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Old 04-30-2013, 07:21 PM   #1
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Default Whats the largest injectors a stock PCM can run?

I did a search, and all the posts are old so Im wondering if theres something new out there. My 60lb are at 91% with 10psi on my 408. Am I tunning wrong or are they maxed out?
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Old 04-30-2013, 08:37 PM   #2
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Heck if you scale the tune, a stock PCM/ECM can run some pretty big injectors. Enough to support 1500+ hp. Some ID850s would be an easy upgrade as Injector Dynamics supplies all the GM data, just copy and paste into your tune.

What hp/tq are you putting out, is your fuel pressure dropping (if so, to what PSI)?
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Old 04-30-2013, 08:38 PM   #3
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Quote:
Originally Posted by MillsMotorvation View Post
I did a search, and all the posts are old so Im wondering if theres something new out there. My 60lb are at 91% with 10psi on my 408. Am I tunning wrong or are they maxed out?
There's no set answer. You can run huge injectors in any PCM as long as the resistance is correct. All you have to do is scale it. Not just that, but different PCMs have different injector flow rate ceilings. But even then, you can get around those limits by scaling.

As far as are you tuning wrong (BTW tuning is spelled with one N) what is your A/F ratio? What fuel? How much power are you making? What's the fuel pressure? Is it falling off up top where DC is highest?
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Old 04-30-2013, 08:47 PM   #4
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For one thing, that duty cycle you see on your scan tool is probably wrong. Use a fast DSO (Digital Storage Ociliscope) to actually measure your injector pulse width during a dyno pull. Some scan tool data is an actual measurement, some (like ink duty cycle) is a calculation. Your making a ton of power, are too rich, or are band aiding low fuel supply to actually have duty cycles that high with those injectors. More fuel pressure not only atomizes fuel better (more power) but is cheaper than another set of injectors. If the air/fuel ratio is correct, I would raise the fuel pressure and re-tune it.
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Old 05-02-2013, 08:03 AM   #5
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Another thing to think about though is that upping fuel pressure will also drop volume from the pump. It depends on the pump as to how fast it drops off. Just something to think about.
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Old 05-02-2013, 08:14 AM   #6
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Only if you don't have enough pump. Non issue with the correct pump.
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Old 05-02-2013, 08:29 AM   #7
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Very correct. I did not see what pump he was using did you? If he is on the ragged edge with the current pump and he turns up the pressure he will run out of pump and go lean.
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Old 05-06-2013, 08:44 PM   #8
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Very correct. I did not see what pump he was using did you? If he is on the ragged edge with the current pump and he turns up the pressure he will run out of pump and go lean.
I have dual walboro340s, just installed rails also. What im wanting to know whats the largest plug and play injectors that a stock PCM can run, i have HPTuners to tune with.
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Old 05-07-2013, 05:16 AM   #9
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The largest high z injector I know of off hand is a 220 lb. I am using 160 lb bosch and they seem to run fine so far. I think either of those choices would be fine for over 1400 hp on e85. What are your hp goals?
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Old 05-07-2013, 01:16 PM   #10
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Quote:
Originally Posted by MillsMotorvation View Post
I have dual walboro340s, just installed rails also. What im wanting to know whats the largest plug and play injectors that a stock PCM can run, i have HPTuners to tune with.
I dont think you are going to get the answer you are looking for, at least until you tell everyone what PCM you are using. As mentioned a few times here, some creative scaling of the tune can allow you to dial in pretty much any size injector, how much you have to scale it and at what point scaling becomes necessary depends on the specific PCM you are using.
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Old 05-07-2013, 08:33 PM   #11
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I rarely go by injector duty cycle off the scanner. You can have it read 150% duty cycle and not run out of fuel. Pretty sure it just calculates off the changes in the tune.

Do you use a boost regulator?
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Old 05-07-2013, 11:22 PM   #12
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Slowhawk is correct, If an injector is really at 150% "which is physically impossible" then you wouldn't be able to adjust fuel changes while in the 100-150 range seen. As it just isn't possible. 100% means full open and never pulsing. So fuel control is non existent.

The computers are not outputting correct duty cycle on a lot of oem computer types. The way to see the correct values is to do like the op said and use a scope.

Or if you really know the exact real MS of the injector opening time and rpm at the range you want to check you can at least get a better idea of what it really is.

There are plenty of duty cycle calculators on the net if you don't want to manually do the math, even though it is a simple calculation..
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Old 05-08-2013, 12:48 AM   #13
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Ok let me try and give all the info I know. Seems you guys are trying to help me. At the time I got the tune Frost set me up on a 6.0 with GT45 turbo. I have since UPGRADED to 408, GT91, dual walboro 340s, and new rails, and line 8AN, Aremotive return stlye regulator, 60lb Semkias, proted 317s, Comp cam, 3300TCI stall, 1981TTA. Been learning to tune doing ok, but need help on whats the best injector, and I can tune.
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Old 05-08-2013, 12:55 AM   #14
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The largest high z injector I know of off hand is a 220 lb. I am using 160 lb bosch and they seem to run fine so far. I think either of those choices would be fine for over 1400 hp on e85. What are your hp goals?
Will they work on stock PCM, who sell them, and part# If they get 1400 on E85, 1400hp on gas, and meth should be no problem.
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Old 05-08-2013, 02:26 PM   #15
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Had a guy tell me to install a FP gauge so I could read FP driving, and heres what it did. Its a boost reg, with line off FP set at58psi. Riding down the road car has aprox 50psi FP, I ease into it FP gos to 60psi, at about 4-5lbs boost FP drops to 40psi real qiuck car go lean. do I have reg hooked wrong it a Areomotive, or is it a bad FP reg? With car off it holds about 40/50 FP for 4mins.

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Old 05-08-2013, 03:30 PM   #16
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How do you have it hooked up? Sounds correct at 50 at idle and cruise and 58 with the line off. But if it is dropping that hard when going into boost either something is wrong with your set up or your fuel pumps are just not up to the task. I have seen multiple failures with the 340 pumps. Mainly the Aeromotives 340s. That is one reason I went to a single large pump. If it shuts down, so does the car. If you have one of your two pumps die it just goes lean.
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Old 05-08-2013, 06:11 PM   #17
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How do you have it hooked up? Sounds correct at 50 at idle and cruise and 58 with the line off. But if it is dropping that hard when going into boost either something is wrong with your set up or your fuel pumps are just not up to the task. I have seen multiple failures with the 340 pumps. Mainly the Aeromotives 340s. That is one reason I went to a single large pump. If it shuts down, so does the car. If you have one of your two pumps die it just goes lean.
I have one running off the PCM, and the other has a 10Gauge wire to a relay that I can set to what ever boost to come on. Im thinking FP reg is bad, I ve killed 3engines do to lean condition! Got it used and the price was to good to be true, thats my dumb mistake!
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Old 05-08-2013, 07:21 PM   #18
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Hmm, think I would change the way I ran my fuel lines too. I split my feed from the pump, go into each rail then do two equal length lines coming out of each rail going to the regulator. Parallel vs series plumbing. Just how I have always done it. My guess is you should not be out of pump. Have you verified that the second pump is activating?
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Old 05-08-2013, 09:34 PM   #19
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Hmm, think I would change the way I ran my fuel lines too. I split my feed from the pump, go into each rail then do two equal length lines coming out of each rail going to the regulator. Parallel vs series plumbing. Just how I have always done it. My guess is you should not be out of pump. Have you verified that the second pump is activating?
Yes second pump come on, its tied to meth, when I prime it it only go up a pound or 2, I was thinking the FP reg was keeping fuel in line should FP spike when Im idle, and cut the second pump on?
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Old 05-09-2013, 04:49 AM   #20
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Yes second pump come on, its tied to meth, when I prime it it only go up a pound or 2, I was thinking the FP reg was keeping fuel in line should FP spike when Im idle, and cut the second pump on?
Not sure what you are asking here. Are you saying your fuel pressure spikes at idle for some reason?
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Old 05-09-2013, 04:49 AM
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