Piranha

Hey, where is the best place to put a fuel pressure sensor? I got the Apex'i pressure sensor and I'm going to use it for fuel. I was thinking of teeing it in between the first and second fuel rails, in the middle of the hose.

duboisr

Garfinkle put in a bigger steel fuel line front to back ,he brazed a tee on the front end of the line for the sending unit , this way there no extra hoses or clamps to leak put it in front of the injectors so it will not pulse with the injectors

Scott 89t2

inbetween rails would probably be ok. best place is after the 2nd rail and before the Reg. but that is impossible unless you have an aftermarket one. other and easiest place is between the fuel filter and 1st rail.

BDC

Place any sensor for an FP gauge _AFTER_ all of the injectors and _BEFORE_ the regulator itself. You'll get the most accurate reading here. Don't deviate from this.

B

Scott 89t2

ya but as I said unless you have an aftermarket Reg it's basicly impossable.

Piranha

Now I'm just going back on what I learned in physics, wouldn't the pressure be the same across the whole system? Unless there is a huge restriction somewhere? It shouldn't be any different before or after injectors, unless there was a very tight bend. I think....

HAILERS

So, is there anybody on this site that has a turboII with a fuel pressure regulator that will share with us what he sees when he is at full boost? At idle? At cruise???

Piranha

if you want fuel pressures, sure, as soon as I can GET to full boost. I have to figure out my lean problem still.

HAILERS

Tell us more about your lean condition. When does it show lean and do you still have your acv and airpump??

Yes, when you get the pressure sensor in, I'd be interested in what you see at idle, cruise, and wide open throttle. I've run with a mechanical pressure gauge tied to my wipers, and under full boost I see a rise to close to 50psi fuel pressure while boost on the engine was approx 8.5psi. Idle, if I remember right was approx 31psi fuel boost, cruise about 40psi fuel boost. Its been a couple of months since I did that.

Piranha

Hey Hailers. I had a post a week or 2 about "chattering sound." I had ordered my A/F gauge just before this started happening. Well, under idle, I get stoich (both green bars in the middle lit up. I bought the Nordskrog or whatever it is gauge, and a new O2 sensor. I had changed the fuel filter (OEM brand, not Mazda ) , and gotten gas... after I changed the filter I was getting THE sound. I changed it back to the old one, still got it. 2 days after the I switched filters back I started it up, and it seemed to be only running on one rotor. It sounded like a helicopter... then all of a sudden it was the normal rumble instead of a whup whup whup. That day I rewired the fuel pump, but still got the detonation.

I've tried letting the tank run down to E and getting new gas, I *just* upgraded the fuel pump but have been unable to try it.

My A/F meter will run stoich under very light throttle in any gear cruising. Any more throttle and I will see it move up and down from lean to stoich, but it doesn't go into the rich. I also had my dad hold my multimeter wires on the primary fuel injector plugs, and both got shot 12 volts as I tried to crank the engine.

Also, I checked fuel pressure with a Napa fuel pressure gauge after the filter, and it was 40 psi. I may have had the pressure regulator vacuum line off, I have had my intake off about 3 or 4 times in a week. Its getting frustrating.. :-/

Piranha

40 psi at idle, and cruising. Also, anytime I go into boost it leans out off the A/F meter, and detonation is sure to happen after that.

HAILERS

Just a word about the fuel pressure regulator. It is a variable regulator. The manual misleads you into thinking it has but two schedules, 28psi and approx 37psi. You NEED to make sure the vacuum hose on the regulator is going to a vacuum/pressure nipple that is after the throttle plates, not before the throttle plates and definetly not disconnected.

I've had the car at idle with a mechanical fuel pressure gauge b/t the engine and the fuel filter. I took a MITTYVAC and applied ten psi to the fuel pressure regulator. The fuel pressure rose as I applied pressure to the fuel pressure regulator(to the vacuum/pressure nipple). Try this on your car. If you have no Mittyvac, blow like the devil in the vac hose to the fuel pressure regulator and watch you fuel pressure gauge at the same time.

I suspect your fuel pressure regulators vac/pressure line is not connected to the intake manifold downstream of the throttle butterfllies. Wada ya think????

HAILERS

I just re-read one of your post that said 40psi at idle and forty at cruise. Does not seem right to me. Idle should be close to 28psi if the fuel pressure regulator vac/pressure hose is connected correct. The solenoid that controls that hose should be passing vac/air virtually all the time, the exception being starting with a hot engine for fifty seconds. At idle I'd pull the hose off the regulator and see if you have a vacuum at the vac/pressure hose.

Piranha

alrighty. If my fuel pressure didn't rise, could that account for my running lean?

HAILERS

I think thats a possibility. I'd tee that line at the same point that the boost/pressure sensor is and see what happens. You'd know for sure then that the fpr is getting pressure. At least try it once. Does your stock boost gauge show any boost?????????????

Piranha

alright, I'll have to go get some more vacuum hose. I followed the lines (I have the intake off) and it looks like the vacuum line from the regulator goes to one of the actuators. Hm.... last time I checked (couple weeks ago) the stock boost gauge was showing boost, but I could be at full boost and it would just barely be at 0 on the stock gauge. I have an apex'i mechanical boost gauge.

HAILERS

In that case, I'd tee it where your mechanical gauge is connected. That way you know for sure that the fpr is getting boost pressure.

I know everybody bad mouths the stock pressure gauge, but I'm worried a bit about your stock gauge not going over zero. Makes one have doubts about the boost/pressure sensor sending a boost signal to the ECU. Lots to worry about. The only reliable way to check that would be to tap into the signal from the boost/pressure sensor to the ECU and go for a drive and see movement of the meter. Well, first things first.

Just came back from a ride in my turbo. I put a meter on the blue wire(pwr) at the fuel pump plug. With the a/c on and fan full blast, at full boost, I get 10.8 volts to the pump. Its a Fluke meter so it should be reliable. I suppose I need to do that fuel pump rewire or get a bigger, better alternator. Maybe, maybe not.

That vac line should go to the orange solenoid. The feed for the solenoid, I believe comes off a nipple just outboard of the rear oil injector that is screwed into your intake manifold. About two and a half inches away. Might blow intot the lines and see if they go to the orange solenoid. Maybe the line that feeds the orange fpr solenoid is plugged with crud etc. Just a guess.

Piranha

sounds good. my pump is rewired, so it couldn't be that. what does the orange solenoid do?

The auto stores around here are closed now, so I'm just going to get on it tomorrow. I'll check the lines tonight though. Thanks!

HAILERS

Orange solenoid feeds vac/pressure to the fuel pressure regulator virtually all the time the engine is running. Only time it does not is during the first 50 seconds of startup. You could skip the regulator altogether as far as I'm concerned. Just connect it to a place ont the intake manifold that is downstream of the throttle plates so it'll see vacuum and boost pressure.

Piranha

I'll try that Hailers. BTW, is the stock boost gauge supposed to do something when you turn the key to on? I thought I read that it is supposed to jump, and mine doesn't do anything.

HAILERS

Its supposed to go to zero when the key is turned to on. When you start the car, it should go down to the bottom of the gauge. As you get on it and get into boost, it should rise up to and past zero, depending how much boost your putting out. I have some concern that you might have a wrong connection from the boost/pressure sensor to the intake manifold. That would explain the lack of movement on the factory gauge. Is the electrical plug on the boost/pressure senor good??

HAILERS

Also wanted to say that the signal wire that goes from the boost/pressure sensor to the ECU, has a spliced in wire in it, and that wire goes to the boost gauge. So what you see at the gauge should be what the ECU sees. And the ECU needs to know what the boost/pressure sensor is seeing.

Piranha

Hmmmm.... yeah, when I turn on my car it doesn't even move. when I got on boost, last time, it didn't even move. I have my mech boost gauge and the boost sensor teed off right above where the ACV use to be, I have a block off plate there now. What do you mean by is the plug good? It is plugged in

Piranha

It seemed like when I first got the car the boost WAS going positive on the stock meter, and last time I was on the highway it didn't go past zero, but moved. How can I test this thing?

HAILERS

This is one way:per the jpg. Another I just tried is to turn the key to on, get a six foot length of vac hose, connect it to the boost/pressure sensor, and blow into the vac hose. The boost gauge needle should rise a little and if you suck, it should go down to the bottom of the gauge. Not very high tech, but you can tell if its reading or working. I trust thta when you go to turn the key just to on, that the gauge moves from the bottom to almost the zero mark. Right? EDIT: This above test is just with the key to the on position, car not running.