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95 toyota tacoma 2.7 - high fuel pressure


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Laurian
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Sep 8, 2011, 8:22 PM

Post #1 of 10 (4136 views)
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95 toyota tacoma 2.7 - high fuel pressure Sign In

So one my pet projects is to try to breathe life into an old 95 tacoma. It stills starts at least. I recently did a fuel pressure test, and it was high: 48psi, when the book says it should be 31-37. It didn't matter if the vacuum was on or off the regulator.

Assuming i didn't miss a kink in the return line, then is a bad regulator the only thing that would do this? or can something else cause high fuel pressure? I applied my own vacuum to the regulator, and got it to drop 44psi, so it seems to work somewhat. And I'm not sure that where Toyota attaches the vacuum hose would really create a vacuum.

Also, how badly would you think that a tacoma with this high of a fuel pressure would run? I'm thinking this is not my primary problem, but i could be wrong.

Unfortunately I dont currently live where my taco is, but i try to get ideas on what to look at the next time i'm in town.


Discretesignals
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Sep 8, 2011, 8:37 PM

Post #2 of 10 (4130 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In


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Also, how badly would you think that a tacoma with this high of a fuel pressure would run?

It would probably run rich.

Appears that either the regulator is stuck closed or you have some sort of restriction in the return line. Some regulator also have a trash screen on the rail side. If the screen is plugged up, that will make fuel pressure high also. If the screen is plugged up with trash, your injectors probably are too.

With the engine running there should be manifold vacuum at the hose. The hose should attach to a manifold vacuum port.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 8, 2011, 8:41 PM)


Laurian
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Sep 8, 2011, 9:53 PM

Post #3 of 10 (4116 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In


In Reply To
With the engine running there should be manifold vacuum at the hose. The hose should attach to a manifold vacuum port.


All the OTHER vacuum hoses are at the throttle body, but the pressure regulator hose is off of some box attached to the air connecter just after the air filter. I've read where other taco owners have found no vacuum there, and were just as perplexed.

thanks for the info about the possible screen in the pressure regulator... something to look into.


Hammer Time
Ultimate Carjunky / Moderator
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Sep 8, 2011, 10:41 PM

Post #4 of 10 (4110 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In

Here's the spec i'm finding


Fuel pressure at idle
(with regulator disconnected) 265-304 kPa (38-44 psi) Fuel pressure at idle

(with regulator connected) 206-255 kPa (31-37 psi)
Are you really sure that your gauge is accurate?




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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Sep 8, 2011, 10:49 PM

Post #5 of 10 (4108 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In

According to a schematic I have, the fuel pressure regulator vacuum hose goes to a vacuum switching valve called the VSV for fuel pressure control(FPC). Another vacuum line goes from the VSV to the intake manifold.

When FPC VSV is turned on by the engine controller the manifold vacuum is blocked going to the fuel pressure regulator. This causes the fuel pressure regulator to increase the fuel rail pressure. When the VSV is turned off, manifold vacuum is allowed to go to the fuel pressure regulator. The VSV is normally off.

The only hose I see coming off the intake ducting is for the PCV system. The vacuum/vapor hoses on the throttle body are for the EGR vacuum modulator and the EVAP system.

That could be partially why you have high fuel rail pressure if you don't have vacuum at the regulator. Disconnect the FPC VSV electrical connector and see if you have vacuum at the fuel pressure regulator. If you still don't have vacuum, pull the hose of the FPC VSV that goes to the manifold and see if you have vacuum there. If you have vacuum to the VSV, but no vacuum coming out of the VSV with the connector unplugged, the VSV is faulty.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 8, 2011, 10:53 PM)


Laurian
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Sep 8, 2011, 11:13 PM

Post #6 of 10 (4101 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In


In Reply To
According to a schematic I have, the fuel pressure regulator vacuum hose goes to a vacuum switching valve called the VSV for fuel pressure control(FPC). Another vacuum line goes from the VSV to the intake manifold.
.


According to my book (Haynes) they only had the VSV on 93 and 94 V6. I have a 95 with 4 big squirrels. Tongue


Laurian
Novice

Sep 8, 2011, 11:23 PM

Post #7 of 10 (4100 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In


In Reply To
Here's the spec i'm finding


Fuel pressure at idle
(with regulator disconnected) 265-304 kPa (38-44 psi) Fuel pressure at idle

(with regulator connected) 206-255 kPa (31-37 psi)
Are you really sure that your gauge is accurate?


I don't know how to tell if a gauge is accurate or not. But why would you think there is something wrong with the gauge? There IS something wrong with the truck, so the fuel pressure could be involved.... is a reading of 48, when it should be 37, outlandish?


Discretesignals
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Sep 8, 2011, 11:41 PM

Post #8 of 10 (4097 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In

You sure it is a 95? What is the 10th digit in the VIN?

Here's the pic for a 95 3RZFE fuel pressure regulator and VSV.







Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Laurian
Novice

Sep 9, 2011, 12:12 AM

Post #9 of 10 (4093 views)
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You sure it is a 95? What is the 10th digit in the VIN?


well i don't have the VIN handy....
but i do have the exact same picture in my book, that says its for 4 cylinder models, EXCEPT it doesn't have a VSV, and the pressure regulator hose goes to a port on the silly looking box on the Intake Air Connector.

And thats the way it looks. So... i dunno why our books disagree.


Discretesignals
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Sep 9, 2011, 12:26 AM

Post #10 of 10 (4089 views)
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Re: 95 toyota tacoma 2.7 - high fuel pressure [In reply to] Sign In

Well it isn't a 95 then. It must be a 96 or newer because that is when they ran the hose to the air ducting resonator box and did away with the FPC VSV.

Fuel pressure on a 96 is 38-44 psi with engine off pump running. With engine idling fuel pressure should be 31-37 psi





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 9, 2011, 12:34 AM)




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