P1128/1130 and o2 sensor voltages

[aklava]

OK here goes. In my attempt to solve my p1128/p1130 errors, i have looked at the rkat values for both banks and both indicate significantly negative values around -4. i understand the engine is leaning off the fuel at the injectors by this value and i am not convinced i have a vacuum leak (otherwise why would the rkat be so negative). Ssen a good thread about the maf solving this issue so i have ordered that. I replaced spark plugs this week and reran the durometric to see if this made a difference but no change to rkat. Still waiting for my new maf. I did check the o2 sensor voltages though which fluctuated widely between 0.1 and 1.0V at idle. Seemed a little strange but not sure if this is abnormal pattern. My car is a 2001 without precats (ROW i guess) and readings taken upstream for cat. Ideas and comments greatly appreciated.

[aklava]

Done a bit more searching. Looks like it should fluctuate under normal idle conditions.

[Cajundaddy]

Over 90% of those codes are caused by a fouled MAF or intake air leak.
Codes 1128 + 1130


Unless you recently changed your O2 sensors and don't trust them, they are probably just accurately reporting a problem upstream. Looking deeply into O2 sensor voltages is usually a wild goose chase with no joy in the end.

[Etienneg01]

Hi,

My name is Etienne, i'm French and i just moved to Miami, Florida.

I have recently bought a BOXSTER 00 2.7 and i get the CEL on.

I went to many stores to switch off this light, but nobody has been able to give me a real diagnostic (or i should pay 150$ at a local Porsche Center to read the ODBII)

As i'm still student i can't afford this operation and i hope you can help me.

I read on this forum that for 90% of the case this i caused by a fouled MAF or intake air leak. But my car is pretty old now and have an high mileage (130.000) i think that the O2 hasn't been change for a while.

I got other issue who are certainly relative to this, my car stalled at red-light (sometimes) or in traffic jam.
When i start the engine i got a white smoke during 10 seconds.

But the rest of the car seems to work correctly, i'm not a pro and i cannot know what is really going on, but do you think that O2 sensor who can possibly be way to old tells the car to lean the mixture and so the car stalled by running with a low gas concentration ?


I hope you can be able to help me, i really don't want to put thousand of dollar to repair it as i purchased this car 4 days ago.


Regards

Etienne GELAS

[Etienneg01]

I forgot to say that every time I to the gas station and refill my boxster the car won't start.

I have to press the accelerator to make it start, this is the same thing when my engine stalled in traffic

Thanks

[mikefocke]

The 1128/1130 codes causes are listed as...in this order...

– Incorrect signal from MAF sensor
– Intake air system leaking
– Fuel pressure too low
– Volume supply of fuel pump too low
– Fuel injectors fouled
– Exhaust system leaking

Now you have to chase which one or several are the cause and that takes either persistence and time (and perhaps spending money to replace parts that don't need replacing) or the labor of a Porsche expert who can do further diagnostic tests to isolate the real cause(s?). Your choice.

You don't say the year of your car (always helpful when asking for help with a code as they sometimes vary) nor the maintenance history of it. Fuel filter clogged (some of the older year models have em accessible)? Air filter clean?

[Etienneg01]

Hello Mikefocke,


I wrote "00" because it is a 2000, may be you don't noticed it, i should have written 2000.

The fuel and air filter are clean, my AOS was changed 8000 miles ago.

I will try to clean the MAF sensor, but don't you think that it could be the oxygen sensor?

It could be the fuel pomp, but i cannot understand why i can't start correctly the engine after refueling.

As i said white smoke during 5-10 seconds when i start the engine in the morning.

So in order : changing the O2 sensor before cat, cleaning the MAF, check the fuel pomp.

right ?

[mikefocke]

Check the AOS by removing the oil filler cover and feeling for suction with your hand. I'd focus on the white smoke as a clue before anything else. Just because you changed it doesn't mean it didn't fail again. Or look at the throttle body and intake and see what kind of oil they have in them.

Check the color of the oil and coolant.

The usual cause is something loose or a plastic part cracked. And with your mileage that is where I'd start.

Why do you suspect the O2 sensors? They give off very specific codes when they get old or fail and these aren't the ones. My experience the sensors are usually good for 60k miles or so. Yours may be a third set. (You have 4 sensors, 2 on each side of the exhaust.)

You are looking for something that would affect both banks (sides of the engine) and a single O2 sensor failure would affect only one side and give one code. If a sensor is the problem, it is going to be the one that is common to both sides and thus something before the throttle body...the MAF. Yes clean it. Seldom helps.

[Etienneg01]

Ok, i checked for suction, I get some at the oil cap, but not too much I can take it off pretty easily when the motor is on.
My Rpm is changin when I do this.

I went to an auto part store and deleted my CEL

I pulled out the MAF connector and wait to see if the CEL is coming back

I have only regular torx so I cannot unscrew it for the moment
It looks like special torx is it a regular thing ?

The car shifts in a way different manner since I have unplugged the MAF

I will look at the throttle body and let you know what's in there.

Thanks for your help !

[aklava]

Ok guys. Just an update. changed MAF sensor today. RKAT values for both banks normalised now. Looks like i could have solved the p1128/1130 code issue. I'll keep an eye on it and post again.

[Cajundaddy]

Etienne,
Diagnosis first, repair second. Before going any further, get the error codes to direct your efforts. A small pocket reader will do:Actron CP9125 PocketScan Code Reader : Amazon.com : Automotive

The symptoms you describe sound more like gas tank venting issues than O2 sensor or MAF. Get the error codes.

[Etienneg01]

Hello, again.
I got some news from the collection in Miami.
I spent around 360 dollars to get diagnosed completely as i'm not a real car technician !

I got an quote, who was really "spicy" like we say in France....

2090 to get fixed.

I gonna need you help and confirmation to be sure.

I came to this famous repair shop in Miami because the were Porsche accredited, i told them that my car stalled every time i go to the gas station and that my CEL in on.

They apparently spent 3 hours to read the codes, what i don't believe but anyway i get some clues from them.

Apparently the spark plug tube seals is leaking and has to be change, what can be done for $450 i guess (i hope) that includes labor.
then the quote mention the purge valve who has to be changed too

and to finish 950 for the read break pad and rotors, what is a freaking joke...

So, do you think the diagnostic is correct and what should i do, maybe i can buy some of the parts on pelican's website and ask a local repair shop to mount them.

Do you think a repair shop would be agree to do it if i bring the parts ?

Thank you so much for your help, i think that car gonna be fixed soon and work as great as she should do

[barlowdo]

I got the same cels on my 2001 996 after doing an oil change. I also experienced rough idle with oil cap off.

I replaced the o ring inside the oil cap and also a broken o ring on the power steering pump and problem went away. I doubt the power steering pump was the culprit but the oil cap o ring was. It did not look damaged and before I got a replacement I added some White Lithium Grease on the old oil cap O ring to help it seal.

Don

[jwgn777]

Originally Posted by Cajundaddy

Etienne,
Diagnosis first, repair second. Before going any further, get the error codes to direct your efforts. A small pocket reader will do:Actron CP9125 PocketScan Code Reader : Amazon.com : Automotive

The symptoms you describe sound more like gas tank venting issues than O2 sensor or MAF. Get the error codes.

Good point. I have had bad tank venting switches and line leaks even bad fuel caps that always set O2 sensor codes along with another code or an O2 code by itself.

[Scubby65]

I only had the P1128 code. It came on at the end of last year so I just reset it but it quickly came back this spring. I cleaned the MAF and while cleaning up the engine a little bit I noticed that the brake vacuum booster connection was wiggly so I removed it and and just re-installed it and made sure it was tight. The main air hose right after the MAF was also not seated so I adjusted that too. It's been a few weeks now and the light has not come back on so I'll keep my fingers crossed but I think it may be fixed but unfortunately I'm not sure which "fix" did it but if the vacuum booster is on the 1-3 cylinder side I would suspect that was it.

[ELoomis]

Scubby,

Can you describe where the brake vacuum tube is located. I am having similar problems.

Thanks,
Eric

[Scubby65]

Eric,

Here's a picture of the part that I was talking about. All I did was take it off, flip the o-ring around and re-installed and made sure it was tight.

Scott

http://www.pelicanparts.com/techarticles/Boxster_Tech/11-ENGINE-911_Engine_Swap/images_small/Pic49.jpg