a moderate change in throttle, the engine hesitates hugely, lambda goes to 1.25 (17:1 afr), and revs drop; its almost impossible to get the engine beyond this zone. If I very very gently increase the throttle, I can get beyond this flat spot and from 2k upwards the lambda is back at around 0.9 - 1 and the engine has great response.

My fuel table is not tuned much beyond the idle points, but is smooth throughout the map; likewise for the ignition. If I try to enrichen the points where the problem arises, it affects the idle. If I increase the resolution of the table at this area, I still cannot get the fuelling right.

If anybody has any suggestions, it would be greatly appreciated. Mucho Gracias in advanced!

I suspect your fuel map at the RPM & loads above the idle condition (but less than 2k) are just too lean (at least 25%). If you can provide details of the operating conditions (MAP, throttle position, RPM), and maybe a view of the fuel map/table, perhaps we can suggest what cells you should change to improve the situation. Can you log data with that ECU? What happens to ignition timing, and fuel pulse width when this happens?

Another issue might be any idle control interaction - sometimes idle control will try to return the revs down to idle, when you really want to start moving. Careful review of the entry/exit conditions for idle control will usually identify what needs to be changed.

Ok, sounds like a great start. When I get a chance I will review, log and update the progress. Thanks David

If it uses a TPS, I would first check it is correctly calibrated in the ECU - if it's off just a little, the ECU may still be getting a signal that the throttle is in idle position, and so not enriching the mixture, as it's actually cracked open.

Hi again Folks, Sorry for the incredible time in getting back, probably a new record!

So after various changes and testing, here's what has been done since:

* I have turned off all Idle control completely. This is no longer a factor.

* All other injection modifying parameters (Accel Enrichment, Warmup procedures etc) Have been turned off. Only cranking parameters are still acting, but they are only lasting 3 seconds.

* DBW Throttle Positions have been calibrated again, and PID has been revised.

Now, saying all that, it has still been doing the same, no matter what I do with the VE table. I have been tuning the idle area on the table by using a setting on the ECU where I can set a desired DBW TPS, and the DBW system holds it at this position. I have been using 3%TPS for 1,000rpm, then moving it by 0.25% at a time to further tune the table up to 2,000rpm. After getting the table tuned at around 0.9 lambda at the relevant cells, if I return the TPS to 3% so that it idles, and then jump straight to 4 or 5%, the engine massively leans out and almost stalls.

However, I think I may have cracked the problem:

One of my fleeting thoughts was 'maybe the MAP sensor is not calibrated correctly,' so I checked my initial settings, and decided to find some info on the interwebs for a calibration table to double check. I went to the engine bay to get the part number of the sensor, and lo-and-behold, I just remembered that the stock system places the MAP sensor BEFORE the throttle body, as it uses a MAF for air volume.

This would explain why I have always had 100kpa at almost every point when keeping a steady state RPM, and only moving off of 100kpa when running boosting conditions. I had never had anything less than 100Kps, even at idle.

So can someone confirm I was being a wally, and that this would be causing this effect? Of is it a red herring and I am pretending I am smarter than I actually am?

Thanks in advanced as always!

It certainly seems likely, but you're the one with the engine and new ECU. We don't even know what the load axis in your VE table is. What happens when you move the MAP sensor to pick up manifold pressure instead of boost pressure (BAP)? Perhaps the ECU just needs to be configured knowing that this is BAP not MAP.

Well, that was the issue.

MAP is now located in Manifold, after the Throttle Body. Much better.