I can google it but if you can give a few sentences about what you mean by "check the fuel trims" I'd appreciate it.
MAS, Code Chasing
Thread Starter
Intermediate
Joined: Apr 2020
Posts: 33
Likes: 23
From: Plano, TX
MAS, Code Chasing
Wanted to share some issues with my 996.1, see whether I'm on the right track (newbie DIY'er, FYI).
Last month the engine stopped holding an idle - it would start and just die. Based on research, I cleaned the MAS. That sort of worked; the car died again twice but then the idle just started barely holding about 1000 RPM. Assuming the MAS was bad, I replaced it with a Walker MAS (half the price of OEM). That seemed to do the trick. It was idleing as it had before.
About two weeks later, the check engine light came on. Engine Code P1123. Again based on what I saw on this forum and elsewhere, it appears this code has a few potential causes. It could be I have a faulty MAS (after all it wasn't OEM) so I bought a new OEM one but haven't installed it yet. Instead I started with checking the fuel pressure. This is where I am now. Key on, engine off, pressure started at 36 psi. Started the engine, pressure went to 45 psi. Let it run for several minutes, and the pressure never budged from 45-46 psi. Turned it off, let the car sit for 15 mins or so, pressure came up to maybe 50 psi or so.
This doesn't seem too far off - supposed to be 48psi at idle, 55psi when off, right? It seems I'm 3psi low, and I'm not sure whether that's cause for a new fuel pump. Some had suggested replacing the fuel pressure valve first. What would y'all do?
Last month the engine stopped holding an idle - it would start and just die. Based on research, I cleaned the MAS. That sort of worked; the car died again twice but then the idle just started barely holding about 1000 RPM. Assuming the MAS was bad, I replaced it with a Walker MAS (half the price of OEM). That seemed to do the trick. It was idleing as it had before.
About two weeks later, the check engine light came on. Engine Code P1123. Again based on what I saw on this forum and elsewhere, it appears this code has a few potential causes. It could be I have a faulty MAS (after all it wasn't OEM) so I bought a new OEM one but haven't installed it yet. Instead I started with checking the fuel pressure. This is where I am now. Key on, engine off, pressure started at 36 psi. Started the engine, pressure went to 45 psi. Let it run for several minutes, and the pressure never budged from 45-46 psi. Turned it off, let the car sit for 15 mins or so, pressure came up to maybe 50 psi or so.
This doesn't seem too far off - supposed to be 48psi at idle, 55psi when off, right? It seems I'm 3psi low, and I'm not sure whether that's cause for a new fuel pump. Some had suggested replacing the fuel pressure valve first. What would y'all do?
RL Community Team
Rennlist Member
Rennlist Member
Joined: Apr 2010
Posts: 6,288
Likes: 1,516
From: Ormond Beach, FL
What is a MAS? Do you mean the MAF (mass airflow) sensor on the air filter box? I know OE is expensive, but the entire engine depends on it. Only replace with a OEM Porsche MAF sensor.
Also, put a vacuum gauge on and check for vacuum leaks (or smoke test your engine to check for leaks).
P1123 - P1123 indicates an over rich condition on one cylinder bank (cylinders 1-3) that the 02 sensor and DME fuel trims cannot adjust for, usually caused by either a leaking injector or excessively high fuel pressure.
If in question, replace the fuel pressure regulator valve before digging into the fuel pump. Again, don't go cheap. Get a new one from Porsche.
Also, put a vacuum gauge on and check for vacuum leaks (or smoke test your engine to check for leaks).
P1123 - P1123 indicates an over rich condition on one cylinder bank (cylinders 1-3) that the 02 sensor and DME fuel trims cannot adjust for, usually caused by either a leaking injector or excessively high fuel pressure.
If in question, replace the fuel pressure regulator valve before digging into the fuel pump. Again, don't go cheap. Get a new one from Porsche.
Rennlist Member
Joined: Oct 2010
Posts: 7,773
Likes: 7,063
From: Alabama USA
When you have an idle problem or fuel mixture codes ALWAYS check the fuel trims ( TRA/RKAT) first BEFORE attempting any repair OR clearing any codes...
The codes/problem can be either rich or lean and looking at TRA/RKAT for "positive or negative values" will put you on the right path and eliminate half of the possibilities..
IE . Code P1123 can mean either "rich limit reached" OR " lean limit reached" and looking at the TRA/RKAT is the best/(almost only) way to know the difference...
The codes/problem can be either rich or lean and looking at TRA/RKAT for "positive or negative values" will put you on the right path and eliminate half of the possibilities..
IE . Code P1123 can mean either "rich limit reached" OR " lean limit reached" and looking at the TRA/RKAT is the best/(almost only) way to know the difference...
Rennlist Member
Joined: Oct 2010
Posts: 7,773
Likes: 7,063
From: Alabama USA
Here is a video where Tony explains fuel trims on Porsche very well, I hope you can wrap your head around it, it is very accurate...He rambles a lot at first but pay attention to the talk on fuel trim/TRA/RKAT when he finally gets going ...
Last edited by Porschetech3; Jun 29, 2024 at 08:57 PM.
Rennlist Member
Joined: May 2024
Posts: 2,049
Likes: 1,067
From: SoCal
If you can get your hands on a generic OBD2 scan tool with “Live Data” capabilities, you can try this:
Compare the short- and long-term fuel trims for Banks 1 and 2. If they differ from each other greatly, then it’s likely a bad O2 sensor.
If both values are practically the same, then it’s unlikely to be an O2 sensor (unless they both happened to freak out at the same time…)
Compare the short- and long-term fuel trims for Banks 1 and 2. If they differ from each other greatly, then it’s likely a bad O2 sensor.
If both values are practically the same, then it’s unlikely to be an O2 sensor (unless they both happened to freak out at the same time…)
Trending Topics
Rennlist Member
Joined: Oct 2010
Posts: 7,773
Likes: 7,063
From: Alabama USA
Be extra careful when using generic scan tools for Short/Long fuel trims and analysis and code interpretation. The generic tools don't use/display the same values as the Porsche Protocols and has confused many people and led them on Wild Goose Chases...
Rennlist Stories
The Best Porsche Posts for Porsche Enthusiasts
Stunning Porsche 356A Super GT Speedster Auction Fails to Meet Reserve
Verdad Gallardo
Every Era of 911 Owner Explained in One Sentence
Verdad Gallardo
Thinking of Buying a Porsche? Do These 10 Things First
Joe Kucinski
Pixar Pals Turned Into 1-of-1 Porsches!
Michael S. Palmer
Theon Goes Full Carbon Fiber With Stunning New Build
Verdad Gallardo
Genius Porsche-Themed Gifts That'll Make Any Dad or Grad Smile
Joe Kucinski
10 Used Porsches Are Selling for Way Too Cheap
Joe Kucinski
Tuner Is Converting Porsche 911s Into Shooting Brakes
Verdad Gallardo
This Coachbuilt Creation Is A Modern Take on the Legendary Porsche 917
Verdad Gallardo
Rennlist Member
Joined: Jul 2023
Posts: 289
Likes: 129
From: Honolulu Hi
You have had your 996 for 9 years and you don't own a Durametric?
What do you do when the CEL comes on? (because we all know it does)
Pay the Dealer $250 to clear the code? (and throw parts at the issue?)
Do as Skip said: Get the Durametric.
You will be glad you did.
What do you do when the CEL comes on? (because we all know it does)
Pay the Dealer $250 to clear the code? (and throw parts at the issue?)
Do as Skip said: Get the Durametric.
You will be glad you did.
Rennlist Member
Joined: Feb 2022
Posts: 687
Likes: 417
From: Annapolis County, NS
You have had your 996 for 9 years and you don't own a Durametric?
What do you do when the CEL comes on? (because we all know it does)
Pay the Dealer $250 to clear the code? (and throw parts at the issue?)
Do as Skip said: Get the Durametric.
You will be glad you did.
What do you do when the CEL comes on? (because we all know it does)
Pay the Dealer $250 to clear the code? (and throw parts at the issue?)
Do as Skip said: Get the Durametric.
You will be glad you did.
RL Community Team
Rennlist Member
Rennlist Member
Joined: Apr 2010
Posts: 6,288
Likes: 1,516
From: Ormond Beach, FL
Did you follow the instructions from Durametric for the download, including the USB drivers, and installation? Some people have had problems with the cable and Durametric replaced it, and then it worked. It also sometimes depends on the operating system you are running, and the laptop. Older operating systems the software works very well. Newer operating systems not so much. If you have a spare laptop, try running it with Windows XP.
Rennlist Member
Joined: Jul 2015
Posts: 2,180
Likes: 360
From: Halifax, NS. Canada
Did you buy the Durametric new? Is it the Enthusiast version or Pro? I’ve got an Enthusiast version, or I’d let you use mine (it only lets 3 VINs be used). If you’re up to Halifax any evenings next week, I’d be glad to try to help out. I’m no expert with Durametric but have used mine a number of times. Feel free to PM or email me. Joe
Rennlist Member
Joined: Feb 2022
Posts: 687
Likes: 417
From: Annapolis County, NS
Did you buy the Durametric new? Is it the Enthusiast version or Pro? I’ve got an Enthusiast version, or I’d let you use mine (it only lets 3 VINs be used). If you’re up to Halifax any evenings next week, I’d be glad to try to help out. I’m no expert with Durametric but have used mine a number of times. Feel free to PM or email me. Joe
Too kind! Yeah, my brother and his wife are visiting from TO and I'm going to ride to Halifax with them on the 12th, and get my car. That's a Friday. Would love to hang and meet you and your car. My durametric is in my car, maybe you have a 'known good' laptop to test with? I'll bring one anyway. Sending PM a little later. Thanks very much.