Boostin

Long story short, I was running LS a couple weekends ago and missed a shift coming out of turn 2 going into turn 3. Rearend locked up instantly and I did a nice 360 and end up about 10 ft from the right hand wall at the entrance to turn 3. I have some in car footage that I'll upload later tonight but wanted to get your thoughts on what damage could have been done.

After the spin, she wouldn't idle and the ECU threw a MAF code. Cleaned the MAF which didn't help the idle issue and the ECU threw the code again. Disconnected the MAF and she would idle but it was quite rough and there was no shortage of popping. Ran compression test and all cylinders were relatively consistent around 160. Ran leakdown and all cylinders were around 18-20% with the exception of number 3, which was at 32%. Now the leakdown was performed cold as I had no way to warm up the motor without risking further damage so I'm not too concerned with the 18-20% across the other cylinders (but should I be?). I pulled the 1-3 cam cover and cranked the motor by hand to see if a lifter was broken or if there was anything out of the ordinary but there didn't appear to be. The one thing I didn't do was measure each valve's travel as it cycled.

So with all that said, my initial conclusion is that I likely bent some of the valves on number 3. What do you guys think based on this video? http://youtu.be/ouBgW7BMG8s

Last night I started prepping the motor to drop it so I can get the heads off and see what it looks like inside. Any thoughts on other diagnostics to run before dropping the motor? Let's say I pull the heads and find bent valves on number 3, do you think I should tear into the bottom end and inspect to ensure everything is good down there? BTW, this is Serge's 4.0L so it only has a couple thousand on it since the rebuild. And no I'm not too happy with myself right now but she'll be running again soon enough The only upside is that now is my chance to swap cams since it's got street 996 GT3 cams currently. I think I'll probably go with 997.1 GT3 intake and leave the 996 GT3 exhaust so I can keep the variocam. But that is a whole different topic of discussion.

Thanks in advance for any thoughts you have!

- Matt

Q&A

I have spun also once, pretty hard into the gravel. Not because of over revving. Just too hard on MPSC on a damped track. This caused my inlet plenum to come loose or some parts around that area connecting the plenum. Forgot what it was exactly but the engine was also running as if it was having false air.

996FLT6

^What he said. Check if the hoses have loosened or popped out. U can see two hoses for sure and check if they moved. If they did engine sputters and dies and sounds god awful with misfires and backfires. Those vacuum leaks creates a lean condition so your car ecu will make the fuel rich ie it smells gas fume heavy. If u can't see nething. With engine cold start it up and spray carb cleaner on affected hoses with engine on and see if idle runs smoother (make sure engine is cold not hot if hot and spraying carb cleaner it could catch on fire). If u have a durametric check for type of overrev duration and what it redlined at. Now when it happened did u push clutch back in as soon as it happened? Mike

Q&A

Went back to my Porsche Center with it and it took them days to find the problem. The read out showed a problem with the mass air flow sensor. They ordered a new one and the problem remained. A smart mechanic put the whole system under pressure and then they discovered a leak somewhere. A very skinny mechanic, with golden hands was able to tighten what came loose without taking the engine out. Any normal arm / hand would not have worked they said.

Serge944

A vacuum leak does not explain the terrible leakdown on cylinder 3.

HiWind

Here's a pic re what mike said - found this to be my idle prob (no prob above 2.5k revs tho) after a lockup/spin .... https://rennlist.com/forums/9506953-post5.html ... From a thread that turned out to be rat chewed wires tho ... Ps you cars sounds just like mine did although as Serge says doesnt explain the 3 leak. Also I got all kinds of vario cam timing error codes.

Boostin

Thanks for the input so far guys. I definitely appreciate it. I will check hoses when I get home this evening. I would love that to be the culprit but I just don't think so given the high leakdown in number 3. Although I am a little confused as to why the MAF blew or was threw a code.

The one thing I meant to do before I started disconnecting electrical was to check for overrevs. Damn. I did watch the in-car footage and it looks like it only revved to 8K as I went both feet in the moment it locked up. The RPMs drop to about 2-3K before jumping up to 8K so I think that is what locked it up and the "shock" from the mismatch b/w motor and wheel RPM is what could've bent the valves.

996FLT6

Was there any oil residue(spray) inside the maf area inside? I spun one time pretty violently ie 720 (LS too at exit t4). It popped one of my intake plenum hoses and afterwards trying to reseal the hose took out airbox and maf to get to it I noticed quite of oil inside. It destroyed my maf. Mike

Boostin

I think that is exactly what happened...oil destroyed the MAF. When I took the airbox and MAF housing out there was definitely oil in the hose / sleeve that connects MAF housing to the throttle body.

996FLT6

So did u misshift from 4 to 1? I misshifted from 5-2. Grenaded my 3.8rsr pp after putting it in 2 weeks before event. Mike

Boostin

I'm still not 100% sure what exactly happened. I was going from 2 to 3 and think I had trouble going into 3 and then think I went into 1 when I tried again. As you can see, there are a lot of "thinks" in that sentence so I don't know exactly what happened.

996FLT6

Let's see the incar video. That should tell a lot. Mike

Paseb

always sad to hear that. hope its only a maf thing

Gt3 Racer RS

Video I need!

Nordschleifer

Video sounds like popped off plenum hoses - had the same thing after a spin when I couldn't get my two feet in fast enough. Drop engine a couple of inches so you can have a look and get access if something is loose. Easy fix if there is no internal damage