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3.4 with no Fuel Pressure Regulator vacuum

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Old 05-25-2011, 06:39 PM   #1
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3.4 with no Fuel Pressure Regulator vacuum

I have a 2000 4Runner Limited with a 3.4 L. It has been running poorly for the past few months. It is very sluggish on hills on the interstate. Anyway it broke down on me on the side of the interstate here recently. Apparently the fuel pump went out. It will actually crank and run now but it can only idle. It will not rev up.

I checked the fuel pressure and it said 45 psi at idle and with the vacuum removed from the fuel pressure regulator. I traced the vacuum line back to the resonator (from what i've been told). It is the big black box between the throttle body and the air filter box. But i have good vacuum on the upper intake. Anybody ever had this problem with no vacuum from the intake tube.
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Old 05-26-2011, 04:13 PM   #2
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There should not be any vacuum on the intake piping the Throttle body, you only have vacuum after the throttle body inside the intake manifold.

The FPR line goes to a small port near the TB IIRC, been a long time since i worked with an NA intake manifold, thats where it is on the supercharger though.

Not having that line hooked up will cause it to run rich under cruise/idle but it should still be drivable. My line came off at one point as well and i didn't even know it once the ECU had retuned itself for it till i was working on the supercharger and noticed that it had come off.

It did run better with it connected but it was not something that will jump out at you after the ECU retuned itself for it.
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Old 05-27-2011, 12:09 PM   #3
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Thanks for responding Texas Ace. Here is a picture of the vacuum line that connects to the FPR.



With the line connected and disconnected it has about 44 psi of pressure. When I take and pull 20 in of vacuum it drops the pressure down to about 32 psi so I know the FPR is working correctly.

I just don't understand why i'm not getting any vacuum at this port. It has about 20 in of vacuum on the upper intake manifold. It seems like it should pull vacuum here since the FPR is connected to it shouldn't it?
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Old 05-27-2011, 12:13 PM   #4
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There should not be any vacuum at that port, that is not where the FPR is supposed to be hooked up i don't think, it makes no sense. That hoes doesn't look factory either.

Try looking up a vacuum line diagram to see where it is supposed to be connected.

Also see if there are any un-used vacuum ports on the manifold/TB. If all else fails just rig up a T fitting into another vacuum port and T it into that.
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Old 05-27-2011, 12:51 PM   #5
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I'll check on it but i'm pretty certain none of these hoses have been messed with at all. I believe that is the factory location.

What would symptoms be if the mass air flow was dirty?
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Old 05-27-2011, 01:27 PM   #6
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I'll check on it but i'm pretty certain none of these hoses have been messed with at all. I believe that is the factory location.

What would symptoms be if the mass air flow was dirty?
That makes no sense for that to be the factory location, it is impossible for there to be any vacuum there unless your filter is REALLY clogged in which case the motor would not even run. Could be wrong though, just doesn't look like a factory hose, also the FPR hose is way smaller then that, no idea why there would be a big hose connected to the FPR.

Dirty MAF would cause your AFR's to be off, cleaning it is always a good idea, can of MAF cleaner is cheap. I do mine with every oil change.

Last edited by Texas_Ace; 05-27-2011 at 01:28 PM.
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Old 05-28-2011, 02:45 PM   #7
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that is the factory location. but texas ace is right, there should not be vacuum there, if that hose was unhooked, it would not make a bit of difference because the fpr is exposed to atmospheric pressure either way, the only reason its hooked to the intake tube is to supply the fpr with filtered air.

have you had anything done recently to help with this problem (i.e. timing belt)?
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Old 05-28-2011, 03:00 PM   #8
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I guess it is not meant to have the FPR adjust the fuel pressure then, rather odd for them to even put a port on the FPR for such a purpose if they are not going to use it.

I know my truck ran better with it connected but i am also supercharged.
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Old 05-29-2011, 09:22 PM   #9
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Alright guys I worked on it today. My buddy is ASE Master Certified so he brought his scan tool over to see what he could find. The Bank 1 Sensor 1 O2 sensor was holding a constant voltage. So we went to town to pick one up. Got it home only to realize we had the wrong one. I live in Alabama and somehow this is a California emission truck so it is a A/F sensor. Went and got the right one $180 dollars later. It fixed the stumbling problem but it still has the low power on acceleration. I did T the vacuum for the FPR into a manifold vacuum which brought it down at idle. But thanks for the post about that location of that vacuum on the resonator box cause that was driving me crazy. I knew I hadn't messed with it. So does that mean that this truck stays at constant fuel pressure of 44 psi? I'm thinking now that the catalytic converter could possibly be stopped up. Wouldn't the symptoms of that be poor acceleration? Thanks again for all the help guys. I'm hoping that after tomorrow I can get it running 100 % again before I change the timing belt.
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Old 05-29-2011, 09:57 PM   #10
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Originally Posted by Luther Grimace View Post
Alright guys I worked on it today. My buddy is ASE Master Certified so he brought his scan tool over to see what he could find. The Bank 1 Sensor 1 O2 sensor was holding a constant voltage. So we went to town to pick one up. Got it home only to realize we had the wrong one. I live in Alabama and somehow this is a California emission truck so it is a A/F sensor. Went and got the right one $180 dollars later. It fixed the stumbling problem but it still has the low power on acceleration. I did T the vacuum for the FPR into a manifold vacuum which brought it down at idle. But thanks for the post about that location of that vacuum on the resonator box cause that was driving me crazy. I knew I hadn't messed with it. So does that mean that this truck stays at constant fuel pressure of 44 psi? I'm thinking now that the catalytic converter could possibly be stopped up. Wouldn't the symptoms of that be poor acceleration? Thanks again for all the help guys. I'm hoping that after tomorrow I can get it running 100 % again before I change the timing belt.
unbolt the exhaust before the cat and see if its better.

Last edited by vital22re; 05-30-2011 at 08:13 PM.
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Old 05-30-2011, 05:40 AM   #11
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The symptoms that you described made me think that it was the cat before you even went into the other fault isolation. A clogged up cat will make the engine run worse and worse over time. The first thing you will notice is poor acceleration, then you won't be able to get it up to speed, then it wont run at all. The best way to find out is to open up the exhaust before the cat, not after it. It will be loud as hell, but if it is the cat, you will at least be able to rev it up.
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Old 05-30-2011, 08:00 AM   #12
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Yeah I was thinking the same thing Runner86. So will the downstream oxygen sensor not getting any flow mess up the idle? Also what are the options for a new cat or an upgrade. Will a high flow cat mess up the reading? It would be easier to get one of those and just weld it in
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Old 05-30-2011, 11:18 AM   #13
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Yeah I was thinking the same thing Runner86. So will the downstream oxygen sensor not getting any flow mess up the idle? Also what are the options for a new cat or an upgrade. Will a high flow cat mess up the reading? It would be easier to get one of those and just weld it in
A clogged cat will usually start out only effecting the upper RPM's and then works it's way down the RPM band.

On my truck i just gutted the cat and made up an O2 simulator from $10 in radio shack parts, been running this way foor a few years now, works great, more power and still passes inspection perfect (they just plug into the OBDII port for 96+ cars, long as you don't have a code you pass here).

If that is not what you want to do then a high flow cat will work fine unless you are in cali.
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Old 05-30-2011, 05:53 PM   #14
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Alright Texas Ace that sounds like a good idea. When you gutted the cat did you just rod it out? Also how did you do the radio shack trick for the O2 simulator? And you said that you have the vacuum hooked up to the FPR right? I still have it hooked up. You think it runs better with it hooked up? Maybe get better gas mileage?
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Old 05-30-2011, 06:13 PM   #15
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Alright Texas Ace that sounds like a good idea. When you gutted the cat did you just rod it out? Also how did you do the radio shack trick for the O2 simulator? And you said that you have the vacuum hooked up to the FPR right? I still have it hooked up. You think it runs better with it hooked up? Maybe get better gas mileage?
I gutted mine but just using a pipe and a sledge hammer and pounding it out. Took some work but i got it.

I did the trick outlined in this post: http://www.yotatech.com/50697664-post28.html

Using this schematic: http://www.vfaq.com/mods/O2bypass.html

Worked great, been 3 years and no issues.

I have the FPR hooked up to vacuum but i am also supercharged, i need to do it that way to allow for more fuel pressure under boost. Like i said before once the ECU adjusted the tune i didn't notice any difference one way or the other in cruise, only at WOT where i was running leaner with it not connected.

Just leave it like factory if you are NA i guess, still says it don't make much sense but guess it was setup to be like that.
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Old 05-30-2011, 07:23 PM   #16
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Yeah it definately doesn't make any sense to have a vacuum port on the FPR if it doesn't even have to adjust fuel pressure.

Would running that high flow cat with this california emissions engine make it run wrong? Would it mess up the reading on the second O2 sensor? The fact that I live in Alabama and we have no emissions laws makes me want to get this thing flowing better so I can actually pass again on the interstate.
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Old 05-30-2011, 08:23 PM   #17
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Yeah it definately doesn't make any sense to have a vacuum port on the FPR if it doesn't even have to adjust fuel pressure.

Would running that high flow cat with this california emissions engine make it run wrong? Would it mess up the reading on the second O2 sensor? The fact that I live in Alabama and we have no emissions laws makes me want to get this thing flowing better so I can actually pass again on the interstate.
If you don't have emissions you can remove both cats and get an O2 simulator for the second sensor, the one i posted above should still work but in the case that you have a wideband sensor for the second sensor there are still devices or DIY options for making it work without the cats in place and it will cost less then replacing the cat with something else.
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