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.

Since there's a check valve on the fuel pump, if it's leaking down faster than specs, then your cold start injector may well be leaking into the throttle body. You can pull it off the TB without taking the fuel line off. Put a catch container under it, pull the electric cable off of it, and turn the fuel pump on with the test jumper. You'll easily be able to see if it leaks with pressure on it.

Don't forget though, it could be any one of the injectors.

Let us know what you find :)
Pat☺

Hydraulic pressure can be lost very quickly because fluid doesn't stay compressed well because of its expansion. However, you're saying the fuel rail is going empty; this indicates 2 things. First
the leak and second the air being introduced.

the loss of pressure when not running isn't really a problem since a properly working fuel pump can repressurize a static fluid very quickly. So, a small pressure leak in a closed system isn't that big a problem. The fact that when the gasoline moves toward gravity it creates a vacuum above it and stops the loss (think of your finger on a straw you pull out of a drink). The fact that the fuel rail is empty means that the system has a leak large enough for passive air to be pulled in which allows the fuel to drain. If an injector is not fully closing it will allow air in and the system to drain. A hole in your fuel line will also allow air in, and since your smart enough to post on yotatech I'll assume you're smart enough to check for fuel leaks outside the vehicle. That said, check the fuel line inside the tank after the pump. It may have a hole that sprays inside the tank so you never see.

Remember, a pressure loss is corrected by a properly working pump in around 3 seconds in my experience. So not a quick start but an "easy" one. Recovering from air in the system from a leak large enough to drain the fuel rail takes longer since the air has to be evacuated.

Thanks. I'm going to try it. As far as the injectors, I replaced them . The truck had been sitting awhile and a set of reman. ones wasn't too expensive so I got a new set from a company I've used in the past.

I guess I didn't post all that I have done and checked on this post? Or you missed it? But I did pull the fuel pump hanger and pressurized it to make sure it didn't have a leak. And yes I've checked every inch of the fuel lines to look for leaks while the truck was running so the lines where pressurized. All the injectors have been replaced with new tested ones and my old ones where sent off and have been tested for leaks. And they where good. Everything tells me there is a leak. I just can't find it.

I really don't see how Yotainmyblood could determine that the fuel rail is "full of air." Crack a banjo bolt, nothing comes out. That does not tell you there is any air in the fuel rail; it only tells you there is no pressure. (Which is exactly what you would expect after sitting overnight.) For any appreciable amount of air to be introduced, you'd need a very large hole near the highest point of the fuel system. (The fuel tank is never under negative pressure because of the vented fuel cap, so you're only talking less than ~0.5 psi from 12-18" of "head" of gasoline.) As soon as the fuel pump starts and raises the pressure to 50psi or so, that hole is going to be spraying a lot of fuel. If it's a fuel line leak, there will be a big puddle under the truck. If internal (any of the injectors), the engine will flood out (and maybe hydrolock), and would never run no matter how long it was cranked.

Yup.

When I've emptied the fuel rail (filling it with air) for maintenance (replacing the head gasket), I "bled" the air out by running the fuel pump with the FP connector. It took less than 3 seconds for all the air to get pushed out (you can hear the air going through the FPR). Pressurizing a zero-pressure fuel rail takes much less time.

I really doubt Yotainmyblood's long-start problem has anything to do with fuel rail leak-down. I think he'd have more luck looking elsewhere.

Given all that you've replaced so far, my guess would be the CSI allowing air in when the fuel pump is inactive. Yes, it's a guess, but I think an educated guess. I would still test it to be sure. If it's allowing air to bleed in, it will bleed fuel out when it's pressurized. Can't hurt to certain. That could also let you know that you might need to check the entire fuel system, back to front, for a small little leak when pressurized, if the CSI checks good.
Don't forget, even a remanned injector could have the leakage problem, too. Again, something to take a look at if the CSI checks good.
Having said all that, I still suspect the CSI. Just me, though. A leaking CSI would cause a rich running condition, so you might be able to tell from that, but I'd pull it off to look at it, as I specified. It might be such a small leak that it doesn't affect the way it runs very much.

Just me, though.
Good fortune to you!
Pat☺

I was saying anything about air in my fuel rail. I was saying there was any freaking gas in it. And there should be , even after sitting a week. Please read the complete post befor. committing on
, it would save people from having to repeat what they have already said and done. I know what my long first start problem is. When there is no fuel in the rail until the fuel pump comes on and puts fuel in it, it will take UT a while to start. And as I have stated before, I can put the jumper in and turn the key and let the fuel pump run for about 10 seconds and then it will start right up.

Thanks. I pulled the CSI and checked it to see if it was spraying fuel, but didn't leave it out long when I was checking to see if it worked. But I'm fixing to got out and pull it and put a jumper in and see if it leaks.

Are you telling me that there should be no fuel pressure in the fuel rail after sitting over night? To be honest, I am not for sure what the service manual says but, I have two more of these 3.0 motors and both of them can sit for a week without being started and I can crack that same banjo bolt on them and there is enough pressure that fuel will spray out. I not saying a certain amount of pressure I'm just saying there's enough to make it spray out. And on this truck , I can crack that same bolt after it sits over night and no fuel comes out. That's why I'm saying there is no fuel pressure in the rail. Now if I start it up and shut it down , I can come back in about 5 hours and crack the bolt and fuel will spray out. I realize it looses pressure after a little bit, but it shouldn't lose all of it. And if it's supposed to , then it's different than the other two I got in my yard and different than any of them I have worked on.

I just pulled the CSI and put in the jumper and it doesn't leak out any fuel. At least after ten minutes whit the pump running. I was hoping that was going to be the problem but it don't seem like it is. I guess I'll end up shortening the metal line on the pump hanger and splicing in a one way check valve between it and the pump. Since most of the line is metal except for the 6" of line on the top of the tank and the foot of line where it comes up from the frame to the motor. Those lines have the fittings but there isn't a check valve that has the 14mm ends where it will screw right in. So I'll have to get one that just clamps on to rubber lines. It just bugs me that there is something wrong and I can't find it. Unless every fuel pump I got has a bad check valve, and I don't think that's it cause I pulled the one off my other truck and it don't have this problem. There are 6 injectors and it just takes one bad one, but I got new ones and just to be sure, I sent off the ones I pulled and they said that they didn't leak or stick. So unless they lied and I got a bad one in my bunch, then that's not it. And if it is.... and not knowing...i mean, where do you stop? I'm saying here. I've spent all I'm going to and I know how to fix the problem, but it just bugs me.

CSI is not leaking. And injectors are new and old ones have been tested. So unless I got a bad new one and they lied about testing my old ones, then that's not it. Plus it's been going on a while and as much fuel that I've put through this thing my oil level should move or At least I should smell fuel in the oil, but I don't.

Have you checked your EVAP can?

I pulled the small line that comes from the back of the motor on that little bimetal valve, and it was dry, but I don't see how that would effect pressure in my sending line since its not between the fuel rail and the fuel pump? I know I would effect pressure in the tank but that shouldn't cause my problem. There's only 3 things that can be wrong with the problem I have. At least from what I know... Leaking check valve......leaking injector..... Leaking line.. Even a very slow leak. I just got to find which one. I'm going to pull the fuel rail and leave the injectors on and put the jumper in and pressurize it and hope the injectors don't fly off and let it set to see if one is leaking. They are new but that's where the leak has to be. Unless the line is leaking somehow that I can't see and it's not letting fuel out when I got it running? But I don't see that happening. One person suggested trash in the fuel causing check valve to stay open? I've checked the fuel and it was clean, plus it should blow out a piece of trash out of that little plunger when it comes on .. I could see that happening maybe once in awhile, but not everytime I shut it down. Frustrating!!

No gas OR air in the fuel rail? Well, then what is in it? Hard Vacuum? We don't expect perfection in posts here, but you shouldn't get worked up when we just can't understand what you're asking.

Sigh ... I'm not suggesting that there is supposed to be no fuel pressure after over-night. All I'm saying is that is within spec. The actual spec is that it "shouldn't" drop more than 23psi (from 44 to 21psi) in 5 minutes. If it's okay to drop that far in 5 minutes, I would expect it to drop the remaining 21 psi in no more than another 8 hours. If you have one or two Toyota trucks that held a pound or two of pressure over-night, that's great. But Toyota doesn't expect that. Toyota expects that your truck, just like mine, will start right up with no pressure in the rail.

Gasoline, like water, is essentially incompressible. To remove all 44psi from the closed fuel system would only require a few drops of fuel to leak back through the fuel pump check valve, or from one of your 7 injectors. I'm not sure you could even see fuel leaking through an injector at 3 drops per hour. So looking at your injectors (with what you know now) is not likely to be useful. Replace the fuel pump again? Remember that Denso is concerned about meeting whatever spec the manufacturer (Toyota) requires, which is only "stay above 21psi for 5 minutes." I don't doubt Denso tries to get their check valves to work "perfectly," but I also don't doubt they go ahead and ship with a leak that will drain all pressure in 8 hours. So your brand-new pump could be, for all you know, the source of your leak down. But you don't care; that's not the cause of your long-crank.

With what you've told us, I can't rule out the possibility that you have a fuel restriction, that is keeping your fuel pump from bringing up the rail pressure quickly enough. Or that the STArt circuit in the COR is not working. A fuel pressure gauge would answer those questions.

Last, do you think you might be acting a little too "prickly" when we're all trying our best to help you?

It just frustrating when someone reads part of a post then answers. Cause if they would read the whole thing they would see that what they are suggesting.. I have already done or ruled out. And when I have already bought 2 denso fuel pumps and tried a fuel pump off another truck that don't have this problem , I'm not about to buy another one. Cause.. Where do you stop throwing money? Even if everything tells you that's the problem. But 2 in a row? And a used one that I know is working. Like I said I wasn't talking about a particular amount of fuel pressure in the rail. I just know that there isn't enough in there to come out of where I remove the banjo bolt. And I know for dam sure there should be. Now if you want to be specific about the amount of pressure in it, then who gives a flying ... When I comes to this particular problem. Now if it was running bad or a different problem then yeah that would be something I should know. But it don't take a freaking genius to know that if there is no gas in the fuel rail then it won't start. Until the pump puts gas in it. This is what I hate about discussing something with someone that either don't read all of a post or just reads ˟˟˟˟ out of a derive manual or doesn't have any f.... Common sense. Not saying you are any of those. Just hate wasting time on stuff I know and having to explain it to someone. I know I have to look up specific numbers on alot of things like oil bearing clearances, but if someone has to look at the service manual to see how something works or ask Google how something works, then I don't need any advice from them. And just for the sake of argument, I'm not saying that's you. I ask questions on here to hopefully get someone to jog my memory or have one of these guys that have been working on these things since they were built, tell me a tip or shortcut. Not to hear someone quote ˟˟˟˟ from a service manual or whine about the way something was written and want to spend more time on that then fixing the problem. I'm new to posting stuff on these sites and I'm beginning to see why alot of people stop asking for advice, and maybe I should also. And this isn't directed towards you but I'm just saying.

A bad evap canister can cause a long start because it can throw your air to fuel ratio off.
while you have your fuel rail off, why don't you pull the pump , drain the system, and pump dyed gasoline in to help you. I understand that not having a banjo bolt leak indicates NO PRESSURE, but it does not indicate an empty rail.

while you have the throttle body easily accessible why don't you check that your throttle position sensor is functioning properly, properly adjusted, and not loose.

I understand why you feel like no one read your posts before posting a reply, but please understand that several of us have experience dealing with people who say they have done something and yet the method they used wasn't good enough. Example, you said you check the fuel lines. As the person who spent 7 years training mechanics end engineers how to care for the robots that build cars in Georgia, I understand that you THINK that was a good enough way to tell us that you checked ALL of the associated fuel lines and did so in a way that would catch any potential leaks, but I don't know you FROM ADAM and I'm 99.9% sure you didn't x-ray all of the lines or remove then fill them with 500⁰ steam then cap them then place them in a vacuum chamber and watch it under a FLIR camera. For all I know you looked at it with the vehicle off and the system depressurized. And your looking for a leaking fluid that evaporates.

AGAIN, I don't know you or your ability to properly check anything, so take what is said to you with a grain of salt because I've trained (alphabet soup) certified mechanics, and degreed engineers, all with years of experience and seen them make rookie mistakes. Heck, this website is full of examples of experienced people asking questions and getting told that a rookie mistake that they overlooked solved the problem.

YOU may be God's Gift to the wrench, but a knowledgeable person will accept ALL advice in GOOD grace, throw out what they don't need, and rephrase to get the information desired. If the same thing keeps getting said to you by different people with experience, THERE IS A REASON. Maybe it's how you worded something, or maybe it's something you didn't actually fully understand, but there is a reason.

Heck, take what I say with a grain of salt because before this year, I'd no meaningful experience in anything older than 2000.

I pray you have success, but you appear to be fixated on only one avenue of possible repair.

Well said sir. And the way I checked my lines was nothing to the sort of how you explained. But as an average mech. My thought was to pressurize them by having the truck running and then go over every inch and look for fuel. I'm definitely not gods gift to a wrench, ( maybe to a wrench) but I do have quite a bit of experience and common sense. Long story short... I found my leak and it was one of my new injectors .
Oh , and if that's what it takes to truly check a fuel line then to be honest if I was to pull of the fuel lines I would have just bent new ones and replaced them. I've done that a couple times. And it's not a bad job. I do have special service tools but not to that extent.So you were absolutely right.

:cheers:
CONGRATULATIONS!

So I can add the information to my tool box... which injector was it, how bad was the leak, did the oil smell of gasoline at all, any other potentially useful tidbits?

Glad you found the issue. It's been an interesting process.
thank you for posting the outcome.

It was drivers side, 2nd one back or middle one. Couldn't hear anything because of the fuel going through the FPR . plus mine didn't leak bad enough to make a leaking sound. I had to pull or loosen the rail enough to put a small cap under the injector and then hooked up the jumper and let the system pressurize, then unhooked the jumper and let it sit over night. I wrapped tape around each injector and rail so that it hopefully wouldn't blow off. I used big plastic bottle caps and put one under each injector cause I knew that it was going to have to sit overnight but did them all at once instead of doing one at a time and taking 6 nights. But came back next morning and found one cap full of gas. Didn't ever smell gas in the oil even though it probably leaked down 20 times. Couldn't tell anything by the spark plugs because I had just replaced them and due to blown head gaskets I had cleaned the tops of the piston when I replaced the head gaskets, so looking at the tops of my piston didn't do me any good. I replaced the bad new injector with one of my old ones and ran the truck. Went out this morning and first thing I did was loosened the same banjo bolt and fuel started to leak out, so I tightened it up and turned the key and after the normal 2 seconds it fired up. So I'm calling it fixed.