mike89z

Im having a little trouble..... I got my p600b kit put in my car and the FMU didnt seem to work(I saw 5#of boost and fuel pressure was only 55psi) so I pulled the boost reference line off the intake started the car and blew into the line thinking that I should see the fuel pressure increase, it didnt! So I bought a new FMU(it was a used kit) had it installed and same thing!

Any ideas as to why this is happening? Just a little more background;
Car has a 340 wahlbro w/ the hotwire setup.
Just had the fuel filter switched.
24# svo injectors.
Already took out that little restrictor that comes with the FMU.
Spoke to the ATI tech and he said that the pump setup I have should be fine.
And last but not least, If I manually change my base fuel pressure The max PSI also increases(bumping it up 5 will net me 5 up top), so it seems like my fuel system has the room.(I have seen 60psi while WOT but only by buming up the base pressure up)

What do you guys think? Could my fuel pressure regulator be screwin me? Has anyone blew into there FMU during idle to see if it increases pressure and if so did it work?

Any comments welcome, but please no "you should install the ati inline cuz thats the way the kit came" comments as I have covered that above on both parts(ati said it was OK) and fuel pressure does increase with the regulator.
Thanks

Damon

You can't generate more than about 1/4 PSI of pressure with your mouth. Not a valid test if that's how you did it.

FMUs have adjustment(s). You need to spend some time getting it dialed in. Work with their tech support guys on this. Your stock FP regulator handles everything up to ambient atmospheric pressure- that's up to WOT WITHOUT boost (which would equate to about 45 PSI fuel pressure or whatever your base FP is). Above that the FMU should be adding about 6 PSI fuel pressure for every PSI of boost (if it's calibrated as a 6:1 FMU).

B4Ctom1

the FMU kit comes with a "plug and play" fuel line ends check to see if it is hooked up backwards. if you hooked it up to the same referrence line as the "bypass" valve uses this could be a possible problem too.

mike89z

Damon, thanks for the info. so I cant really rule out the FMUs operation until I can get a air pump. So at 5 PSI what are u guys seeing for fuel pressure(My air bleed on the FMU is turned all the way down). Im just worried about leaning out and popping my motor. Thats why Im beeing so cautious. At 6:1 I would think that the PSI should be at least 25 - 30 PSI higher which would be in the 75 - 80 PSI range

Tom, I hooked the reference line to its own port to rule that out. Also Ive checked and double checked and the fuel lines are hooked up right. Thanks anyway

So lets hear what everyone has for fuel pressure when they are seeing 5 # of boost!!

Do these things have a buffer for the first few PSI in that it doesnt start the increase until it sees a few #s?

mike89z

Well I just moved into my new place and started thinking about the Iroc. Could it be that I need to clamp the reference line down on the intake port? Maybe boost is finding its way out there.... Ill have to try that this weekend although I think its gonna rain !!again!! Anyway, still wondering what everyone is seeing for fuel pressure at 5# of boost w/ the procharger(especially if you have the air bleed on the FMU turned in all the way) and what there base is.

mypontiac

I checked my ATI FMU by blowing into it with a air compressor. Maxed out the Fuel Pressure Gauge!!!!

This is the check you need to do.

Basically the FMU restricts the gas flow return to the tank.

You can get the same increase in pressure by crimping down on the return fuel line.

This is how you check the pump capacity. If you crimp down in the return line and the FP goes up, then the pump is fine.

I went through all of this too.

Found out the orafice in the air line was clogged.

Hope this helps.

maniacc

Okay, i went out and did alittle test....i see 60-65 psig @ 5 lbs...

hope this helps ya...

later
larry

rooster433

You need to recheck what walbro pump you have.


There is a High PSI version and a regular high flow. I tuned a camaro a while back with a walbro pump. He was convinced that it should be enough because it was the largest pump they sold.

We had a problem with the car going lean at high revs put the T-Rex on (not hard at all BTW) and picked up like 13psi. The inlines are geared more towards achiving high pressures while the intakes usually are not.

My experence with walbro has been they will tell you just about anything you want to hear.


Have you been able to tune the car in? Or is it not enough fuel pressure to get you in the ball park.

B4Ctom1

yeah I have seen guys thinking they are smarter than the blower companys by refusing to install the inline thinking it will somehow restrict them because they already have a 255 LPH, considering that there are different versions of intank 255 listed in the catalogs offered through walbro I dont take a chance I run my inline, I suggest others do it too. It sucked to tell a dyno customer that he is going to have to pay me for the time he has already been on the dyno and setup, go home put the pump on or pay me to put it on for him because his 42# injectors are draining the system faster than his 255 lph pump can do with his FMU, then come back and try to dyno later. funny thing is when they did it all the fuel problems went away.

rooster433

Ditto...

I've been tuning cars now pretty much for a living for a while now. I had a guy 2 years ago try to run without a FMU, 255 in-tank and 42SVO's. Flat out couldn't get fuel in it. Put the T-Rex on and bam.. good to go.

It doesn't take but 2 hours to install the pump and you should have more pumping capacity with both pumps.

I love it when they try to go without the FMU and 1 bar speed density setup.

B4Ctom1

Trust me it doesnt matter what our experience here is rooster, it wouldnt matter if we dynoed 100 guys and saw this improvement in every case someone will still show up trying to show us some equation or chart telling us what we saw over and over again is some fluke because "so and so says so" and they should know even though these non-dynamic equations and charts are usually sourced from a person with something to sell. ATI and Vortech have nothing to sell to me, it's already been bought by that point if you already have the kit. so why not just trust thier experience and install the inline or FMU they included in the kit-hell!

mike89z

Hey guys, sorry its been a while.

Rooster I have the high PSI pump and the hotwire setup. Im positive because I had the original wahlbro 255 that was in there(one year old) swapped out since it wasnt the high pressure one.

Also, I know everyone says that if it came with two the thats what it should have, 2 pumps. Well I called ATI to ask them and the tech said I should be good w/ my setup. Apparently he was mistaken? Its not like I disregard what ATI says. I did ask them and they didnt see a problem. And the fact that if I raise my base PSI, then the max is more shows that the fuel system should be adequate, doesnt it?

Scenario 1 Max pressure 60 PSI w/ high 40s at idle

Scenario 2 Max pressure 55 PSI w/ low 40s at idle(turned the pressure down to see if the max went down with it which it did. This would leave me to believe that the pump isnt the problem because between idle and WOT FPR controls thing and with boost no difference both times. )

Which leads me to the reference line. Maybe its leaking under boost. Has anyone seen this?

Im ready to throw an inline in it. It just doesnt seem like it would help and I would hate to add a noisy inline for no reason.

Thanks for all the replys and ideas and keep em coming!

B4Ctom1

do you have a mity vac hand pump tool? use the pressure side of this tool and have someone rev the engine a bit (it will try to flood it) when you are pressurizing the referrence line. you must ensure you are running off the "pressure" side of the miny vac instead of the vacuum side. watch fuel pressure. when performing this test, pressures should come close to - or will max out you fuel pressure gauge. I have seen 88 to 100 psi doing this test dependant on the mityvacs pressure. if it wont reach those kinds of pressures then sounds like you have found your problem. install your inline and perform the same test and see what the results are.

83 Crossfire TA

iTrader: (2)

Apparently, no one here seems to know how an FMU works.

In a nutshell, it’s a fuel pressure regulator that will raise pressure faster then the boost pressure goes up. Most do not have a base pressure setting like a normal FPR, so without any boost it will allow all the fuel to bypass. A normal FPR has a ratio of 1:1, so if you set a base pressure of 45psi, at 10psi boost you’ll see a fuel pressure of 55psi. An FMU is just a FPR with a x:1 ratio (the x could be anything, but typically is a 4, 6, 8 or 12). You will not see any change till the FMU calls for a pressure higher then what your fpr wants. (BTW, you should be setting your base fuel pressure with the vacuum line disconnected, your actual pressure at idle will be significantly lower, basically your base fuel pressure – idle vacuum).

In your case you’re only seeing 5psi boost and probably have a base FP of around 45psi (may be as low as 40, but in that case just lower the numbers I give by 5psi). At full boost you will be seeing 50psi FP. Typically most blower kits for V8 cars come with a 6 or 8:1 fmu. At 6:1 + 5 psi the fmu will only be calling for 30psi, and at 8:1 it will only be regulating to 40 psi. In neither case will you see any additional fp under boost since both #’s are lower then what you’d be seeing anyway. Even a 10:1 won’t raise fuel pressure any, but a 12:1 will raise your fp at 5psi boost to 60psi.

If in doubt that its working at all, try pressurizing the thing to 10psi or so, I bet that you see a fp spike…

mypontiac

Shouldn't those # be plus the base FP?? When I go into boost gauge gets to at least 75 psi with a base of 45 psi.

B4Ctom1

hmmm sounds familiar?

mypontiac

Huh!?!

83 Crossfire TA

iTrader: (2)

No, it works just as I described it, which was my point.

B4Ctom1 - I'm sorry I agreed with something you said, it won't happen again

B4Ctom1

no, thats fine, rare as it may be....

mike89z

Crossfire thanks for clearing that up. I always thought that the FMU worked differently. Im not sure but I thought that the ATI FMU was adjustable to 12:1 which is where I have it. So I should be seeing around 60 around 5#. The strange part was that my base PSI setting effected the max under boost. I still have to get a pump to make sure the FMU is working(just moved away from my car ).

So thanks for all the info guys and I ll fill ya in when I get back to my car(hopefully tommorrow).

83 Crossfire TA

iTrader: (2)

With a 12:1 and 5psi boost a base pressure would have to be under 55psi to see any change...

an FMU is not a substitute for properly tuing a car, it's just a means of getting more fp, and for that matter, a very good way of adding fuel, since the additional fuel delivered with the rise in fp would happen at the same ratio as the additional power from the boost (assuming that you have an appropriate fmu ratio). I suspect that most people would be MUCH happier with FMU setups if they tuned the car to run well at a lower then stock pressure NA, then added the boost and the FMU, or in general, if they took the time to get the car tuned right after installing the setup.

88GTAinRI

Correct me if I'm wrong, but isn't the inline pump sent with the kit needed to increase the pressure of the fuel? The Walboro set-up with the hot wire increases the volume of fuel delivered? The FMU is looking for more pressure not volume.

B4Ctom1

bingo

Grumpy

The downside to the FMUs is that mandate running higher fuel pressures, and as you raise the pressure, the volume of fuel the pump can deliver decreases. With any of the higher ratios you can get to the knee over point where this occurs.

And in order to make any real difference you have to run the higher ratios.

Installing a set of used 30 PPH injectors might be something for you to consider. And reading up on the 749 ecm in the DIY-PROM archives. Doing a 749 and your own chip would be the proper way, IMO.

B4Ctom1

Not to mention when you have a combo that makes enough power that even a 30# injector with its pressure cranked via FMU still isnt enough fuel for the HP. You cant just add more injecter (bigger) without ECM tuning and expect to drive it. How big of an injector can you get for the 749? they are still high impedance only right? that leaves us with some 50'ish # ones?

Grumpy, I am so glad to see you posting over here, there are a few enthusiasts over here now using the 749 with appearantly great success. I think the 749 may be the biggest contribution to boost for out cars since sliced bread. I cant wait to try my own burning. I am reading over there like crazy trying to make sense of it all.

misterjuice

let me ask you guys this then....

I'm running 13 psi on my P600........idle FP is about 36 psi.......when i see about 5-6 lbs of boost, my FP is at about 46PSI........is this enough? or do i need to raise it up higher??

stock computer programming, 305 LB9, 24 lb/hr SVO injectors...

let me know guys......if i can get more power out of this heap, i'd be happy

B4Ctom1

probably

misterjuice

mooooooo. thx tom

SATURN5

Raises hand... works fine so far...

Plus theirs more coming in regards to the 749 code.

BW

mike89z

Hey guys, so it seems to me that bigger injectors and this new code would be the way to go. So the 749 is a SD setup that I can run with little modification to my current config. Any info on how hard it would be to accomplish this swap would be appreciated. And also dont the 30s seem a little small if used without an FMU? I was thinking 36s with 8# of boost (Ill be changing my pulley soon to the 3.40)