P1126 and low rpm hesitation - all troubleshooting listed- Help greatly appreciated!

[porschefan76]

Hello all. I'm hoping to get some help solving some issues with my "new-to-me" 2001 Porsche Boxster S 6-spd manual. I purchased the car in December of 2019 with 52,500 miles on the original engine and it ran perfectly until early November 2020. The car now has 56,980 miles on it. The issues began with a momentary perceived lack of power while merging onto a major highway shifting into 3rd gear and a check engine light later that same day. I purchased the Durametric tool and read a P1126 code, no others. The car wasn't acting up significantly until I cleared the P1126 code. Once I cleared the code, the engine began to idle poorly while cold and would backfire into the intake manifold when pressing the gas pedal, especially a sharp rev.

For reference, when cold, the engine has a tendency to perform much like the engine in this video around the 8 minute and 55second to 9 minute mark: https://www.youtube.com/watch?v=hddx5Ux1v4Y

It has not stalled on me, even when backfiring into intake etc. Once warmed up, the engine still hesitates going back on the throttle following shifts, but idles well and runs smoothly above 3,000 rpms. Fuel economy is terrible, I'd estimate at 12-15 mpg. Previous to these issues, fuel economy was over 20 mpg.


I got to work:
1. Removed and cleaned the MAF sensor with CRC MAF sensor cleaner. Cleaned/dried thoroughly twice - NO CHANGE
2. Replaced the air filter and removed the connector to the MAF and drove the car - NO CHANGE
-assuming this means good MAF, also when warmed up MAF data from Durametric matches Spec (15-16 kg/h at idle) with MAF connector installed
3. Dug into intake manifold, removing the throttle body, plenum and resonance tube and cleaned thoroughly and reassembled - NO CHANGE
- very little to no oil in intake. AOS tubes in good shape. Oil fill tube outside coated in oil and dust but no visible cracks. Cleaned the tube for reinspection at a later date.
4. Smoked the intake using a smoke machine, finding no smoke emitting from the intake - NO CHANGE
-smoked long enough for smoke to stream from the oil fill port when I removed the cap
5. Ran a full bottle of Techron fuel system cleaner in a full tank of gas. - NO CHANGE
6. Removed fuel filter and tested the fuel pump flow rate using the steps in the Bentley manual. Pump flowed 1.25 L in 30 seconds (exceeding spec 850mL in 30 sec) - NO CHANGE
7. Replaced what looked like the original fuel filter and tested the fuel pressure at the fuel rail. 3.8 bar with engine off and 3.3 bar with the engine at idle, meeting specifications in the Bentley manual - NO CHANGE
8. Tested vacuum at the oil filler with a manometer. With engine fully heat soaked, read between 4.95 and 5.05 inches of water column, meeting specifications I've found online. - NO CHANGE
9. I've purchased new fuel injectors and fuel pressure regulator and will replace the original fuel injectors (along with pressure regulator while the fuel rail is out) when the weather improves so I do not crack the plastic window (I do all work in unconditioned garage or outside).

The car leaks no fluids. I replaced the water pump, thermostat and coolant in May 2020. Spark plugs were replaced in June 2020, coils in excellent shape, not replaced. Spark plug electrodes were worn, but the plugs were not fouled. I changed the oil & filter at the 6 month mark with 2,900 miles on the oil.

Only knowns worth mentioning:
1. Original clutch, original IMS (at least no records indicating otherwise). Planning clutch/IMS when the weather breaks.
2. Camshaft deviation on bank 1 is -8.2 degrees (out of spec: +/-6deg) Still doing research but considering an engine out when I do the clutch to replace cam wear pads as well as chain tensioner. Bank 2 in spec at -4deg. Dropped oil pan when I bought the car, a few specks (maybe 15, size of ball point) of dark brown plastic in there. Have monitored since and no additional plastic in the oil or filter. Have 6 oil changes (back to 43,000 mi) worth of UOA's and all are good; 2 from me and 4 from P.O. (yes, I know this doesn't mean anything other than "so far, lucky")

I have driven the car 250 miles total throughout all of the steps listed above. I have captured data from durametric while driving on 3 separate occassions. I captured RPM, Banks 1&2 FRA & RKAT, banks 1&2 pre-cat O2 sensor & post-cat O2 sensor voltage, MAF hot film and voltage and intake air temperature if anyone is willing to dig into it. The only data I'd call "suspect" that I captured would be the post-cat O2 sensors, which appear to change while driving (voltage moves up and down) but they remain steady at ~0.74 mV on both banks at idle. The RKAT values shift from 0 to -2.4 on both banks and FRA shifts from 0 to 1.3 on both banks throughout the data acquisition period (I reset the ECU to clear the values and watch them change as I drove the car over time).

I've also actuated both bank Variocam at idle using the Durametric and I can verify that they are both functioning properly, causing the sound/feel of engine to change noticeably when activated.

I'm hoping for some experiences as I know this code and these symptoms are not rare. I've read every forum post I could find and I've tried to follow the troubleshooting steps in those posts, but I'm not getting any success. I've attempted to be succint and demonstrate my version of a methodical approach to troubleshooting the issues. I'm willing to try additional troubleshooting steps and procedures and answer questions as time permits. Thank you for your time!

Best Regards,

Rich

P.S. - should I post to other forums as well and if so, which?

[blue62]

Do you still get the P1126 code?
Is it the only code you get?
Any pending codes?

[JFP in PA]

I'd start pulling the fuel injectors, looking at the tips for carbon fouling.

RKAT is the adaptation value near idle.
FRA is the adaptation value under load and further divided into FRAU (lower load range ) and FRAO (higher load range) ranges (perhaps the durametric doesn't display these divisions).

The RKAT values near idle are used to change the length of the injector pulse to account for deviations from ideality (ie intake leaks) to maintain the proper O2 sensor reading. The RKAT value is an additive factor and can deviate by +/- 4.5%. The FRA value is a multiplicative factor and can deviate by 1.32 to 0.70. The positive values or values greater than 1 increase the injector pulse length to account for a lean mixture, and negative values and values less than 1 are to compensate for a rich mixture.

[porschefan76]

First, thank you both for responding so soon.

blue62
Do you still get the P1126 code?
Is it the only code you get?
Any pending codes?

P1126 is the only code I get legitimately. When I ran with MAF disconnected I got some codes for the MAF, but not since reconnecting. Also have not gotten P1126 back since first time. No additional pending codes.

JFP in PA
I'd start pulling the fuel injectors, looking at the tips for carbon fouling.

RKAT is the adaptation value near idle.
FRA is the adaptation value under load and further divided into FRAU (lower load range ) and FRAO (higher load range) ranges (perhaps the durametric doesn't display these divisions).

The RKAT values near idle are used to change the length of the injector pulse to account for deviations from ideality (ie intake leaks) to maintain the proper O2 sensor reading. The RKAT value is an additive factor and can deviate by +/- 4.5%. The FRA value is a multiplicative factor and can deviate by 1.32 to 0.70. The positive values or values greater than 1 increase the injector pulse length to account for a lean mixture, and negative values and values less than 1 are to compensate for a rich mixture.

Great, as soon as it gets warm enough to mess with the plastic window, I'll pull the fuel rail and look at the injectors as I change them.

I guess Durametric tool does not divide further because I do not see FRAU or FRA0.

RKAT values of -2.4 indicates rich at idle and FRA 1.3 (positive) is lean above idle then correct? I was considering smoking the intake again but if it's over-rich at idle, likely unwarranted?

Anything else I should be checking? Thank you for your time!!

[JFP in PA]

Originally Posted by porschefan76

First, thank you both for responding so soon.



P1126 is the only code I get legitimately. When I ran with MAF disconnected I got some codes for the MAF, but not since reconnecting. Also have not gotten P1126 back since first time. No additional pending codes.



Great, as soon as it gets warm enough to mess with the plastic window, I'll pull the fuel rail and look at the injectors as I change them.

I guess Durametric tool does not divide further because I do not see FRAU or FRA0.

RKAT values of -2.4 indicates rich at idle and FRA 1.3 (positive) is lean above idle then correct? I was considering smoking the intake again but if it's over-rich at idle, likely unwarranted?

Anything else I should be checking? Thank you for your time!!

You may be seeing a lean situation because the one or more injectors are carboned up and not delivering a full pulse fuel volume.

[porschefan76]

Originally Posted by JFP in PA

You may be seeing a lean situation because the one or more injectors are carboned up and not delivering a full pulse fuel volume.

OK, this is kind of where I was going when I ordered the replacement fuel injectors, so hopefully, I get some progress there.

One more question, the -8.2 bank 1 camshaft deviation alone should not be enough to cause these hesitation issues etc, should they?

Thank you again.

[blue62]

Following your issue with interest.
Please post results once you have changed out the injectors.

[ike84]

Happy hunting! Keep us posted

Sent from my POCOPHONE F1 using Tapatalk

[ike84]

Hey fan, glad to hear you're making progress. I could be wrong but I think that p1126 is a lean condition? Your negative fuel trim would support that. If you've got new injectors and good pressure then I would suspect a small leak. I know you said you smoked it but as we all know small leaks can be a pita for even the best to find.

Somebody else chime in on this, I don't wanna steer you wrong.

Sent from my POCOPHONE F1 using Tapatalk

[blue62]

Porschefan: Have you looked at the freeze frame info when the p1126 code triggers???
Could be a clue in that info.
I know you have smoke tested it and that the code is for just the one bank but the p1126 code is most often associated with some form of vacuum leak!!

[blue62]

Originally Posted by ike84

Hey fan, glad to hear you're making progress. I could be wrong but I think that p1126 is a lean condition? Your negative fuel trim would support that. If you've got new injectors and good pressure then I would suspect a small leak. I know you said you smoked it but as we all know small leaks can be a pita for even the best to find.

Somebody else chime in on this, I don't wanna steer you wrong.

Sent from my POCOPHONE F1 using Tapatalk

Yes a vacuum leak of some sort has been my thought from the beginning.
Faulty injectors, Faulty O2 sensors, Or a Faulty MAF sensor can all cause a lean situation.
Porschefan has replaced or proven all those things good so I am still betting on a vacuum leak of some kind.

[porschefan76]

Originally Posted by blue62

Yes a vacuum leak of some sort has been my thought from the beginning.
Faulty injectors, Faulty O2 sensors, Or a Faulty MAF sensor can all cause a lean situation.
Porschefan has replaced or proven all those things good so I am still betting on a vacuum leak of some kind.

I am truly hoping this turns out to be vacuum! I will get that smoke machine back on the intake ASAP (weather/plastic window ugg). Thanks again!

[Gilles]

just curious, could a Dry fuel injector Seal could cause a vacuum leak..?
.

[porschefan76]

Originally Posted by Gilles

just curious, could a Dry fuel injector Seal could cause a vacuum leak..?
.

Hi Gilles. Having just replaced all of my fuel injectors, on the fuel rail side, I think you'd have a fuel leak (pressurized fuel rail). On the intake manifold side, I suppose you would have an vacuum leak, yes.

If you have to replace your injectors or o-rings, I used a small amount of the recommended white lithium grease on all of the o-rings and it really made everything go back together nicely and prevents the o-rings from twisting upon insertion. Thanks!

[porschefan76]

Originally Posted by ike84

Hey fan, glad to hear you're making progress. I could be wrong but I think that p1126 is a lean condition? Your negative fuel trim would support that. If you've got new injectors and good pressure then I would suspect a small leak. I know you said you smoked it but as we all know small leaks can be a pita for even the best to find.

Somebody else chime in on this, I don't wanna steer you wrong.

Sent from my POCOPHONE F1 using Tapatalk

Hey Ike! Thanks for following up! Yes, I've had some progress, and it's driving much better, thankfully. I finally experienced those "smiles per gallon" again yesterday. I did notice a SLIGHT hesitation coming back on the gas in third gear yesterday while being slightly aggressive on an empty stretch and corner, but otherwise much improved.

I am honestly not sure one way or the other if it a lean or rich code. I have this excerpt from the Porsche/Bosch DME code list:

In above, being "below limit" can go one of two ways in my mind. If it's referring to the fuel trim being below limit, that would indicate a rich condition to me, because fuel trim would be subtracting from the injector time. If it's an O2 sensor that is below limit, to me that means lean because below .45mV is lean and above .45 mV is rich, unless I've got that reversed. The fact that Banks 1&2 RKAT are negative seems to support rich at idle to me as well, as RKAT is "range 1" so far as I can tell, which includes idle.

Other news and updates, I just had some warm temps in the garage, so I vacuum tested the power brake booster line and it held vacuum. I also started the car, pulled the vacuum hose from the fuel pressure regulator (rpms surged) and pulled about 10 psi of vacuum (over Porsche specification, I wonder if this means anything?). So the intake vacuum appears intact, if not high. That said, once outdoor temps are above 55F, I'll be smoking the intake again to look for leaks.

Anyway, if anything jumps out at anyone, please let me know. I need some next troubleshooting steps.

[ike84]

Before you bust out that smoke machine I would look at some vacuum diagrams so you're familiar with the system. The vacuum houses, changeover valves, vacuum resivoir, etc are kinda complicated - not so much in theory, just in the layout. Hairline cracks in the vacuum resivoir, for example, have driven people to the brink of insanity. If you go over everything with the smoke machine and get nowhere I would bust out the brake cleaner to double check. Good luck!

Sent from my POCOPHONE F1 using Tapatalk

[porschefan76]

Originally Posted by ike84

Before you bust out that smoke machine I would look at some vacuum diagrams so you're familiar with the system. The vacuum houses, changeover valves, vacuum resivoir, etc are kinda complicated - not so much in theory, just in the layout. Hairline cracks in the vacuum resivoir, for example, have driven people to the brink of insanity. If you go over everything with the smoke machine and get nowhere I would bust out the brake cleaner to double check. Good luck!

Sent from my POCOPHONE F1 using Tapatalk

Hey! I've had the plenum, throttlebody and resonator tube off quite a bit and I'm actually pretty familiar with the routing of the vacuum lines. It appeared to be messy to me the first time or two I looked at it, but it's actually pretty straightforward! That said, I take your point, especially with respect to the smoke machine.

I'm fairly certain it's not the reservoir, because if I pull the vacuum line between it and the one-way valve after running the car, I can hear it suck in air. Perhaps I'll get in there and just test lines and y-fittings with my hand pump because it's easy to do and doesn't stink like the smoke machine. I also wouldn't mind some information on how to test the change-over valves. I have a 12V power supply and the ability to regulate voltage, so I'd like to actually test them for operation. I'll keep looking.

All this said, I just pulled 10 psi of vacuum at the fuel pressure regulator which is pretty healthy intake vacuum, if I am not mistaken. Porsche troubleshooting manual for checking fuel pressure regulator operation specified 6-9 psi of vacuum on this hose. I HOPE it's a vacuum leak, but at this point, with RKAT at -3.5, it appears this motor is running rich at idle, not lean like I'd expect for a vacuum leak.

To further muddy the waters though, when I used my cheap bluetooth OBD-II with Torque Pro, the LTFT (not divided into RKAT and FRA in Torque app) showed that they were pegged POSITIVE for both banks, which would support a vacuum leak.

[ike84]

I just realized that I said something that doesn't make sense and I am now far more confused. 1126 is lean, but negative fuel trim is the car pulling fuel out. I typed that earlier in a rush and didn't realize what I had said.

But that was the original reason I recommended changing the o2 sensors in the first place - things are pointing to a lean condition but the sensors are reading rich and hence the ecu is pulling fuel.

I'm not sure I'm helping at this point lol. This seems really screwy to me though and I'm not sure I can explain it any further at this point. Sorry dude . I would still check for leaks if you've had every off recently but the continued 1126 when sensors are detecting rich and pulling fuel back has got me thoroughly confused.

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[JFP in PA]

P0107 Ambient Pressure Sensor – Below Limit

Possible causes:
- Short circuit to ground

The ambient pressure sensor measures the air pressure.
The ambient pressure sensor is incorporated in the DME control module.

[porschefan76]

Originally Posted by JFP in PA

P0107 Ambient Pressure Sensor – Below Limit

Possible causes:
- Short circuit to ground

The ambient pressure sensor measures the air pressure.
The ambient pressure sensor is incorporated in the DME control module.

Hi JFP, thank you for the reply. I did see something like this in one of the posts while I was searching.

From what I understand, the proper way to diagnose this would be to check for voltage and ground at the appropriate pins in the harness to the ECU and if that's good, then to look for the MAP output in Durametric? My problem is I'm not seeing anything labeled ambient pressure sensor in the wiring diagrams for the DME 7.2 in the Bentley manual. I see a "Sensor, Differentiale E12/E11", but it looks to be external of the ME and feeds to the two Camshaft Sensors. I also don't recall seeing a PID for MAP in Durametric.

Does anyone have troubleshooting procedures or pictures, or even past experiences to help me dig into P0107? Also wondering if this can be causing P1126? Any help is appreciated. Thanks!