cant rev past 2k rpm when driving

[shaeff]

i put my old T-belt on just for shits and giggles. it took like 20 minutes. base timing is re-set and perfect, as is ignition timing.

my AFPR is an aeromotive. why does my fuel pressure drop when i rev the motor? if i rev it and hold it there, the fuel pressure constantly drops. it builds back up to around 30psi with vacuum line on when i let off, just like it's supposed to. (well, it's actually supposed to DROP from whatever elevated FP it happens to be at..., but it goes back to around 30psi regardless)

i cant figure out why it's dropping when i rev it up?! the fuel pump is brand new, and i did the 12V mod as well. still no go! i can hear the fuel pump hissing, but could it possibly be bad already? i mean, it's brand new, i just put it in not too long ago.

i'm going to measure the voltage that the pump is getting with a multimeter... i'll report back.

edit: i tried the AFM trick, and the exact same thing happens. it's gotta be because of the dropping fuel pressure. right? grrr....

-shaeff

 

[shaeff]

ok, i'm getting 12v back to the fuel pump. i tried re-connecting the resistor, and the problem only multiplied, so i changed it back to the 12v mod again...

pressure still drops with RPM.

-shaeff

 

[IJ.]

Bad Ground back at the pump?

 

[shaeff]

i tested the ground back there before i put the pum back in, and there was 0 resistance. unless something got messed up when i put the tank back up, it should be fine. i'll doublecheck it tomorrow. i'm at work now

here's a question:

i tested my fuel pump relay. the manual says that there should be continuity between two separate sets of terminals, and no continuity between another set.

two sets of terminals tested fine, one didnt have continuity where it was supposed to. could that cause a drop in my fuel pressure when the RPM rises?

-shaeff

 

[mkiiSupraMan18]

FUEL PUMP...... sounds like my 82 when the pump went out.... it would do everything fine w/ no load..... but it wouldn't go above 2k-2500, not sure which... Sorry, I didn't really read all of this.... if it's been covered, send me a bill.... :icon_razz

 

[stevevangst]

i tested the ground back there before i put the pum back in, and there was 0 resistance. unless something got messed up when i put the tank back up, it should be fine. i'll doublecheck it tomorrow. i'm at work now

here's a question:

i tested my fuel pump relay. the manual says that there should be continuity between two separate sets of terminals, and no continuity between another set.

two sets of terminals tested fine, one didnt have continuity where it was supposed to. could that cause a drop in my fuel pressure when the RPM rises?

-shaeff

well dude I tryed lol But hey one thing about pumps, they can be bad out of the box, I had two that was. both walbro's.....

 

[mkiiSupraMan18]

lol.....
I wasn't meaning to be an ass by suggesting that..... I guess I could have atleast looked at this page before saying anything....... my appologies.......

 

[shaeff]

anyone have a comment on the fuel pump relay? there's two terminals that are supposed to have continuity between each other that dont... could that cause my problem? i'm going to the junkyard tomorrow to pull one out of a junked supra, (the ONLY one i've ever seen in a junkyard...)

i'll see if that cures my problem, and if not, perhaps i'll try replacing the pump. after all, it IS only $80... (that wasnt sarcasm)

-shaeff

 

[sigmanin]

do u have ur old stuff???
if u do what i would do is start changing out parts with the old stuff u have
fp should stay almost constant i would think a fuel pressure regulator is there to keep the pressure up by blocking fuel from returning to ur tank and releasing fuel when the pressure get to high

the idea that ur pressure should get lower is kinda right in thought but that whole problem is the reason ppl get better fuel pumps i mean if ur on crazy boost and power lvls and ur pump is stock i could see pressure falling

 

[shaeff]

heh, i cant even reach boost, nor would i want to with dropping pressure like i have i do still have my old stuff, but i'm not about to put the stock FPR back on, and hack up my nicely soldered new injector clips to put my 440's back in.

well, i'll report back after i return from the junkyard tomorrow. maybe that relay is my problem. if not, i'll change out the fuel pump, and slowly work my way forward.

-shaeff

 

[stevevangst]

heh, i cant even reach boost, nor would i want to with dropping pressure like i have i do still have my old stuff, but i'm not about to put the stock FPR back on, and hack up my nicely soldered new injector clips to put my 440's back in.

well, i'll report back after i return from the junkyard tomorrow. maybe that relay is my problem. if not, i'll change out the fuel pump, and slowly work my way forward.

-shaeff

Fu$k.....going insane with these problems.... :aigo: lol hehe Dang supra's got us on lock now don't they :evil2: lol

 

[shaeff]

seriously. i just called the only junkyard around me that has an mkiii. it's a white '89 N/A. the body was nearly perfect, and it's what i've been taking parts from for over a year now. the moldings were awesome, and after my fuel pump relay, i was going to pull them off along with the side markers.

guess what? they sent it to the crusher last week. now i have no mkiii's in junkyards anywhere near me... now THAT sucks. my problem persists... steve, i feel your pain man.

-shaeff

 

[lagged]

do u have ur old stuff???
if u do what i would do is start changing out parts with the old stuff u have
fp should stay almost constant i would think a fuel pressure regulator is there to keep the pressure up by blocking fuel from returning to ur tank and releasing fuel when the pressure get to high

the idea that ur pressure should get lower is kinda right in thought but that whole problem is the reason ppl get better fuel pumps i mean if ur on crazy boost and power lvls and ur pump is stock i could see pressure falling

not quite...

as the manifold pressure (what the FPR is referencing) approches 0inhg from idle (which should be around 20inhg) the fuel pressure should increase, reaching your base FPR setting when mani press reaches 0.

 

[shaeff]

right on.

-shaeffisreallytiredofhiscarnotrunningright

 

[stevevangst]

right on.

-shaeffisreallytiredofhiscarnotrunningright

hehehe lol....that's funny bro, "shaeffisreallytiredofhiscarnotrunningright" lol god forreals you know how it is to have these dumb problems.....haha now I just laugh about it since I can't find the problem..... :nono: cause if I bithc$ about it then it drives me nuts.....you know what I mean...

 

[shaeff]

hell yeah. i know exactly what you mean!

on a side note... here's another question:

on my aeromotive AFPR, the vacuum nipple is NOT on the same side of the AFPR as the return side of the fuel rail. (read: the nipple is facing toward my drivers side fender) is this normal? the diagram i recently saw shows the nipple being on the same side as the return from the rail TO the FPR. can anyone comment on this? if the top of the FPR was put on backward would it cause my fuel pressure to decrease as the throttle is applied, rather than increase in pressure?

can anybody post a pic of their setup?

-shaeff

 

[IJ.]

Shaeff: It would have to be on the other side of the diaphragm to do that!

 

[stevevangst]

Shaeff: It would have to be on the other side of the diaphragm to do that!

Yes IJ is correct, as long a the diaphragm is on the correct side there is no different ether way the nipple is facing, all it is is just vac pulling the frame to open or close under boost to get more fuel. there is one way you can check if your fpr is good or not, go get a vac test pump and hook the vac lines up onto your fpr and pump too see if it holds good air, I mean ofcouse it's going to leak a little due to the design of the top scew that has no kind of seal build into it, but other then that your pressure you pump or suck out of it should not drop too fast, one other note, if your frame is rip inside your fpr you will get fuel into your vac line which will go into your intake mani and will cause your car to not rev past a certain rpm, are you awhere of that, I had a customer's car that came in awhile ago and his car was running like crap, fuel didn't hold a certain bit, so I opend it up and guess what? the frame was rip and it was leaking fuel into the vac line then into the intake and making the car burn extra fuel which it ofcouse couldn't at such low rpm, so you might have something that is kinda like what i have stated, check it out, it doesn't harm anything to open the fpr up, unless you don't know what your doing, then becareful, those suckers are really easy to rip, and it does sound like your fpr is not holding pressure, change it out with one of your buddys or something, if I was near you I would let you use mines well give that a shot...good luck man....

Steve

 

[shaeff]

hmmm. i'd be pissed if the brand new FPR's diaphram is ripped! but happy at the same time becaue it would solve my problem. i dont have any supra buddys close to me, unforutnately. it's just me. infact, the only person/ supra enthusiast i've talked to/met is "TONY!". i'll give that diaphram a check. thank you all for your input. we'll get to the bottom of this!

-shaeff

 

[shaeff]

ok, so i just got home from work, and pulled apart my AFPR, and the diaphram is in perfect condition. so now we've narrowed it down to what? the fuel pump is the only thing left that could cause a drop in fuel pressure.

when i gently blip the throttle, the fuel pressure bumps up about 2psi, but if i really rev the motor, it drops to 10psi. i've determined that the coughing and sputtering at 3krpm is due to lack of fuel. now i just need to be positive that it's my fuel pump! maybe i'll pick up another walbro and just throw it in...

-shaeff