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1999 Boxster P1126 & P1124

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Old 04-10-2015, 12:34 PM   #1
steveltx
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Default 1999 Boxster P1126 & P1124

Hello all,

I know these check engine codes have been covered many times everywhere.

My 1999 Boxster has both P1126 & P 1124 codes for at least 3 years.
Sent to two independent garages and they couldn't find the problem.

One garage did a smoke testing and found leaks around oil filler tubes and
replaced both oil filler tubes (upper and lower). They also found the cracked
idle control valve and replaced it. The AOS is new. The MAF is also
replaced with a Bosch MAF.
They used the smoke machine to do the smoke testing and there was no vacuum leak found.
The P1126 & P1124 always came back after driving 20 miles.
What's the next area I need to check?

Should I send to Porsche dealer for diagnosis? Will that be expensive?
I have spent a lot of money so far and am running out of ideas.

Thanks.

Steve
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Old 04-11-2015, 01:00 AM   #2
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P1124 is oxygen sensing adaptation range 1 (cyls. 1-3) at enrichment limit.

P1126 is same error for cyls. 4-6.

If DTC P1124 or P1126 logged then fuel/air mixture is too lean.

Possible causes: intake system leak; fuel pressure too low; fuel injectors contaminated; volume supply of fuel pump too low.

Air leak would have to be common to both banks.

My first guess would be the AOS, but you say this is new. Barring a premature failure of the new one I'd say the AOS is off the hook.

I bet there is still a small air leak. Before you take the car to the dealer replace the oil tube filler cap.

A leaking cap mimiced a failing MAF so perfectly I replaced a $300+ MAF when a $13 cap was all that was needed. The cap probably costs more now but not nearly as must as a new MAF.

That leaves fuel pressure too low; fuel injectors contaminated; volume supply of fuel pump too low. For fuel pressure, possible contaminated injectors, or a sub-par fuel pump supply these tests are best left to a professional tech.

Assuming the gas tank is not low then you have to check for proper fuel pressure and supply.

You can test fuel pressure at fuel rail test point and remove the fuel pump relay and bridge terminals 30 and 87 (id'd as 3 and 5 on the relay panel) with home made test harness. Fuel pump should operate and pump fuel.

Engine off pressure should be 55 +/- 3psi. Engine running 48 +/- 3psi.

Test pressure ports require new seals. Check with Porsche parts counter guy and get extra ones before you test fuel pressure.

Be careful working around running engine and testing fuel pressure and flow.
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Old 04-12-2015, 05:29 PM   #3
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Other possible causes for vacuum leaks are the gas tank venting/purging system and the auxiliary air injection system.
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Old 04-14-2015, 04:22 PM   #4
steveltx
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Hi,

Forgot to mention that I have also replaced the fuel pump. The gas filler cap is also new.
So the fuel pressure should't be the cause of the problem.

Regarding the gas tank venting/purging system, how do I check if it has the vacuum leak?
Can this code P1126 be generated by the faulty Fuel Line Vent (Bleeder) Valve?

http://www.pelicanparts.com/techarti...Vent_Valve.htm

I don't have the problem filling up the gas tank. Ocasionally, I heard the hissing sound when I opened the gas cap. Does this mean the valve is bad?

Another possibility is the leaking exhaust pipe before the converter? Or dirty fuel injectors?

I am running out of ideas. Hate to send this car to dealer and spend a fortune.

Thanks.

Steve
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Old 04-19-2015, 12:36 PM   #5
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Quote:
Originally Posted by steveltx View Post
Hi,

Forgot to mention that I have also replaced the fuel pump. The gas filler cap is also new.
So the fuel pressure should't be the cause of the problem.

Regarding the gas tank venting/purging system, how do I check if it has the vacuum leak?
Can this code P1126 be generated by the faulty Fuel Line Vent (Bleeder) Valve?

http://www.pelicanparts.com/techarti...Vent_Valve.htm

I don't have the problem filling up the gas tank. Ocasionally, I heard the hissing sound when I opened the gas cap. Does this mean the valve is bad?

Another possibility is the leaking exhaust pipe before the converter? Or dirty fuel injectors?

I am running out of ideas. Hate to send this car to dealer and spend a fortune.

Thanks.

Steve
Well, you have already spent half a fortune and apparently are no closer to a final solution.

Fuel supply/pressure problems are rare, but you are running out of other things to blame the behavior on. I am always reluctant to advise a DIY'er to mess with the fuel lines and check fuel flow and pressure.

The most common cause of the error codes is an intake leak of some kind. Since both banks are generating the same error -- so to speak -- the leak is a common leak to both banks.

I know the AOS is new but it has to still be suspect. If not bad out of the box, it has gone bad or perhaps the installation was botched. Just saying. I would not expect you to replace this again on my suspicion. But you might give it a close inspection to see if you can see a hose loose, a tear in the rubber tube or something with the AOS out of the ordinary.

Next the new MAF. There have been reports of seemingly the "same" part but not an OE part while appearing to be the same not performing the same.

But like the AOS would I *not* expect you to run out and buy a genuine Porsche MAF for your car just on this alone.

Now I have to mention that the early Boxsters initially used a MAF that was superseded by a newer one, with a different part number. The "problem" with this newer MAF was in order to work properly the DME had to be flashed with a program upgrade.

If you bought the wrong Bosch MAF that while it is the right part number it is the newer MAF which requires the DME upgrade this might account for the behavior you report.

Sorry, but I have nothing really concrete to offer. You have been around the engine a time or two and are no closer to having this resolved. I think it is time to call in a pro.

Oftentimes, while a repair job by professional tech is the most expensive, initially, it is also the least expensive, longer term.
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Old 04-20-2015, 04:08 PM   #6
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Is this garage you took it to Porsche specific? Before doing the dealership option, I'd try to track down a specialist and see what they have to say.

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Old 03-19-2017, 05:19 PM   #7
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I have the exact same problem with P1124 and P1126. I will have to thoroughly check out this new AOS that a "so called INDI' supposedly did for me. He did not change the accordion lower boot but I did when I found it leaking a fine mist of oil around that part. However, I still get the same codes. Now I wonder did he actually change the AOS in the first place. I was not getting these codes before he changed it, which I paid him to change. I will have to go in myself and check his work. I have a camera scope which will come in handy when checking the AOS connection points. I probably will remove the alternator, (no prob as I have done this about 7 times already to do other work on the car) also the plenums etc to have a good look and feel around. Ah well, these things are sent to 'try us'.
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Old 03-19-2017, 07:06 PM   #8
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The smoke machine test of the vacuum system is very useful but not definitive. That is because there are many valves that my block the smoke from entering an area with a leak. There are some significant tricks to learn to use the machine effectively.
Another technique is to use propane.It is very effective if you use a small 'torch' on a flexible extension hose. It is more precise than using carb cleaner.Lots on Youtube.
Be very careful verifying Interchange/aftermarket parts. There are many examples of mistakes in the Interchange info for O2 sensors, the MAF, spark plugs
A competent Indie with a PIWIS or Durametric would probably identify the issue quickly.He would also be able to check the vacuum in the whole system(AOS test) using a manometer.Ask here for a recommendation?
But you'd feel miffed if the issue was the wrong generic parts fitted.I am not knocking generic parts. You just have to be very, very careful the Interchange numbers are correct. I just got O2 sensors for mine from a well respected source and the Bosch Interchange info was incorrect in their listing ! Yes, the Bosch numbers were wrong. Just use the Porsche part number. If it does not have the Porsche part number on it, how can you be sure it is the correct part. Another example - the P.O. had fitted new, top quality spark plugs. But they were for a different engine size Boxster. Yes, they worked but the heat range was one level off. Who knows what issue that caused- if any ? The MAF was the wrong one( there are new/old versions like Macster wrote) you can tell the later one by it's droopy 'nose' . Yes the old one works but ...how well? The coils had feint hairline cracks developing - difficult to see except with a lens after cleaning. Lots of picky details to research & clarify.
Good luck & please tell us the outcome.
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Old 03-20-2017, 03:22 PM   #9
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I am waiting for my new iPhone wi fi link OBD2 mini scanner to arrive. I found a small coolant leak and cured that. Also going to change the tie wraps I had on my accordion bottom AOS hose to the crank case. When I complete that job this wednesday, I will hopefully clear the codes p1124 and p1126 (no cel) and get the car on the road again. Hopefully the bottom tube of the AOS was sucking in air via the accordion type bottom hose and the metal clamps will cure that possible vacuum leak. I am not doing this work to get the car through the smog test, but for my own satisfaction. My evap monitor is in the 'not ready' zone. I am allowed 2 monitors to be in the 'not ready' zone and still can pass the smog test. I have the 99 996. From 2000 onwards only one 'not ready' zone is allowed in PA.
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Old 03-20-2017, 08:00 PM   #10
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Quote:
Originally Posted by Hurdigurdiman View Post
I am waiting for my new iPhone wi fi link OBD2 mini scanner to arrive. I found a small coolant leak and cured that. Also going to change the tie wraps I had on my accordion bottom AOS hose to the crank case. When I complete that job this wednesday, I will hopefully clear the codes p1124 and p1126 (no cel) and get the car on the road again. Hopefully the bottom tube of the AOS was sucking in air via the accordion type bottom hose and the metal clamps will cure that possible vacuum leak. I am not doing this work to get the car through the smog test, but for my own satisfaction. My evap monitor is in the 'not ready' zone. I am allowed 2 monitors to be in the 'not ready' zone and still can pass the smog test. I have the 99 996. From 2000 onwards only one 'not ready' zone is allowed in PA.
The accordion tube can experience considerable pressure difference with the crankcase being under very low pressure while of course the outside being at atmosphere. To give you some idea of the amount of pressure involved (due to the surface area) even something as relatively "small" as an oil filler tube cap can be difficult if not impossible to remove against this pressure difference.

I'm thinking that zip tie will allow the accordion tube to come loose.

Thus my advice would be to secure the accordion tube with the proper hose clamps.
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Old 03-21-2017, 10:29 AM   #11
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i know there are allot of guys out there who have the vac leak theory but i have had the same codes and changed the maf sensor some lines oas and a few other parts. On a trip down to florida after driving for 4 hours i broke down yet again and had it flat bedded to the closest true european car shop. This guy had nothing there but bmws vws and porsches, after reading codes and putting a pressure gauge on my fuel system he correctly diagnosed the issue even though there really is no real code for it, it was a bad fuel pump. The car would run but because the pump was old it started to slow down which in turn threw the codes and had the car run badly. i bought a brand new pump off ebay for 200 bucks now all is good and no more codes. i would check that fuel pressure if its varies and goes low at idle it the pump, easy peasy.
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