Went to 30# injectors, think ill run rich?

i dont think so. its a 331 with some good heads. what fuel pressure were you running with the 24#ers?

i think ur hit or miss was the improperly calibrated maf for 24's and not 30's. I say 44psi is fine.

I run around 48psi on my blown stroker with 42lbers

88SC_GT said:

i had 24# injectors and a pro-m maf calibrated for 24's.

it would have run horrible if it wasnt calibrated.

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my fault i miss read thought u said the maf was out being calibrated so i assumed u were using 30's with a maf caled for 24's

The injector will only feed the amount the computer tells it to. You could use 60# injectors and it will work. Injectors are NOT like carburetors because they do not mix the air and fuel together, but follow the orders from the ECM. The poundage only determines the MAXIMUM amount of fuel it will flow when fully opened. As our MAF tells the ECM how much air is coming in, the ECM tells the injectors how long to stay open to get the proper A/F mixture for that particular flow of air.

JB66 said:

The injector will only feed the amount the computer tells it to. You could use 60# injectors and it will work. Injectors are NOT like carburetors because they do not mix the air and fuel together, but follow the orders from the ECM. The poundage only determines the MAXIMUM amount of fuel it will flow when fully opened. As our MAF tells the ECM how much air is coming in, the ECM tells the injectors how long to stay open to get the proper A/F mixture for that particular flow of air.

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true but the stock eec is setup for 19lb injectors and fuel curves, so if you put a 60lb injector in its place the eec still thinks it has a 19 and therefore it would run extremely rich. cold start open loop closed loop fule tables are all setup for stock. When i went with my 42lbers i used my tweecer to change all those tables.

With that all being said, the EEC is expecting to see stock feul pressure. Adjusting it with an afpr really does nothing. The EEC changes the pulse widths of the injectors to get what it believes is a correct A/F ratio. Get the 30's and the MAF cal'd, and then buy a Tweecer or get a chip burned to tell the EEC that you are running 30's.

bmo37, I see your point and where you're coming from, but the EEC is a learning system (that's why we disconnect from the battery to reset) and would sense too much fuel being put into the cylinders and would correct the pulse of the injectors to compensate and bring about the proper a/f ratio. I do agree that for optimum performance (to utilize the full benefit of the larger injectors) a chip is the way to go.

JB66 said:

The injector will only feed the amount the computer tells it to. You could use 60# injectors and it will work. Injectors are NOT like carburetors because they do not mix the air and fuel together, but follow the orders from the ECM. The poundage only determines the MAXIMUM amount of fuel it will flow when fully opened. As our MAF tells the ECM how much air is coming in, the ECM tells the injectors how long to stay open to get the proper A/F mixture for that particular flow of air.

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While this is true, you can run in to problems due to the minimum injector pulse width delivering too much fuel. This would be noticeable at idle and part throttle more than anything. The problem being that the ECU has a limited scope as to how much it can narrow the pulse width. You can generally get a custom chip burned that will help narrow pulse width further.

Hope this helps

The 'calibration' performed on the meter is what is supposed to resolve the difference between a 30# injector, and the 19# units the ecu is expecting. It's an electronic adjustment of the maf voltage that is proportional to the size of injector being used. Done properly, it usually does a reasonable job of altering the voltage to the ecu so the computer thinks LESS air is flowing, and therefore tells the injector to squirt for a shorter period of time (pulse width). A shorter pulse width on a 30# injector makes it inject the amount the 19# unit would - how much shorter? 19/30 -- simple ratios. That's what the calibration on the meter is all about.

Alternatively, you could leave the stock meter in place, and use a chip or tweecer or pms to tell the ecu that a 30# injector is in place, and the ecu will recalculate accordingly. The problem with that is that the stock meter is flow limited, so most move to something larger that has a similar transfer function as the stock meter - albeit adjusted for injector size.

The best of all worlds is to get the maf calibrator to provide you with a detailed flow vs. voltage function (transfer function) for the meter, use your chip/tweecer/pms to input the data into the ecu (so there's a perfect match between transfer function in the computer and the one from the maf) and then select the size injector you have in the chip/tweecer/pms software - letting the ecu make the adjustment for injector size.

Once that's done, it's all fine tuned by the adaptive strategies of the computer -- using O2 sensor data to trim things out in closed loop. If your maf is accurate, there's no need to ever adjust fuel pressure from stock 38-40 psig.

Having said all that - back to where we started - if the maf calibration is accurate, it should run on 30's just like it did with 19's. If you have to play with fuel pressure to make it run right, it's an maf problem - fuel pressure is a bandaid.

....and the pulse width limitation likely won't be a problem on 19's to 30's; it might well be on 19's to 60's. In any event, those running the big injectors usually have to tell the ecu to back off fuel during start up mode as the big injectors (seems to be a problem around the 36-42 size) just put too much fuel in at start up and tend to flood the motor. Chip/tweecer/pms can fix that.

If the calibration is correct -- it will run at idle/part throttle cruise/w.o.t. just as well as it did with the other maf/injectors. Tune is required most often to correct maf calibration issues....