Lean @ Part throttle ONLY!!!! ****NISMO FRP VS WALBRO 255****

[JN1AS4]

I just developed lean conditions while at part throttle(cruising on hwy). My car was professionally tuned 4 months ago and my AFR were a consistent 14.7:1-15.4:1 @ idle/part throttle, and 11.4:1-11.7:1 @ WOT. But as of yesterday something changed, I was cruising on the hwy I could feel my car hesitate a little so I glanced at my wideband and sure enough my AFR was 17.5:1+(part throttle). So I exited the hwy and came up to a red light I noticed that @ idle it was still a consistent 14.7:1-15.4:1. So I was curious about my WOT AFR so I stumped it, and it was still 11.4:1-11.7:1. So apparently my part throttle is the only thing thats been effected somehow. So when I finally got to my destination I parked the car for about 45 mins then I came out and popped the hood and to my amazement my fuel pressure had dropped to 0psi. I know that this has something to do with my current problem because before this incident it would hold 30-35psi overnight. So I popped the vac line off my Nismo FPR to check and see if it smelled like fuel and it didn't. My Walbro 255 have been hardwired to a constant 12v source for about 6 months now. So I know its not a drop in voltage causing the problem. The Culprit is either the Nismo FPR or the Walbro 255. Ill go out and check for vac leaks too when I off work today which I highly doubt is my problem. But I do know that can be a issue too. Im leaning towards the FPR myself though. What do you guys think?

[Agent S14]

i have never heard of a fpr going out i sold my nismo fpr to a friend for his brand new tomei in box fpr. i had no issues with my nismo fpr.

[ultimateirving]

I just developed lean conditions while at part throttle(cruising on hwy). What do you guys think?

See if you can monitor the fuel pressure in cabin, or log it for a quick cruise and see if it is indeed fluctuating that a broken FPR might indicate.

Also maybe try small things like clogged/old fuel filter, or a vacuum leak somewhere from you abusing the car on the new tune..
HINT HINT BOOST LEAK TEST

[JN1AS4]

I planned on running my fuel pressure gauge into the cabin so I could monitor it while driving. When I think of boost leaks I think about running extra rich. So I never even thought about that. I sure don't have any obvious boost leaks though, I may also test it tomorrow.


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[JN1AS4]

After further investigation it's lean at idle too. But WOT seems to still be good. Now I'm leaning towards the fuel pump being the issue. It's still dropping fuel pressure to 0psi in about an hour or so. I even bumped my base fuel pressure up 10psi and I'm still having the same issue. Which leaves me to believe the pump can't flow enough volume to even push the regulator.


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[BoredEE]

I had an issue with a walbro, the easiest way to test it is set the FPR to ~60psi then disconnect the return fuel line and feed it into a gallon jug. Hotwire the pump and time how long it took for it to fill the jug. There are many graphs out there that tell you the flow rate of a walbro under certain pressures. Do some maths and see if the pump isn't within ~5-10% of those graphs.

If you have a pressure gauge measure the pressure out of the fuel pump, by teeing it in. That'll tell you if there is a pressure drop across the fuel line.

I'm not responsible for any damage or injury resulting from this procedure. This is extremely dangerous and should not be attempted without utmost care.

[s13 drifta]

I have problems with a lean spot on part throttle. Idle and WOT are normal, but at part throttle I hit 16-17 afr. If I let off slightly or give it more throttle, it goes away. I have a Nismo FPR and changed my Walbro pump to a Denso Supra pump. Still have the same issue. I think it might be the FPR. I plan on running a in cabin fuel pressure gauge to diagnose it.

[JN1AS4]

I had an issue with a walbro, the easiest way to test it is set the FPR to ~60psi then disconnect the return fuel line and feed it into a gallon jug. Hotwire the pump and time how long it took for it to fill the jug. There are many graphs out there that tell you the flow rate of a walbro under certain pressures. Do some maths and see if the pump isn't within ~5-10% of those graphs.

If you have a pressure gauge measure the pressure out of the fuel pump, by teeing it in. That'll tell you if there is a pressure drop across the fuel line.

I'm not responsible for any damage or injury resulting from this procedure. This is extremely dangerous and should not be attempted without utmost care.


So if I don't see any fuel pressure drop when I install the in cabin fuel pressure gauge does that cancel out the fuel pump being the issue? Or does that further point the fingers at either the regulator or fuel pump?


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[slider2828]

So you have a custom tune. Did you watch him tune it? Did he use a load bearing dyno, like a dyno dynamics to tune for part throttle? Air Temp also changes how the ecu burns and reacts to how much fuel is dumped.....

[JN1AS4]

Yes I have a custom tune. And it was tuned on a mustang dyno. Yeah, I thought about the weather too. But how come I can turn the base fuel pressure up 10+psi and still run into the same issue. Do you guys think perhaps it can be the o2 sensor or something failing. I've also heard of our mafs doing some funky things too when they're on the verge of failing also.


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[JBPUSA]

My injector o rings were messed up once and my fuel gauge would read 0 psi after 3mns

[JN1AS4]

Yeah but my car is running lean. Leaking injectors would would cause you to run rich.


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[Def]

Check for a vacuum hose that's popped off your throttle body - usually it's one of the small ones underneath it that aren't barbed. I doubt it's your fuel pump if it's ok at WOT.

Also, you might try cleaning your MAF.

[ultimateirving]

Check for a vacuum hose that's popped off your throttle body - usually it's one of the small ones underneath it that aren't barbed. I doubt it's your fuel pump if it's ok at WOT.

Also, you might try cleaning your MAF.

This is what i was getting at, a small leak causing a lean issue at part throttle but not bad enough under wot to make signicant difference

[JN1AS4]

I'm still struggling with my lean AFR's at part throttle. I've checked/double checked everything. I've even replaced my fuel pump but I'm currently still running my old sock which is dirty, the fuel pump kit came with the wrong sock. But my replacement one will be here tomorrow and I'll install it and hopes of curing my problem. I've also replaced my nismo fpr setup with Aeromotive setup. I replaced my maf. And I've boost/vac leak tested the entire system. And the problem still exist. I'm almost out of ideas now. O2 sensor, knock sensor, tps, or ecu are the only other things I can think of. I feel as if it has to be something electrical because no matter how high I raise my fuel pressure it does the same thing. Almost as if the computer is trying to compensate for something. And I'm not so sure that this problem just came when I did did the trans swap because before then I didn't drive it for a while and when I did it was just a cruise around the neighborhood or something so I doubt I would of noticed the issue. But I can say that when you left here my AFR's were on point. Any help/suggestions is greatly appreciated.


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[ultimateirving]

I'm still struggling with my lean AFR's at part throttle. I've checked/double checked everything. I've even replaced my fuel pump but I'm currently still running my old sock which is dirty, the fuel pump kit came with the wrong sock. But my replacement one will be here tomorrow and I'll install it and hopes of curing my problem. I've also replaced my nismo fpr setup with Aeromotive setup. I replaced my maf. And I've boost/vac leak tested the entire system. And the problem still exist. I'm almost out of ideas now. O2 sensor, knock sensor, tps, or ecu are the only other things I can think of. I feel as if it has to be something electrical because no matter how high I raise my fuel pressure it does the same thing. Almost as if the computer is trying to compensate for something. And I'm not so sure that this problem just came when I did did the trans swap because before then I didn't drive it for a while and when I did it was just a cruise around the neighborhood or something so I doubt I would of noticed the issue. But I can say that when you left here my AFR's were on point. Any help/suggestions is greatly appreciated.


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Any chance your bov is opening under light vacuum?

[JN1AS4]

Not to my knowledge. It's a tial BOV, so it should be easy to check.


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[Def]

Running a vented bov with a draw through MAF is stupid. It causes problems like this all the time. Run a proper bypass valve.

[JN1AS4]

Running a vented bov with a draw through MAF is stupid. It causes problems like this all the time. Run a proper bypass valve.

My car was properly tuned for my current setup. Its been properly tuned for the past 5 years. But it was recently retuned 6 months ago due to me upgrading my setup. And it ran perfectly fine all this time until now. So I doubt thats my problem.

[Def]

You cannot tune around the stupid stuff a vented bov does to a draw through MAF. Period. It's stupid if you know anything about engine management.

[JN1AS4]

Stupid or not, I doubt that's my issue. Especially since it took 5+ years to act up.


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[aga]

fuel pressure dropping to zero after an hour is normal. in case it's dropping fast, first thing i would check is the injectors.

also, clean your MAF.

[JN1AS4]

Injectors have been checked, none of them are leaking. Maf was also cleaned then replaced.

[aga]

O2 sensor?

[JN1AS4]

I have no way of checking the o2 sensor but it can definitely be a problem. So I'll probably just replace it too.


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[aga]

you can go to a shop that cleans injectors, they usually have a machine that can check O2 sensors ( i don't remember how it's called)

[Def]

Stupid or not, I doubt that's my issue. Especially since it took 5+ years to act up.


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Well, given that it's creating a post-MAF leak, and could possibly be leaking slightly - it's not smart to keep running it that way.


You should stop throwing parts at this and guessing - fix known issues with your setup, then run a Consult feed to find out what the car is doing. This is one of the big disadvantages of ROM tunes and the like - the average user is lost whenever they have a tiny problem because they won't use diagnostic tools.