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Gen 3 Tuning Issue

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Old January 7th, 2021, 10:40 PM   #1
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I have a gen 3. 20k miles. Headers and adding the paxton kit with fuel system.

On the dyno now. As HP and rpm increases fuel pressure goes to 130 and the motor goes lean. We shut it down as soon as it starts going lean. It goes from 11.5 commanded to to13 then 14 rapidly. Under boost this is around 5000 rpm hitting 538 rwhp.

The manufacturer has passed it on to engineering and is now reaching out to thier VARs.

As tried and true as these kits have been I cant believe this is the first time they have seen this.


All I can think is the injectors cannot keep up or the pressure is too high and collapsing them. Tuner says duty cycle data was inconclusive. All over.

I did order some blue O-ring injectors from ROE to test with. They say they are good well beyond the power range I am looking at.

Any thoughts would be greatly appriciated!?

Last edited by bradtabor; January 8th, 2021 at 08:28 AM. Reason: Added injector info
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Old January 7th, 2021, 10:43 PM   #2
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Sorry for the double post earlier
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Old January 7th, 2021, 10:47 PM   #3
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Any thoughts?
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Old January 7th, 2021, 11:21 PM   #4
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Is this common?
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Old January 8th, 2021, 08:25 AM   #5
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Vortech acts like they have never seen this issue. They originally thought it was their equipment but not are reaching out to tuners so I thought I would do the same. I am taking the injectors over now to give it s shot this morning.
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Old January 8th, 2021, 09:03 AM   #6
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Do you have an upgraded fuel pump setup? Are you sure you're getting VOLUME and not just pressure? Fuel is consumed in pounds per hour to make horsepower.
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Old January 8th, 2021, 09:18 AM   #7
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I have the paxton twin setup that comes with it.
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Old January 8th, 2021, 11:18 AM   #8
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There's not much fuel "tuning" with that setup. You could swap out washers in the fuel pressure regulator to change the pressure ratio, that's about it. Your pressure seems okay, but Dean is right, you're probably not getting enough volume either through injectors or fuel system.

Has the fuel filter been replaced?

Another thing to keep in mind, mods outside of what the kit was designed for may require extra fuel. You mentioned you have headers. Has headwork been done as well?
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Old January 8th, 2021, 06:06 PM   #9
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I'll have them check the fuel filter but I'm sure that was already done.

To my knowledge there's no head work that has been done on this car. Judging by the previous horsepower numbers it was pretty close to stock.

I will mention the spacers in the regulator to change fuel pressure.

When I talked to Roe racing today they said that the pressure should only be 60 at the rail. Not 110 to 130.

Am I missing something there?
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Run with boost
Old January 8th, 2021, 06:13 PM   #10
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Run with boost

I attached the dyno run with boost to 4800rpm. Without boost it performed normally. Hope this can help!
Attached Files
File Type: pdf 8to1 no boost.pdf (88.1 KB, 9 views)
File Type: pdf 8to1 boost.pdf (79.7 KB, 9 views)

Last edited by bradtabor; January 8th, 2021 at 06:22 PM. Reason: Added Dyno Charts
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Old January 9th, 2021, 07:53 AM   #11
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First I don't see any reason why people need to run more than 90 PSI fuel pressure with todays tunners.

Its not like we are just using stock injector pulses and a 6:1 FMU anymore.

I would have to say that your injectors are not opening at the higher pressure, and this is not consistent. Opening the injectors takes current and voltage at the injection which may not be reproducible at that fuel pressure.

Second as Dean pointed out somewhat, if your needed to more that much fuel and its inconsistent. You need to feed the rails from more than one point, many people don't agree with this or say its not pessary.

On my V8 I fed to the front of both rails and ran fuel out the back of each rail to a fuel pressure regulator, this reduced the injector pulse by 15% back in the day and made more power... maybe I was rich before etc...

For the Viper you just have to look at the rail, is it at least a 1/2" rail? Are you feeding each rail with a 1/2" line.

Finally do you have enough pump, considering you have the pressure at the guage is that the actual pressure in the rail (see above small fuel lines and rails).

You can't go wrong upsizing fuel lines rails and pumps.

I'm surprised your tuner is confused...
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Old January 9th, 2021, 08:05 AM   #12
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Quote:
Originally Posted by GTS Dean View Post
Fuel is consumed in pounds per hour to make horsepower.
Yes exactly do this...

Whats your expected HorsePower

You need about 0.5#'s per hour per horsepower, to be safe this is my minimum level and you should probably use closer to 0.7 boosted applications.

550 HP x 0.6 = 330 LBS per hour

Convert this into fuel injectors we have 10 of them so you need a minimum 33lph injectors. Viper is suppose to have 69 lbs/hr injectors stock pressure is I believe ~60 psi...

You can increase the size of the injector by upping the fuel pressure. (Double the fuel pressure increases the injector by about 50%).



Oh dear god... I just saw this, your running an FMU with an 8:1 puck... very old school good luck. Your probably going to have to reduce you stock pressure and increase injector size, then use a lower .... forget it just listen to what your tuner tells you. Sounds like your trying do this on the cheap so good luck.
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Old January 9th, 2021, 11:22 AM   #13
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I'm far from trying to do this on the cheap. I would spend what needs to be spent. This is the kit my tuner recommended after doing research. It's a tried and proven kit from what we saw. I have no issue spending money lol.

If it needs an entirely different fuel system I'm looking for recommendations on what to do. I will get it done.
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Old January 9th, 2021, 06:29 PM   #14
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Your fuel pressure continues to rise whereas the engine slowly leans out up top, this appears to be a classic volume/restriction issue somewhere in the fuel system.

If I recall, these FMU setups are generally much richer than what your graph shows. I thought they were somewhere around high 10's, low 11's.

I'm going off memory here, but do you have a splitsec box? That controls timing, but I think it also contains logic to engage a second fuel pump via relay at around 1.5 psi (you have two in-line pumps in the kit?). If you do have two pumps, maybe the second isn't engaging.
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Old January 9th, 2021, 07:04 PM   #15
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Quote:
Originally Posted by bradtabor View Post
I'm far from trying to do this on the cheap. I would spend what needs to be spent. This is the kit my tuner recommended after doing research. It's a tried and proven kit from what we saw. I have no issue spending money lol.

If it needs an entirely different fuel system I'm looking for recommendations on what to do. I will get it done.
Ok well Iím not 100/100 on the fuel pressure but 6psi boost with a 8:1 rise from a base puts the line pressure way too high based on past experience with other cars.

To me it sounds like injectors not opening at the high fuel pressure.



Either way I appreciate you actually posting a true viper tech question for discussion, please donít tell us which way you voted for gods sake...
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Old January 9th, 2021, 10:59 PM   #16
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Lol.. I wont bring up politics here. A time and a place!

I will let you know how the new injectors work out.

After talking to ROE the next step will be to pull the paxton fuel system out. Use the stock pump since its a Gen3 it can handle 6 lbs of boost, put in a 2 bar map sensor and do a SCT tune on it.
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Old January 10th, 2021, 03:53 PM   #17
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Step into the future. I'm running 3 in tank e85 compatible pumps, with 170lb injectors, controlled by an M150. No issues here.
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Old January 10th, 2021, 07:26 PM   #18
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Dan Cragin is a great tuner if you are looking for help.
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New Injectors tomorrow
Old January 11th, 2021, 06:31 PM   #19
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New Injectors tomorrow

Thank. I will reach out to Dan and keep you guys posted on what we find. They said both pumps are engaging.

I agree. It is either fuel restriction at some point or too high of pressure on the injectors. They will hopefully give the new injectors a run tomorrow.
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Old January 11th, 2021, 07:15 PM   #20
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Well I think its both...

Plus you should have said you had new injectors planned in the initial discussion.

6psi is not a lot of boost, should be a nice increase but not crazy levels with complete redesign of the system.

I would have went either way, upgrade the fuel supply issues with lines and rail on the existing injectors (potentially with a cleaning) or new injectors of a larger size.

Try the new injectors... but I'd also go with a 6:1 puck if you were going to use an FMU.
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