introuble

Guys,

I've been having a problem with my AFR's lately (within the past 2 weeks). I have a wideband O2 monitor and every so often it goes very lean - like 16.5 -18.1 while driving around and when it goes under boost it doesnt change until it hits around 12psi. I have a mafterburner and when I changing the fuel curve I doesnt seem to help. I know that its not the chips either or the AEM wideband giving a false reading (been to a dyno to test it). My injectors are siemens #48lb and they are also new. Everything was working just fine and sometimes does bust recently its becoming more of a problem.

The last and only thing that I can think of would be the wiring harness to the injectors. Is it possible that there is low voltage coming from them? Or is the DME going faulty? Would a LR wiring harness fix a low voltage issue?

special tool

You need to check the vacuum signal to the fuel pressure regulator.

AND NOT JUST THE CONNECTION AT THE REG, BUT ALL CONNECTIONS DOWNSTREAM ALSO!

introuble

I will check that as I can see it might be a problem under boost. I have the LR fuel rail and adjustable regulator and the pressure guage switch shows a drop in pressue when the line is attached. I dont know why this would cause it to go lean in idle.

fast951

If the FPR is fine, investigate the fuel filter then the pump.

Rogue_Ant

How old is the sensor? They do have a lifespan.



Rogue

Tom M'Guinn

This is what happened when the line to my FPR developed a crack -- I never really understood why it was intermittent like that. At first i thought it was a tuning issue, and I kept adding more gas, then going pig rich, then pulling gas, etc. Finally, my HG popped and I found the cracked hose when pulling it apart.

indi9xx

Check for a potential exhaust leak anywhere between the exhaust manifold and the o2 sensor (including all the way to the wastegate).

If there is a crack, blown gasket or hole, then as well as blowing out exhaust gasses, between exhaust pulses it will draw in air (o2).

If once you start getting boost past a certain point the ARF normalises, its probably due to exhaust back pressure causing exhaust gasses to be lost, but no air being drawn in.

Remember, an O2 sensor senses oxigen and gets the AFR from how much oxigen is remaining after combustion... if you have an exhaust leak it will not be showing whats left after combustion, but also whats being drawn into the exhaust from the outside world.

Does the car seem to be running fine, even though it has seemingly bad AFR?

Jon

introuble

The car seems to run ok except when at idle when the AFR is past 17.1 and leaner the car feels like its going to die, but never does. When I am in boost 10 psi and after when it seems like is normalizes then I take off like a rocket. I have deleted the O2 sensor and I am just running the wideband and fuel controller. I will check for an exhaust leak or maybe cracks.

introuble

I am doing exactly the same thing. I am adding more gas by turning up the pressure and adjusting the fuel curve. I certainly do not want to blow a HG so I wont continue to do this. I will check all the lines running the the FPR and before to see if there are any cracks.

I just recently installed a Bosch HV fuel pump and fuel filter. I have checked both of these for leaks and found none. The pump seems to be working just fine as I hear a buzzing noise.

After all this is checked and "if" I continue to have the same problems, could there be an issue with low voltage in the wiring harness?

Tom M'Guinn

What kind of fuel controller are you using? A bad connection or faulty controller can also cause problems.

indi9xx

Introuble, Wideband 02 and 02 will both pick up exhaust leaks as a lean condition. Check it out for leaks anyway..

But if you car is seeming like it wants to die at idle, it does sound like a vacuum leak somewhere between the MAF and intake valves... I would suspect a cracked J-boot between the MAF and turbo, intercooler hard pipe rubber couplings onto the intercooler, or a vacuum hose blown off somewhere.

An intake leak on the low pressure side (MAF to turbo) would cause a lean condition which would be most severe at lower rpm and possibly getting closer to normal AFR as the revs or boost (airflow as a whole) increases as the volume of unmetered air becomes less of a ratio versus metered air on a constant flow leak.

An intake leak on the high pressure side (anywhere between the turbo and intake valves) would tend to cause a lean condition off boost and possibly a slightly rich condition on boost.

Go hunting for a hissing sound in the engine bay (or possibly around your boost controller or hoses to the wastegate)... Some times they can be a pain to find, so good luck.