Where/How to install Fuel Pressure Gauge on ST185?

I am troubleshooting a fueling issue and bought a gauge to install to verify proper function of the regulator and pump, but there doesn't look to be any obvious place to install the gauge downstream of the regulator since the regulator mounts directly to the fuel rail and the only things coming off the fuel rail are the return line and what looks like a sleeved hard line for the cold start injector. Is the return line (shown top) pressurized so I can tap into that maybe? Or do I need to find some way to tap into the hardline to the cold start injector?

I replaced the banjo bolt on the fuel filter and added a gauge. The banjo bolt is the same on a Honda.

Russell 640700 Fuel Pressure Take Off Banjo Belt https://www.amazon.com/dp/B000CPJI8I/re ... UTF8&psc=1



The pic on Amazon doesn’t really show much. There is a 1/8” npt port on the top of the bolt.

You need to check fuel pressure "upstream" of the fuel pressure regulator, not "downstream". There is no pressure on the fuel return side after the fuel pressure regulator going back to the tank. What RedCelicaTRD said is likely the best way to check the fuel pressure, as there are no test ports in the fuel rail for test gauges on these engines.

Fuel filter is fine. You can also use the fuel rail. The "head" of the 185 rail is near the oil filler cap. Fuel flows towards the pvc outlet side of the valvecover, then hits the regulator, then returns to the tank.
You can buy an adapter from ko racing (and other vendors I'm sure) to tap the fuel line at the head for fuel pressure. Basically.... Just go with whichever works better with your setup.

Edit: here's the item I'm talking about http://www.koracing.net/viewproduct.php ... oduct=1087

Well... After looking at the link I found and what RedCelicaTRD posted... They appear to be the same thing. So in order to try to be at least somewhat helpful, attached is your photo but with the fuel feed line in red. 93celicaconv is correct, you need to get your pressure signal before the fpr. Either the banjo bolt at the head of the fuel rail or the banjo bolt at the fuel filter are fine locations to use and replace with the adapter.

grip-addict":3fgatwqj said:

Well... After looking at the link I found and what RedCelicaTRD posted... They appear to be the same thing. So in order to try to be at least somewhat helpful, attached is your photo but with the fuel feed line in red. 93celicaconv is correct, you need to get your pressure signal before the fpr. Either the banjo bolt at the head of the fuel rail or the banjo bolt at the fuel filter are fine locations to use and replace with the adapter.

Click to expand...

Ok but if I get it upstream of the FPR then how do I check function of the FPR?

The red is the return line not the feed line. The feed line runs from the right side of the picture to the FPR.

EDIT: or am I completely misunderstanding the function of the FPR here?

The function of the fuel pressure regulator is to maintain a target pressure level in the fuel rail. That is why the pressure regulator is downstream of the fuel rail. There is almost zero pressure in the fuel line immediately after the pressure regulator. So that is why you put a pressure test gauge upstream of the fuel regulator. If your pressure is below target, the source of the problem isn't known (between the fuel pump and the pressure regulator). Either of the two could be faulty. But then you check if you have fuel being returned to the fuel tank or not. If the pressure is lower than target, but fuel is being returned to the tank, your fuel pressure regulator is likely faulty. If no fuel is being returned to the tank, your fuel pump is likely faulty. That is basically a high-level summary of the fuel pressure checking process.

Although, now that I think about it, I'm not sure if the fuel pressure regulator ever closes off 100% or not - it may have a fail-safe from completely blocking flow by having an small orifice in it that the fuel can get around. I'm just thinking it might close 100%. Have others ever checked the fuel pressure regulator to see if it does have the ability to completely block fuel flow to create the back pressure? Or anyone confirm that is certainly doesn't block off 100% of the fuel flow?

^ Spot on.
I don't think the FPR can come anywhere close to completely closing off flow, though I've never checked.
You can check the fuel pump flow by running the fuel line into a pail and running it for a certain amount of time then measuring the amount in the pail. I don't remember the specs.

EvilStig":22zh3rjq said:

grip-addict":22zh3rjq said:

Well... After looking at the link I found and what RedCelicaTRD posted... They appear to be the same thing. So in order to try to be at least somewhat helpful, attached is your photo but with the fuel feed line in red. 93celicaconv is correct, you need to get your pressure signal before the fpr. Either the banjo bolt at the head of the fuel rail or the banjo bolt at the fuel filter are fine locations to use and replace with the adapter.

Click to expand...

Ok but if I get it upstream of the FPR then how do I check function of the FPR?

The red is the return line not the feed line. The feed line runs from the right side of the picture to the FPR.

EDIT: or am I completely misunderstanding the function of the FPR here?

Click to expand...

FPR creates pressure upstream of itself. So you check function (pressure) upstream.

Yes, red is actually the return line. It's before the FPR but after the injectors. So it is pressurized.


The easiest way to check pressure is put one of those fittings at the fuel filter as said. You will need something to thread into the linked fitting for your fuel pressure hose. Does that make sense?

Also, if it's too confusing you can ignore this part. Personally I like all the info so I can make my own decision, so I try to give all the available info. But this stuff isn't necessary, you'll be fine doing what others have suggested.
There are actually 3 places you can check fuel pressure. The banjo bolt at the filter, the banjo bolt at the other end of the fuel rail (I think this has been mentioned too, and I THINK it's the same thread? But a shorter bolt? You'll have to confirm size. The third place is the cold start injector (CSI) port. I'm pretty sure you can just remove this hose and permanently install a banjo fitting here. This injector only runs while the starter is working and the engine should still start without it. Though with you being in Canada and colder than here you may need it.
The thread for the CSI port is smaller than the other 2 and I don't know if you'll even be able to find a fitting for it.

As far as the banjo fitting you need, you can use the linked one. There are other options (at least there used to be?). That one has a female port, so you'll need some type of male fitting to go into it.
There are (were) fittings with male extensions you can also use.
Whatever fitting you get has to have the correct metric thread to attach to the factory fuel filter/rail. The other side of the fitting has to match whatever you're attaching to it. In this case your fuel pressure gauge hose/connection. Which will probably be standard thread (at least here in the US, not sure what's available up in Canada).
You can set this up to be a permanent test port if you want to. You'll just need a way to seal your opening. Either a plug for a female port or a cap for a male. Something that will hold the pressure.
There's also the possibility of a self sealing fitting (think your tire valve stem, but for fuel) if you can find something that will match thread wise.

I'm currently on the other side of the planet from my gen 2 engine so I can't double check, but- the red line I drew should be going to right before Injector#1. The return line doesn't start until the fpr itself, since the fpr directly screinto the rail and then has the single fuel hose outlet that heads back to the tank.

By the by, both my gen 2 and 3 fpr's failed on me and the fuel pressure never rose. It's supposed to be 1:1 fuel pressure to boost pressure. When looking at the data, I'd only see fuel pressure drop when the injectors went under more load, never stay steady or increase. How this helps if you're trying to validate your for is functioning correctly.

That line is how fuel gets from the other end of the rail ( #1) back to the FPR and to the tank.

Fuel comes in through the rail, out that line, to the regulating portion of the FPR and back to the tank.

* I guess it may not strictly be a return line, it may even out the pressure/flow to some extent. But that's how the fuel from the other end gets back to the FPR. *

Fuel goes inside the rail before hitting the fpr. As far as the fpr is concerned, the first time it sees fuel is from the rail, not a hose. It's job is to uncompress its spring as boost increases, thus increasing the pressure downstream of itself (pump, lines to and including fuel filter, fuel rail, injectors 1-4 and csi.) It's the last thing in the line before the lines to the fuel pump. So tapping any source prior to it for fuel pressure is fine.

The idea is that the pump over-supplies pressure, something 60+ and the fpr regulates that down. Something around 32psi fuel pressure at full engine vacuum, 42-44 psi fuel pressure at 0 boost, then 14.7 fuel pressure at 14.7 boost.
This is what you should see in your logs, and if you don't, your fpr is bad. Since your manifold will have 1 psi of pressure at 1psi of boost, your fuel injectors will also need 1 psi extra to overcome that extra pressure in the manifold and squirt fuel at the same rate.
+7 psi fuel for 7 psi of boost, and 14.7:14.7.. It just increases linearly.
Hope this helps and we're not arguing for no reason

grip-addict":1fzn1lfx said:

Something around 32psi fuel pressure at full engine vacuum, 42-44 psi fuel pressure at 0 boost, then 14.7 fuel pressure at 14.7 boost.

Click to expand...

Not intending to pick on you, because I think what you were saying in general is spot-on - just this part is confusing.

A turbocharged engine just parked an idling will have high manifold vacuum (or low absolute pressure), so the fuel pressure in the rail can be at it's lowest (the vacuum in the manifold will assist pulling fuel out of the injector into the manifold).

When the turbocharged engine is on the highway heading up a hill under moderate load, and say the intake manifold pressure is at zero (or 14.7 psia - absolute pressure), the manifold is at atmospheric pressure (just as you are inside the car), and the manifold no longer has any effect to pull fuel from the injectors into itself. The fuel rail pressure needs to be higher in this scenario than in the paragraph above since the manifold is no longer assisting pulling fuel from the injector.

When the turbocharged engine is at highway speed and the accelerator pedal is floored, the engine is under full load, the turbo is now pressurizing the intake manifold up to the level of your turbo pressure setup (let's just say 10 psig in this case, which is the same as 24.7 psia - absolute pressure). Now the manifold is working against the fuel injector, so the fuel injector and rail pressure needs to be even higher than in the previous paragraph, ideally 10 psi higher.

Ideally, the fuel rail pressure and fuel pressure at the injector needs to increase as the intake manifold vacuum decreases (or, stated a different way, as the intake manifold pressure in absolute pressure terms increases).

I'm thinking the fuel pressure regulator is "analog" in how it reacts, since the regulator is controlled by the intake manifold pressure. I think on these 3S-GTE engines, there are resistors in the fuel pump electrical supply that are involved with slowing down the fuel pump when high fuel pressure is not required, but speeds up the fuel pump when higher fuel pressures are needed (so the pump isn't working so hard when high fuel pressures are not required, which is a vast majority of the time).

The amount of fuel being delivered, ideally, in a working fuel pressure control system, is strictly dependent upon time duration that the injector is energized.

At least this is how I understand/interpret how these fuel systems function on these cars. Please correct me on any errors I've made, so I can better understand them from your perspectives.

:bThank you for correcting me and catching my mistake. 14.7 psi of boost should equal base fuel in pressure +14.7 psi of fuel.
On my setup , i run 44 psi base fuel pressure. At 1 bar of boost, I get 58 psi fuel pressure. This is expected behavior for a reusing rate fuel delivery system (which 3sgte's have).

So to correctly recap,
At full vacuum, 30-32 something-ish psi fuel pressure
At 0 bar boost, 42-44ish fuel pressure (please review bgb for exactly numbers)
At 14.7 psi boost, 58ish psi fuel pressure.
1:1 is the law of the land.

The amount of fuel delivered is fuel pressure + injector orifice width * time.
My 1000cc injectors don't need to stay open as long as factory 440's to deliver the same amount of fuel.

Edit - not sure what the op has but most cars with an EMS just run the fuel pump at full voltage all the time and disable the under-volting circuitry that Toyota installed in the factory. otherwise we'd have to tune two fuel maps and add an extra axis, which.... No. To much extra effort for no gain.

grip-addict":3t9nynxy said:

:Edit - not sure what the op has but most cars with an EMS just run the fuel pump at full voltage all the time and disable the under-volting circuitry that Toyota installed in the factory. otherwise we'd have to tune two fuel maps and add an extra axis, which.... No. To much extra effort for no gain.

Click to expand...

Wasn't intending to find mistakes - I often am the one in error - just wasn't sure what was right.

Regarding cars with an EMS, does the EMS replace the factory fuel pressure regulator? If not, since the fuel pump doesn't control pressure (the fuel pressure regulator does), the factory circuitry that changes fuel pump running speed doesn't come into play, right? The Toyota circuitry is based on manifold pressure - the higher the absolute pressure, the greater the fuel demand - and a low speed pump can't supply sufficient fuel, so it switches to high speed. As long as the fuel pump supplies more fuel than the injectors are controlled to dispense, the fuel pressure regulator is the only element controlling fuel rail pressure. This is where I lack understanding with aftermarket setups.

Good question.
With an EMS, we still NEED a mechanical fpr. Whether it's factory or aftermarket is agnostic to the EMS, as long as the fpr is working correctly.

If I understand correctly, what you are asking is "'does the fuel pump wiring need to be modified when running an EMS since it's on the fpr to set pressure" and the answer is yes. The voltage drop between low and high flow will affect a fueling table in an EMS and make it nigh-impossible to get a good tune. We need consistent operation from the fueling components to input data with confidence. Modding fueling table cells that the tuner thinks are "high flow" that instead apply to "low flow" could be catastrophic. Most fuel pumps are designed to only run at one voltage anyways, so it's pretty uncommon to tribe a dual voltage fueling system. It's even less of an issue on our cars since the pump's wiring is so small. Upgrading to anything bigger than factory necessitates a wiring upgrade, so most people just disable the dual voltage stem then.

I'm not sure I can speak to the last part of your message as I'm not sure how the factory ECU handles injection. I know timing was rampant in the aftermarket in the 90s but I'm not confident how Toyota had their fueling setup.

The factory ECU has a single fuel map. It works on the principle that the pressure difference between the fuel rail and in intake manifold is constant. Which it is with a factory fuel pressure regulator (as absolute pressure on the intake manifold increases, the absolute pressure in the fuel rail increases by the same, via the fuel pressure regulator). I would have thought the EMS would be set up the same way, but as you said, it is not.

Modern EMS do operate the same way you describe, at least on a fuel system with a rising rate fpr.