Nikzilla

So I just finished up a bunch of work on the car, mostly maintenance and stuff, put it back together, set the timing, idle stop screw, TPS, IACV, got it to run smooth. I also put in a Fuel Pressure Gauge, a boost gauge, and a wideband.

The SR is stock apart from a FMIC and a 3 inch elbow-back.

Went for a test drive to Autozone and back. It felt a bit sluggish under boost, the car jerked forward (kinda like when you drop the clutch too fast) and the exhaust sounded like it was flapping (dunno how else to explain that sound). Checked my AFR's and fuel pressure. Fuel pressure is 35-37 psi at idle, 42-43 psi under boost. AFR is at 13.4-14 at WOT under boost at 3-5k RPM. I didn't wanna rev it past that.

Now, I'm thinking my fuel pressure is low. I should probably get a Walbro 255 and an FPR, but why was it running smoothly before? Or did I just not notice it?

ultimateirving

wallys are recommended for SR swaps and would definitely be a good idea to upgrade. And correct my if im wrong, but it should increase fuel pressure by 1 psi for each psi of boost. So if at 7 psi, it raises to 43-44ish psi, you should be ok.
If you took a bunch of stuff apart i would run a boost leak test make sure nothing is leaking where it shouldnt be.
And the ecu check for codes too

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Z32 with lq4 swap
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Nikzilla

From what I understand, it's supposed to idle at 43.5 psi, and with 7 psi of boost, it should be at 50.5. Mine is idling at 35-37 and boosting at 42-43.

I fixed all my vacuum leaks with the cigar test. It idles smooth.

This is gunna probably sound dumb, but I don't think my car has a consult port. How do I check for codes? It's pre OBD.

ultimateirving

The fuel pressure should be at about 43psi with the vacuum line unplugged. and i think your right about being closer to 50 psi.. I forgot that the vacuum pulls the pressure down to 35ish...

I think any boosted car should at least have a walbro but thats just me.
Also the codes can be checked if your ecu has a led in it, you need to search check ecu code sr20det and there are plenty of tutorials

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Z32 with lq4 swap
Desert Street Scene || Dssevents.com

Mikester

Just to be clear, a Walbro IS a higher output pump; and definitely flows beter... but it has zilch to do with fuel pressure and everything to do with volume. An adjustable FPR just puts an additional potential point of failure into the system and really serves no purpose on a stock SR... OEM FPR will perform nicely up to 400+ hp. Just my opinion- I'm a huge fan of the KISS concept.

Definitely add a Walbro to the 'get this' list; but I think you have a vac/boost leak somewhere... or a fuel leak.

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Nikzilla

Aight, I'll do a pressurized boost leak test. I did a visual inspection around the new fuel pressure sensor, no leaks detected. Is there some special way to hunt down fuel leaks? Note: It did not reek of fuel.

Kingtal0n

Finally someone with common sense I can retire

in reference to your engine, check for leaks between the maf and the compressor. And if it's a redtop, I suggest trying several different SOHC maf sensor hot-wires (and cleaning yours) because they all perform differently. I've done back to back testing.

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Nikzilla

But wouldn't the fact that it's failing to pressurize to 50 psi under boost be a sign that the fuel pump can't keep up?

Also, it's an S13 blacktop

Kingtal0n

Of course. I was only adding to the discussion. I never disagreed with anything. Someone already said the obvious: 43.5 + (X) psi of boost is where your pressure usually sits. You seem to have gotten that idea quite well, why repeat?

As a side note, since you made me post about fuel pressure. If you DO happen to install a completely unnecessary regulator, you may as well take some load off your fuel pump and lower the pressure a bit. If you have enough injector, drop the psi a few (3-7psi) and your pump will live longer, and the fuel will stay colder.

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https://tinyurl.com/turbo240

Nikzilla

The aftermarket FPR may be unnecessary, but won't it kill fuel efficiency?

But the butt of my question is. Is the fuel pump likely to be the main cause of my lean condition? Should I make time to drive to FRsport to pick up a Walbro before the weekend, or should I not worry about it and instead hunt for more vacuum leaks?

Kingtal0n

What do you mean by fuel efficiency? your car has a regulator. If you install another one, then theres two of them. They do not work differently. One may have larger ports and a more reliable, newer design, or it could be a worse design with cheap parts. Either way, they do the same thing.

You should have a walbro in the tank, yes. Everyone with an sr20 on a budget needs at the very least, that. If you are about to tell me that you have an sr20 with a stock pump in the tank... Just do not tell me that.

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https://tinyurl.com/turbo240

Nikzilla

I was under the impression that the stock FPR with the walbro will run at like 70 psi, hence making the car run stupid rich, wasting gas. I thought the point of an aftermarket FPR was to relieve that extra pressure.

And yeah I do have a stock pump. I bought the car like that lol. I'll get it swapped this weekend then.

Mikester

1. No. Aftermarket FPR does the very same thing as stock... It just gives a broader effective range of pressure regulation so you can set it up for specialty tunes and boost levels you will likely not see for quite some time.

2. No. My money is either on a vac/boost leak or shitty power or ground. Most times in my experience (not a mechanic, just a guy who's had an SR for 8+yrs), the fuel pump will eoither work, or not work. HOWEVER, I've seen a lot of stock, 20yr old 240's with tons of 'shit' swirling around the tank; and the filter sock had fallen off a decade or so ago... any debris in the pump plumbing or lines could cause this as fuel demand increases. Also, although a higher volume fuel pump IS a good thing to have, the stock 240SX fuel pump will handle the SR's [stock] fuel demand all day long. If you don't want to pay for a Walbro, a 300ZX fuel pump is a nice alternative.

3. MORE vacuum leaks??? LMAO!

Just because it idles smooth, does not mean you don't have a leak somewhere. This is one of the problems with forced induction- any leaks may only be detectable under [boost] pressure... Boost pressure falls, so will fuel pressure. Check every single line, fitting etc in the system... make sure they are tight and pliable.

- Have you verified a good, tight fuel system from the tank to the motor? A slightly loose or hairline-cracked fuel line will be fine at idle, but as pressure/demand go up; fuel will start to leak out... meaning less fuel pressure at the rail.

- Have you verified a good charging voltage (should be 14.2 - 14.6VDC) at the battery? If it reads more like 15 - 15.6VDC, I'd recommend you check your charging circuit- this will absolutley affect your fuel pump's output under load (found this out the hard way on the dyno recently). There is a connector near the main fuse box that should be connected with an SR swap.... Sometimes, it gets overlooked.

No. See note #1 above.

Okay... A Walbro does not add pressure- it only adds capability in the way of flow rate & volume. The regulator controls the pressure; and it doesn't matter what kind of pump is in there... The fuel pump output (volume/flow rate) is based on the regulated pressure... Higher pressure = less flow. At stock boost levels, a stock pump can handle the steiffeling of flow... However, once system pressure requirement goes up (like boosting 15-20+psi), THIS is where the higher volumetric output of the Walbro comes into effect, keeping you from turning your pistons into 86mm cockrings. Even though the thought process is 'less flow to the rail is bad,' it's the PRESSURE it's under and volume being sent via the pump that keeps the rail full, not the other way around. It's pretty cool, actually.

On that note, if your alternator charging voltage is up, that means that there is unnecessary load (resistance) somewhere in the electrical system. Larger load on the electrical system means there is less available current for the fuel pump to use. Remember- as boost goes up, it requires more juice (current) to push fuel out of the tank under higher pressure. End result = lower-than-normal fuel pressure under load.

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Nikzilla

Mikester thank you very much for your amazing detailed reply!

I just bought the Walbro and a Tomei FPR, might as well, they're good modifications.

I just started the car up to look at my fuel pressure, and I noticed something. it idles at about 35-37, when I rev it to 2-3k, it goes up to 42-43, but if I hold it, after 2 seconds it falls back down to 35-37. Is that normal?

The reason I said "more vacuum leaks" is because I already replaced 2 different cracked hoses lol.

I'll follow your advice and check for boost leaks by pressurizing the intake system to 7 psi. I'll also check the charging voltage.

Thanks!

Kingtal0n

Not always. I've swapped quite a few cars in the last 10 years and 90% of them would not boost 7psi with the stock in tank fuel pump.

My money is on the pump

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

Nikzilla

Well, we shall find out on saturday when I put the sucker in!

ultimateirving

Nik, see about getting a new fuel pump cover o-ring too. They often aren't reusable because they swell and are damn near impossible to put back in.

__________________
Z32 with lq4 swap
Desert Street Scene || Dssevents.com

Nikzilla

Shit. Every fucking time I drive down to FRsport, when I come back I always have a "SHIEEEEEEET I FORGOT ABOUT THAT!" moment.

Nikzilla

Yay! Local dealer has em in stock! Today is a good day.

pablito_s13

i have a trick for that o ring

1. Just do a cut on it

2. match the size to the gas tank hole

3. Cut the extra peace that overlaps off

4. Tape it back together with electrical tape.

Worked for me. i got tired of buying that "O" ring every time i remove my fuel pump

Mikester

^^Don't get me wrong... First time I did a Walbro swap, I did exactly ^^that^^ (minus electrical tape)... But I wonder... How many times does one realistically remove their fuel pump?

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Nikzilla

Haha exactly what I was wondering!

Nikzilla

Ok, so I swapped the fuel pump.

People who said that FPR's aren't necessary were 100% correct. The fuel pressure is 100% to spec without the FPR.

So I took it for a test drive, awesome! The AFR seems dead on. I decide to go to Firestone to get an alignment. So I'm turning onto the main road, hit boost in 1st gear, hear a loud PSSSSSSSSFT, the car stumbles and dies. The hotpipe just flew off the intake turbo elbow. I call my mom to bring me a damn 8mm socket and put it back in lol.

So I decide to go for a drive. Under WOT, the FPR starts at about 14 at 3k and goes down to 11.7 by 5k. I'm pretty sure that's dead on.

BUT,

I notice something REALLY weird on the highway. If I drive with the throttle juuuust barely in, (pretty much exactly how much throttle you would need to maintain 60mph) the AFR's shoot up to 20 in about 2 seconds and the car starts to stumble. But if I push the gas just a BIT more, you feel like a kick as the AFR's come back down to normal and the engine returns to normal. This made it very annoying to drive, as I had to go from 0% throttle to 50% throttle every couple of seconds to maintain speed. And after about 30 minutes of driving my hotpipe flew off again lol. Good thing I had the wrench with me.

So, since I did a full idle stop screw, TPS, IACV and timing adjustment to get the thing to run, I thought maybe I didn't tighten the TPS well enough, and it slipped, causing the TPS to read as idle under part throttle, and hence the ECU is using idle fuel map tables.

When I got home, I stuck probes down the TPS connector and it read 0.5V dead on.

So WTF is going on?

TheRealSy90

You aren't using the idle screw on the throttle body to adjust idle right? The tb should close fully.


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TheRealSy90

And do you have a wideband or are you just looking at fuel pressure while your driving?


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Nikzilla

Have a wideband.

I used this thread to setup my idle:

Idle Problems ? this worked for me SR20DET - Hardtuned.net

So basically I closed the IACV, disconnected TPS, adjusted stop screw until it idled at 750rpm, then adjusted TPS until it read 0.5V with the throttle closed, then adjusted IACV until it idled at 825rpm (although it's more like 750 right now, I gotta adjust it again (the car prolly wasn't all the way warm)).

Kingtal0n

1. never adjust the throttle body open/close
2. the tps is rarely a problem, just leave it "centered" and forget about it
3. Check for boost leaks, fill the plumbing with compressed air (15~ PSI). If you had done that your hot pipe would have come off during the boost leak check instead of the on the road.
4. your oxygen sensor sounds like it is bad. Try unplugging your O2 sensor (NARROWBAND) to see if that fixes the problem of leaning out on the highway.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

TheRealSy90

Yeah you never use the throttle body to adjust idle, it's supposed to close all the way that's what the iacv is for.


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Nikzilla

Yeah well my friend accidentally touched it in his ignorance when I asked him to adjust idle while I watched the revs lol, so I had to follow the procedure to reset the whole system.

The O2 sensor sounds like a good point, but I thought it trims the fuel through the whole powerband, no? Why would it only happen at 10% throttle? I'll give it a shot right now, if that doesn't work, I'm gunna have to build a bloody boost leak tester.

Nikzilla

Ok so I unplugged the O2 sensor. The symptoms are pretty much the same, except now instead of leaning out continuously, it just holds at 16.5. Add a bit more throttle and it settles down at the 14-15 it's supposed to be. Oh. and also, if you give it half throttle in high gear at low rpm (like 2-3k) it jerks a bit.

I'll try to build a boost leak tester today.