1999 996 CEL P1124/26 P0130/50 P1410/11

Hello. I recently got this 996 with 95k miles, which I already knew had issues. I spoke to the shop its going being to for the past 10 years and the last owner has been dealing with these CELs and was over spending money trying to fix it. The shop had changed the secondary air injector which didn't seem to do much. I've done smoke test and saw some leaks so I put on a K&N CAI along with new MAF, I have not tested again to see more leaks but I will. The car runs alright, but definitively doesn't have full power. At 6k RPM the car would basically lose all power, I changed the fuel pump and now it will at least get fullish power to redline. I plan on changing all the obvious stuff like oxygen sensors, plugs, coils and whatever other basic maintenance I can think of to help it out. I have seen the P1124/26 in a lot of posts and nothing seemed to really stand out for me on what the issue is. Not expecting anyone to solve my issues, but I will take any advice anyone has. I have a Duremetric scanner so if there are any good tutorials on how to look for for these kinds of issue that would be great. Anyway thanks for any assistance I do appreciate it but I plan on keeping track of what I do, what works, doesn't work here so maybe in the future this will help someone. Trying to finish another project at the moment so I can have my garage space to put more work into the 996 so progress will be slow for a few more weeks.

Small update. This codes also appear, it seems only when pushing the car a bit more. I'm starting to think there is more related to the fuel issue causing some of these. Or maybe it really is just O2 sensors. That would be great.

replace all four o2s. beware they may be rusted shut to the bungs and you will never want to work on a car again after trying to get them out. Take it to an exhaust shop and they will cut and weld new bungs. ur misfires are most likely going to go away with new o2s and new plugs/coil packs. u said u already did maf. SAI I would only worry about if u care about the environment (kidding but not really). 1602 scares me a little. the germans were always sh*t electrical engineers. change the oil if you haven't already. i personally use liqui molly 5w-40 synthoil premium. cheers / enjoy the car. Drive the **** out of it!

lol thanks. Hopefully all this stuff works out. the previous owner didn't want to spend more money on it. Luckily im dumb enough to try myself.

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do it yourself. just because someone has the credentials or gets paid hourly at a "porsche specialist" shop doesn't mean the work they do is any good. just wait until pt3 chimes in here telling you to get his uaos. out of curiosity, what're the last four numbers of your VIN, or what's the month/year build date?

5175 Date of Production January 14, 1999 Very basic 996. Nothing fancy but I love it

Try a factory airbox instead of the k&n. Lots of reported issues with maf readings using that set up.

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This is good advice. The K&N air filter causes all kinds of problems. Stock air filter box w/MAF sensor is the way to go.

interesting i haven't seen that before. maybe because most k&n intake jobs are botched / not done correctly? parts missing, etc... dunno. OP fabspeed makes a sweet intake you could look at if interested. Has been proven to make some power too.

I have gone between the stock air box and the k&n as I have read people having weird issues, unfortunately i have all the same problems with both. And the k&n sounds so nice I think id have to figure out the problem before getting rid of it lol

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My experience with CAI's over the years is less than stellar. It's probably not the cause of your current problems but extended use will likely lead to more issues than you wish for. I get the whole noise thing, but you are sacrificing filter density & surface area for aural pleasure. The cars with CAI set-ups I have worked on exhibit excessive amounts of fine particulate build-up on the MAF sensors...and we all know where that dust ultimately ends up. Oiled filters are no better for the MAF. If it's noise you want why not look into removing and blocking off the resonance balance tube on the factory air box?

As gbarron suggests, or if you want the sound...Fister Exhaust is the way.

Replaced the 2 before cat 02 senors and fuel filter. Coils are on back order, which is taking about 1.5 months to get for some reason. These things seemed to restore power that I felt was not there in the 4-6k range, which is nice, but still want this codes gone. Ill just keep plugging along and keep updates here for future reference. Thanks, Tyler

Coils r in stock at fcp. https://www.fcpeuro.com/products/por...nclkt1#fitment

I would do a hard reset by disconnecting the battery for a few hours I was chasing some codes recently and it did the trick

Ill try FCP. I bought from Pelican which said they were in stock, then back ordered after I bought til end of January. I'll put my stock air box back in, leave the battery disconnected and see what happens. Better to keep everything how its suppose to be while I have a bunch of codes. Thanks

Connect a jumper wire from your positive battery lead to your negative battery lead with the battery removed or disconnected to fully dissipate any remaining charge and get a clean slate for your electronics.

Thanks I will do that. I let it sit for a few hours disconnected but not change. Today I should be finishing up my Downstream 02 sensors, new plugs and coils, along with some other non engine related things to fix. Then ill do the discharge before I start up again and hope for the best. Thanks - Tyler

Update. Changed downstream 02 sensors (all 4 replaced now) New Plugs New Coils Stock intake CELs deleted Battery disconnected and discharged electroics And no change whatsoever. So back to worse than square one. No idea what to do next other than check for intake leaks again.

I have a Durametric scanner but have no idea what the values should look like for the live diagnostic information. Is there any source that has a breakdown of what each value should be around and what it means if it is not correct? Probably a long shot as it would probably be a lot of work for someone but just curious if there is something like that. Or maybe there is a shop that I can send my diag. information to that can see if they see things that are wrong? Thanks, Tyler

Could this be caused by a busted AOS?

I was told by previous owner and shop that had this car the AOS was replaced recently, probably trying to figure out this problem with no success. Could still be the issue, that shop did not seem like it was very high quality. They wanted to send the dash to be repaired because the brake wear light wouldn't turn off. Turns out the harness was broken that I just fixed. So I should probably really check the AOS as well.

Graph the pecat o2 side by side. They sould be between 0-1. And should react to throtle inputs sumilarily. This will tell u if the dme is seeing the cats. If they r stuck at .46v then its not readin cause thats the default setting for a noread.

Seems like this is right. I am not good with looking at this kind of information and see what is going on. Something I need to figure out for sure.

Im not very familure with the durametric but the o2 sensor voltage should never be zero. Not sure how it can be 0 and ramp up. My gut tells me u have an intake leak somewhere. The o2 response is tricking the car into thinking the sai pump is not working. This is why (i think) these codes r showing up. I currently have an issue with an o2 heater and its my theory its forcing a sai fault on a single bank in my car. It should be imposible in my car to get a sai failure on that bank and not the other because of how the air is pushed on a mezger motor. On your car i think it all leads back to a lean condition.....i think this is what u should be concentrating on. Can u figure out how to do a smoke test? Also whats the maf reading?

**the spikes in all the picture are pushing the gas to around 3k rpm. If anyone knows any shops that do diagnostics on Durametric logs that would be great. I've tried searching but no luck and i'm guessing it is not a service offered, or not common. I do have a smoke tester, I tried it once and seemed to see some leaking, tried tightening the spots but did not retest. That will be my next thing I guess as I have no other ideas right now. I did fuel pump/filter but if I don't find any leaks I might have to look at the injectors as well? I am considering going line by line of the engine values and finding all documentation on each value to start comparing what looks normal and abnormal. Anyway thanks for the help.

I have some leaking from the right side manifold as you can see in this video. I guess I will have to take this apart to see as the next step. I'm guessing this is enough leaking smoke to be an issue, hopefully the one I have been chasing. Any typical culprits anyone knows about in this area? Anything I should pre-purchase that tends to break during disassembly or commonly goes bad? Again thanks for the assistance, hopefully as my knowledge increase Ill be an asset to Rennlist rather than a sponge. Video of Smoke test

A very common issue is not getting the plunum tube collars seated and clamped correctly. I use an endoscope everytime i need to remove and reattach. Btw thats a fair amount of smoke and should be addressed.

I found some issues with the collars and re seated them, they were not put on well. The bigger issue was the little vacuum tubes that go inside the collars, i'm not sure one was even attached on the drivers side. I pulled out the 4 ways vacuum splitter, which had a piece of the black plastic tubing still inside it and broken off. Not sure if it was me, I don't think so since they seem hard to break, but i could not find where it went for the life of me. So I just plugged the 4th hole that goes to the second Change over valve that i couldn't find and put it back together. Right now its running smoother and better than ever since iv had it, and I am really hoping this was the issue. I will report back in a few days to see if my CEL comes back. **also I noticed there was a intake hissing noise that was pretty loud from the engine. It was like this since I got it and kind of (dumbly) assumed it was normal. Now that I redid these vacuum lines I no longer here it and have since realized it was not normal. Thanks for the help - Tyler

Very cool and it makes sence. Those drivers side vac lines go to the sai pump and rear plenum cross over tube change over valves. U will want to make sure they r connected properly.

**Update** Been about a week, only 2 codes have come back now, both for SAI implausible numbers, which makes sense considering that is probably the 4th vacuum hose on the 4 way that I plugged. So now I feel pretty confident to say that this was just a broken vacuum line this entire time. Now just to figure out where this SAI is and fix the last issue. Hopefully someone finds this useful in the future, I've learned a lot from it and now ready to fix my next problem, whatever that might be. *** Also, the K&N was giving some random codes as well. So I did have to go back to the stock box as much as I was trying not to. But I guess I am on team stock air box now. Thanks, Tyler

The change over valve for the sai is behind the alt, under the intake. There is a few vac lines in that area to check. And yes the kn will cause random codes associated to the maf.

To close out this I took off the alternator and was able to get to the SAI and reconnect the vac line to where I had closed off the 4 way vac splitter. This cleared the last codes, and in the end this broken vac line was the cause of all the engine codes I had from the beginning.