So I swapped my fuel rail and injectors. New injectors are 835cc and the rail now has a gauge. I noticed the gauge fluctuated rally rapidly at idle between 40-48psi. (adjustable reg) It fluctuates at whatever its set at. I don't recall it doing that before on my last setup. I don't believe that's normal, so I'm curious if its a sign my pump is going or if the regulator is bad all of a sudden. Thoughts?
12.6 @ 114.6 MPH
Do you have a vaccum gauge on the car? What is vaccum doing at idle?
what does the fuel pressure do when you bring the RPM's up?
FU Tuning
Vac is steady at -20inHG according to the gauge on there now (electronic boost). I'll hook up a mechanical gauge tomorrow and look because thinking about it, when I first started this whole setup/engine I had a mechanical gauge on there and it bounced/fluctuated rapidly too which if it still is would make sense why the fuel pressure is doing the same.
12.6 @ 114.6 MPH
--Glowin Cavy-- wrote:Vac is steady at -20inHG according to the gauge on there now (electronic boost). I'll hook up a mechanical gauge tomorrow and look because thinking about it, when I first started this whole setup/engine I had a mechanical gauge on there and it bounced/fluctuated rapidly too which if it still is would make sense why the fuel pressure is doing the same.
The vacuum was fluctuating with the mechanical gauge, or the fuel pressure was, or both?
ASE Master Certified Automotive Technician
Checked the vac with 2 different mechanical boost gauges plus the electronic one and all show steady vac around -20inHg. Fuel pressure continues to fluctuate at higher RPMs as well. So I'm still confused whether its a sign of bad pump, bad regulator, or maybe its just normal with large injectors (although I wouldn't think so since its still adding the same amount of fuel at idle).
12.6 @ 114.6 MPH
--Glowin Cavy-- wrote:Checked the vac with 2 different mechanical boost gauges plus the electronic one and all show steady vac around -20inHg. Fuel pressure continues to fluctuate at higher RPMs as well. So I'm still confused whether its a sign of bad pump, bad regulator, or maybe its just normal with large injectors (although I wouldn't think so since its still adding the same amount of fuel at idle).
it is not normal with larger injectors.
What AFPR do you have?
Does it do it with the vaccum hose off?
Edited 1 time(s). Last edited Tuesday, December 13, 2011 3:05 PM
FU Tuning
AFR is 13.8-15.4 at idle. With the vac hose off the AFPR it steadies out.
12.6 @ 114.6 MPH
AFPR= adjustable fuel pressure regulator.
So with the vac hose off does the fuel pressure still move around or is it steady?
What AFPR are you running?
FU Tuning
What is the vac reading on the mechanical gauge if you take it from the spot the FPR would be plugged into? The FPR could just be pulling from a weird spot in the manifold. If thats not the case then your fuel flow is insufficient.
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Sorry, I read that wrong. I thought you asked what AFR i had, not what AFPR. I know what AFPR is. Brand is Accel and as I said, its steady when when vac hose is off it. When I hooked up the 2 mechanical gauges, I taped into the line going to the AFPR just for that reason. So you think its the pump rather than the regulator? In boost it's able to supply more than enough fuel so far (only had it up to 10psi so far), so I would imagine its can keep up at idle. Seems like the regulator to me, but you guys are more knowledgeable in this engine than I am. It doesn't seem to be hurting anything so far with the fluctuation. The idle AFR moves from 13.8-15.4 but its a slow transition like the computer keeps adjusting rather than the fluctuation causing it. Is it normal to have the idle AFR to move back and fourth on our engines? It takes about 2 seconds to go from the low end to the high end, then back.
12.6 @ 114.6 MPH
Well if could be 2 things. 1 is that the regulator has a slow transient response to the changing fuel pressure in the rail due to something sticking in the reg and the other is that the the slow transient response by the regulator due to not actually getting enough flow from the pump. Either way you will see the same thing all the time. Even with a perfect setup it happens but typically happens so fast it never registers on the gauge.
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so fuel pressure is steady with the vac hose off right?
Leave the hose off and drive it, does it stay steady?
I do not like the accell AFPR for a boosted setup. I have had one fail on me on a boosted setup. I know back in the day 2-3 others also had one fail on boosted setups.
If fuel pressure stays steady with the hose off at idle and driving, then I would think you have a issue with the vac source. Maybe the hose is cracked?
If the fuel pressure does not stay steady with the vac hose off at idle, and/or driving then you have a issue at the AFPR, or fuel supply.
My first bet would be AFPR.
FU Tuning
Addicted to meth wrote:so fuel pressure is steady with the vac hose off right?
Leave the hose off and drive it, does it stay steady?
I do not like the accell AFPR for a boosted setup. I have had one fail on me on a boosted setup. I know back in the day 2-3 others also had one fail on boosted setups.
If fuel pressure stays steady with the hose off at idle and driving, then I would think you have a issue with the vac source. Maybe the hose is cracked?
If the fuel pressure does not stay steady with the vac hose off at idle, and/or driving then you have a issue at the AFPR, or fuel supply.
My first bet would be AFPR.
I don't like the accell either had one fail shortly after install. Get a adapter and run a aeromotive fpr.
Edited 1 time(s). Last edited Wednesday, December 14, 2011 6:57 PM
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Boosted2point4 wrote:Addicted to meth wrote:so fuel pressure is steady with the vac hose off right?
Leave the hose off and drive it, does it stay steady?
I do not like the accell AFPR for a boosted setup. I have had one fail on me on a boosted setup. I know back in the day 2-3 others also had one fail on boosted setups.
If fuel pressure stays steady with the hose off at idle and driving, then I would think you have a issue with the vac source. Maybe the hose is cracked?
If the fuel pressure does not stay steady with the vac hose off at idle, and/or driving then you have a issue at the AFPR, or fuel supply.
My first bet would be AFPR.
I don't like the accept either had one fail shortly after install. Get a adapter and run a aeromotive fpr.
agree, or the Casper opne that bolts to the rail.
FU Tuning
I keep fuel pressure around stock, so would a stock FPR hold up? I've got 2 or 3 of those laying around.
12.6 @ 114.6 MPH
stock should do fine for now. At least as a test.
FU Tuning
Thank god for saving those stock parts ! FTW!
Well I changed out the pump to a new Racetronix/walbro pump and also swapped over to another regulator, and the fluctuation is still there at idle. That both with and without the vac line hooked up to the regulator. It doesn't really seem to be causing any issues, but just seems strange to me. The injectors are 835cc, but are only at about 1% duty cycle at idle. So no one else has this issue? My gauge is on the rail.
12.6 @ 114.6 MPH
Its possible. I mean this is a transient system, in the real life world there are pressure pules moving all around in the fuel rail, normally they happen too fast for most gauges to register. And on at least the 02/ss style rails there is a fluid damper on the return line that makes it really hard to see.
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Matt, i could come over this weekend if you want/need any help. I should be free Friday night and all day Sunday.
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have you replaced the fuel filter?
Yeah, brand new filter as well.
Mike, I'll shoot you a text Sunday.
12.6 @ 114.6 MPH
How did it turn out?
PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO
I got busy with things and didn't get to it for a few days. Still can't figure out the fluctuation thing for sure, but I kind of think its just the gauge being extremely responsive, or maybe since I tapped it at cyl 3 instead of the end of the rail like most people on here do. It doesn't seem to effect anything. Vac is stable. Fuel flow is unimplemented. New pump and filter. 2 diff regulators did it. Does it both when the regulator has vac and doesn't. Only thing left I can think of is that its just from the fuel pressure in the rail changing slightly so fast when the injectors open. Either my gauge is super fast to react or it just happens to be from where I tapped it (right across from injector 3) so it sees more of a constant pressure drop when the injector fires.
12.6 @ 114.6 MPH
Here's a quick vid of what its doing.
[URL=http://s1084.photobucket.com/albums/j403/NitrousNitro/?action=view¤t=Video02192012172805.mp4]
[/URL]
12.6 @ 114.6 MPH
