I need some suggestions for finding the correct fuel pressure regulator for a fuel injected turbo 12a. It's a JDM factory turbo motor from a 1983 Savannah GTX turbo but now resides in my 79 SA. I have new 720cc (blue) injectors, a new DeatschWerks 9-250 fuel pump and a regulator that someone gave me with the motor that is a rising rate type. I believe the ECU is the same as a GSL-SE as are the relays and such. It also has new NGK plugs, wires, cap and ignitors. The engine starts and runs well but as soon as I put a load on it it falls on it's face. if I keep trying to accelerate it will start popping and almost die. the regulator has a gauge and it is reading approx.30 psi at idle but I don't know what is happening under load because I can't see the gauge when driving. I tried putting my GoPro in the engine bay to see the gauge but I can't see it clearly. I am going to rig a temporary extension hose to locate the gauge on the outside of the windshield . I'm wondering if there is a better type of regulator to use with this engine? It's a non intercooled setup running 7-8lbs boost. I can hear it try to make boost as it goes flat. I'm suspecting a fueling issue but I have another issue as well...
When timing the ignition with a light.. I get the leading timing set then try to set the trailing and the pulley mark for the trailing timing always ends up on the leading mark. If I move the trailing dashpot on the distributor nothing really changes.. What could make the leading and trailing fire at the same time? I have double check the wiring and everything seems correct. But would that even cause such a drivability issue as to make the car undriveable? I heard that formula Mazda cars have their leading and trailing timing wired together but I don't know why.



Any help or suggestions are much appreciated.

 

You do not want a rising rate fuel pressure regulator. Rising rate regulators were a bandaid for putting turbos on Hondas that have no way of measuring airflow or knowing that it's in boost, they have no place on anything with an airflow meter.

IIRC these cars just used the same rail/regulator as a GSL-SE.

 

Disconnect trailing, you don't need it and it may be causing some of your problems off idle if it advances too far or is not timed correctly. I have no clue about turbos/boost etc.

 

That's the first I've heard that. Trailing is super important and I havent had a car that would even idle leading-only.

 

I run leading only. No problems here with idle or driving.

 

Hacks on hacks on hacks. Disabling trailing to fix a drivability problem is idiotic.

 

Double check that the leading and trailing connectors aren't reversed, too. I've done that. Also make sure the coil wires are not routed next to each other very closely, you can get crosstalk where one spark induces another one in the wire sitting next to it for a couple feet. (This can wreck American V8s where the two rear left bank cylinders fire one after the other). The wires should be as far apart as possible. Sitting them on opposite sides of a 4 wire holder is usually enough, and if they have to get close make sure they cross at as close to a right angle as possible.

If you have a rising rate regulator that could explain why it runs like crap under boost. The base fuel pressure is 37psi (2.5 bar). At idle at about 15" of vacuum that is going to be about 30psi, or 37psi pressure differential from fuel rail to manifold pressure. This is good and correct fueling.

At 7psi boost the fuel pressure should be about 45psi, or again 2.5 bar above manifold pressure. If you have a 4:1 rising rate regulator, then the fuel pressure would go up by 28psi not 7psi, so you'd have about 65psi fuel pressure, which is 57psi above manifold pressure - close to 4 bar! It's going to be insanely rich.

The fuel computer is very simple. Airflow goes up, duty cycle goes up. It assumes a certain injector flow and that the fuel pressure stays the same relative to manifold pressure. Mazda also already calibrated things to be very rich under load to keep EGT down and prevent free oxygen in the exhaust, because they want to protect the converters. Adding extra fuel on top of all that is asking for issues.

All that said, the injectors should be 800cc. If you have 720s, which is their rating at 3 bar, you effectively have 660cc injectors when adjusting for the lower pressure...

 

Thanks to all for you response and all the good info.. I'm going to try a few of the suggestions tonight and will report back. I'm confused about the rising rate regulator though. This set up came directly from a friend's car and he helped me swap it into my car.. it always ran perfect in his car. The fuel pressure needs to increase increase with the boost so how does it do it without the rising rate regulator? I double checked my injectors and they are Denso 195500-0610 (660cc) so maybe I need 800cc injectors? again, these are the same as what it was running before. I am going to see what happens wit hthe timing if I disconnect the trailing wires. Even if it shouldn't stay that way it's still a good way to eliminate things. I will post back tomorrow with my results. Thanks again to all for you input, this is a great community!

 

All fuel pressure regulators should be manifold pressure referenced so that the fuel pressure is the same relative to manifold pressure. That's what matters, because you are spraying into an area of varying pressure (what we think of as vacuum or boost) so the fuel pressure needs to follow that.

A rising rate regulator increases pressure out of proportion to manifold pressure. Usually 4:1.

It's possible that you do not have a rising rate regulator but you are calling a manifold pressure referenced regulator "rising rate". The key with a rising rate regulator isn't that the pressure goes up with boost, but that the pressure goes up at a faster rate than boost, thus "rising rate".

They were a band aid way to add fuel under boost for cars with stock computers that didnt measure airflow directly and didn't measure manifold pressure higher than atmospheric.(Hondas, pre-MAF Ford 5.0s) They sort of worked, in that you got to make a few drag passes okay before you melted a piston. They can't be used on anything that measures airflow.

 

Here is the regulator that I got with the engine. It doesn't have any identifiable markings on it. the vacuum hose coming out of the top is connected to a port below the throttle plate. I don't know how this regulator works so i don't where it should be getting it's vacumm from. Also, does anyone know what the little cannister is that looks like a fuel filter? I wondering if some debris from the tank could have made it's way up here and is restricting the flow?

 

The canister thing is a fuel pressure regulator. It works by applying vacuum to the tube inlet to the left, which moves an internal diaphragm valve toward that port - opening up the valve passage to allow more fuel to flow through under pressure. You should test this using appropriate Fuel Pressure gauges. On N/A cars, the intake plenum vacuum is used for the source for this as load increases, vacuum increases. This helps EFI systems to maintain fuel pressure and volume flow according to the fuel map and incoming air volume.

Is it hooked up to anything right now? If not, your fuel pressure isn't modulating properly, which could explain a number of problems. Also, there's a vacuum port on your intake plate pointed toward the firewall that doesn't have any hose attached. If it's open to the air, you have a big vacuum or boost leak.

Sidenote; the Fuel Pressure Regulator shown in your pic above is NOT the same as a GSL-SE. The SE regulator is attached to the end of the Fuel Rail and the vacuum sensing hose is operated off of a solenoid valve which gets vacuum reference from the Dynamic Effect Intake plenum. When vacuum is asserted to it (*the SE part) it CLOSES the valve which goes to Fuel Return, thereby restricting the RETURN side to increase effective pressure at the Rail which feeds the Fuel Injectors. Also, the SE has 2×680cc Injectors. A turbo installation would likely require higher volume, higher pressure, or both.

 

Thanks for the info Long Duck... So you're saying that event though it has an aftermarket pressure regulator, that it still needs the original regulator to be functional las well? As stated in my previous post, the engine ran perfectly in the last car with the exact same set up. Also the open port you are reffering to is not a vacuum port, it a water port for cooling water to warm the manifold. It is not open to the inside of the manifold.

 

You have two regulators. The one on the engine is the OE regulator, and should get manifold pressure referenced. Im assuming that it isn't gutted.

Let's worry about all that after you can see what fuel pressure is doing. First up is sorting your ignition, especially if it was working before. Are your coil leads spaced apart? Do you have hoses going to the distributor cans? It's been a hot minute since I saw a 12AT but I'm pretty sure that boost retard happens at the vacuum cans, it's all mechanically controlled and not controlled by the computer.

 

Agreed - do what Peejay recommends. I've never seen a 12AT because they're unicorns in the US market. I'm just trying to clarify that what you have controlling Fuel Pressure isn't SE parts, but something different, likely specific to the 12AT.

 

I discovered that I had a restriction in the tank.. I hooked up a portable outboard motor gas tank to the filter inlet and drove it and can feel it make power now. However it is running EXTREMELY rich!! It sucked down a whole gallon of fuel just driving it a half mile! So, back to the regulator.. My regulator is in a photo up top and I was told it was a rising rate regulator but I'm not certain what it is. The injectors are blue 660cc x2. My 1984 12a turbo only has two injectors. If I shouldn't be running a rising rate regulator, what should I be running? I called Deatschwerks and they recommended a rising rate regulator. It uses a GSL-SE ECU and MASS air flow sensor. What else would work for a regulator with my set up?

 

It shouldn't had a mass airflow sensor, I don't think those even existed in 1982. Should be a flapper door airflow meter.

 

My bad... Yes it does have a flapper door air flow sensor.. It's all out of an 84 GSL-SE It also has what appears to be the original fuel pressure regulator from the 12AT or a GSL-SE.( looks like a little beer keg) The vacuum line is disconnected but the fuel still runs through it.. I'm baffled by this fuel system It's simple yet a little bazar. Something else worth mentioning is that because I was using an outboard motor fuel tank and the return line was still plumbed to the car's fuel tank, all of that recirculated fuel went back to the gas tank causing it to empty the outboard tank quickly. But it's still running rich and I don't know what to do about that. I would also like to upgrade the ignition but all the info I have found is very old. Any thoughts on that?

 

the 12A-T and GSL-SE have a really similar fuel injection system, and share a few parts, which is nice. the regulator is the same as the GSL-SE, and S4 T2. it needs to be hooked to manifold vacuum.

the Air Flow Meter is physically the same size between the 12A-T and GSL-SE, and would be electrically compatible, but may have a different calibration, slightly. they have a Nippon Denso part number on them, the 12A-T looks to be 197100-2550 and the GSL-SE looks to be 197100-2480. not sure it matters too much, it would be easier to upgrade the ecu than find the correct one. the 12A-T actually uses two

GSL-SE stuff is mostly N304, and the 12A-T is N25x, there are a few versions of the 12A-T depending on what car it came in