GavinJuice

HAHAHHAHA **** YOU PROXY.......

So i've been having this demon of a fuel issue on my 85 SE. Finally hooked up a fuel pressure gauge to see whats going on. The problem i've been having is the car just completely stops accelerating sometimes; whether it be moving from a stop or not. But much more so when it's warm out. It also likes to die frequently at an idle once warm. Those being the symptonms here's what i've done.

First thing i've done it hook a DMM up to the fuel pump connection in the storage bin so i could see what the pump was doing. Whenever the car would stop accelerating and just bogggg, the voltage would spike up to ~(13-13.20). It seemed like an average voltage would be anywhere from (12.2-12.5) If i let it sit at an idle for any period of time, the voltage would usually creep to 12.8 and up, which means its about to stall. I thought maybe it was pushing too MUCH pressure when the voltages when up, BUT it is just the opposite as i figured out today.

What i did today was "T" a fuel pressure guage from the fuel line in the engine bay and through the window so i could monitor it while i drove. I noticed about 62-64psi at idle and usually while driving. NOW, the times i got the voltage to spike to the ~(13-13.20) range the fuel pressure would just drop down to ~20psi. And then sometimes like someone clicked the switch back on the voltage would zing back to average and the fuel pressure would bump back to normal. When the voltage started to creep up to 12.8-12.9 the pressure would also drop. I also noticed the voltage while driving would sometimes fluxuate by say .10volts back and forth and the fuel pressure would coencide with that.

So what i am thinking is possibly 2 things. and no it's not the fuel filter. 1) i have a faulty fuel pressure regulator BEFORE the fuel rail. The FSM shows a "Pressure Regulator Control Valve Solenoid" on 4B-55 2)reading the FSM on one of the ways to check fuel pressure, it says to disconnect the pressure regulator control valve. Judging by the picture it's either the orange or green solenoid under the dynamic chamber. Maybe that could be faulty? Not sure on how it works. That all i can think of, I am so close to figuring this out and im not gonna let this SOB beat me. Please all your SE Gurus i need some help!!!!!!!!!!!!!

QuagmireMan

are the injectors clean? Some times junk can build up inside the lines.... I am not familiar with the high pressure fuel systems in the FBs so don't take my word for it

Love the thread title.

GavinJuice

It is possible, but i don't think that alone would be giving me these symptoms. Longduck you need to chime in and pick your brain on this one. Think of what electrical devices control the fuel pump or send information to tell it what to do. Or if you think it's fuel related what could be fubaring the psi before my "T" in the engine bay?

gsl-se addict

iTrader: (3)

Gavin,

So the fuel pressure gauge is teed into the fuel supply line, correct? That fuel pressure is way off. You should be about 28 psi at idle and about 37 psi WOT. I imagine that the fuel pressure regulator on the rail is stuck closed. The fuel pressure that you are seeing corresponds to what the pump puts out into a dead head (no return). The pump itself (dead head) should put out 50-70 psi. It sounds like the fuel pump is also cutting out (increased voltage, drop in fuel pressure). It also may be that the pump is working so hard that the voltage that you normally see (12.2-12.5 volts) is so much less than system voltage.

You are probably flooding out with this high fuel pressure. At 62 psi, your injectors are delivering sqrt(62/28)=1.488 times more fuel than at 28 psi.

As for the fuel pressure solenoid, that is the orange one. What it does is makes the fuel pressure regulator reference atmospheric pressure instead of manifold pressure during hot starts and for about 1 minute afterwards. This increases fuel pressure from 29 psi to 37 psi at idle during this period. It is suppoose to help reduce vapor lock. Hope this helps.

Based on what you have said. I would say replace FPR and possibly the fuel pump as well. I have a spare FPR if you are looking for a cheap fix.

Kent

GavinJuice

But if i am flooding out, why would a spike in my voltage cause my fuel pressure to drop. See i initially thought i WAS flooding out because at an idle i was able to shut off the pump when the volts got high and it would immediately smooth out. But my guage is telling me otherwise, i'm loosing pressure.

GavinJuice

Ok so tell me this, the first time i hooked up my guage i tapped into the return line. I was getting nothing on the guage even when it was running, I was thinking well **** maybe the guage it bad. I pulled everything apart and checked the line and sure enough both sides were dry. Then it registered that i had the wrong line. So i pulled off the send line and *duh that had the fuel.

It hasn't even registered till now that If i have something plugged that isn't allowing the fuel to flow out the return line then that whats giving me the ******* 60psi reading. I need to check that out again just to be sure, i was turning the pump off and on so i didn't get blasted in the face with fuel.

Also if i track back the return line from under the dynamic chamber where does that hook up with, i'm assuming it connects with the FPR right? And if it is closed like you said would that be preventing the fuel from flowing out the return line?

gsl-se addict

iTrader: (3)

As for the pump voltage, the increase voltage could correspond to decreased if the pump was dying/shutting down. The voltage measured is quite a bit lower than battery voltage (14.3v or so). So either the wiring is bad/dirty connectors or the pump is drawing a large current to drop the voltage that far. The excessive current draw (the possible cause of the voltage drop) could be from the pump working so hard having no return. In addition, I wonder if you are getting fuel vapor in the lines since the fuel pump is providing heat into the fuel, but the fuel is not circulating back to the tank to keep cool. Maybe pump cavitation vapor lock is occuring as a result (more likely in warmer weather).

The lack of pressure on the return side and the high pressure on the feed side tells me that the FPR is the problem. What happens is the fuel enters the front side of the rail (where the PD is), it flows to the injectors and anything left over goes to the back of the rail (where the FPR is). The FPR regulates pressure by opening the return line. The FPR is just a diaphram and a spring. Once the fuel pressure increases to a high enough value, the diaphram pushes inward, there by opening the the return line. If the fuel pressure drops, the outlet closes letting the fuel pressure build back up. Likely your problem is that the FPR is stuck closed. This would explain the higher fuel pressure and no fuel being returned.

Kent

GavinJuice

Well it sounds like a have reason for my problem now. I wonder what my cars going to run like without running double the fuel pressure. Hahah