This is a bit beyond my knowledge but Im trying to learn.

History, restoring a 996 that sat in someones driveway uncovered for 10 years, after they parked it because they could not afford to maintain it.

I've been restoring it the past year and its come a long way (you can see the process here if you like: https://rennlist.com/forums/996-foru...ggestions.html)

After getting it running, it ran fairly well and was smooth, but I had a lot of random issues with strange electrical related problems (you can see that thread here: https://rennlist.com/forums/996-foru...s-come-on.html)
and Check Engine light coming on randomly at least once every longer drive.

I sent my ECU away as that seemed to be an issue and their diag was that it had failures and needed to be replaced. They also got me a new key because there were problems with that too.

ALSO I paid to get their PROGRAMMING UPGRADE to give more torque and power, just for the fun of it.

Got the ECU, IMMOBILIZER and KEYS back yesterday and put it all back together.

FIRST, ALL the weird electrical related issues are FIXED! No problems starting, all the locking/unlocking works, everything is GREAT!

However, it seemed to run rougher than EVER! I checked the codes, cleared them and it would be ok for a bit and then rough again. I took it out and there were backfires, something that never happened before I sent away the ECU.
It smelled awful, like it was too hot and running very rich. You could smell fuel.

Later that night when it was cooler outside I took it out again. This time it ran almost perfectly but when I accelerated the check engine light would come on and it would be a bit rough. Was it better because the air was cooler outside???

This morning, it ran much better, and I took it out, almost seemed like the issue was gone....but upon full throttle the check engine light came on.....then went off after a minute when not pushing the car.

My gut feeling is that the programming has changed fuel mixtures etc and that is why its worse now with more miss fires. But that also means there are other issues underlying.

I'm leaning towards O2 sensor issues? Seems that the symptoms are matching O2 failure.

The car has 98,000 miles so its at the top end of O2 life expectancy.

I replaced the MAF sensor a few months back which cleared up the rough running back then.

One more strange thing. When I was testing things yesterday, I pulled the MAF sensor out to see if it would idle better, it did a bit but when I did this I got PCM and ABS brake light errors on the instrument panel. How in the world is that related to MAF sensor being disconnected???? This went away after I plugged it back in and cleared the error. I can repeat this problem every time by removing the sensor connection. Isnt that strange?

I am including the screens from my iCarsoft reader hoping someone can spot something obvious.

Thanks!














idle

medium rev

high rev

 

Are there any trouble codes? If so, what do they say?

Are you using 93 octane gasoline?

The biggest warning sign shows up in your 5th image. The MAF value of 12.7 kg/h is a lower than spec (I assume this value was taken with the engine idling). I would start my investigation here to see why it’s not roughly 17 kg/h.

 

Yes to Octane 93

Trouble codes are missfire on cylinder 2

Yes that was at idle.
MAF was just replaced a few months ago. Maybe I'll take it out and shoot it with some MAF cleaner.

Geeze I hate to bring this in to the shop, it will cost a fortune. I still think maybe the O2 sensors?

I forgot to take pics of the error codes., I'll do that this afternoon.

 

At a quick glance, I’d more likely suspect the spark plug or ignition coil, especially if they haven’t been replaced. Although I do think it’d be a good idea to replace both upstream oxygen sensors - if you suspect that they’re old - just so you know that they’re fresh.

But the MAF value still bothers me, and it leads me to wonder whether you have multiple issues concurrently.

I understand your hesitance in bringing your car to a shop, and I don’t think you should give up so easily. You’ve demonstrated your meticulousness so I believe you can sort this out yourself without a problem.

If I were in your position, I’d start by inspecting the spark plug & ignition coil of the offending cylinder. Then I’d swap them with another cylinder and see if the problem remains the same. If cylinder 2 is still misfiring, I’d then perform a compression test and consider swapping the fuel injector with another cylinder.

I’d also do a smoke test to check for vacuum leaks, and measure the crankcase vacuum with a manometer to see whether the AOS is healthy.

 

If you disconnect the MAF, you will indeed get the PCM and ABS error. Nothing weird there. But I agree that it sounds like coil are failing. If they are original, replace them all.

 

OKAY guys, you all sold me. I've been really immersing myself in this and yes, after reviewing the data again and doing a fresh review on new data, the O2 sensors appear to be working good, though like 996 says wouldnt hurt to replace.

Glad to hear about the errors when I remove the MAS, that really bothered me, thought maybe they messed up the reprogramming of the ECU.

And yes, looking at the MAF again it does look like it might be off, so I removed it, and used a MAS cleaner. Will be taking it out for a test run in the morning, seems to be idling better but still seems off.

Finally I agree, I had that in the back of my mind about the coils and plugs. I'll bet they've never been replaced, so its probably a good idea to get that done. Not sure if the car sitting for 10 years helped or hurt, but it might very well be that is the issue. I'll have to go through the previous owners maintenance records, but my recollection is that he had never done it and the car has 98K on it.

I looked at the process for replacing the coils and plugs....don't believe that is something I want to take on given I dont have a garage and I would have to do it in my driveway with the weather. Just did it on my 991, wasnt cheap so I know what I'm in for.

 

OK guys an update. I took out the MAF sensor and cleaned it. Just took it for a ride and it was noticeably better. It gave me a little rough behavior at first, but I really torqued it a few times up and down the road (have a nice stretch down road for me with no traffic and straight 1 mile run) and the Check Engine like came on and then went off a few times, and after a few more runs it never came on again.

I did read somewhere that the ECU does need some input a few times running it, turning off and then running it again to average out the data and get things in order, so that might be part of it too.

Took it out onto the interstate and really gave it a hard run, and it all seemed ok. Not perfect but LOTS of power, more than I had before the ECU performance programming that they did along with the repair.

There still were a few times on acceleration it just seemed a bit flat....so thinking the coils and plugs are the next thing to take on.

Will drive it again in the morning and see how it acts. If I can get through this, then I have the confidence to start working on the seats and other cosmetic items.

So far so good.

 

This morning I took it out for a ride, and no matter how hard I pushed it, I could not get the Check Engine light to come on. No stalls, no hesitation, just amazing acceleration.

If it was just a matter of cleaning that MAF sensor....thats unbelievable. Or maybe the combination of that and more data put into the ECU to run smoother.

All I know is that its like a new car right now.

I'll put the coils and plugs on back burner for now and start the work on the interior.

Thanks for all your help!

 

Remove the battery polls to reset the ECU adaptations.

check this video:

Also:https://www.ecudoctors.com/pages/thr...urbo-2000-2004

 

Wow...so it is true! Its no wonder it was running like an old truck when I reinstalled the ECU.

Will note this for the future but I'm not going to touch anything right now given its working perfect.

Thanks for that video....yet another bookmark for reference in the future.

 

It will only make things better. Just do it

 

while I have all you experts here, the chassis could use some work. When I roll over the curb leaving the driveway and going down the road and corners, there are a number of groans and such, and I know I cant compare it with my
991, but what would you all recommend to look at changing on the suspension or look at for wear to make this a more comfortable quiet driving car?

thanks!

 

When the car is lifted, take a look at the bushings in the suspension arms and if they look stock then it's likely the are the culprit of the clunking. They're likely worn, busted from the decades and miles. Push, pull, tug at parts to check for any excessive movement or noise.

 

Thanks for this. Would it also ring true if a car's battery was disconnected for a number of days? Or you need to bridge with the test light

 

I saw my mechanic do this trick. he took a rubber mallet and tapped firmly on components. Anything that made a loudish metallic sound = dead bush. Doesn't show up tired bushes.. but quickly highlights dead ones.