Boost/Manifold Pressure Compensation | AEM
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paulclaude
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Last seen: 4 months 1 week ago
Joined: 08/21/2017 - 01:02
Boost/Manifold Pressure Compensation

Hi,

I read in an earlier post that the Infinity should automatically compensate for manifold pressure/boost, i.e. 200kpa would be 100% more fuel etc. However, I am presently tuning a supercharged E46 M3 and have found that it doesn't compensate at all. The engine had previously been tuned NA and the VE map was dialed on a dyno using load control, so fairly accurate. On initial pulls with supecharger, A/F was going super lean, hitting max lambda FB as soon as it hit any significant boost. What I have done to compensate for this, is use FuelTrim_2 table with Axis set to RPM vs. MAP and set fuel trim on a linear scale from 105-200kpa (0.05-1.0). I have then been able to dial VE with reasonable values.

Is this behaviour normal and expected or am I missing something?

Thanks, Paul

EDIT: Just to add, I am running an AEM 2 bar map sensor and it is reading correctly as per datalog.

AEM_SB
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Last seen: 2 months 3 weeks ago
Joined: 06/07/2014 - 14:29
Yes the ECU will compensate

Yes the ECU will compensate fuel based on the MAP sensor reading. You can double-check this by disconnecting the MAP sensor line from the engine so it reads atmosphere instead of vacuum while the engine is idling.

If you need extra compensation to hit your AFR targets, that could be a sign that the original injector data wasn't quite right. If the ECU isn't measuring fuel pressure, it's also possible the fuel system isn't keeping up with demand and you're adding extra pulsewidth to compensate for low fuel pressure. Some OEM fuel pressure regulators use atmosphere and ignore manifold pressure, that could also explain the behavior you're describing.

 

Hope that helps,

SB

paulclaude
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Last seen: 4 months 1 week ago
Joined: 08/21/2017 - 01:02
Thanks for the swift response

Thanks for the swift response SB. Ok, will try as suggested. I believe the injector data to be correct - i'm running Siemens Deka 60lb Shorty injectors so used the AEM preset data for those in the wizard, which closely matches the Siemens spec sheet.

I do suspect the fuel pump is not coping with demand as even with the Fueltrim_2 compensation set linear as described, i'm out of injector duty at the top end no matter what VE value is set (runs from 55% to 99% Duty cycle in the last couple thousand RPM). Changing the regulator had no effect, so I have a 450LPH Walbro drop in on it's way. Hopefully the compensation will work correctly once thats changed.