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Bandit
Dodge Dakota
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1/05/2006
06:18:49
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 Subject: 36lbs. Fuel Injectors
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I am not sure what size injectors to run. I have a 1997 dodge dakota 5.2L 318 with a supercharger(6-11psi), M-1 intake manifold,F&B 52mm throttle body w/ spacer,437lift cam, mopar360 R/T heads that have been ports and polished, PCM flash, gibson headers w/ 40 series muffler no cats, under-drive pulley kit,and 24lbs injectors give or take a few other minor mods. I took it to the dyno and found that is was running really lean. The guy said that it should be at a 12.? something A/F ratio. My truck at idle was at 15.? and it got a little better as I brought the rpm's up, but it was still really lean. I was only running 6psi at the time. My question is should I run 30lbs injectors or 36lbs injectors. We tried to up the fuel regulator and the FMU which helped, but it was still running lean. I contacted B&G who programmed my pcm, he said up injectors. He did not know what size. HELP....
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crow318
Dodge Dakota
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1/05/2006
07:35:25
|  RE: 36lbs. Fuel Injectors
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http://www.rceng.com/technical.htm
Try that.
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Duner
Dodge Dakota
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1/05/2006
20:23:41
| RE: 36lbs. Fuel Injectors
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You probably can't get away with much larger than 24# injectors if the PCM is still controlling them for idle and cruise. What kind of FMU, aux. fuel pump and FMU ratio is on the truck?
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Bandit
Dodge Dakota
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1/05/2006
23:17:59
| RE: 36lbs. Fuel Injectors
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I have the FMU and fuel pump that came with the supercharger kit. The kit was made for a stock engine, but after adding all of the mods to the engine. I think the 24lbs. injectors can't keep up. The company that flashed the pcm said to add bigger injectors than the 24lbs. So I am thinking that the pcm should be able to control the bigger injectors. I was told to not change the FMU flow control plates, because they can sometimes cause bigger problems. The dyno guy told me that he has seen people change them plates and everything is good until high-rpm. Then out of nowhere the engine leans out. The dyno guy said that most people just up fuel pressure or change injectors. The pcm guy said to change injectors. I don't know if that will fix the problem completely, but I don't know what size injectors to go with.
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95V6
GenII
1/06/2006
03:54:44
| RE: 36lbs. Fuel Injectors
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PCM will keep air/fuel ratio at 14.7, not 12-something. That's the standard for all gas engines. Actually, since you have supercharger and higher compression, you can run even leaner.
The dyno guy just confuses you.
95 3.9L 4WD V6, K&N, Gibson exh, JBA hdrs, JET stage II, MSD 6A, Rancho shocks , Transgo kit, 4.10 LSD, F&B 48mm TB
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crow318
Dodge Dakota
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1/06/2006
08:36:01
| RE: 36lbs. Fuel Injectors
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14.7 is the ratio of air to fuel for complete combustion of the fuel. You don't want to be there even with a N/A engine. The PCM is looking for less than 14.7
To run safe, more pressure = lower A/F numbers.
The dyno guy is right. 12.5 is where its at.
What you need to do is get a fuel pressure gage and figure out how much pressure you are running. Use your FMU to increase pressure to keep the A/F at the right level.
If you find that the fuel pressure stops increasing before the boost, you have an insufficient fuel pump setup. If the fuel pressure increases past the rated pressure for the injecters and/or the fuel system you will need larger injectors.
If you surpass the rated pressure for the system, you should only step a few pounds at a time. If you have stock 24's, a good set of matched 26 or 28's may be plenty to take care of your problem.
Tuning a charger takes lots of time and testing (and $$)
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Bandit
Dodge Dakota
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1/07/2006
00:33:03
| RE: 36lbs. Fuel Injectors
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I found that my FMU is running at a 12:1 ratio. Which means for every one pound of boost the fuel pressure/rate is increase by 12lbs. I also found that my fuel pump is a 200lph pump that can support 19lbs-36lbs injectors or 600hp at the FW. I am planning on upping to either 30lbs injectors or 36lbs injectors. I do not have a fuel pressure regulator, technically my FMU is acting like a regulator. The dyno tech thinks that I should run with 36lbs injectors, because of all the engine mods and the boost. I was thinking that if I run the 36lbs injectors and it is running to fat, to where the PCM is helping, but not enough. Then I will change the FMU plate to a 10:1 or an 8:1 ratio. The first thing that I would try before change the FMU plate would be to up the boost alittle to equal out the extra fuel with extra air. I will let you know what happens.
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Duner
Dodge Dakota
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1/07/2006
10:12:38
| RE: 36lbs. Fuel Injectors
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Where was it lean at?
Just at idle? or at WOT in the upper rpms?
After re-reading your initial post it sounded like it was only lean at idle?
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crow318
Dodge Dakota
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1/09/2006
08:36:53
| RE: 36lbs. Fuel Injectors
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The pump flow rate is important, but so is the pressure. You can have a 800 lph pump, but if its max pressure is only 70psi, then you will have problems even at low boost.
Say your baseline is 45psi. With a 12:1 FMU, you will have your pressure will stop rising at only 2 psi boost.
I am pretty sure the pump you have is not the problem. It should be good for alot more pressure than that.
The problem with the 36's is not too much fuel running wide open. You said yourself, that you can tune the FMU by changing plates. The problem is that under normal driving conditions, your computer can not compensate for the larger injectors. If you go to big, there is nothing you can do, short of adding a stand alone fuel managment or flashing your computer.
Both ford and chevy have computer programs that you can buy and use to adjust the ECU. As far as I know, no such software exists for dodge. And now that the 5.2 is no more, we will most likely never see such a program.
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Bandit
Dodge Dakota
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1/10/2006
05:29:17
| RE: 36lbs. Fuel Injectors
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The computer is after market. The original computer was shipped to michigan to a specialist that only works with dodge products. The computer was flashed for all of the mods that were added to the truck. I contacted him and he said to go with bigger injectors, and the computer should control the impedance of the injectors through out the rpm range to manage the fuel curve. The Fmu will add fuel pressure according to the amount of boost. The PCM will run the injector wide open if needed and the FMU will make sure that the injector are provided with what they need. The company I bought the supercharger from said that they could not give me advise on injector size, because of all the modifications done to the engine. They did say that the 200lhp fuel pump will provide more than enough fuel to 36lb injector. So with that I was already asuming that the fuel pressure is high enough to do what I need it to do. Almost every mechanic and performance shop I have spoke to lately has told me to run the 36's. Because if I run 30's and they get maxed out then I will be a little richer, but I will still require more fuel. So I purchased the 36lbs, hoping that they will work. I will let you all know what is the out come. I am hoping that it works. Otherwise that was 389.00 dollars wasted. The injectors are ordered and should be in this week.
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crow318
Dodge Dakota
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1/10/2006
07:53:28
| RE: 36lbs. Fuel Injectors
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Yeah, please let me know. I am in the market for injectors also. I have been looking at 24's, but I dont have as many mods as you. My next purchase is gonna be a knock sensor. Then I can procede from there.
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bandit
Dodge Dakota
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1/10/2006
23:50:20
| RE: 36lbs. Fuel Injectors
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If I get it working, I will sell you my 24lbs injectors, unless you want a new set? They are the Ford Racing injectors which go for about 229.00 new. They only have about 3,000 miles on them. I think that I will get rid of them for about 150.00 or make an offer.
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crow318
Dodge Dakota
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1/11/2006
08:03:32
| RE: 36lbs. Fuel Injectors
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Did you get them from Five-o?
I did want new, but 3000 miles is close enough to new for me.
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bandit
Dodge Dakota
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1/11/2006
23:54:14
| RE: 36lbs. Fuel Injectors
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Yup, they came from a 5.0 mustang a 1985-1993. I bought them from the dealer. They are matched flow injectors. These injectors are in great shape. Well let me know. Thanks for the interest. I ordered my 36lbs injector today. They should be here friday or saturday the guy said.
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bandit
Dodge Dakota
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1/12/2006
04:49:56
| RE: 36lbs. Fuel Injectors
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Once I get the new injectors in and they are working good. I will put the 24's forsale. They are Ford mustang 5.0 high impedance flow matched injectors and almost new with only 3000 miles on them.
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crow318
Dodge Dakota
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1/12/2006
09:36:59
| RE: 36lbs. Fuel Injectors
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I'll buy them once you get things going. I will be on vacation next week, until friday. I will have a computer with me, so shoot me an email when you are ready.
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janesy
Dodge Dakota
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1/12/2006
17:13:48
| RE: 36lbs. Fuel Injectors
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Hold on a second, did you order the new injectors?
Did you ever get it on the dyno to see what it is doing at WOT. At WOT on a blown engine you are good and safe at 11.5-12. The fact that you are lean at idle means absolutly nothing. What did they use to test this? 15:1 at idle is not dangerously lean, if anywhere above during WOT you would have something to worry about.
Also, the FMU does not use the fuel pump itself to adjust the pressue. Not in this case anyway. It basically constricts the flow in order to boost the pressure. And how could the tech try to up the fuel regulator when it is in the tank?
I think you have found the wrong tech. You should be fine with 24lb injectors and a 12:1 disc. In fact the 12:1 disc is designed for engines with 19LB injectors, so it is flooding in with more fuel. With the same exact setup on mine, I ran BELOW 10:1 AR.
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Duner
Dodge Dakota
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1/12/2006
17:44:01
| RE: 36lbs. Fuel Injectors
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I'm certainly not going to argue with anybody about their injector selection.... but I'm running 24# injectors on both of my trucks... and with 10:1 plates at that. Going from 24# to 36# is a 150% jump!
My truck is the black one....
http://members.cox.net/duner/Turbo/RT/Duner%20vs%20Mike.wmv
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bandit
Dodge Dakota
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1/12/2006
23:43:17
| RE: 36lbs. Fuel Injectors
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When the truck was at WOT, the ratio was still at 14.1. The regulator is aftermarket and adjustable on my truck. They tested my A/F ratio with a wide band meter stuck in the tail pipe. I asked them if it was an accurate reading. The tech said that unless I have a cat on the truck it is accurate. I am running eldelbrock headers, custom Y-pipe, and 2 3/4in. pipe straight back to a single inlet dual outlet muffler. We upped the fuel pressure and it didn't help either. The tech said that my injectors were most likely maxed out. I read and talked to several of shops about the problem. I asked them what they thought about 36lbs injectors. All of them said they would run 36lbs over 30lbs anyday. Because if it is running rich, the pcm should control the injectors. Otherwise all I have to do is adjust the fuel pressure and change plates in the FMU. So I am planning on running the 36lbs.
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bandit
Dodge Dakota
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1/12/2006
23:47:45
| RE: 36lbs. Fuel Injectors
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crow318, I will fly you an e-mail, when I get the 36's in.
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Duner
Dodge Dakota
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1/13/2006
09:01:18
| Fuel pressure?
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What is your fuel pressure at idle?
What is your fuel pressure at WOT with 6 psi of boost? At 10 psi of boost?
Are you sure you have a 12:1 plate in the FMU?
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