Fuel Pressure falls off as boost builds

[Mitsu725]

I recently upgraded my stock lines to a -8 russels pushlok that feeds into a Lg Golan fuel filter and i drilled out my stock fuel rail and tapped some threads and put in a pt to an thread fitting so it would go together nicely. Also i upgraded from stock long route "ghetto" I/C piping to some aluminum 3" piping. And since I have the GST my gas tank isnt that deep so i had to cut the stock fitting off the fuel tank cap and I had someone take a bulkhead fitting and step the inside so the walbro will slip nicely inside almost as if it was a stock application, well now it takes my car freaking four hundred cranks to start and when it does run, when i get into boost the fuel pressure falls off drastically, I mean when we had it on the dyno the A/F was at 18 like ready to freaking blow up, anybody have any ideas? i was thinking maybe the fuel rail got clogged or the fuel filter could be on backwards but i was pretty aware of things when i was doing the install.

 

[scottsee]

Whats your fpg doing at cold start/idle? Is it holding pressure? test it to see if it's rasing fuel with boost 1:1

 

[goodbye]

How high is your base pressure? Most pumps decrease flow drastically at anything over 72 psi, which a lot of guys are hitting with big turbos and high base pressures. I actually turned down my base pressure to 35psi because I've got dual pumps with plenty of flow.

 

[Mitsu725]

actually i have my base set at about 37/38 lbs, because I have such large injectors I lowered the base, I dunno I'm confused i mean I think it could almost be anywhere, o a small piece of information i left out , I removed the emissions from the car, I took out the carbon canister and disconnected all the emissions and vacuum lines on top of the throttle body, and I didn't do anything else. It basically started out as I was just gonna upgrade to some aluminum I/C piping and then it ran the -8 fuel lines and went with a golan fuel filter and from there I removed all emissions and ran everything back the same way but I dunno if since i removed the emissions the EGR valve could be messed up or something. Also I would love to run dual fuel pumps but with the GST setup i don't think it's possible due to the lack of space we have in the gas tank, i mean the GSX gas tank u can run a hose to the fuel tank cap and your set but for the GST guys I had to take a bulkhead fitting and cut the head off and slip the walbro with an O-ring and stick it up inside the bulkhead, i was thinking that was the first problem like it wasn't creating a good enough seal and was dropping it right into the fuel tank but i have to admit im stuck on this one.??

 

[scottsee]

When you say you eliminated all of the lines from the throttle body, you did cap them off right?

base fuel pressure is 43.5 on the 2g. What size injectors?

 

[Mitsu725]

i have 850cc injectors so while on the dyno we lowered the bfp to 38 lbs and tuned the safc way down.

 

[scottsee]

wow, 38psi on 850cc's create a flow rate of 799cc. Your drowning your cylinders. Your really should either step up to somthing that can controle that size of injectors. IIRC, 660cc are about the max you can controle with an SAFCII, and that would require you to take your BFP down to 26psi then lean out your SAFCII Hi & low all the way!!

If you have your 0ld 450cc's I'd put those back in untill you get your DSMlink (wishlist)

 

[twicks69]

Are you sure that you have a fully sealed fuel system? If you have a pressure leak, it will be evident by having someone watch the pressure gauge on your AFPR from OFF, then cranking (should go to base pressure), then OFF. If it drops quickly (faster than 20-30 seconds), you more than likely have a leak.

I would FIRST make sure that the bulkhead fitting you machined to fit the inlet of the fuel pump is a SEALED connection.

This alone, will make it hard to start, and you could be losing pressure @ the pump while under load.

Next, make sure that you have a good vaccuum connection for the line that should be running between the intake manifold and your fuel pressure regulator for its boost reference. Also make sure that you are not leaking air out of the adjustment screw on the AFPR. Also as a tip, I would reccomend adding another nut onto the adjustment screw (so you have two -- locking the screw securely).

The bulkhead fitting/fuel pump and the AFPR/vaccuum connections should be looked at first.



FYI -- I had no problems running 880cc injectors on a S-AFC and a 99-ECU at stock fuel pressures. So, don't think that they are freaking huge. The S-AFC just isn't the best tuning tool for that size injector. Look into DSMLink, or AEM EMS for better tuning.

 

[Mitsu725]

unfortunately , i do not have the stock 450's but i think i might have figured out my problem i think when i ran the fuel line i ran it in between the body and the actual subframe i think since the hose is so thick it is slightly pinched in between the car and the frame, it sounds possible but i wont know until i rip it back apart. But yes i do need dsmlink but for right now I would like to get the car tuned as well as i can. but correct me if im wrong if I am flooding my cylinders with fuel then my FPR would be getting PLENTY of fuel right??

 

[Mitsu725]

actually twicks at first i had a leak between the bulkhead and the fuelcap and then i JB welded the fitting where it was leaking and now its no leaking on to the cap ne more but im almost definite that i have a leak. Is there ne other way to connect my FP to the pushlok line other thatn using a bulkhead in between because I believe that is my problem, i mean i know if i had the GSX gas tank, i could use a hose from the FP to the gas cap but im stumped with this shite, ...

 

[scottsee]

FYI -- I had no problems running 880cc injectors on a S-AFC and a 99-ECU at stock fuel pressures. So, don't think that they are freaking huge. The S-AFC just isn't the best tuning tool for that size injector. Look into DSMLink, or AEM EMS for better tuning.

You obviously know what your doing, but how on earth did you get away with 880cc's on an SAFC and stock fuel pressure? The airflow compensation would still make closed loop fuel opperations a nightmare. I know the 2g factory ecu stft/ltft tables will adjust for somewhere on the upwards of +/-29.8% and the SAFCII compensates for +/-50%. Thats cutten'er pretty close.. You got some kind'a secret?

 

[scottsee]

then, not to mention the fuel/timing maps you would be restricted to with that kind of -HZ calibration. You would have to flow like 50lb/min just to get into the 2.1g/rev area.

 

[dsm-onster]

You obviously know what your doing, but how on earth did you get away with 880cc's on an SAFC and stock fuel pressure? The airflow compensation would still make closed loop fuel opperations a nightmare. I know the 2g factory ecu stft/ltft tables will adjust for somewhere on the upwards of +/-29.8% and the SAFCII compensates for +/-50%. Thats cutten'er pretty close.. You got some kind'a secret?

-50% fuel compensation = 900cc. If the injectors truely flow 880cc at 43.5 psi then the ecu needs not compensate at all. All the compensation can be accounted for w/ the SAFC.

The only dificulty is tuning out the deadtime and keeping the timing in check. . .

Also I would love to run dual fuel pumps but with the GST setup i don't think it's possible due to the lack of space we have in the gas tank, i mean the GSX gas tank u can run a hose to the fuel tank cap and your set but for the GST guys I had to take a bulkhead fitting and cut the head off and slip the walbro with an O-ring and stick it up inside the bulkhead, i was thinking that was the first problem like it wasn't creating a good enough seal and was dropping it right into the fuel tank but i have to admit im stuck on this one.??

why run dual fuel pumps if the walbro 255hp is good for 650+ hp at 35 psi boost .

I would FIRST make sure that the bulkhead fitting you machined to fit the inlet of the fuel pump is a SEALED connection.

This alone, will make it hard to start, and you could be losing pressure @ the pump while under load.

Next, make sure that you have a good vaccuum connection for the line that should be running between the intake manifold and your fuel pressure regulator for its boost reference. Also make sure that you are not leaking air out of the adjustment screw on the AFPR. Also as a tip, I would reccomend adding another nut onto the adjustment screw (so you have two -- locking the screw securely).

The bulkhead fitting/fuel pump and the AFPR/vaccuum connections should be looked at first.

Dito
. . . I had the exact same problem and cured it when I realized I didn't tighen my worm clamp at the fuel pump enough.

 

[Mitsu725]

man i wish i knew what was wrong and if I could somehow rig that fuel pump setup differently than just a slip in with an o-ring do u guys have any suggestions on how to do that maybe a little hose or something??

 

[scottsee]

-50% fuel compensation = 900cc. If the injectors truely flow 880cc at 43.5 psi then the ecu needs not compensate at all. All the compensation can be accounted for w/ the SAFC.

The only dificulty is tuning out the deadtime and keeping the timing in check.

450/880 -1 = .488

That and only have 2% HZ correction to lean out durring open-loop. It'll do the job at idle/cruise, but durring WOT its kinda pointless, especally with any aftermarket turbo..

 

[dsm-onster]

Isn't the injector offset separate from the WOT tuning of the safc?

I.E. injector offset + the 2% increments (as far as the increments go)

I could be wrong. . . I havn't messed w/ an safc in a long time. Only a little on a friends 240sx.

 

[scottsee]

Kevin Jewer explains the big injector problem in this post. I'm wtih you on that one dsm-onster, I went right to DSMlink.

That maft thing will still completely bollix timing though, and since I can't live with that, I still have to recomend DSMlink.

660s require 32% adjustment for injector compensation, 450/660-1. That leaves 18%, 14% of which is required to get to 11:1, 9.5/14-1. Which then leaves only 4% for trim adjustment, or futher leaning out on race gas, which isn't much. Either way, I don't recomend using that much of the AFC's 50% range unless you have some way to lower base timing (1g, or 2g with 1g CAS). I've gone over some of the math in the past outlining how to figure out how much air you have to flow to make a particular adjustment factor give stock or at least reasonable timing curves. Without going through it now, I would guess that a 16g is not even capable of enough flow make 660s look stock as far as timing advance goes.

I've also never been much of a fan of the "80% rule." Probably just because I have run injectors at 100% and more for years on end with no noticeable or measureable side effects. In fact I just upgraded the EVO to 950s, just because I can, but it's run the last year at 102-103% IDCs on the stock 580s. Doesn't mean it's a good idea, but I have to ask myself what is worse, running an injector at 95% IDC which seems to have no real side effects, or running 28 degrees of ignition timing on pump gas, which does have known side effects This is a very tough topic to debate, since there are so many variables, most of which are in the mind/strategy/budget/risk tolerance/etc of the owner. My recomendation can even change slighty depending on the mood I'm in

To try to make my take on this short. If you are on an AFC or other ECU porking device, with no way to compensate for base timing (still a hack mod, since it makes changes across the whole rpm range, which is of course undesireable at idle for example) keep the injectors on the smaller side of what you can get away with. For example, 550s will support 40 lbs/min at 100% with all the usual variables accounted for. It takes a bit of work to get that from an EVO 16g on pump gas. On race gas they are good for ~42 lbs, and not many poeple will ever see over that. I get 43 on occasion, and at least one other person reported 44. But on race gas, you've got some fudge factor anyway. This will be acceptable to most poeple. To take it one step further, you would need to be flowing about 32 lbs/min at 6k rpm to keep the ECU over it's percieved 2.1 g/rev point, keeping WOT timing in control. Certainly attainable by the average guy, even at relatively low boost. Though it may take a little more than 16 psi, IIRC.

In contrast, 650s make much more sense. They can support 48 lbs/min, and with a maxed out evo3 at 43, you're looking at 89% IDC. Certainly reasonable, and at something like 35 lbs you're down at 73%. So even if your boost line falls off the WG and you completely max out the turbo, the ECU will know this, try to add fuel, and if you have enough pump, the capacity is there to save your motor. Certainly makes good sense to go this route.

But let's look at the other side of the coin now with 650s, with an AFC-like device, and no way to adjust for timing. Airflow is going to be hacked by about 46%, as described above (injector compensation and leaning to ~11:1 only, no other adjustment). You need to be flowing ~51 lbs/min at 6k rpm to stay over the 2.1 g/rev cutoff. Not going to happen So timing will be increased. To try to get an idea of how much, let's use the 35 lbs/min example again since it's not hard to reach that on pump gas. At 6k rpm the ECU is going to see 1.4 g/rev. WELL below the 2.1 rev range. Unfortunately I have no good way to calculate or look up what the target timing advance will be at that point, but it will be well into the 20s. No longer very safe or reliable IMO.

So this becomes a difficult decision between having plenty of fuel on hand to cover the unthinkable (but inevitable) but with excessive timing advance, or pushing your luck with less fuel capacity, but having safer timing advance. It's not an easy choice, but I have to lean to the smaller injector here, which is very unlike me. And this is the reason I always seem to push DSMlink so much. Eliminates the compromise, and is good not only for making the most power you can on your setup, but for increasing safety as well!

[speech]

You can also see that the more you know about this stuff, the harder it can be to make these choices. 99.9% of poeple have never even considered the numbers I went through above. And they may be pretty successful. But we really need to be fully informed. Even if it makes things a little more scary and a little tougher to decide, at least we know we are making educated decisions. So while all the jackasses say things like "Just get the 550s, so and so ran 9s on them!" I feel we should all take the time to make the right choice for the right reasons.

[/speech]

I could go on for hours about this, so I regret having to cut it so short. Hope this helps people out anyway.

 

[Mitsu725]

ummm yeah my thread has been hi-jacked

 

[scottsee]

Sorry for trying to show you why running your 850cc on your SAFC was a bad Idea..

Whats showing that you are running 18:1. Wideband or your pocketlogger?

 

[Mitsu725]

the wideband that we used on the dyno. and my watching my fuel pressure fall off while getting in to boost.

 

[dsm-onster]

Sorry for trying to show you why running your 850cc on your SAFC was a bad Idea..

Whats showing that you are running 18:1. Wideband or your pocketlogger?

yea apparently it is a bad idea! It's ok Scot. Now that I'm on track I'll still help him even though he's been rude. . .

Your fuel pressure regulator is faulty, IMO. I have an Aeromotive FPR and mine does great. But others have reported that their Aeromotive FPR has not risen 1:1 w/ boost pressure. Likely this has happened to you as well... In fact mine doesn't seam to be wirning right now properly. Though it was, it seams that I'm getting lean on a 30 psi pull when before I was holding 10.9:1 on my LM-1. . .

 

[scottsee]

I was thinking that too, You have the correct high pressure spring installed in your regulator? Can you hook up your regulator to compressor and test if it's rasing rate is 1:1, or swap it out with a know good one?

It could be a few other thing. Possable failing fuel pump not being able to keep up with the fuel demands of the vehical or faultly wireing. Clogged fuel filter, pinched lines, fuel pickup filter from at the pump being dirty, bad feed location in the tank, HUGE vacuume leak. You just have to start the process of elimintion. I'd start with testing the rasing rate of your regulator, then the voltage at your fuel pump.

 

[Mitsu725]

I apologize for all of my rudeness, bad day last week,my truck got broken into at work. yeah I tried today with the fuel pressure drop test, I started the car and turned it off while watching the gauge and immediately the pressure went to 0. Give me some feedback on this; I ran the -8 pushlok line in between the firewall and the sub frame, where the stock steel lines went but it was a LIL to tight I mean I had to put some balls on it and pull it through. I didn't think twice about running it there while I was working but now I think I messed up. Personally I couldn't think of a better place to run it unless i drilled the space out where the firewall meets the sub frame a little bit and made it more open. I mean I could have ran it closer to the exhaust and come in the engine bay and be closer to the fuel rail but I was worried about the exhaust being so close to the fuel. Where would you have ran it??

 

[Mitsu725]

I don't know if this helps but the car is a mutherfN u know what to get to start when its been sitting a while, like if i drive it here and there and go to start it, it takes like 15 turn overs but Geezuz, when it hasn't been started your looking at like 30 turn overs. Also my Golan billet fuel filter has arrows are those flow directional arrows or are they supposed to point to the tank??

 

[Mitsu725]

sorry for answering my own posts so many times but I think I solved it...well maybe, I read this somewhere "It is important for the plate to seal to the tank because of raw fuel and vapor leakage.

This problem sounds like some kind of small leak somewhere in the system. I would chack all AFPR connections and o-rings, teflon your AFPR adjusting screw, and make sure the fuel pump sock is on correctly and that it isn't clogged (I know its brand new).

Keep in mind that you will want to re-wire the pump also."


Well I know that ever since I put the bulkhead fitting on, my fuel pump hits the bottom of the tank, thus not making a correct seal because its keeping my fuel cap off the top of the fuel tank and I remember I had a hard time making the tank seal , but now that I remember there is a FOUL stench of gas in the car enough to give me a migraine headache everytime I drove it. I thought that was from the fuel tank vent like being open now in the engine bay just coming in through the ac vents but now im almost sure thats the fix, I need to take back off the fuel cap and remove the bulkhead from the cap and step the inside a little more so the walbro goes up a little more in the fitting so its not so far down and hitting the bottom of the gas tank and not making a perfect seal on the tank.