Running Lean - Troubleshooting

[SNaray8442]

P1124/P1126

Possible fault areas; intake air system leaking, fuel pressure too low, volume supply of fuel pump too low, fuel injectors fouled.

I've already replaced o2 sensors without any results. Where should I look to next?

My post-cat o2 sensors were white, looked very lean. Pre-cat were not.

Any suggestions what to troubleshoot first?

Thanks!

[SNaray8442]

First thing's first. How would I check the intake and exhaust systems for leaks?

Is brake clean around my intake gasket safe?

I don't see any obvious carbon trails out of exhaust.

Edited November 28, 2007 by SNaray8442

[vizcarra44]

First thing's first. How would I check the intake and exhaust systems for leaks?

Is brake clean around my intake gasket safe?

I don't see any obvious carbon trails out of exhaust.

Are the codes Above limit or Below and what year 996?

Regarding checking for a vacuum leak, the best way is to use a professional smoke machine or use Butane kit sold at Home depot with control valve. Just put a vacuum hose on the valve and start spraying around the intake and monitor your upstream oxygen sensor voltages, if there is a vacuum leak you will see the sensor voltage lock at almost 950mv.

Do you have any Driveability issues?

Vizcarra44

[1999Porsche911]

Check to make sure that there are no intake leaks or vaccum leaks. Check oil cap is on properly. Run a can a fuel injector cleaner through the gas tank and clean the MAF. If you had a scanner, you could get closer to identifying the problem. There are many other things that can cause those codes, including exhaust leak ahead of the sensors (unlikely), fule pressure or flow too low (also unlikely).

BTW: Don't just replace the O2 sensors when they report a probem. They are simply doing their job.

[SNaray8442]

The sensors are sensing rich threshold. The car is a 1999 911 C2.

Oil cap is on tight, as is the gas cap. I used a whole can of MAF cleaner on the MAF. I'll put some injector cleaner through today.

I've never checked for vacuum leaks before, is it something that's fairly straightforward or should I take it to a shop?

Edited November 28, 2007 by SNaray8442

[1999Porsche911]

The sensors are sensing rich threshold. The car is a 1999 911 C2.

Oil cap is on tight, as is the gas cap. I used a whole can of MAF cleaner on the MAF. I'll put some injector cleaner through today.

I've never checked for vacuum leaks before, is it something that's fairly straightforward or should I take it to a shop?

You can visually check the hoses in the engine bay to make sure they look ok and are connected properly. Also check for leaks betwwen the air filter housing and the throttlebody. Since you have a 99 C2, also remove and clean the ICV (Idle control valve) that is connected to the left side of the throttlebody by 2 screwes. Removed (saving gasket for reuse) and liberally spray with carb cleaner. Clean you're throttlebody while you're at it.

Jim

Edited November 28, 2007 by 1999Porsche911

[SNaray8442]

Cleaned out the throttle body when I cleaned the MAF, it was surprisingly clean.

I'll visually follow vacuum lines and check for cracks and whatnot.

I'll also clean the ICV as a precaution.

[SNaray8442]

I haven't found any leaks and I've run a tank of injector cleaner. The code came back.

What next?

[1999Porsche911]

I haven't found any leaks and I've run a tank of injector cleaner. The code came back.

What next?

I asume you have a scanner? Take a look at the the following readings at idle, AC off on a fully warm engine:

MAF

Calculated load

STFT and LTFT for both banks

also check that your before cat O2 sensors are cycling every second or so from low to high voltage.

Edited December 1, 2007 by 1999Porsche911

[SNaray8442]

I don't have a scanner unfortunately. I'll try to find one locally.

[SNaray8442]

Nobody local has anything that they'd let me use to read my fuel trims and whatnot.

Any ideas what else to check for? Seems like drivability is pretty normal to me.

[1999Porsche911]

Nobody local has anything that they'd let me use to read my fuel trims and whatnot.

Any ideas what else to check for? Seems like drivability is pretty normal to me.

You can order several online. Search and you'll find out what many here use. This is a good one IMO: http://www.autoenginuity.com/

Edited December 3, 2007 by 1999Porsche911

[viper501]

A *major* air leak source is the rubber bellows between the oil separator and the engine. Inspect it for cracking on the backside of the bellows. It is a horrible design using an entirely inappropriate material for the heat and oil that it is exposed to.

[SNaray8442]

Thanks viper, I'll check it out.

Edited December 4, 2007 by SNaray8442

[SNaray8442]

So my CEL hasn't come back in quite some time.

It seems like every time the code is tripped is when I've been on the highway, get off, throw it in neutral and coast to a redlight.

[SNaray8442]

I think I've found the culprit... and you'll never guess what it was.

.....

.....

oil cap?

[Loren]

Oil cap is still a leak - so the OBD II (intake air system leaking) was right on.

[SNaray8442]

Code came back. Took much longer this time, but the same P1124 and P1126 are back.

Any suggestions on what to look for next?

I've already put it on a smoke machine, showed no problems.

Thanks!

[RFM]

Look for good connection rubber intake hose to throttle body, small crack in oil filler pipe, AOS + connections and pipes, vacuum line to the brake booster and brake booster as well, all small vacuum lines coming from the engine area and their connections etc.

Good hunting.

[wurger]

Another CEL with P1124 and P1126

First off, thanks for all the info and input here on this excellent site!

Not long ago I purchased a 1999 Carrara with 44k miles. In preparation for the 45k service, I removed the airbox to check if the car had a K&N filter before purchasing the filters for the service. I put the car back together and the next time I drove the car the CEL light came on after about 5 min of driving. The idle seemed to be a bit inconsistent (600-1200 rpm) when letting off the gas at a stop also.

So after searching through RennTech and the PCA site for info. I performed the following checks:

1) I performed the 45k service, replaced the pollen and air filters, oil, oil filter etc.

2) Used the Durumetric cable to check for fault codes and found:

P1124 Oxygen Sensing Adaptation Area 1 (Cylinders 1 - 3) - Rich Threshold

P1126 Oxygen Sensing Adaptation Area 1 (Cylinders 4 - 6) Rich Threshold

SO, I did all the things people mention for P1124 and P1126...

Cleaned the MAF with CRC elec cleaner.

Cleaned the throttle body and Idle Control Valve (ICV) with carb cleaner (this helped smooth the idle out).

Checked the Air Oil Separator (AOS) for leaks, none found.

Checked coils for condition/cracks, none found.

Replaced o-ring in the oil cap.

Checked the fuel cap.

Ran a bottle of techron fuel sys cleaner through.

I also checked for vacuum leaks but the CEL keeps coming back after 5-30min of driving.

So, I still think there is an air leak but Ive yet to find it. Maybe the oil filler tube? Any suggestions on what method to use for finding an air leak? Ive heard mention of a smoke test but dont have the equipment.

Any other thoughts would be appreciated. Thanks in advance.

Edited January 22, 2008 by wurger

[Stefan]

One way to find a vacuum leak is to use flammable gas, such as from a torch. You wave the (unlit) torch around in the suspect areas of the engine compartment. When the gas gets sucked in, the idle speed goes up.

[SNaray8442]

I've still got this code.

Any other suggestions?

[RFM]

You need a PIWIS tester in ACTUAL VALUES mode for further examination and testing, otherwise it will become a guess.

[SNaray8442]

Is the dealership the only shop likely to have that tester?

[Loren]

Is the dealership the only shop likely to have that tester?

A few of the really good shops have it too - but it is quite expensive so I doubt many small shops have one.

You could also find a shop with an older PST2 tester - it will work fine on your car and give the same diagnostics (on your model year) as a PIWIS.

Most dealerships upgraded to PIWIS and then sold their PST2's to independent shops so they are much more plentiful.