Running lean...Help!

Since getting my boost issues sorted, I've had some spirited drives and notice that the car is running lean @ WOT.

This is what I'm seeing on my AFR guage;

Warm idle and gentle cruising = 14.5 to 15.3

3rd and 4th gear pulls WOT ;

From 2k rpm to 3.5k @0.7 bar = 12.5 - 13.8

Transition 3.5k to 4k rpm = 14.3

4k rpm to 6k rpm @1.0 bar (EBC off) = 11.3 - 12.1!

4k rpm to 6k rpm @1.2 bar (EBC on) = 11.7 - 12.9!!

EGT's don't go above 900 deg C.

The car always used to run rich at what at 10.5 - 10.8

I have just replaced the fuel filter as it hadn't been done for a while and it was dirty but it has made little difference.

I've got STP injector cleaner in the tank now to see if that helps.

What checks can I do at home to help identify the problem?

At these levels am I right in thinking I may suffer from det even on a stock ECU?

Spec;

Guages:

SARD BOOST GUAGE,

AEM WIDE BAND AFR GAUGE

BLITZ EGT GAUGE

Turbocharger & Induction:

Blitz Dual SBC Spec R EBC

APEXI INDUCTION

TRUST 4 ROW SMIC

HKS SSQV DUMP VALVE

Fuel, Tuning & ECU:

Stock ECU

DENSO IK22

WALBRO 342 fuel pump

FUEL CUT DEFENDER,

Exhaust:

Whifbitz double De-cat

BLITZ NUR SPEC

I wouldnt say thats lean at all, touch on the high side of safe but certainly not lean.

I wouldnt say thats lean at all, touch on the high side of safe but certainly not lean.

Really? I've been doing a fair bit of reading on here and I thought the general consensus was mid 11's was best?

A few weeks ago I had my friends supra on my dyno, we measured AFRs too. He has the same spec as you do, only that he has the full 4 row greddy FMIC, but othwr than that, same.

We maxed out the turbos by pulling the hose that controlles them (regarded as unsafe ) but he is putting a td07s on it and knew his turbos are far from new cionditions, so he drove it like that every day and wasn't scared of blowing them. anyway, he only had 1.2bar at 4k and going down to 1.1 at 6k. What we saw on the AFR gauge shocked us - the car was running in mid 13s above 6000RPM, sometimes we have seen 13.6 at the redline! Stock ECU, just with a greddy FCD. apart from that more less same AFRs as you wrote. just at full pressure quite lean.

I wouldn;t worry in your case. When you tune a car, you shoot for safe 11s, but many stock cars drive in high 12s and are fine.

A few weeks ago I had my friends supra on my dyno, we measured AFRs too. He has the same spec as you do, only that he has the full 4 row greddy FMIC, but othwr than that, same.

We maxed out the turbos by pulling the hose that controlles them (regarded as unsafe ) but he is putting a td07s on it and knew his turbos are far from new cionditions, so he drove it like that every day and wasn't scared of blowing them. anyway, he only had 1.2bar at 4k and going down to 1.1 at 6k. What we saw on the AFR gauge shocked us - the car was running in mid 13s above 6000RPM, sometimes we have seen 13.6 at the redline! Stock ECU, just with a greddy FCD. apart from that more less same AFRs as you wrote. just at full pressure quite lean.

I wouldn;t worry in your case. When you tune a car, you shoot for safe 11s, but many stock cars drive in high 12s and are fine.

Would the stock ECU with knock sensors etc be able to deal with any det if there was any in the mid to high 12's at high boost and RPM?

If it could that would be nice because it's going like a rocket at the moment!

I think what's worrying me is the fact that over time this has happened. It used to run rich as expected over 1.0bar, so I'm thinking something is wrong.

4 year old Walbro maybe?

I was thinking of temporarily doing the 12v mod to eliminate the Fuel Pump ECU.

stock FPR ?

Faulty Afr sensor? although the readings seem right at lower boost/revs?

Can you recalibrate the sensor / gauge combination in free air? There are some real bargain genuine new Bosch LSU 4.0 sensors available at the moment, I just bought 5 of them. They do wear out.

Can you recalibrate the sensor / gauge combination in free air? There are some real bargain genuine new Bosch LSU 4.0 sensors available at the moment, I just bought 5 of them. They do wear out.

Hi Chris,

I did wonder about that, as when I turned the ignition on the gauge done its calibration sweep and settled at 15ish. So yesterday I took the sensor out of the exhaust and turned the ignition on and of a few times to let it calibrate in air and it went full scale lean (which I assume is right as there is no fuel in air). On the next run the readings were the same.

If it was faulty would it not be out across the whole range?

Would the Bosch LSU 4.0 sensors mate on the existing AEM UEGO wiring? How much are they?

I may change it just to eliminate it.

I wouldnt say thats lean at all, touch on the high side of safe but certainly not lean.

No - it's lean on boost. Don't worry about the TT transition that's normal to go lean.

Higher the number = leaner

Lower = Richer

12.5:1 is a race engines on the limit AFR.

10-11:1 is safe rich motoring.

So explanantions;

1. The AEM is goosed

2. The engine has an issue since you played with the fuel system.

3. You're getting in extra unmetered air before the sensor.

4. Electrical signal disrupted.

5. Fuel pump on it's way out.

I don't think it's 1 or 3 from the other readings.

I'm guessing the flow is limited, I think you may have upset something when you did the filter change...have you tried another fuel pump? Could you have pinched a hose? Upset the fuel pressure regulator? Are you running a stock regulator?

No - it's lean on boost. Don't worry about the TT transition that's normal to go lean.

 

Higher the number = leaner

Lower = Richer

 

12.5:1 is a race engines on the limit AFR.

10-11:1 is safe rich motoring.

 

So explanantions;

1. The AEM is goosed

2. The engine has an issue since you played with the fuel system.

3. You're getting in extra unmetered air before the sensor.

4. Electrical signal disrupted.

5. Fuel pump on it's way out.

 

I don't think it's 1 or 3 from the other readings.

 

I'm guessing the flow is limited, I think you may have upset something when you did the filter change...have you tried another fuel pump? Could you have pinched a hose? Upset the fuel pressure regulator? Are you running a stock regulator?

Hi Alex, thanks for the input.

I'm on a stock FPR. The car was running lean before I changed the filter. That was part of the reason why I changed it.

I put the pump in about 3-4 years ago. I have got the original j-spec one in the garage, I could try that.

Today I've looked at the FP ECU and there is a relay attached to it. It appears that the 12v mod has been carried out, so could this have worn my pump out? It buzzes away merrily still.

Are the FPRs prone to failure? How can I check?

Are these AFRs likely to cause damage as they are?

Stock FPR's are pretty tough, don't go wrong often, I was cheking it wasn't a nasty Ecotek one... I'd suspect the pump. They aren't very expensive - could be worth just getting a new one.

Hi Chris,

 

I did wonder about that, as when I turned the ignition on the gauge done its calibration sweep and settled at 15ish. So yesterday I took the sensor out of the exhaust and turned the ignition on and of a few times to let it calibrate in air and it went full scale lean (which I assume is right as there is no fuel in air). On the next run the readings were the same.

If it was faulty would it not be out across the whole range?

 

Would the Bosch LSU 4.0 sensors mate on the existing AEM UEGO wiring? How much are they?

I may change it just to eliminate it.

You would need to check the documentation and see if the guage software allows for an LSU4.0 sensor. I got five off Ebay, he had 300 and is down to the last 30 or so. Search Bosch LSU sensor.

Just an update, after running an STP fuel system cleaner through it has improved slightly but still a little on the lean side i.e high 11's with a flash of 12.1 on WOT.

I will fit a new pump and see if that sorts it. If not I'll try the FPR.

I see you just went full BPU. There are a lot of posts about how BPU fuelling works but basically it's this:

• When you approach 1 bar of boost the ECU will initiate fuel cut - everyone knows that
  
• You install a fuel cut defender that clamps the signal to the ECU to about 0.98bar of boost, to avoid fuel cut
  
• What it also does as it approaches 1 bar of boost is lock the injectors open, i.e. it runs at 100% duty cycle.
  
• This means if you run 1bar of boost you run very rich
  
• You now adjust the fuelling by running more boost (1.1, 1.2 bar) to 'dilute' it
  

This is why the mix will lean off the more boost you run - the injector duty remains the same no matter what you hit (if you went to 1.4bar you'd deliver the same amount as at 1.0bar).

This is also why you see it lean off as the revs climb - the window of time to ingest the constant stream of fuel gets smaller and smaller so the mix leans off.

As to why you are seeing leaner conditions than others, well, that's an interesting question I don't think it's the FPR if it's stock, as I've never heard of one of those failing yet. It probably isn't a weak pump but it's an easy component swap to test.

What AFRs did you see on your dyno run (which, I might add, has a very odd torque figure when compared with the non-BPU one in the same thread...)

Also, where are you taking your EGT readings from? I used to run 920degC worst-case with my hybrids, that was measured at the #1 runner.

I see you just went full BPU. There are a lot of posts about how BPU fuelling works but basically it's this:

• When you approach 1 bar of boost the ECU will initiate fuel cut - everyone knows that
  
• You install a fuel cut defender that clamps the signal to the ECU to about 0.98bar of boost, to avoid fuel cut
  
• What it also does as it approaches 1 bar of boost is lock the injectors open, i.e. it runs at 100% duty cycle.
  
• This means if you run 1bar of boost you run very rich
  
• You now adjust the fuelling by running more boost (1.1, 1.2 bar) to 'dilute' it
  

 

This is why the mix will lean off the more boost you run - the injector duty remains the same no matter what you hit (if you went to 1.4bar you'd deliver the same amount as at 1.0bar).

 

This is also why you see it lean off as the revs climb - the window of time to ingest the constant stream of fuel gets smaller and smaller so the mix leans off.

Great explanation, thanks.

What AFRs did you see on your dyno run (which, I might add, has a very odd torque figure when compared with the non-BPU one in the same thread...)

AFR's on the dyno on AEM wideband were;

4th gear pull

2k rpm to 3.5k @0.75 bar = 12.5 - 13.8

Transition 3.5k to 4k rpm = 13 - 14.3

4k rpm to 6500k rpm @1.1 bar = 11.3 - 12.1 - 11.7

If the revs were held above 4k and you floored it and let off and floored it and let off etc.. the AFR's stayed between 11.3 and 11.7 at WOT

I noticed the torque figure was exactly the same on the 2 runs On the first one I did have all the BPU mods fitted but with just a restrictor ring and not the EBC which is now holding the boost steady and obviously higher at higher revs.

I assumed that as the max torque is produced lower down the revs and that fitting the EBC has given more power high up the rev range thats why it hadn't changed ?

I'm also not convinced that my IACV vsv wasn't already a bit faulty at the time of the first run.

Also, where are you taking your EGT readings from? I used to run 920degC worst-case with my hybrids, that was measured at the #1 runner.

Probe is in the runner nearest the front, not sure if thats 1 or 6?

EGT's were around 900degC at WOT then just crept up to 920 @6500rpm so we let off. (Thought I read on here above 950degC is possible damage territory?)

As to why you are seeing leaner conditions than others, well, that's an interesting question I don't think it's the FPR if it's stock, as I've never heard of one of those failing yet. It probably isn't a weak pump but it's an easy component swap to test.

Yes the FPR is still the stock one. I may try the pump change next. I noticed that I have a relay attached to the pump ecu I assumed it was the 12v mod, but at idle and pottering around this relay clicks on and off loading and unloading the pump quite regularly. It has always done this for the 5 years I've had the car. Unfortunately I can't hear if it still does it when giving it any beans due to Nur Sec. I thought if it was the 12v mod it would just keep the pump loaded continuously?

Right, I put in a brand spanking new Walbro today and it hasn't changed a thing the old one was fine.

I'm gonna remove the 12v mod relay tomorrow so it's back to stock but I don't think it will help.

Any other ideas? Your help is much appreciated.

I would first ascertain that another wide band probe and readout agreed with your unit.

I would first ascertain that another wide band probe and readout agreed with your unit.

Thanks again chris, that's probably a good idea. You got one I can borrow?

Seriously though, I assume if I can't borrow one from someone and check myself on the road, it would mean paying for some dyno time and getting them to check?

I use a Motec PLM, which probably uses a different connector type, plus it's now in use on my RB26 engine. The RB26 uses two sensors, one in cylinders 1 to 3, and one reading cylinders 4 to 6. I wire one sensor to the PLM (Lambda meter) and the M800 itself reads the second. You can set the M800 software to read either sensor separately or average the two. With a laptop I can read both sensors independently and have a sanity check if one seems to be reading very differently, and assess if it's a sensor going down or a mixture problem on 3 cylinders, IYSWIM? It has proven useful, in finding an intermittent spark issue, and allowed me to narrow it down to one of 3 coils.

Removed the 12v mod relay so now using the fuel pump ecu and as expected still no change.

I´ve also got the problem.

when 0,5 bar and wot the afr begin from 10,5 and raising to 13 and higher when boost builds up.

If I turn up the evc5 to 1bar it gets worse, it begin with 10-12 and goes up higher than I have the balls to.

When idle the afr shows 12.

The fuel system is original. and the car is a euro spec. mod? see my profile

Any ideas.

Is it the same afr. if single or twin?