MAF Recalibration
12-22-2009, 03:30 PM
#11
5th Gear Member
Join Date: Aug 2005
Location: Whitehall, Michigan
Posts: 2,638
So pretty much what u are saying is that after i get my car tuned with the 24# injectors that it will be fine no need to recalibrate anything? and if i put the injectors in before i go get it tuned will the car run right cause i will have to drive the car to the tuner
24# injectors aren't that much bigger than stock. It will still start and run with them. It will run rich, but you won't have any major issues. Clear the KAM in the ECU by disconnecting the battery for 10-15 minutes while you make the injector swap. You'll find that it probably isn't even running rich by the time you get to the shop - but the CEL may come on.
You will not need to recalibrate your MAF. In fact, they won't even have to mess with your MAF transfer function - if they do, they don't have a clue what they're doing and you should go elsewhere.
If you really still feel uncomfortable about the injectors - just swap them in the parking lot of the shop. It doesn't take too long, and only requires hand tools. Just bring rags to catch the fuel.
Edit: Also noticed you have a 93 octane tune. If you've still got your handheld, lean the mixture by 15-20% (19 divided by 24) if it will let you... should correct any issues you might be having.
Last edited by ShadowDrake; 12-22-2009 at 03:34 PM.
12-22-2009, 03:35 PM
#12
2nd Gear Member
Thread Starter
Join Date: May 2009
Location: MO
Posts: 204
The tune will be "re-calibrated" by changing the Low and High Injector Slope values. But that's all that will need to be changed. Don't expect any amazing power increase (or any), as the 21 lb/h stock injectors can supply enough juice for any sort of bolt-ons. They get pushed to 90% or so duty cycle but they'll do the job. The 24's will be running down around 80% duty cycle or less.
The PCM should be able to adjust the short term fuel trims so that it will run OK in closed loop mode, you're only moving from 21 lb/h to 24 lb/h injectors. In open loop it will run a bit rich, and since the OEM tune is rich anyway you may get some bogging--but just don't get into open loop and you'll be OK.
After it's tuned you might want to disconnect the battery for 5-7 minutes to clear the KAM (Keep Alive Memory). That where the long term duel and idle air trims are stored, clearing it will force the PCM to learn new values sooner.
The PCM should be able to adjust the short term fuel trims so that it will run OK in closed loop mode, you're only moving from 21 lb/h to 24 lb/h injectors. In open loop it will run a bit rich, and since the OEM tune is rich anyway you may get some bogging--but just don't get into open loop and you'll be OK.
After it's tuned you might want to disconnect the battery for 5-7 minutes to clear the KAM (Keep Alive Memory). That where the long term duel and idle air trims are stored, clearing it will force the PCM to learn new values sooner.
12-22-2009, 04:06 PM
#13
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Those are flywheel HP number in the chart. The OEM 21 lb/h injectors are running at 95% duty cycle at 265 or so rwHP--which is too high, you want to stay around 80% to 85%.
If you assume a 15% loss in the drivetrain and running the accessories then 24 lb/h injectors at 85% duty cycle would be 266 rwHP--30 lb/h would be a better choice if you are really going to get to 300 rwHP.
To do that n/a you'll need better flowing heads on top of what you have done.
Here's the formula for sizing injectors:
Again, HPmax is flywheel HP...
12-22-2009, 05:43 PM
#14
2nd Gear Member
Thread Starter
Join Date: May 2009
Location: MO
Posts: 204
Here's a "rule of thumb" type injector sizing chart:
Those are flywheel HP number in the chart. The OEM 21 lb/h injectors are running at 95% duty cycle at 265 or so rwHP--which is too high, you want to stay around 80% to 85%.
If you assume a 15% loss in the drivetrain and running the accessories then 24 lb/h injectors at 85% duty cycle would be 266 rwHP--30 lb/h would be a better choice if you are really going to get to 300 rwHP.
To do that n/a you'll need better flowing heads on top of what you have done.
Here's the formula for sizing injectors:
Again, HPmax is flywheel HP...
Those are flywheel HP number in the chart. The OEM 21 lb/h injectors are running at 95% duty cycle at 265 or so rwHP--which is too high, you want to stay around 80% to 85%.
If you assume a 15% loss in the drivetrain and running the accessories then 24 lb/h injectors at 85% duty cycle would be 266 rwHP--30 lb/h would be a better choice if you are really going to get to 300 rwHP.
To do that n/a you'll need better flowing heads on top of what you have done.
Here's the formula for sizing injectors:
Again, HPmax is flywheel HP...
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