RB26 running lean like a MOFO

[judasentinel]

Hi all,

First time posting up a technical thread in the GTR section since I did the RB26 swap in my GTS.

I am faced with a few problems, which perhaps some of you have experienced before and resolved. I have tried going thru threads of idle/hesitation/bog/hunting problems and have kind of eliminated most of the obvious causes. But my engine is still running LEAN.

When you start the car up, it runs a little rich and then goes to a lean condition (17-18), and it stays that way when the car has warmed up. Since I have put a new clutch in, we havent boosted it as such and not floored the accelerator either. But under mild boost, the afr goes to 12-13 and then climbs back up.

I am concerned that its fuel related and not vacuum. It could be a clogged fuel filter, weak fuel pump (I have a Walbro 255 lph pump), or injector(s) not throwing in enough fuel.

The first test could be to check the condition of the plugs, but they are brand new, so may not show much in the way of discoloration due to rich or lean conditions.

If I were to check for vacuum leaks again, what are the usual spots on an RB26DETT? I know what they could be on the RB25 and RB20, but if there is something different on the RB26, I would love to know it.

Thanks, guys

[mcfly]

are you using a rb26 ecu?
rb26 mafs?
take the filter off and replace if needed, it could be the issue.

If you had a vacuum leak under boost it would make you very rich.

[judasentinel]

are you using a rb26 ecu?
rb26 mafs?
take the filter off and replace if needed, it could be the issue.

If you had a vacuum leak under boost it would make you very rich.

I have an RB26 ECU and MAF, plus I am using M's (by K&N) filters on both MAFs. They seem to be in very good shape. But besides that, if the filters were clogged, wouldn't it restrict airflow and make me run rich?

Or are you talking about the fuel filter? If so, I had replaced the fuel filter with a larger Z32 one less than a year ago. Could it still be the problem?

Is there a way to test if the injector is firing? Could I disconnect each injector one at a time and see if there is any drop in revs? That could tell me something, wouldn't it?

Anything else to check?

[Brendan]

Check for vacuum leaks between the turbos and the MAFs. It doesn't sound like a fueling issue to me because it runs lean at idle, then when you accelerate it gets rich for a second showing that it does have enough fuel to supply for idle.

[speedfreak]

Are you running 2 O2 sensors and what are there outputs.

Also might want to check the mafs, might have one bad one.

[judasentinel]

Good idea, Brendan. I will check the MAF to turbo piping.

However, even if the car does run richer upon acceleration/mild boost, it could simply mean that it had an air restriction for a few seconds during which the fuel ratio increased, couldn't it?

I am also thinking that perhaps its not the injectors but maybe the fuel pump?

How do I check if it is the MAFs, though? I dont have any spares. If the MAF is bad, wouldn't it go lumpy for a bit on idle or throw afr numbers all over the place?

I have 2 O2 sensors, and both seem to be working fine. I dont have a way to check their reading, since stock ECU would at best show me rich or lean thru them. My wideband (AEM) however, is showing lean condition. I am sensing that if it is running dangerously lean due to faulty injection, wouldn't the ECU be compensating it by increasing the pulse width?

Is it worth my time to check the conditions of the plugs?

[malibusst]

what kind of AFR gauge are you using ????

[judasentinel]

I have an AEM wideband with gauge.

I can rule out the MAFs because the car idles smooth. The spark is all there, so no need to worry about the ignition side either I suppose.

It could also be the stale fuel that has been sitting in the car for four months. And like you said Manny, I will check the Walbro to see if has gunked up while sitting in that stale fuel and causing a pressure drop under vacuum.

Otherwise, does anyone think it could be injectors?

[Brendan]

Just throwing this out there... but other than the wideband reading, does anything else seem wrong with it?

If it feels normal... is there an exhaust leak before the wideband sensor? That would cause some weird readings.

[mcfly]

how about the fuel pump wiring?

Did you run new power wires to the pump or use the oem ones? The oem powerline run variable voltage which could cause an issue.
Or a leaky fuel line in the tank.

Four months isn't enough to cause "stale" gas.

[judasentinel]

The fuel pump was changed almost a year ago in April 2008. We used the stock wiring, and it ran alright. I remember having issues with the car last summer before I changed the fuel pump that while driving, suddenly the engine would cut out and then come back on. It wasnt like the lights come on when the car stalls, but more like a strong jerk as if there suddenly no fuel at all.

I decided to change the fuel pump and the problem seemed to have gone away. But then it would come back every now and then. All this is from 2008 when I had an RB25DET. I then installed NisTune and was very happy with it. I tuned it and the maps worked great. My afr would stay around 14.7 under normal driving and go down to between 10.5 and 12 under boost. So it was all good. For some reason, I could not drive my car throughout July 2008. And then when I started driving it again in August, the afrs had gone up. I would be idling at around 15-17 (warm). The car would have 12 at cold start and then immediately jump up to 15 or 16. This continued to happen until I decided to ditch the RB25, and sold everything including Nistune and the engine, etc..

And now that I have an RB26DETT, the high afr problem seems to have crept up again. The only common factor that I can think of between the two is fuel pump, fuel lines, and the wideband itself. But I would not think its the wideband as the performance should not be suffering due to it.

Fuel pump seems to be the obvious culprit, but then how come it is able to give enough fuel under boost to bring it down to 12-13? I mean it is still high for boost conditions, but it does come down. Do you guys think it is the stock FPR? Any way to check it other than hook up a fuel pressure gauge to it? I might have one kicking around, so will see if it helps.

So, as per the suggestions:

1. Fuel pump
2. Fuel lines
3. Messed up pump wiring - how much voltage or range of voltage should i notice?
4. Stock FPR
5. O2 sensors (dont think so, but let's see)
6. Vacuum leak between MAFs and Turbos
7. Vacuum leak in the intake piping (from turbo outlet to the intake manifold)
8. A loose vacuum hose somewhere under the plenum or around the head
9. An unplugged vacuum line
10. Bad gas - sounds farty!!
11. Faulty injector(s) - now that would be a PISS OFF!!

[mcfly]

do you have anything tee'd on the fuel pressure regulator?

[speedfreak]

Where is the wide band bung welded , if it is too far down stream then readings may be wrong.
Also are you sure the ECU is not reflashed for larger injectors.

[judasentinel]

I think I need to be clearer about what exactly is happening. I drove the car myself today and here is how it is behaving:

The car starts fine, with a high idle (around 1400 rpm) and then settles down to 1000-1100 rpm, which is where I like it to be. The afr at idle stays at around 14-16, which is alright, manageable.

I put it in gear and drive off. Since I have a new clutch, I am taking it easy on the accelerator. As I accelerate, the afr starts to increase, until I reach around 3500 rpm, at which point it goes off the chart on the lean side (more than 18). If I let go of the accelerator, the afr comes down to within readable range 15-17.8 or so. If I boost the car, the afr richens up and goes down to around 12-13, and then suddenly, the engine cuts out at around 5500 rpm with a 'whooosh' sound (BOV). For some reason, if I boost it, it is very hard to go past 5500-6000 rpm while staying in boost, but if I accelerate slowly, I think I might be able to go past it (although I havent tried since the afr goes too lean at around 3000+ rpm). Now when the car hits 5500-6000 rpm, the BOV goes off and it sounds like a fart (not like an explosion). I am using an HKS trumpet style single BOV at the stock location under the battery on the FMIC pipe. It is not recirculated back, but is vented into the atmosphere.

Initially the idle was higher (1500 rpm) when warm. But I turned the idle adjustment screw in and it came down. I also tried to disconnect the AACV after the car was warm and there was no change in revs.

This is getting a bit frustrating now. Why would it kind of bog out or cut at 5500-6000 rpm? I have an MBC connected as well to the wastegates, but it is fully open, so its non-functional right now. When the MBC is connected but not working, is the car running stock boost? Can we classify the bog/cutting out as boost cut or fuel cut or is the ECU retarding the timing by jumping to the knock maps rather than normal maps?

I am wondering where I need to start now, but here is my list:

1. Check coils for resistance and voltage
2.Check spark plug condition to identify if any of the cylinders are leaning out
3. Check the fuel pump and see if it is wired properly and if there is any leak in the fuel delivery system for it to be losing pressure
4. Check for vacuum leaks between MAFS and turbos
5. Try running the car with the Power FC that I have and see if it improves anything - apparently, it has the stock maps loaded on to it
6. Check the TPS voltage and set it to 0.47-0.5V on idle

I am more concerned now due to the cutting out around 5500 rpm, as this could signal something dangerous.

What do you guys suggest? i want to finish sorting this out in the next few days while I am off from work. Thanks.

[speedfreak]

I think you should start with the pfc
It would eliminate alot if you are familiar with the sensor data info it can provide.
Also what MAP sensor are you using and how have you hooked it up?