maybe misfire from water and cracked coils? but no stored code?

Had to park my car outside over the very rainy weekend and on my way to work had some funky symptoms. Engine started and car drove fine. While Idling at the light to get on the highway, once felt a pretty big "wobble" from the engine, where RPM's went down, then up, then came back. Light turns green and pull I away. Then engine briefly "shudders" (best way I can describe it) and BEEP! "Check Engine Drive to Workshop" pops up on the info light and check engine light goes on. I'm in the thick of things getting on the highway so I keep at partial throttle and "feel the car out." The check engine light blinks for a bit, then goes solid and message on info display goes away. As I proceed in stop and go traffic (1st through 3rd gears), engine continues to behave strangely. In 1st gear or neutral the engine revs fine (maybe feels a little "wobbly"). 2nd gear under increasing throttle/load I can start to feel a shuddering (a fast "dunk, dunk, dunk") as if the engine is missing on a specific cylinder or cylinders. In 3rd gear it's worse. Didn't attempt 4th gear. Feeling is less strong or gone at partial throttle/load in all gears. Get to work, shut down the engine and restart. POOF! Check engine light is off, car revs fine. I drive it around and all is fine in all gears. I get home that night, plug in my cheap ODB-II reader and it shows no stored codes ("0/0") and gives me the green light. Huh! I'm guessing the heavy rain got the engine wet and I've got one or more cracked coils (based on the readings I've done in the forum), then the drive to work cooked the moisture out and all's good. But I found it weird that the engine was in some kind of funky mode all the way to work that disappeared immediately upon a restart. Is there a "limp home" mode for the engine when it detects a bad coil or misfire which is reset upon shutdown? I'm also surprised there are no stored codes. Thoughts?

Yes, sounds like coils. The DME monitors for misfires whenever the engine is running. It will know also if the misfires are no longer there. There may be pending codes that your scanner couldn't retrieve. You may be able to pull more codes if you use Duremtric.

+1

Thanks for the quick response. When the DME detects a misfire, does it put the car into a "limp" mode and not fire that cylinder anymore? It was unusual to me that the car could be in a strange state (shudder shudder) with CEL on that totally disappears when turning off the car and just turning it back on. I don't have a Durametric. We just picked up a Boxster and Cayenne too, so I guess it's time to invest.

I'm not aware of limp mode unless you have a tiptronic. The shudder you were experiencing was basically misfires, engine running on 5 cylinders.

The DME does have a shut down to protect the Cats if there is a misfire that it deems damaging to the Cats. It will shut off the injector on the effected cylinder to keep raw fuel from being introduced into the Cat and will only turn injector back on after key cycle. It definitely should have set a code though, something screwy about that !!

Right, the DME can shut down the injector(s) momentarily but once the misfire is gone, the engine will be back to normal. A "limp mode" to me is a state that lasts much longer such as the rest of the drive even if there are no more misfires e.g. the limp mode of an automatic transmission.

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Maybe on the 7.2 or 7.8 it is momentary, but I know that the 5.2.2 will not turn back on until the key is cycled. OP, what year car have you got? EDIT: or it could be that it depends on the severity of the misfire, it may try to turn on the injector a couple of times and if it is still misfiring it could turn it off for good until the next key cycle.

Thanks Ahsai and Porschetech3 for the replies. The engine clearly was in a mode that got changed by the shutdown/startup. Glad to know it can do that. I will find my way to a durametric to see if there is any more info hidden in there. Will report back when I�ve got new data. This forum is great. Thanks folks.

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2004 C4S, bone stock no mods.

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Well I take that back, I think me and Ashai are both right, I think it depends on the severity of the misfire, the DME may try to turn the injector back on a few times and if the misfire is still present it will turn off for good until next key cycle. I had this happen to me on my 99 and I could cycle the key going down the road and get the injector back on.

I had the same problem when I bought my 04 C4S last fall. Once the engine was dry, the light went off and no problems. Still, based on what I read here, I figured it was the coils and it was. Five had minor cracks. The one under the coolant drain (furthest back on the driver side) was a mess. It was in terrible shape. I replaced all six coils and plugs. I really struggled with the coil that's furthest back on the right side. I just couldn't see how it would ever come out. I came for help and as always, I got it!!! Thank you rennlist!!! BTW, I didn't get any codes either on my generic scanner.

A better code reader would show the misfire counts and an intermittent code for misfire.

I definitely had misfires due to cracked coil packs and water that were not picked up by the DME and my Durametric. Drive thru a puddle: misfire/hesitation Pull over, check codes with Durametric: Nothing. No codes Replace coilpacks (which had visible cracks, hard to see until removed) Drive in the wet: No more misfires

^^^^ This...2005 C4S. Mine did the shudder and clear-up several times in the past with no CEL-no warning. Progressed to plainly evident miss with CEL and drive to shop warning mostly associated with moisture. My bet is coils...

The Porsche misfire monitor is adaptive. If the DME has been recently reset, the misfire monitor is very unsenitive to misfires. It will still show faults for injector or primary coli failure, but secondary coil and spark plug and combustion are less sensitive until the adaption process allows them to be more sensitive. The monitor looks at the 60 teeth of the flywheel for slight variations in speed during each cylinder combustion. This is to help stop false misfires signals from rough roads/ potholes railroad tracks and cold starts.

Hi Guys, this thread is awesome. Thank you. Ahasi and Porschetech3, thanks for the info and advice. It's interesting to understand how the DME works and adapts. It makes me want to be a part of building those algorithms. I checked my records tonight and I can see a spark plug replacement at ~60k in Dec/2012 (at 91k today) but not coils. So it's clear new coils are in my future. Lots of threads online how to do this. Seems like you can do contortions with various sockets and skinned knuckles to change the coils with only removing the cover...OR...you can remove the muffler/silencer for easier access. My experience with old exhaust on my other cars, gives me reason to pause and hope I can tolerate the contortions. Inputs welcome. As montauk says above, "I came for help and as always, I got it!!! Thank you rennlist!!!"

You can replace the coils without touching the mufflers. Takes some patience and the right extensions. I like using the snapon 4" 3/8" drive wobble extension. You also need those mini ratchets that takes small 5mm hex bit. Make sure you get the upgraded coils (thicker). Check with Jason from warehouse33 for parts

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It's really only that last coil on the right that's a trouble maker. As Ahasi said with patience and the right combination of socket extensions and swivels it's not difficult. There's no way I remove the exhaust to do the coils. Dave

I did mine a few years ago. Only one is difficult but all doable. Next car I did I took the opportunity to get Fisters on the car so while Mufflers off coil packs on.

Thanks for the encouragement guys. I'll be doing this job later this year...

Continued rain led to additional misfire events, so this weekend I replaced the plugs and coils. Success! The job went smoothly (2hrs first side 1.5hrs second side) because I researched posts on rennlist and was prepared. Thanks everyone! Thanks esp. to Ahsai for the pointer to the mini 1/4" ratchet to for 5mm hext bit and to Dave/montauk for the suggestion to have various swivels on hand. Both made the job easier. (I also discovered that ordinary sockets work fine with the e-torx bolts on the replacement coils. https://rennlist.com/forums/996-foru...l#post15742523 ) The only stupidly frustrating part was getting the dang cover back on over the right side plugs (4,5,6). I have no idea why it was so easy to remove and took literally 30min to get back in place. It's like the holes in the cover were just a little too far apart. The other tricky part was a bit of rubber left in the #4 spark plug hole (doesn't it figure it had to be #4, the hardest plug to get to???). My biggest concern of the whole job was accidentally stripping threads when installing the new plugs, so I used hand-turns to install all plugs to finger tight. Plug #4 was tight going in and got my heart rate up. So I pulled it back out and a semicircle of rubber fell out. Checking coil #4 showed the whole rubber collar was gone so naturally the question is where the rest went. See first image below for details. I jimmied up the shop vac with appropriate hose sizes and duct tape and vacuumed away at the #4 hole but didn't pick up anything. No issues with car running since then so I guess the bits came out while I didn't notice. It turns out ALL 6 coils were cracked in basically the same spot. See last 3 images below. The crack was at the bottom of each coil with varying lengths. It was satisfying to fire up the engine and get no CEL's. Now let's see what happens when it rains next...