Question for the paxton guys out there..

[rich v.]

I just installed a paxton on my 05 viper and have some questions/issues.
-how much boost is this kit supposed to make? i only see a solid 5 psi.
-how much fuel pressure is there supposed to be on idle and at boost? i see 50 then over 100psi when boosting.
-with these additional fuel pumps, do they come on together? or is one boost related and one rpm related?
-also my car breaks up under full throttle at higher rpms, don't know why fuel pressure stays up?
in addition to the the blower i have a DC flashed cpu, 170 thermostat, and cat back corsa exhaust.
any and all insight in this matter would be greatly appriciated.
also i will be taking the car to DC in the near future for a final tune.
thanks!!!

 

[Bobpantax]

Rather than have us guess, you should just take the car to DC now and have DC check out your install. The Paxton, assuming your engine is otherwise stock and you installed the stock kit, should be producing 7 pounds of boost at about 5900 RPM. It should be 4 pounds by 4500 RPM, 5.1 by 5100 RPM and 6 pounds by 5500 RPM. Of course, I am sure that there must be slight variations from car to car. I am sure that you know this but if the car is breaking up under full throttle, stay out of full throttle until you get the system sorted out.

 

[Billy Coons]

I get to 8lbs of boost at 6200 rpms on both the dyno printout and my mechanical boost gauge.

I will be re-dynoing it again on Monday with a fuel pressure gauge installed and expect to see over 100psi on WOT. Mine seems to run lean above 5200rpms (gradually increasing from 12.2-12.9 A/F).

 

[Bobpantax]

Hi Rich. Something else occurred to me. Which FCU washer do you have installed? The smaller diameter one or the larger diameter one? Change to the other size and carefully see what happens. See Figure 9a in the installation instructions.

 

[PowerKraus]

Possibly too much fuel pressure. For every pound of boost, you should see 1 to 2 pounds more fuel pressure. 100 is WAY to high and may cause the injectors to actually 'stick' open on occasion. Also, it may be as simple as reducing the spark plug gap. Before you go digging 'deep' into the motor/fuel system, check your gap. I would go with .032 on a 1 to 2 step colder plug.

Point is, try the simple things first....

Good luck, your gonna have a nice running buggy when done!

 

[GR8_ASP]

I get to 8lbs of boost at 6200 rpms on both the dyno printout and my mechanical boost gauge.

I will be re-dynoing it again on Monday with a fuel pressure gauge installed and expect to see over 100psi on WOT. Mine seems to run lean above 5200rpms (gradually increasing from 12.2-12.9 A/F).

Do you have a recal with a higher fuel shut-off? Stock fuel shut-off is 6050.

My system, stock except for exhuast, achieves 7.5 to 8 psi at redline. If I hit the limiter it can hit 8.5. Anything that you do to improve performance (porting, lower back pressure exhaust, etc. will reduce the boost due to an increase in air flow. In that case lower boost actually mens higher performance.

Fuel pressure starts about 50 psi. Jumps to 70ish when just starting to hit boost (actually, per the controller it is just before you hit boost) and then increases gradually as boost builds up to a maximum right about 100 psi. The fuel pressure system, the FMU, is boost related only. It has no idea what the rpm is so you can test it statically if you want.

 

[Billy Coons]

Do you have a recal with a higher fuel shut-off? Stock fuel shut-off is 6050.

My system, stock except for exhuast, achieves 7.5 to 8 psi at redline. If I hit the limiter it can hit 8.5. Anything that you do to improve performance (porting, lower back pressure exhaust, etc. will reduce the boost due to an increase in air flow. In that case lower boost actually mens higher performance.

Fuel pressure starts about 50 psi. Jumps to 70ish when just starting to hit boost (actually, per the controller it is just before you hit boost) and then increases gradually as boost builds up to a maximum right about 100 psi. The fuel pressure system, the FMU, is boost related only. It has no idea what the rpm is so you can test it statically if you want.

I have a DC tune, and the dyno RPM's have gone over 6100 with no shut off or fuel cut out. I'm right around 7.8#'s @ 6k. Your fuel pressure #'s are what I'm expecting to see with the FMU larger disk I have installed. Even with it though, I still am running a bit lean up top. So I'm running the new tune on the dyno to be sure my fuel pressure is good and checking it with a fuel pressure gauge. Should have it done on Monday or Tuesday afternoon.

 

[pteam]

On another note. Took my porsche to the store today, viper at woodhouse getting supercharged. A few year old cobra mustang totally revvs his engine at me and my girl as I go by in a parking lot at 5mph, actually scared my girl.

Boy I cant wait til I see him again in my supercharged viper 750 hp vs his ~320 hp mustang. I'm gonna have some kind words for him and politely tell him if he aint the big dog in town probably shouldnt be revving your engine like a fool.

 

[GR8_ASP]

ok, now I understand th erpm aspect. First, a dynojet is measuring engine rpm via a spark plug wire inductive pick-up. Somewhat unreliable device, and given the 1992-2006 spark strategy of the Viper to fire on the compression and exhaust strokes (sometimes referred to as a waste spark system as it spark every revolution instead on every other), the potential for error is high. The other aspect is that the engine rpm coordinate on the Dyno graph is created from the composite of the dyno drum speed (the only speed with reasonable accuracy) and the spark signal it is easy to see how it could give a false reading of a hunddred rpm or so. This comes from using an average engine speed to dyno drum speed calculation. But, given the expansion of the tires at high speeds the engine speed is actually a little lower at high drum speed than the calculation. Not a big deal but rest assured if you have not increased the shut-off speed it is indeed set at 6050 rpm.

I went for a drive and confirmed the first boost fuel pressure as about 80, not the 70 I stated earlier. Being a little leaner at high rpm is consistent with th emeasurements I have seen on various measurements, including my own. That can be fixed by increaing the fuel map slightly at high rpm. That should be able to be done quite easily by DC so that you do not have to mess with anything else. Note that the slight leaning out (actually still rich just not as rich) will actually result in more power, but with less reliability.

 

[Joseph Dell]

Possibly too much fuel pressure. For every pound of boost, you should see 1 to 2 pounds more fuel pressure. 100 is WAY to high and may cause the injectors to actually 'stick' open on occasion.

This is incorrect. If it were a fuel pressure regulator with a vacuum port, it would be correct. But the FMU is an 8:1 or a 12:1 increase (depending on the washer). so an additional 60psi @ 5lb of boost is expected.

Question for the original poster: was your PCM DC flashed BEFORE or AFTER the Paxton? If before, you have WAAAY too much timing advance at the higher RPMs and this is why you are breaking up. there should be a slight timing retard as the RPMs increase. I'd guess that you are only seeing 5psi b/c the car is breaking up / misfiring / detonating and you can't get a good full pull to 6k RPM.

I'd start with that. and if you can get an air/fuel gauge (or if you can find a dyno that has one) i'd start there.

good luck!

JD

 

[ACPERFORMANCE]

Rich,

If you have an NA flash, changes are the timing is too aggressive for your paxton setup. If your plan is to get it re-tuned, be easy on the car until you do. The ring lands on your GEN3 pistons are very thin and just a little detonation can turn into a big problem fast.

I would suggest pulling some timing out of your split second to keep things safe. Once you pull a few degrees you should know immediately if this was your issue. Fuel pressure sounds like it's right where it should be.

Once you pull some timing, check out all your hose clamps and the o-ring in your blow off valve. Boost should be between 7 to 8.5 psi depending on the weather, hot day vs cold day.

Todd
A&C Performance

 

[mjorgensen Woodhouse]

Wow Billy I hope you are not driving or have been driving aggressively with that lean of a motor. It does not take much above 12:1 to really give you a bad day. I hope it all checks out Monday. Be sure to check the extra pumps for proper grounding and that the "terminal post are tight" I have seen this be the cause of a random "quick lean out" that appears random but is caused by these connections coming loose.

I get to 8lbs of boost at 6200 rpms on both the dyno printout and my mechanical boost gauge.

I will be re-dynoing it again on Monday with a fuel pressure gauge installed and expect to see over 100psi on WOT. Mine seems to run lean above 5200rpms (gradually increasing from 12.2-12.9 A/F).

 

[MikeR]

Another thing to consider is belt slip. If your only getting 5 lbs, belt might be slipping. This happened to ILLSMOQ. DC performance was able to catch it once they started montioring boost. It would be at 4, then 6 then 3, then 5lbs etc. He had alot of belt slip. Installled a DLM tensioner and getting 8lbs is no problem now. I installed a DLM belt tensioner also. I see anywhere from 8-9 lbs on my stock kit, with headers and exhaust. This is all being read thru spit second box.

 

[rich v.]

i do have a DC blower flash.
i see a steady 5psi, it really doesn't vary.

i also want to know if the fuel pumps that come with the kit are supposed to be on all the time? or are they boost related? or rpm related?

i tried to fake out the vacuum system with the car in the garage and it appears that only one of the fuel pumps comes on when i put boost in the system. does the other come on with rpm?

 

[mjorgensen Woodhouse]

Fuel pumps are boost activated, check the terminals on the pumps and also the common ground for them. I have seen problems here and the intermittent pump switching can be very costly. What else do you have done to the car besides the Paxton? If you are running no cats or trying to run headers with them the indicated boost pressure will be less because of the reduction in back pressure. The reduced boost could be a fueling issue also because the engine needs more fuel than the pumps are giving because of the decreased pressure.

 

[Viper X]

Rich,

Having read this post and having experienced all of the above issues and many more, I'd get the car to DC ASAP. Some very good information above. Not sure what "breaks up" means but it can't be good. Stay out of the throttle and let them take care of it.

Some observations:

1 - 100 psi is normal under boost if both pumps are working properly. On my car, the pumps came on sequentially based upon a vacuum line carrying boost pressure. Check all of your vacuum lines. The line at the blow off valve has caused me issues in the past. I either clamped them or zip tied all vacuum lines. You can and should do this before you drive the car again. My installer also managed to chafe / slice the vacuum line to the split second box, which didn't help.

2 - There is no provision for rpm based fuel pump operation on the base system as stated above. Check the wiring to the pumps and specially the ground wires.

3 - Check the FMU washer as stated above. Use the bigger one.

4 - Boost should be about 7 to 8 psi max unless someone has increased the rev limiter. This can be a fatal error on a stock bottom end. It was for me.

5 - An air / fuel ratio above 12 under boost is dangerous with cast pistons.

Good luck,

Dan

 

[rich v.]

I need to give a big thanks to Viper X for his help in finding my issue. The vacuum line was not on the blow off valve. the car still does not run 100%, but its close and hopefully after a trip to DC it will be done.