Hi guys, got a 383 pushed by a vortech s-trim blower running 14lbs of boost. Have a granatelli 255gph intank, the vortech boosta pump, vortech fmu, fuel pressure reg and 24lb injectors. I pinned my pressure regulator and installed the 6:1 diaphram in the FMU and at idle am only getting 38-40lbs of fuel pressure. Is this right? I was under the impression stock fuel pressure was around 47lbs, at least according to my chiltons, is that WOT? Vortech told me my fuel pressure should be around 80-90lbs. Is this right? What do you other guys out there with s-trims run for fuel pressure? Do I have a problem with my fuel pressure at these levels, or is this normal?

 

What does that mean?

You should be making 85-100 psi under full boost with the FMU. Try using a mity-vac hand pump putting the hose on the pressure side (not the vacuum side) of the hand pump tool, then put the hand pump pressure againt the FMU sampling line (the little vacuum line connector on top of the FMU). You may want to check to make sure your FMU isn't connected backwards. It also needs to be in the return line not the pressure line, this is the "smaller" of your two fuel lines.

There is an extensive post here with a guy that had a paxton, a 383, and a miniram. But the search won't find it.

 

Could not having good vacume to the fmu cause it? I installed a bypass valve, and spliced into the vacume line that the fmu is connected through, and the bypass would not work, so I had to run a dedicated line to it from the intake.

 

I believe you need a dedicated port for the FMU as well.

 

hrm, I'm out of dedicated. I would assume it wouldn't be too much to split just the fmu and the bypass valve would it? I'll try it tomorrow and see what happens.....

 

And pinned my pressure regulator meant it is screwed in as far as possible....Just coming out on it a fraction of an inch and it jumps down to like 35lbs

 

it should be set like normal, not "pinned" the only time you raise it up is when you need more initial fuel.

besides that sounds like you got a more serious problem. if I walk outside and crank up the fuel pressure adjustment screw on my non supercharged car it will go so high (60-70 psi?) the car wont even run.

 

Well what I'm thinking is I'm not getting good vacume to the FMU (it is inline before the regulator) and thus it's not opening, or closing, whichever it does to build up pressure, and thus preventing the fuel pressure from rising. I'm going to test this theory in the morning to see if I can fix the prob that way. I'll let you know how it goes.

 

Ok got the vacume lines switched on the fmu, under boost I'm jumping to about 95lbs, but still only 38lbs at idle. Guess the FMU is just stopping all fuel pressure except under boost. Gonna turn my regulator down a bit, don't think I need it quite that high.

 

The fuel pressure should be around 45psig with the vacuum line removed from the regulator and plugged. normally the FMU only effects the system under boost condition. vacuum should have no effect on the FMU.

later
larry

 

hrm, well I will try disconnecting the vacume line to the FMU tomorrow and plug it up and see if it effects the fuel pressure.

If I take that step and I'm still at 38lbs whats the next step to check?

My Air/Fuel from the Dyno is as follows (5600Ft Elevation)

RPM
3200 11.8
3600 11.0
3800 10.5
4000 11.0
4400 11.5
4600 11.8
4800-5200 12.0
5400 11.5

According to my speed shop for our elevation I'm a point rich there at the peak....Opinions? Comments?

 

You seem very confused. Unless it is a super FMU it is inert (doing nothing) when not under boost. It is simply a part of the return line. If it were doing something, the only THING it could do is RAISE the fuel pressure. It can't lower fuel pressure. Fuel pressure at idle is 100% the regular regulator. to raise "base" fuel pressure at idle adjust the regular fule pressure regulator! If you get no adjustment when you turn in the screw, then its likely it is damaged, ruined, worn out, or no good. Likely bad from being "pinned".

THE FMU WOULD, COULD not LOWER the pressure at idle.

if you get 95 psi at full boost and it is that rich, you might need a 4:1 ratio. But its more likely you just need to add a simple bleeder valve (sold by Vortech) but we will cover that after you fix/adjust the regular regulator to get 40-45 psi base fuel.

 

Ok it sounded to me like he was saying the fmu could cause the restriction. It was my intention to put a new BBK regulator on from the start, but when I pulled the plenum I found this old one on so I left it there. I will go ahead and put the bbk one on and see what happens.

I already have a bleed valve on my FMU. Haven't messed with it yet. Let me get the other regulator installed and we'll see where I am.

Thanks

 

You have it on the return line right?

 

it really really really sounds like you have it on the feed and not the return line....

 

that was basically my point there is no way that any restriction of any kind in the "return " line could cause fuel pressure to "lower" or be reduced.

 

I will double check that it is on the return line, but I'm almost positive it is.

 

The return line is the one coming from the stock regulator.

Anyway, your in take pump is 255lph. THe vortech suplied "booster" pump is 155lph..

WIth the 255lph intank pump, the booster pump is not required. I think having it inline is going to cause problems..

-- Joe

 

hrm that's the first time anyones told me that. I do have the secondary pump on a toggle switch. The only time I use the pump is when racing. What kind of problems would it cause running it if I do not indeed need it because of my intank?

 

And just to verify, the return line...from the regulator, goes into the lower of the two inlets on the FMU correct?

 

Ok I just double checked and the return line coming from the regulator is indeed going into the inlet on the FMU.

So does that put me back at the bad regulator area? Or are there more things I can check?

PS: I checked the fuel pressure with the secondary fuel pump running, and not running. No variance what so ever.

Another sympton I've had, and it's probably related to all this, is watery discharge from my exhaust when the car is warming up.

 

First check the OEM regulator, as i stated earlier, remove the vacuum line from it and plug the line. this will give you your base fuel pressure. Adjust this to 45-47 psig as a starting point. then when you reconnect the vacuum line to the regulator, your fuel pressure should drop.i believe mine runs around 38-psig.

Then once that is correct you can start tuning the FMU. depending on the ratio of your FMU, this will determine the amount that the fuel pressure is raised, i.e. 4:1 will raise your fuel pressure 4 psig, for every 1 psig of boost.

I know the ATI FMU's come with a bleed valve for tuning purposes, the more you turn out the bled valve, it will change the ratio of the FMU. (lowering the ratio).

As far as the fuel pumps go, if you do have a smaller in-line pump then the in-tank, you will cause a flow restriction. it is never a good idea to run the in-tank pump and not the in-line at the same, because you will create more work for the in-tank pump causing it to fail prematurely. so do some research on the in-line that you have. to see what the flow rating actually is.

hope this helps
later
larry

 

yeah leave the second pump in line, and get rid of that switch? how come people decide to ditch the instructions and then are unhappy with the performance of the system? anyhow we know the inline isnt hurting hell it makes the fuel go high enough to make the system run too rich right?

I think maniacc above is dead on! I totally agree with his statement above.

 

so is this comment still true?

 

Absolutely it is true to the letter. But the cars I have seen on FMU's that cant create the pressure needed under boost on the dyno when the inline is removed justifies leaving it on until the car is switched to a programable set-up that uses huge injectors and no FMU.

A) why else would Vortech AND ati include them?

B) why do top of the line foriegn cars use the same setup?

C) the only businesses that tell you not to have something "better" to sell you...

 

First, before this goes any further, do as you've been told: Disconnect the vacuum line to the FPR and measure your fuel pressure. You should get somewhere in the 40-45psi range.

You need the inline fuel pump. Pump capacity goes down with pressure and an fmu tries to raise the fuel pressure way over where most pumps will not have sufficient capacity to feed anything. At the 90 or so PSI that the FMU will try to get at full boost neither, the 255 intank or the 190 inline pump can supply any real fuel volume, but with both in the same line both only have to supply part of the total pressure. Switching the inline pump off while you're driving around doesn't accomplish anything but add a restriction to the fuel line, making the intank work even harder.

FWIW, looking at those A/F ratio numbers it looks like if anything you're running a little rich. In most cases you're trying to stay in the high 11:1 range with a blower.

 

Ok I will double check the fuel pressure with the vacume line off of the regulator and see where I am.

It seems the majority will win me on the fuel pump issue. I'll go ahead and keep the boosta pump in and on at all times. My assumption on not using it all the time came from the fact that the kit was designed for a stock in tank pump.

Crossfire yah I'm running 1 point or so rich..But I'm sure once I get all this figured out I can fix that.

 

the little 5/16 fuel line and return orrafice in the regulator have no problem returning any unused fuel to the tank. The guys at procharger know that most people have better than stock pumps. If it helps you feel any better; remember the flow rating of that 155 LPH pump was never tested while it was helping with a 255 lph pump was pushing fuel to it. So its likely flowing plenty now

 

Ok, with the vacume line to the regulator disconnected and plugged I have 41lbs, when I reconnect it drops to 38lbs.

Comments other ideas?

 

that sounds good to me, thats what you should have.

41 psi is what would be around normal for stock.

 

Ok good deal. Thanks for the help

 

Alright got some new information. We got the baseline fuel pressure figured out, and I've since put a fuel pressure guage on and checked it under boost. I am spiking way past 100 psi.

So 2 questions.

1: What is a good fuel pressure under boost for the 383 and the 14lbs of boost? Vortech had told me 90-95, does that sound right?

2: I am currently running the 6:1 diaphram in my FMU to provide more fuel, should I try and go back to the stock 10:1 that came with my kit and see if it lowers it?


(Yes I am planning on switching to the $58 mask so I can eliminate the FMU, but for now I'm stuck with it)

 

I understand your need to run the FMU, I don't think its a bad place to start. This is what I intend to do on my own ride and what I have done in the past. changing the FMU ratio will put you in the neighborhood, but you really need to dyno tune with WB o2 and get it close as you can.

 

Vortech has no idea what will work for your combo.

What you want is at 6k, your inj pw to be around 8.5ms, and your o2 volts to be around .900-.950.

Adjust your fuel pressure accordingly.

65psi WOT at 6k on my sv0 24s produced .800-.850 mv at 9.3ms. Thats when I realized I needed bigger injectors.

With the FMU gone, I run 55psi WOT with the 36# sv0 injectors and $58.

-- Joe

 

We would have to know about just about everything else about your combination to tell you if that's about right or not… how are you tuning for the 383…?

FWIW, if you're running too rich at WOT you'll want a smaller ratio FMU, if you're running lean at over 100psi I'd say that it's just as likely that you're running out of fuel pump as you are actually running out of fuel (most fuel pumps completely quit somewhere in the 100-135psi range and have little if any flow above 100psi)

 

Not sure until we know his injector pw's.. He needs time with a scanner, and some prom programming to test the limit of his hardware.

-- Joe

 

Gotcha. I have the scanning software, and a laptop, just have to get the ALDL cable now so I can see what's going on.

I put new plug wires on today, and changed the oil, along with moving my mat sensor from under the plenum to the intake hose and now I'm getting an 02 sensor rich, and a map sensor code all of a sudden. I'm wondering if my 02 hasn't been working and I bumped into or something, and I can't figure out why the maps throwing the code all of a sudden, vacumes fine.

Where's the best place to get the aldl cable from?

 

Another twist to the puzzle. I just went out and replaced the fmu diaphram with the 10:1 fired it up and a couple things have happened. (Yes I realize it shouldn't effect anything accept under boost. But that's the onlything I've done since earlier)

1: Both engine codes are gone
2: It's loping real bad, jumping between 500 and 1000 rpm, barely running.
3: I'm puffing gray smoke out of the exhaust.
(I didn't let it warm up)

It's so frustrating not knowing whats going on. I'll order than aldl cable tonight.

Also whats the best 02 sensor to go with? Whats everyone else running?

 

You need to scan your car, and burn a custom prom..

-- Joe

 

Aye I know Joe, all I'm lacking is the cable. Just gotta find a good one, thats the right one.


What cable do you have Joe?

 

I made one.. the 2-transister type off www.moates.net. Easy, made it in like 15 minutes..

-- Joe

 

I know that everyone believes that the trick is to see what the ecm is seeing and then "make things right" but the fact is that very rarely are the problems with the actual ECM… they usually just go about, doing what it's supposed to do with no issues, and when there is an issue it's usually severe enough that the car will barely run if at all. Otherwise it's usually something to do with a mechanical system that is not doing what it's supposed to or expected to do.

Now if you're using a stock tune on a dramatically different then stock engine you might end up with something undrivable (mostly with BIG differences in cam, displacement…) but for the most part you can get it drivable by messing with your fuel pressures and timing.

Now you messed with the fmu and you san you're getting smoke out of the exhaust, but didn't say anything about what the fuel pressure is doing or anything.

For the most part, if we're talking a narrow band O2 sensor then they're pretty much all the same and are not exactly a great deal of help with tuning…

So how about before we start throwing technology and parts at this thing and get really frustrated and waste money, make sure that you're starting from someplace reasonable… A reasonable base fuel pressure (with the vacuum disconnected, FMU status should not change your base fuel pressure at all if things are working right). The 6:1 disk would be a reasonable place to start, make sure that you fuel pressure goes up with boost and that it does not drop off. You should have about 100psi fuel pressure at 12psi boost with it, 110-115 at 14psi (this is where I think that you're getting into some vague weird spot where the fuel pump, fuel injectors… won't be happy). Make sure that the base timing is set to something reasonable and that with the timing connector reconnected it actually moves. If you have something like a BTM I'd also try to apply a few psi to it's pressure transducer and make sure that it's retarding timing like it's supposed to.

Not looking back at this thread, WHAT PROBLEM ARE WE ACTUALLY CHASING? I seem to remember that we started with a car that ran some slightly rich but safe and happy mid 11-12:1 a/f on the dyno… so? That's good, what's the problem there. You might be able to find a little more power by opening the bleed on the fmu and getting that into the low to mid 12's, but that's not guaranteed, and I wouldn't do it unless you're messing with it on the dyno or at the track so you can compare results. Doing this on the street will accomplish absolutely nothing but take a happy/safe combination and make it into something that lunches your engine. If it's a little rich across the rpm band then you can usually fix that by lowering your base pressure a little, that will lower your pressure EVERYWHERE (opening the bleed screw will only change your WOT fuel delivery and how fast it reaches that level).

At that point, if you know that everything is relatively happy and you want to do some tuning/chip burning to make things perfect, fine. If you want to ditch the FMU and burn a custom chip for that, fine (be aware that the fuel pressure that you're seeing with that 6:1 fmu will take roughly a 40lb/hr injector to duplicate without an FMU, which means that you're either looking at getting the 42lb/hr ford injectors, the 50lb/hr msd's, converting to peak and hold (with an aftermarket driver or even ecm) or some custom injectors. At that point I STILL haven't found anyone that has gotten 42's or anything larger to idle well with a factory V8 ecm…

 

See I don't agree. 99% of the time the problem is with the programming. Even in closed loop when the ECM tries to correct, it usually sways too far in each direction.

Now the biggest problem is under boost, cuz at that point he is in PE. Pe is open loop, and makes absolutely NO correction based on .02. So who the hell knows what's going on under boost.

I think his problem is he is trying to use mechanical devices to make up for a stock prom thats completly wrong for his setup.

Hell, his injectors might be going erratic simply because the FMU is throwing too much fuel pressure at it..

I'd drive around, get some good scans (part throttle, no boost) then fix your ve tables there. THen scan under boost and see where your at. Change the 02 sensor if you havn't..

A 40# injector with a BSFC of .55, and a duty cycle of 85% is good for 550hp.

No way will anything larger than stock idle "correctly" on a stock tune, let alone a 42#. He needs to get into prom programming. Using the stock prom is just silly.

If he ditches the FMU and the BTM and goes with $58 he can really fine tune his fuel and timing requirements. The FMU might get him close, or may not. Either way its a really bad aftermarket approach.


-- Joe