RB26 running lean like a MOFO

[judasentinel]

I dont have the capability to see the data, as I have no controller or datalogit - just the ECU.

Secondly, I have twin MAFs, so no MAP sensor.

[speedfreak]

GTRs do have a MAP its location under the hood is on the firewall just to the right of the brake booster.

[judasentinel]

I dont have a GTR. Its a GTS-T with an RB26DETT in it.

And its news to me that GTRs came with MAP sensors. Didn't know that

[BenC]

News to me aswell. Maybe hes talking about the boost gauge box?

[mcfly]

GTRs do have a MAP its location under the hood is on the firewall just to the right of the brake booster.

Thats just for the oem boost gauge, gtst's have it too.

[judasentinel]

OK this is funny or should I say freaky.

There is a weird sound coming from the turbo side of things on my RB26DETT while it is under load, until the BOV kicks in and releases the pressure into the atmosphere. The sound is like a fart, but more like when you rip a piece of cloth quickly. I dont know how to explain the sound. But yu hear it only under boost. And while I am boosting, the sound comes and goes.

So far, no concrete solution in place. I might have to go thru replacing the fuel injectors and fuel pump plus FPR to see if that solves my problems. Would the fuel lines still maintain pressure if the fuel pump was weak or on its way out?

mcfly, you mentioned about the wiring of the fuel pump. What do I need to check if it is alright? I know that we used stock GTS-T fuel pump wiring to get the Walbro to work. And it did, but I had this cutting/leaning out problem even on my RB25DET in its twilight weeks. And there is only one major thing that is common between that engine and this one - the fuel pump.

[Brendan]

Does this weird "fart" sound get louder with higher boost and generally start at a certain PSI?

It's hard to say without hearing it myself, but when the manifold-to-turbo gasket leaks it sounds ridiculous and it's super common on Nissans.

[judasentinel]

Brendan, I just installed turbos with new gaskets and sealant, so there is not much chance for the manifold-turbo gasket to leak. As for the sound, if I am boosting, it comes and goes while in boost. It definitely happens when my stock boost gauge moves past the zero mark.

My afr is also all over the place, which is making me think that perhaps the ECU is doing a boost cut. I think this sound varies with the afr - if the afr goes too lean, I hear that sound and if it is rich, then its not there. The idle is quite smooth around 12-13, which is on the rich side but as soon as you rev the engine while driving, the mixture gets leaner and leaner, until it hits 3500 or so, and the wideband goes blank or shows 18. Now at this stage if I give put load on it, the afr goes richer, which is great but then at some point it could potentially hit a lean spot again while I am in boost and it might end up frying things up in my engine. So I am not going to do anything stupid.

Could the farting/ripping cloth sound be coming from the turbo itself that its on its way out? Or could it be due to air interference? The inlet pipe I am using in the rear turbo has a ring inside it that could be interfering with the air going into the turbo. Its a ghetto arrangement until my inlet pipe arrives, but if there is turbulence right before the compressor wheel, could it produce this sound?

Or could it be a boost leak somewhere close to the turbos and the sound comes off only where there is increased pressure and air is trying to escape thru a tiny/tight hole or something - hence the farting sound due to the analogy of air trying to pass thru a tight hole..........

Let's assume that the fuel pump is bad, or weak. Would I have a relatively rich idle? And without putting a load on the engine, if I accelerate, the afr goes lean, but under boost it tends to go richer to an extent (12-13). Would this be an injector related problem? Shouldn't the fuel pump make my idle be really really rich all the time? Or could it be the fpr?

[Brendan]

Okay, as vulgar is this is... I can't think of any other way to understand the sound a bit better.

Is the fart noise closer to a fat man ripping a deep bassy one or when someone tries to hide a fart and it's more of a long squealy one?

LOL. I can't read this thread with a straight face. But seriously... which is it?

[judasentinel]

Hey Brendan, its a TIGHT fart sound. So between a fat man passing a bassy one and a normal guy trying to hide his toot, I would say it is a medium sized man freely letting one go and then bragging about it to others around. It starts off a bit bassy and then turns shrill, like if I had to draw the shape of a fart, it would be a cone - start off thick and bassy and then tapering off to a pointy sound.

Does that help?

I opened the fuel pump and there was no pressure at all in either line upon disconnecting the two hoses going into the pump. Is that normal? I didnt disconnect the fuse under the dash or anything. Do you think the pump is toast? I thought the line would be pressurized and would spray fuel all over me when I disconnected them but nothing at all.

Also the filter thingy hanging from the side of it was rusty. I sprayed it with carby cleaner and cleaned it up as much as I could - it does not come off. But there is no difference in the afrs.

Do you suggest I install the fuel pressure gauge and see what pressure the line is at? Or can I assume the fuel pump is toast or the stock fpr?

[Brendan]

If you have the option, throw in the fuel pressure gauge and see what it's saying, that will give you a definite answer on the fuel pump.

Also, I'm dying of laughter at the description of your cone-shaped fart. Yes, I'm very mature, LOL.

[judasentinel]

You seem like someone with a genuinely good sense of humor. And that can only happen if you are a very intelligent person. Seriously, Brendan....humor is the most significant behavior of the human mind, and to have a sense of it, is testimony to a healthy and versatile brain.

What do you think is signaled by the fact that when I disconnected the two lines going into the panel on top of the fuel pump, there was no pressure at all? I had driven the car 4 hours before I disconnected the lines, BTW.

[Brendan]

Do you notice the tank holding pressure when you fill it with gas? What I mean is, does it go "PSHT" when you take the gas cap off after running the car for a bit?

In theory, it should hold pressure in the lines at all times if everything is working correctly... lots of things could cause the loss of pressure. I'd just start with the fuel pressure gauge and see what it's doing.

And thanks for the compliment!

[PL_GTR]

the engine thinks its getting X amount of fuel but in reality it is getting less, there could be a fuel leak. This would bring you Fuel to air ratio supper rich. That's why on idle you get smooth because idle doesn't need much fuel, but once you start increasing Rpm, there isn't enough fuel to support the air that the engine is designed to take in. That's why the fuel to air ratio could be messed up, check for fuel smell. If you have time, take off the fuel filter and blow through it, if it is difficult, you need a new one as it is clogged

The farting sound when it is under boost is probably a boost leak, but i am not 100% sure, maybe your blow-off valve is surging the whole time, who knows

[judasentinel]

the engine thinks its getting X amount of fuel but in reality it is getting less, there could be a fuel leak. This would bring you Fuel to air ratio supper rich. That's why on idle you get smooth because idle doesn't need much fuel, but once you start increasing Rpm, there isn't enough fuel to support the air that the engine is designed to take in. That's why the fuel to air ratio could be messed up, check for fuel smell. If you have time, take off the fuel filter and blow through it, if it is difficult, you need a new one as it is clogged

The farting sound when it is under boost is probably a boost leak, but i am not 100% sure, maybe your blow-off valve is surging the whole time, who knows

There are two different sounds - the BOV goes off AFTER you release the accelerator. The farting sound in the shape of a cone is even while I am accelerating under boost. My BOV is at the stock location under the battery and the fart is happening at the turbos.

As regards the fuel issue, if the fuel lines are supposed to maintain pressure all the time, then there is some sort of a breakdown somewhere. I will have to disconnect the fuel filter and see if I can blow it, although I have NEVER blown anything or anyone. This will be the first.

I am getting a used GTR pump on the side anyway, just in case I need to replace it. So let's see how things go over the next few days. If it is not the fuel pump and not the filter, then my only option is the injectors. Now that would be a b i t c h to narrow down, as to which one it is.

Could there be ANYTHING ELSE that could cause this? I wonder why people say a vacuum leak could cause this. I am assuming that if there is a vacuum leak and the car is under boost, the pressure IN the vacuum lines is higher, so the air would be escaping OUT of the leak, not going in (pascal's law - things move from higher pressure to lower). And this would cause the car to run richer.

Contrary to that, under vacuum condition, a leak would cause the air to seep INTO the lines. And this would make the car run leaner. My issue is that it is running lean under all conditions, except when it is idling. So I doubt it would be an air leak somewhere. But then I could be wrong.