ok,ive been having a hesitation problem around 2-3 minutes into driving my car, and have recently replaced coil,icm,and rotor in my dizzy.i am now considering it to be a fuel problem.

i have an fmu installed,and have just made a fuel pressure gauge out of some hose and a psi gauge from a compressor.it is going from my fmu "out" to where it originally was going(to the part at the fuel rail).
it is reading a steady 20psi..
The gauge has a dial on it to open and close the valve,and when i close the valve some,i can raise the pressure all the way up to 60 psi if i wanted.

My question is,does this all sound like i did it right?And 20psi would show that i do in fact have low fuel pressure correct?meaning my fuel pump is bad?

Also,the pressure drops almost to about 10psi when i apply the throttle.is it supposed to do that?

Thanks for any help you guys can give me!I just really dont wanna spend $150+ on a fuel pump if it's not going to fix my problem..

 

fp should be at 39-45 i think thats for ls and gsr

u can adjust the fp with the guage? why dont u just turn it up then?

i have a similar issue but i think mine is a ground or somethin

and it should drop but i dont think by 10psi i think it was like 3 or 4 at snap throttle with fpr vac line pinched.

 

well the gauge is connected from the fmu to the rail,so if i bump it up,i believe its only bumping it up from the fmu to the rail,not from the fuel pump.so when the actual fuel pump drops pressure it really wouldnt do anything for me..

thanks for the input!

hopefully we can figure this out soon!

 

oh...i dont know much about fmu's, what setup are you running?

been learning about how a fmu works

so since your turbo? your not running a fpr? i was confused at first but i guess you can run both or just the fmu? seems like muscle car guys are running both i think for switching between n/a and boost w/ a SC

also what kinda fmu? has it been calibrated? how much boost u running? no tune? stock pump?

 

tbh, i wouldn't base a solid diagnosis off a bojanged fuel pressure gauge.
hypothetically though, if the gauge were reading correctly, i would definitely say you have a flow issue. if that were the case, i'd start with the filter before hanging a pump on it.

how exactly does this fmu that you speak of work?

 

at the moment,i am all motor.am planning to put my turbo kit back on,but want my car running right first..

its a vortech fmu,i believe it is a 10:1 calibration disc.
feed fuel line is cut in half and the fmu goes there,seperating the two lines.
then there is a vacuum line for when it senses the vacuum draw,or especially in boost,it will raise the fuel pressure.I have always understood that an fmu keeps your balance between lean and rich.only thing i notice when i install them is a little better throttle response.I was running super rich before the fmu,and with it installed i no longer smell the rich gas smell.
this is on a stock fpr
no tune
stock fuel pump(for now.if mine is bad,i will be replacing with a 255lph pump and adjustable fpr.)


Let me know if you guys need to see anything,i can easily take pictures and videos.

and here is everything you need to know on fuel management units
http://www.redz31.net/pages/fuel/fmu.html

 

You need to check the fuel pressure at the fuel filter to see what the fuel pump is doing. 94

 

agreed. that's usually where a gauge is tee'd into.
with the gauge installed, you should read roughly 35-40 psi. if you pinch off the vac line to the reg and the vac line to the fmu, that should increase by 10 psi or so. if you don't get that extra 10 psi, there is a regulator problem. if you do, with those lines pinched, snap the throttle 3 times. pressure should drop by no more than 3 psi. if it drops by more than 3 at any time during snap throttle, you have a flow issue. either pump or filter.
try those steps, with a proper gauge installed in the correct location, and lt us know how it goes. tbh, if you have any issues with the first 2 steps, i'd remove the fmu and retest

 

thank you guys very much,i will do that and let you guys know.

 

ok ive got an update..

i found out that the hose to my gauge was leaking majorly(i forgot to tighten one of them lol..)
so after that it read about 30 psi

i tried pinching the fpr and fmu vacuum lines and,if i did it correctly,which i tried them by themselves and together,i didnt hear any change,or see any change in pressure..does that mean anything?

i put the pressure at about 35psi and drove it for a bit and it didnt do the hesitation,but when i shut off the car and try to start it back up,it doesnt always want to just fire right up..sometimes it cranks and rumbles like its about to start but just keeps cranking..
sometimes ill crank and hold the gas and let go of the key and keep holding the gas and it will just sit there and rumble in 100rpms..after every new crank it gets a little higher and a little higher and then it shoots to life and kinda sounds like **** for a sec and doesnt rev up the best..

let me know what you guys think

 

Its 2012 and you're using an FMU...that's your problem.

Crome + fuel injectors + fuel pump + tune = problem solved

 

agreed. get rid of the fmu and retest

 

ugh..not that it was a lot of work,but i did what you said and removed the fmu and retested.its showing about 35 psi.still having the issues..
a lot of people have been quick to blame the fmu,but the problem was occuring before i installed it..
i appreciate the input,but i need help,not opinions please.

 

Are you checking the fuel pressure at the fuel filter?

If not, do so. 94

 

also, without the fmu, did you try pinching off the vac line to the fpr and see what the pressure increase was? if you don't get 10 psi, there's either a problem with the reg or the vac line. if you pull the vac line off and see any fuel in there, the diaphragm is leaking..
if you get the 10 psi, try snap throttle.

 

What is the setup on this car? It would be helpful to know a little more about it.

 

i wont have a different gauge until tomorrow.i will do that first thing in the morning.


I did try pinching the line while the fmu was off,it still did absolutely nothing..and my vacuum gauge shows 20psi..
just looked right now and didnt notice any gas in my vac lines.
when i snap the throttle now(fmu off) and with the fmu on,it drops about like 5psi.i thought it was dropping almost 10psi,but i guess not.




2xxx miles on this thing currently.
B18a1 motor
B18b cams
race Piston rings
race Rod bearings
b18b oversized valves
b18b valvesprings/retainers/keepers
fmu
cold air intake
headers,full 4' glasspack exhaust




when my car does the hesitation and i ride through it and get it home,eventually it does this:
(click to view)


I just replaced coil,cap,rotor,and dizzy with brand new ones just before i considered this to be a fuel problem...where should i look next?

 

Why are you running an FMU if its not turbocharged/supercharged?

I must be missing something...

 

i have a turbo kit,it is just uninstalled at the moment, until i get this thing running correctly.and to my understanding,it is supposed to correct the fuel mixture whether it is boosted or not.the vacuum tells it what to do.correct me if i am wrong.

i smoke a little and run a little rich without it.with it,runs perfectly fine,doesnt run rich at all,no smoke.I also can notice a better throttle response.

 

Have you checked FP at the filter yet?94

 

check pressure at the filter housing, as mentioned. if you aren't getting that extra 10 psi with the reg vac line pinched, then your reg is pooched. since WOT= no vacuum, by pinching the line you're simulating WOT. you need the extra pressure as throttle is increased and vacuum is decreased

 

i wasnt able to get an actual fuel pressure gauge unfortunately..

but..
i raised the fuel pressure to 40psi from my gauge and took it for a drive and it didnt give me ANY problems,and fired right up everytime..

and i also just tried pinching the lines in every way i could think of,removing my vacuum gauge and anything that could have caused a leak,and it still didnt bring pressure up..

and,when i hold the throttle WOT it DOES in fact drop the pressure about 10psi...

 

it's not supposed to drop the pressure. it's supposed to increase. it's not a vacuum issue, it's a regulator issue. you need a gauge hooked up at the filter housing. just buy one and and leave it on there. it's great to have for diag in the future as well. you can get one for like 30$. it's a drop in the bucket compared to the peace of mind it'll give you.

the system needs to be regulated. right now, it's not.

 

I have seen them on Ebay for under $20, Ihave the B&M one, under $45. 94