Intermittent Leaning Problem (r34 Gt-t + Power Fc)

[Charbzilla]

I've had my car (1998 R34 GT-T + Power FC + 3.5" Exhaust turbo back + GTR intercooler + K&N Pod Filter + Walbro Fuel Pump) for 18months now and have had an insignificant surging problem at idle ever since I purchased the car. (Read on - gets worse)

(Background info - The timing belt was claimed to be changed by the previous owner at 44,000km, which was 30,000km ago)

I finally decided get rid of the bleed value it came with (eekk!!!) and have recently installed a Apexi AVC-R boost controller to properly maintain the 14psi at full boost (stock turbo). I also have had a trusted turbocharging specialist (popular on supra forums) dynotune my Power FC hand controller as I had altered the timing map myself over the last 18months to completely eliminate pinging that was occuring on boost due to a terrible tune it had when i purchased it.

THE ISSUE IS

On the dyno an issue arose by where the power fc or prehaps a sensor will lean out the timing map by where the air/fuel ratio of 12.7 will intermittently increase to as high as 19 all on its own and then return back to normal. (very similar periodic behavior to the "insignificant surging problem" I was having pre-tune, however now that the car's tune is pushing the limits of its performance the "insignificant problem" is now very significant in the sense that I would usually need to switch off the car or give it WOT to correct the problem of the leaning out (It feels like a dog to drive when its in that state)

The timing belt was not an issue as we adjusted the timing belt adjustment bolt on the dyno yet it still did the intermittent leaning out problem.

Because it comes and goes randomly I am having major issues diagnosing it.

What are your thoughts?

Could a faulty sensor be responsible for its periodic leaning out behavour? Power FC at fault? Please Help!!

DYNO RESULTS (for your interest)

The dyno results (done at NT Performance (Footscray, VIC)) are attached (before and after)

You'll notice the blue line has two dips in it.

One very noticable at the 115km/h mark and one at the peak power of 235rwkw due to a slippery clutch which only started happening on the dyno due to the freak power the engine was able to produce thanks to NT Performance.

[paulr33]

the dyno plot looks ok, the blue line is ok except for the surge where you said is the clutch slip

if the AFRs are dropping to 19 with no direct cause and the maps look ok, something is horribly wrong

check the basics

check is the ECU secured into the connector properly or it is loose and flopping around

check the fuel pump (what type, how old)

check the fuel pump (how is it installed, is it on the factory bracket at the back of the tank or is it floating around)

check your airflow meter, is it clean and OK or are the wires mangled and cut

when the problem occurs on the dyno do you see the engine check light flash or stay on?

if a sensor is f**ked the powerfc will turn on the engine check light (different to flashing engine check light)

when this happens you can you view ETC, SENSOR SW CHECk to see which sensor is dead

if you dont get the engine check light coming on and staying on, basic sensors are OK (throttle, airflow meter, water temp)

[Charbzilla]

Thanks for the prompt reply Paul.

There is no check engine light at all.

The fuel pump is a walbro pump, I will have to look into its state of health tomorrow, however Im not sure it would cause a 'periodic' issue, would you agree?

The AFRs just drop intermittently and return back to normal as it pleases.

I will run an extra earthing wire tomorrow for the ECU. Hopefuly its only an earthing issue..

Has anyone heard of anything like this before?

[TiTAN]

dont just rule out the fuel pump, on idle the ecu drops the voltage to the pump to reduce noise and if the pump doesnt work properly on the lower voltage the pressure can drop causing the engine to run lean (the ecu has no way to check fuel pressure so it is assumed that its where it should be)

[Charbzilla]

dont just rule out the fuel pump, on idle the ecu drops the voltage to the pump to reduce noise and if the pump doesnt work properly on the lower voltage the pressure can drop causing the engine to run lean (the ecu has no way to check fuel pressure so it is assumed that its where it should be)

This explains why it would happen intermittently when left at idle, and why it might 'correct itself' with WOT. I will have to inspect the damn thing tomorrow.

[scotty nm35]

Check the wires inside the AFM while you are there, it could be a dry joint on the board. Simple and cheap fix.

Fuel pump can be checked with a pressure gauge. I haven't had any issue running my pump at low idle voltage, not to say they don't chew out on the standard wiring.

[STATUS]

have you noticed at is 14 degrees and intake temp is 43.... nice way to inflate power.

That said check your pump and also check boost as it must be pretty high if its making over 210-220rwkw, they like to drop exhaust wheels over 13 psi.

also check the feedback 02 setting it could be trying to pull to an unrealistic setting (1.047 should be ok) or your o2 sensor is shagged.

[Charbzilla]

OK so today I've changed the fuel filter just to be on the safe side (problem still exists obviously)

Having a look at the sensor check (Power FC) i can see that the o2 sensor reading is high at 1.66V

I then figured i'll try switching off the FEEDBACK Control for the o2 Sensor.

o2 Feedback ON (default) - holding 2thousand revs sounds very wonky with the periodic splurt of fuel.

o2 Feedback OFF - holding 2thousand revs now seems to be running fine again (smooth). A quick drive around the block was a success. Im wondering though, how will my fuel consumption be now that the o2 sensor feedback control is off? Will it make a drastic effect on the fuel/timing maps as they have just been tuned?

...

status, i didn't notice the huge difference in the temperatures (AT vs IT), as I haven't had a car dynoed for about 4-5 years lol

I will have to get it redynoed to see what it actually is pulling. THanks for the heads up.

Edited June 8, 2010 by Charbzilla

[Charbzilla]

i did notice at one point the o2 sensor hit 0.00v

Thoughts?

EL falcon o2 sensor will do the trick?

[Charbzilla]

the intake temp of 43 on the dyno was correct because it was dynoed after 5-5.5 hours of dyno tuning (as we were having problems with the leaning problem).

my oil is so black now as a result. just purchased some turbolight 4100

Edited June 8, 2010 by Charbzilla

[paulr33]

yeah just leave the 02 feedback off until you replace the sensor

you can find the sensor and matching plug or replace with ford el falcon 02 sensor, but youll have to cut the wires

when 02 feedback is off your economy will be ordinary, but still OK

ie it might be 250kms to a full tank instead of 350kms+

[Charbzilla]

yeah just leave the 02 feedback off until you replace the sensor

you can find the sensor and matching plug or replace with ford el falcon 02 sensor, but youll have to cut the wires

when 02 feedback is off your economy will be ordinary, but still OK

ie it might be 250kms to a full tank instead of 350kms+

THanks paul,

is it eventually neccessary to have the o2 sensor feedback fnction back ON for the powerFC? Lets just say i get it retuned without this function on, can the car depend on the ignition/timing tune alone. (i.e. can i still achieve 400kms with a perfect tune and NO F/B o2?)

OR

will i definately still need to use the o2 sensor feedback function? (better performance for a range of different weather temps, fuels, etc)

Edited June 8, 2010 by Charbzilla

[STATUS]

THanks paul,

is it eventually neccessary to have the o2 sensor feedback fnction back ON for the powerFC? Lets just say i get it retuned without this function on, can the car depend on the ignition/timing tune alone. (i.e. can i still achieve 400kms with a perfect tune and NO F/B o2?)

OR

will i definately still need to use the o2 sensor feedback function? (better performance for a range of different weather temps, fuels, etc)

you can get good economy with it switched off, provided the fuel mapping and afm curve is right. You will need to check it over. My GTR used to get 595kms out of a tank and make 360awkw... no o2 sensors at all...

[Charbzilla]

you can get good economy with it switched off, provided the fuel mapping and afm curve is right. You will need to check it over. My GTR used to get 595kms out of a tank and make 360awkw... no o2 sensors at all...

thats amazing! thanks Stat.

My question is though... how many maps did you need to have to allow optimal driving conditions for all year round?

i'll only have the one map (power FC) so the lack of adaptability might be the reason i might need the o2 sensor perhaps?

[paulr33]

its nothing to do with how many maps you have (or need)

the 02 sensors will trim your AFRs if they are rich on cruise

ie if the tuner hasnt tuned every cell for a prefect AFR on light cruise, the powerfc (and stock ecu) will self correct and lean out to stoichometric

you can, however, if your tuner is good enough and has enough time (ie cost $$$) he can lean it out beyond stoichometric

and either set the PFC stoichometric to lower than 14.7 or like trent said tune the cells (takes time with a wideband)

on my gtst i was able to set my afrs around 15/16 ish on light cruise with no issues & you get good economy