instantly losing total fuel pressure in rail
 

i have had long cranking issues at cold start for a couple months, and it progressively got worse till now, as i turn the key off, within 3 seconds i lose total fuel pressure in the fuel rail... it takes 10 seconds of cranking to start now every time its turned off for more than 5 seconds. its been in the shop for a while and they are stumped.

it isnt the injectors, no fuel in the cylinders, and the pressure regulator has been replaced twice since it is the apparently obvious culprit, but if i pinch off the return line into the tank, the pressure remains within factory range and the truck starts perfect after 1 minute or 1 hour or 1 day... WTF? tested vacuums, injectors... We are going to try a third NEW regulator in the unlikely chance i got back to back defective/incorrect regulators already...

any other ideas if this fuel pressure regulator doesnt turn out to be 3rd time lucky??? Thanks a lot for your ideas.

fuel pump?
there's a check valve in the pump, IIRC, that keeps pressure from leaking back through the pump.

was going to edit, but decided not... may not be the pump since you say you can pinch the fuel return line and hold pressure.... :think:
but if there's a lot of crud in the tank and the filter isn't catching it, it could ruin the pressure regulator(s) in fairly short order.

Its not likely the regulator.

Sounds like the fuel pump may be weak, since plugging the return line is forcing pressure to stay in the injector rail. That, or it may be the fuel dampner.

Is it possible that the fuel pump is shutting on and off, not giving you enough pressure unless the return line is clamped shut?

Isnt the return line completely open to just dump unused fuel in to the tank. I put a Corvette Tuned Port Injection system into my Jeep and there was nothing on the return line. It just was open to the tank. Toyota truck different?

Yes, the return line should just flow freely into to the tank. The regulator just controls how much fuel "leaks" back.

Since blocking the return line keeps the pressure up, it isn't being lost back through the pump. I know it's been replaced multiple times, but it really sounds like the regulator to me. :think:

i have a 1991 3vze and my fuel pump will not quit running. when i do start it it instantly revs very high between 2500 and 3000 rpm. im new to toyotas but does any one have any ideas for me. iver replaced the regulator and still no change. the pump seems to be fairly new also along with a new filter and the tank had little to no rust in it..
post ideas through this or you can call or txt at 18128309467 thanks

You are probably better off making a new thread as your problem is different, you may have a bad relay or a short to power.

Ditto on the new thread ....

But you're barking up the wrong tree. The fuel pump is SUPPOSED to run all the time; it pressurizes the fuel rail, and any flow in excess of what the injectors use goes back through the regulator to the fuel tank.

It sounds like your idle is set too high (or the throttle is stuck).

I thought he was trying to say it wont turn off even with the ignition off and key out, if that is not the case then scope is correct.

okay thanks alot guys really appricate it

Fuel pressure itself won't make the idle race up. That takes air too, to make that happen. Start a new thread for your issue, and explain EVERYTHING that you do, what goes on.

Fuel pressure problem
 

Hey guys , I got a fuel pressure problem also. It's losing fuel pressure at the rail overnight causing long first start. I replaced the fuel pump from another truck( that I know worked, twice) cause I thought bad check valve. I then thought sticking injector, so I replaced all of them. No dice. Then I replaced the FPR off of my 91 3.0 that holds fuel pressure for a month after shutting off. But that didn't work. I have checked every inch of the fuel line and no leaks. I finally went ahead and spent 125 bucks on a brand new denso fuel pump and( that was a waste of money) cause that didn't help. I pulled the fuel pump bracket and checked for a crack in the steel line that the pump connects to thinking that I may be leaking where I can't see it, but there is no leak there. I tried to pinch off the return line but it still drained back down the sending line into the tank. I've owed and still own several of these trucks and 4runners and never ran into something I couldn't figure out after a while, but this one has got me pulling my hair out. It's a 95 with the 3.0 that I'm going to sale but I've got to get this figured out? I guess there's a ghost in this truck just messing with me? I'm to the point of putting an aftermarket one way check valve on it somewhere if I can't get this fixed. Has anyone ran into this at this level? And don't say have I put a fuel pressure tester on it to see if it's losing fuel pressure.....cause if you crack the banjo bolt on the rail and fuel doesn't come out...then there's no pressure. Duh. Everything tells me check valve in the fuel pump, but I've put on 3 off of trucks that I don't have this problem on and also brought a brand new one. .So it's not the fuel pump or regulator. Other than a ghost, what could it be?

Just put a inline check valve on the sending line and call it good :) Gas cap supposed to hold pressure? Put fuel pump in bowl of fuel while connected to truck and see if it leaks out inside the tank plumbing? Thats a good one for sure. At least youre home and not on the side of the road.

shem

Hmm. The "parts cannon" didn't work for you? Don't look so surprised.

Well, let's see what Toyota has to say about your issue:
"Stop the engine. Check that the fuel pressure remains above 147 kPa (1.5 kgf/cm2, 21 psi) for 5 minutes after the engine is turned off."
http://web.archive.org/web/201003261...87fuelpump.pdf
So your fuel pump is (and was) fine.
(If Toyota can't convince you, my fuel pressure drops below 21psi in just over 3 minutes, and it still starts on the first crank.)

So replacing the fuel pump (twice), injectors, and fuel pressure regulator were all a waste of money. (and your suggested check valve doubly so.)

So what is causing your "long first start"? That can be due to a zillion things, from ignition timing to vacuum leaks and beyond, but I would check for an open in the STArt side of the COR. If the STArt signal isn't closing the COR to start the fuel pump, you'll have to wait for enough air flow to close the FC switch in the VAF. You can disconnect the starter solenoid and see if you can hear the fuel pump with the key to start. Or use a multimeter and look directly. https://www.yotatech.com/forums/f116...-quits-312747/

If you have a fuel line restriction (causing the fuel pressure to come up more slowly than it should), you can determine that easily with ... a fuel pressure gauge. This $55 one comes with the adapter you need to plumb it in at the FPR. I'm sure you don't want to spend the money, but compare that to what you've spent already.

Last but not least, "cracking" a banjo fitting is not only an incredible fire risk, but you must replace the two crush washers (one-time use). I've only found them (reliably) at the dealer, but even there they're cheaper than dirt.

Good luck!

I know what's causing my long first start. There us no fuel in the fuel rail first thing in the morning cause it's draining back down in the tank. Maybe you didn't read it all ? I did put a jumper in and yes it runs when I turn on the key. I don't need a fuel pressure gauge to tell me there is no fuel in the rail, when I can loosen the banjo bolt and see that there is no fuel in the rail.Common sense. Trust me when I say that whatever you read from the service manual, I already know and have read several times and that I was hoping to hear from someone that has many years of experience of working on these or has ran into this same issue. I didn't throw parts at the truck , other than another fuel pump cause I brought the truck a few weeks ago and it had blow head gaskets and many other things wrong with it that needed to be replaced cause it had been sitting for a long time.

Oh, well, excuse me. Your post sounded like you were concerned that you were losing fuel pressure at the rail overnight. Which (as you know) Toyota says is normal.

Yeah I'm to that point of putting on a inline check valve. But there is no easy spot to do so, as in I'll have to find one with the right size fittings to screw in in between the filter and line or make a new segment of line to put it in. Either way there isn't any spot of rubber line where I can cut and just put on in. As far as it leaking in the plumbing inside the tank? I pulled the fuel pump bracket and put air pressure on it and couldn't find any leaks on the metal lines.

I guess I should have said that I am losing all the fuel in the fuel rail after it sits over night. My bad.

Does anyone know if a bad cold start injector could cause it to lose pressure and the fuel leak back down the sending line? I guess just like a bad injector would do? That's about the only thing I can think of that I haven't messed with. And it's hooked directly to the fuel rail.