injector upgrade questions?

Jeff Chambers · 01-06-2001, 08:29 AM

Look at it this way. Your 19# MAF and 19# injectors worked together to produce an A/F ratio or 14.7 (just an example). When your motor was moving 600cfm of air at 5000rpm, your MAF sent a 4.8V signal (again just an example) to the computer, which was alot of voltage and high on the air/fuel curve. Based on this 4.8V, the computer looked in its tables and sent a wide pulse width to the injectors...wide because the 600cfm was a lot of air and the computer sees that a lot of fuel is required to get to the 14.7 A/F ratio.

Now, you've swapped out those 19# injectors for 30# injectors but left the MAF >>AND<< computer alone. At that same 5000rpm and 600cfm engine point, the MAF is sending the same 4.8V signal and the computer is interpreting that same 4.8V signal and sending the injectors the same pulse width it looked up in its tables. Problem is though that the new 30# injectors flow nearly twice as much fuel for the same injector pulse width. This makes your A/F ratio well under the 14.7 value the computer thinks its going to get from the amount of fuel the computer has dumped in.

Basically, the MAF calibrated for the larger injectors would send a 2.4V signal to the computer for the same 5000rpm and 600cfm engine point. The computer now interprets this as a lower engine setting and shortens the pulse width so that the desired A/F ratio is maintained.

Hope this helps...hope it makes sense...too early on Saturday morning to be thinking this hard.

------------------
Jeff Chambers
Trophy Stock #3
11.97 Seconds / 114.5 MPH
www.kellnet.com/chambers

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01-06-2001, 08:29 AM	#3
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	Look at it this way. Your 19# MAF and 19# injectors worked together to produce an A/F ratio or 14.7 (just an example). When your motor was moving 600cfm of air at 5000rpm, your MAF sent a 4.8V signal (again just an example) to the computer, which was alot of voltage and high on the air/fuel curve. Based on this 4.8V, the computer looked in its tables and sent a wide pulse width to the injectors...wide because the 600cfm was a lot of air and the computer sees that a lot of fuel is required to get to the 14.7 A/F ratio. Now, you've swapped out those 19# injectors for 30# injectors but left the MAF >>AND<< computer alone. At that same 5000rpm and 600cfm engine point, the MAF is sending the same 4.8V signal and the computer is interpreting that same 4.8V signal and sending the injectors the same pulse width it looked up in its tables. Problem is though that the new 30# injectors flow nearly twice as much fuel for the same injector pulse width. This makes your A/F ratio well under the 14.7 value the computer thinks its going to get from the amount of fuel the computer has dumped in. Basically, the MAF calibrated for the larger injectors would send a 2.4V signal to the computer for the same 5000rpm and 600cfm engine point. The computer now interprets this as a lower engine setting and shortens the pulse width so that the desired A/F ratio is maintained. Hope this helps...hope it makes sense...too early on Saturday morning to be thinking this hard. ------------------ Jeff Chambers Trophy Stock #3 11.97 Seconds / 114.5 MPH www.kellnet.com/chambers