fuel pressure drop when boosting?; is -17VAC at idle normal? weak brake + clutch

[s13_240_rb20]

Ok...here is the continuing story. Decided to start a new topic since my problems aren't matching the symptoms previously listed in the other topic.

Once again, here's the mods:

1990 240sx hatchRB20DET 5sp w/ecuWalbro pump (hardwired, battery voltage)Datascan is available for troubleshootingvac/boost gauge (-30 to +30)Fuel Pressure gaugenismo FPRNGKBPR6 plugs, gapped to .8mm

Okay, well...after fresh plugs, new pump, cleaning injectors' filters, etc....It runs. However, my brake and clutch feel extremely weak when idling. When the engine is off, my brake feels really good (I'll check the clutch later, now that I think about it). when I pump the brake while idling, I can see on the gauge that my vaccuum and RPM fluctuate.

My normal idling vaccuum is -17. My gauge is plugged into the back, top of the intake manifold. (is that a normal vacuum reading?) I have been told that the RB20 had a outlet for the stock boost gauge, but I am not sure if I am tapped into it. I DOOOO have one hose unplugged from that location so that I could tap the gauge directly onto it. At WOT, I do build up to 7psi. Fuel pressure responds and builds up to the building vac towards boost. However, about the time I get there, my pressure drops out.

Can someone show me where my stock boost gauge was plugged on? I don't want to "t" this line because there should not be a hose hooked up where the stock gauge was, so therefore I must be on the wrong vac-line. I'll be double searching the FSM even though I can't seem to find it.

And back to the brake and clutch issue: They are full of fluid. Both are weak when idling. These pedals are weak EVEN WHEN I have that vacuum line plugged on correctly.

But, in summary, any info about the boost gauge port location (preferably a pic or page number in the FSM), the expected normal idle vacuum reading, or the fuel building then dropping...will be greaaaattttly appreciately. In the meantime, I will be tinkering and experimently.

--TJ

[240z4u]

Vac sounds fine, it should not matter where your grabbing the signal.

The clutch pressure has 0 to do with the engine, and with 17 vac the brakes should be fine.

Evan

[s13_240_rb20]

Vac sounds fine, it should not matter where your grabbing the signal.

The clutch pressure has 0 to do with the engine, and with 17 vac the brakes should be fine.

Evan

but the brake does have weak pressure behind the pedal...guess I'll bleed them whenever I get the chance and see it that is all that is wrong.

Any idea about the dropping fuel pressure at high throttle?

--TJ

[s13_240_rb20]

Just took another test drive. Still drives fine as long as I barely touch the gas pedal (doesn't call for a large need of gas). Fuel pressure drops out the bottom when I stomp on it and hold it. I also put the above mentioned vacuum line back in place and tested it, but it did the exact same thing. I have painted the vacuum line below and pointed an arrow to where I removed the vac line and plugged my clear boost gauge line onto. That is where I measured -17vac at idle.

Can someone tell me where the stock boost gauge plugged onto the motor?



Also, I popped the hood and revved from the throttle body to trace down a weird sound. I can't be exact about the rpm's, but around the time that the fuel pressure starts to drop during hard revving (around 5k rpm "thrusts"), there is an odd noise that is coming from the back of the engine (near the firewall). It is an unsteady series of about 8 to 12 "clicks". It really does sound almost the same and sticking something into a spinning fan.....almost like something is moving really fast and something clicks with the cylinders pace??? Is this detonation or some other phenomenom that is only a RESULT of the fuel pressure loss, or could this be the CAUSE of my fuel pressure loss??

Also, by the way....my car still hangs up on 2k rpms unless I rev harder to shoot past 2k.

And just out of curiosity: Can stock RB20 (KA, right?) injectors pump more fuel than a Walbro can push?? Just making up theories now...I need to inspect my o2 sensor, but I am wondering if a bad o2 sensor can give a false reading and make my injectors max out, thereby dumping in more fuel than the pump can push??

I'm confused.....

--TJ

[s13_240_rb20]

*bump*

[s13_240_rb20]

*bump*

This is what happens when I push too hard on the gas. It happens in any gear and also in neutral.

This was on my way home from work this morning. I was in second gear, around 30 mph or so. The fuel pressure gauge is on top. Ignore the vac/boost gauge on the bottom. It is still not hooked up because no one has helped me figure out where the stock skyline boost gauge plugged in at, so it is sitting at 0 and remains there.

The video begins with the fuel pressure steady at 37psi, cruising 30mph or so. Although the video quality is crap, you can see that the fuel pressure drops to the high 20's during the FIRST time that i apply HALF of the gas pedal, hence NO acceleration due to lack of fuel? After that the fuel dropping and rising is due to pressing halfway on the gas and letting off completely. Keep in mind that if I apply less gas pedal, the engine needs less gas to accelerate, so that is how I am driving it to work...like a grandma....i've slowly accelerated all the way to 110mph and it help perfect fuel pressure. But if I step on it just a little too much....fuel loss = no power = sad day

click below for video:http://s268.photobucket.com/al...5.flv

--TJ

[l0nestar]

I don't have my FSM here at work with me to tell you which nipple to tap, but that _seems_ like the right one (it is similar to my 25).

My main question is, what does your CONSULT interface tell you? Are you throwing any codes on your ECU either?

[craz4240]

Thats the right line for the boost gauge.

Do you have a fuel pressure gauge???How do you know your fuel is dropping off??? It could be running rich and bogging out the motor.

Your fuel pump should not be hard wired....it should be wired in correctly.If you don't have an adjustable fpr get one.

[s13_240_rb20]

I don't have my FSM here at work with me to tell you which nipple to tap, but that _seems_ like the right one (it is similar to my 25).

My main question is, what does your CONSULT interface tell you? Are you throwing any codes on your ECU either?

ok...I am just a little confused then. If that is where the stock boost gauge was plugged in, then why do I have that hose hooked onto it....should it be plugged somewhere else...?

and, ya, I have an adjustable FPR and a fuel pressure gauge. The ecu is not throwing any codes...

--TJ

[s13_240_rb20]

I will love mine if I can ever stomp on the gas pedal again. I have to drive like a grandma, because my car drops fuel pressure if I press the gas too hard. And this is with a BRAND NEW WALBRO!!!

don't know if this is related, but it also has a miss at almost exactly 2000rpm. I absolutely cannot idle around 2200-2500. I either miss at 2k or it revs past 3000 before it starts to balance out.. I managed to idle it at 2500 ONE TIME, and the exhaust sounded like it was missing (air in-and-out) the WHOLLLEEEE time..

--TJ