Fuel Pressure?

[RS12Turbo]

I've been having problems with black soot spitting out on my driveway at idle, rich smelling, and hesitation at wot at 14-15psi......all started about a month ago or so.I was thinking my oe fuel pressure regulator was crapping out from age/ walbro 255. I installed a fuel pressure gauge today in the line that goes from the fuel filter to the fuel rail. Fired up the engine, and the gauge said 30psi @ idle. I unplugged the vac line on the regulator, and went up to 38psi. When I shut off the engine, the gauge slowly started going down, and after about 10 mins, it showed like 13psi.Now, I was thinking my fuel pressure was low, because I thought I had read on here somewhere, it should be around 34psi @ idle.........but after looking at the FSM, it seems that it's actually high The FSM says it should be at 28psi at idle, and 36 psi when the vac line is unplugged.So, am I high, or low? Also, should the pressure hold when the engine is off, or is it normal for it to drop?

[r34 gtr]

You are slightly high (heh). it should be 28/36 but I dont think it is enough to cause your problems. Mine never held pressure for all that long. It would maintain 36psi for a little while, then slowly drop off. Sounds like yours is doing it a little faster than mine though. You could always have your fuel injectors cleaned, one might be sticking a little bit.

It definitely sounds like its running too rich. Do you have a wideband you could throw on it? Maybe go yell at those guys in trussville (walker dynotune?) and see if you can use theirs for a few minutes? It would definitely tell you what the problem was, and how severe.

[RS12Turbo]

I just went out after about an hr of it sitting.....and the gauge was on 0 psi. I don't think thats normal.....I know it's a different car, but my '95 maxima still has squirting pressure after sitting for several days without cranking....if I take the hose off the fuel filter, fuel shoots everywhere.I know it was running pig rich when I first got the engine.......took it and got dyno tuned, and they had to lean the crap out of the s-afc2 to get the afr's within range. Before I went I had the same symptoms.....rich smell, spitting soot, and hesitation under boost........all that went away once I got it tuned.......now it's back.Yeah, I may need to hit up that place in Trussville, or get a wide band, which I need anyways

[r34 gtr]

Sounds like you might need to check out those injectors. Mine still holds some fuel pressure until the next morning, though not necessarily a ton.

[float_6969]

Yea, I'll still have 10-15psi overnight.

I'll bet that walbro has toasted that OE FPR. Get a NISMO regulator. I'll bet it will fix your problems.

And get a real tune on that thing man!

[RS12Turbo]

Yeah, I'm gonna go ahead and order the Nismo fpr....and see what happens. I've got a set of dsm injectors......should I go ahead and through them in with the nismo fpr....or will it be an overkill with a t25g at 15psi?

To confirm......the NISMO fpr part is 22670-RR580 ?

[r34 gtr]

I understand the stock fuel map can compensate for up to 444cc injectors, but I have never tried it so I cant tell you for sure. I dont think it would be overkill at all, but you would have to adjust the fuel maps and stuff with the larger injectors, so its up to if you have the means to do that or not. Wait, you have an SAFC. Just throw them in.

Your part number sounds right. I just ball up in my nissan dealership and they get the NISMO catalog out automatically. Oh, its that guy, get out the 240sx, pulsar, and NISMO catalogs, he's gonna need $100,000 in parts.

[RS12Turbo]

Do I need the NISMO adaptor bracket also? I see it listed, and says it needs to be used with the "universal fpr".Anyone got a part # for the bracket, if it is needed? Also, where is a good place to buy?

[r34 gtr]

Dont get the universal one, get the one for the SR. You only need that adapter bit if you get the universal one like I did. It still works just fine, but you have to make a mounting braket and junk for it, and its not worth the extra hassle considering they cost exactly the same.

[RS12Turbo]

Ahhh, good to know....so the fpr for the sr fits the ca-det, and doesn't require the adaptor thingy?

[RS12Turbo]

So I noticed something kinda weird today. Went for a drive, popped the hood, checked fuel pressure gauge........still at 29-30psi. Turned off the engine, and the gauge shot up to 33-34psi......is that normal? I cranked it up again, and it went back to 29-30psi. Shut it off, and this time it went to 23-24psi

On a different note.....my hesitation issue @ wot above 3500 is gone For kicks, I checked the timing, and it was roughly at 20 degrees. I put it back to 15-16 degrees, took it for a drive, and the hesitation was gone. I must of been drunk or something when I adjusted the timing a few weeks ago.......because I swear it was on 15 degrees. I wonder if my hesitation was detonation with the timing being so high??

[r34 gtr]

Could have been. What is it with people's cars and the timing going wonky.

[float_6969]

The fuel pressure is lower at idle. It should go up when you turn the car off.

It sounds to me like that FPR is just weak.

The 444's should be fine.

[RS12Turbo]

I've been having problems with black soot spitting out on my driveway at idle, rich smelling, and hesitation at wot at 14-15psi......all started about a month ago or so.

I think I might of figured out why all of this was going on......minus the low fuel pressure issue.I was going through the afc-2 settings, and noticed all of my hi throttle settings had reset back to 0 I re-entered all of settings back in.....haven't taken it for a spin.....but I'm almost positive this is it........I had these same symptoms before I got it dyno tuned.Has this happened to anyone.......I thought the s-afc2 was suppose to retain your settings?I did get new tires put on about the same time my symptoms started......maybe the tire guy screwed with it.......but I had the password locked.........so I dunno

[Buddyworm]

I understand the stock fuel map can compensate for up to 444cc injectors

The map isn't affected by the size of the injectors. It's the K value and latency that matters. You can run 1000cc injectors on the stock fuel map just as long as your K and Latency are tuned properly.

Has this happened to anyone.......I thought the s-afc2 was suppose to retain your settings?

Does the SAFC use volatile memory to store the information? Perhaps it's not hooked up properly and losing power when the car is shut off? I'm just putting it out there, I don't know the SAFC goes about completing it's job. It's a bandaid as far as I'm concerned. I'd say get a proper rom flash and FPR.

[RS12Turbo]

well............the settings on the afc have been set since early spring, and it hasn't had a prob retaining the memory, even with the battery disconnected for several days. I don't know what happened.......I just checked it after sitting for a couple of hrs, and the settings are still there.......I guess I'll keep an eye on it for a while.I bet it was that little bastard at the tire shop

[Indecisive]

as far as i understand, the SAFC does not use volatile memory.

I've had mine disconnected completely from the car for months at a time before hooking it back up with the settings still in the system.