Below is a trace for a run on my boosted Z. When on the dyno I was concerned that the duty was in the high 90's so I graphed the fuel pressure. As per the below the FP is reducing with RPM but i would of thought that the reg should hold the pressure a little better.

Any advice?

Setup:
CJ Stage 0 RFS
Cosworth rails
Aeromotive reg
DW 300
Stock feed line
48 psi base pressure
ID 725 injectors
Stock power feed

 

Is the fuel pump on a relay? Looks like it might be running out of power and losing flow, either way you are above 80% duty cycle which is not good.

 

Agree +80% DC is not good but by having the fuel pressure stabilize then the DC should drop.

Fuel pump is running off oem feed.

Since I kept the base fuel on the lower side I would of thought that the voltage drop wouldn't be as high and the amp draw less.

Am I expecting to much from the oem power source and wire gauge?

Is this considered normal for the setup? If it is then i'm happy and can work on improvements to fix the issue.

 

Yeah I've seen this before with my setup...likely running out of pump...you could decrease your base fp to 40psi to improve pump performance but then your injector DC would get worse...

I ended up upgrading my fuel setup to a CJM stage 2 and upgraded my pump to a walbro 400....which happens to be for sale if you're interested, already installed in the fuel bucket

I also directly wired the pump off the battery and ran it off a relay, that helps as well...

 

seems to me that something is going on causing the pump to loose flow, what are you running in terms of filtration? it might also be possible the stage 0 is becoming a restriction to the flow needed, 17 psi should be somewhere north of 500 hp mayby even close to 600 depending on setup not aware of anyone running a stage 0 on that power, especially considering thats closing in on the limits of a stage 2 according to what cjm says if everything were working correctly. my guess is factory wiring combined with the stage 0 is causing issues. i would definitely look into upgrading to the stage 2 at a minimum or something similar.

 

I'm using the oem bucket and the filter that came with the pump from memory. Enlarged swirl jet also

Not sure why I was seeing 17psi on that run but all others are around 12-14psi which is what it is targeting.

UPDATE: I pressurized the top intake pipe to 10psi with a leak down tester and found 2 small vacuum leaks on the lower plenum collector. I'm holding relatively stable boost so not sure if fixing the vac leaks will have a positive improvement on fuel pressure.

 

even still i would upgrade the stage 0, it honestly was designed for stock block power and 6-8 psi, dont have to actually upgrade to the cjm parts but i would change out parts to what they use, example rails shouldnt be needed mainly just a bigger feed line and cut and weld new fittings of appropriate size on the stock rails if looking to do it on a budget. the boost leak honestly shouldnt help much if at all, i would actually expect it to worsen since more air going into the engine.

 

thx Jerryd87 an 006, The current setup is pretty much equivalent to the STG2 kit. The only difference is I do not have the hard line. Unfortunately the hard-line is over 1m in length so is not supported by international post

 

mayby try and replace that then with something larger in diameter then? if not i would look at possible rewiring, that pump definitely shouldnt be cutting out at your power level, mayby contact deatschwerks see what they can recommend as well

 

^+1....The CJM hard line is basically an -8an line...you can try using a -6an or -8an fuel line in its place and route it from your fuel pressure regulator up to your pump...

 

I will need to look into that. I don't have any of the lean spot issues that others have faced with a RFS. If I go down the hard-line upgrade I need to work out options to retain the fuel damper on the feed side of the fuel rails. Maybe a marren damper inline etc

Anyone got any good links on how to upgrade the power feed line on Z without using a boost a pump. I'm assuming like this?

http://www.enginebasics.com/Advanced...p%20relay.html

 

as far as power feed honestly i would just run new wire, not so much needing an increase in voltage as the stock wire is tiny and entirely possible the pump isnt getting full voltage or amperage because of it.
as far as dampening i think it depends on the pumps, i know with my 255 in tank and dual bosch 044's feeding the rails from the swirl pot i had none of the pulsation issues, my setup now with the dual 044's feeding from a sump also has no such issue.

 

Run a 10 gauge wire. It will help a bit. Voltage definitely drops throughout the electrical system at high rpm, particularly with a stock alternator.

 

Ya, stock 22g wire is tiny and voltage would drop quite a bit on a 255 under load so a 300 would draw more amps.

I agree increasing that supply line will take the resistance way down and load off the pump which will in turn reduce the power consumption. I would just make an 8an line and use the CJM oem adapter (6an) to an 8an step up then the 8an line. 10g wiring to a relay for the fuel pump.

how did you get fuel pressure in cipher? I didn't know our cars oem system had fuel pressure in it.

 

^ I think that is a Haltech log...

 

if the pump wiring was really too small, you;d be blowing fuses. Less voltage means more amperage.

The way the fuel pressure bounces back immediately after you left off means that pump is bad, or its too small (my FP graph looked the same way when my pumps died)

That DW pump doesnt draw anymore current than a 255lph, and if there was a problem with stock wiring, it woulda been all over the forums with the high number of stage0/ fuel pump swaps sold.

So its either your FPR isnt rising 1:1, or your pump is too small/dieing

 

You don't think the 15-20 amps the the pump draws is too much for 22g wiring that is likely to be 20 feet long? That's some huge resistance with that long of that small wiring.

I see your point though and wondered why the rising rate regulator wasn't keeping the pressure up.

 

Ya, but how did he get fuel pressure? Does he have an aftermarket sensor with an I/O box attached or something?

 

I have a fuel pressure sensor plumped into the FPR and then hooked into one of the haltech inputs of their PNP unit.

@str8dum1, You will notice in the graph it is nearly rising 1:1 between 2k and ~6k. It is only between 6-7k where it has taken a huge dive. Do you think it can still be a faulty pump or fpr? The pump has about 6000 miles on it.

To be honest I do not know what the graph should look like as I have nothing to compare to. All I can assume it is supposed to be flatter than it is.

I have fixed the vac leaks. They were not as small as once thought. At 10psi there was 2 audible leaks between the lower half of the plenum and the block. I know a few said probably wont make a difference but only way to know is to test.

 

It's not gradually rising. It takes a hard drop right at 3500 rpms and 65psi of fuel pressure. When you hit full boost the fuel pressure will stay exactly where it rose to all the way to redline.