Misfire, no codes
 

Drove to Boston the other night from CT (2hrs each way)

On the way there, holding 70-75, slight uphill, light throttle, and intermittently - the car would skip occasionally, felt like a hard jolt. More throttle would smooth it out.

Filled up in Boston with 93.

On the way back it was doing the same thing, intermittently. Seemed to be getting a little worse. At about mile 100 from the fillup (5min from home) it went into full random misfire and brought on a flashing CEL. Took it out of gear, revved it to 5 or 6k and it cleared up. Finished the drive home with nothing more than the random skip.

Brought it to pepboys for a free scan on my way home from work yesterday - no stored codes.

Had a friend bring over his Innova 3150 scanner, no stored codes.

Will a durametric be able to show me what's happening? Anyone have any ideas?

A Durametric might give you more info. You might check your coil packs for cracks. Good plugs and good connections?

Plugs have 653 miles on them. Some of the coils may have had cracks back when I was replacing plugs. I don't want to go and get a whole set of coils unless I can prove that's the issue, or narrow it down to 1.

Was it rainy or humid that day? If yes, check the coil packs and do a visual inspection of the coil pacs.

If they have cracks that doesn't mean that they are bad. Mine had cracks but they worked. Replaced them all precautionary and sold the crack fee ones on ebay.

Did you check the spark plug electrode distance when installing the plugs? Are the spark wires 100% connected?

What tool did the workshop use to read the codes? Porsche specific or generic OBD2?

Regards, Markus

Its been dry here for weeks. I checked all gaps as I was installing the plugs. Connections seemed solid, and car ran 100% up until this trip.

Tools are both generic OBD2. Anyone have a durametric near central CT?
I have a VCDS, so I'm going to try that tonight.

Did the tach act weird when misfiring? Perhaps CPS getting weak?

Nope, tach holds steady.

Cleaning the MAF is pretty simple and inexpensive. I'd try that before throwing new parts at it if a Durametric isn't handy.

I'll give this a shot.

I got my VCDS cable back from a friend and hooked it up. Still no codes.

But now I can have a passenger sit with the laptop and monitor timing/MAF/throttle/load/etc...

Attempted to drive it to work this morning, but started misfiring badly.

I drove it home, and kept it running - grabbed vagcom and scanned it quick

Wednesday,27,April,2016,08:02:52:42003
VCDS Release 15.7.4 (x64): Generic OBD2
Mode 07: Pending emission related fault codes

Address 11 (Engine): 3 Faults Found:
P0300 - Random/Multiple Cylinder Misfire Detected
P0306 - Cylinder 6: Misfire Detected
P0302 - Cylinder 2: Misfire Detected

Hi,

so i would say change the coil packs from 6 to 5 and 2 to 1 and see if the error moves along with the changed coil packs. Then you know it's the coil packs and which one it is.

Else you could also clean the MAF, but that seems to be the coil packs, sparks or wires or connectors.

Regards, Markus

I think that will be my plan, but if I'm going under there, I may just swap in new coils anyway. at 98k miles, it could probably use them anyway.

The part number on my coils is 996 602 102 00
Does it make sense to use the same ones, or the updated 99760210700?

Disconnected the MAF, just to rule it out, and drove around. Still misfiring.

Painfully loud with the intake and no engine cover at WOT.

Hello alm001,

maybe this is helpful for you: http://986forum.com/forums/472643-post10.html

Regards, Markus

Thanks for the info, and the help!

I swapped the #5 and #6 coils, still misfiring, but it wouldn't throw a code on a short drive. I'll try again tomorrow.

I pulled the #5 and #6 plugs just to have a look.

https://lh3.googleusercontent.com/-M...=w1185-h667-no

Could be lighting but I'd say the plug on the right is running extremely lean.... that insulator appears to be scary white appears to be getting too hot to me.

I agree with you there. I thought the tip looked odd when I pulled it out, so I took #5 out to compare - and it is definitely lighter. If that is the case, I would imagine the misfire is more fuel related, rather than ignition.

It's a bit frustrating have the motor skip, and not throw a code. I have to drive it more to cause a stumble so I can rule out the coilpacks.

Hello alm001,

i agree, this looks more like a fuel injector problem.

So i have some questions:
When did you clean the sparks the last time? / How many miles ago?

is your car a daily driver or a seasonal car or did it sit for a longer time in the past?

If is had sit for a longer time, did you use a fuel stabilizer before you got it to sleep?

Did you use an injection cleaner in the near past?

Was the engine really warmed up before you pulled the sparks? Because they should look a bit more brownish.

Thanks & regards,
Markus

Replies above

Hello alm001,

first thanks for answering my questions.

So it seems that the sparks are pretty new and that the car didn't sit for a longer time.

Why did i ask for sitting for a longer time: i had a motorcyle with carburettors that was sitting for 8 years. I started it and it run well, but had some problems with upper revs. I dismatled the carburettors and found a kind of gumming (Verharzung is the german term for that) all over. It looked like a breaking up clear code on a car. This harnish clogged everything and that is why the bike didn't run well at higher revs.

So if the car has sit for a longer time in the past that could cause problems by gumming.

So there are 3 ways fuel injectors can fail.
1. they can fail completely, but that would give us a dtc.
2. they can be clogged
3. they can leak

If they are clogged than the clyinder would run lean but in general you won't get misfire.
If they are leaking you will get missfire, because there is too much fuel in the cylinder or fuel in the cylinder when it had not to be there.

So, because you don't get a dtc and because you have misfire and because of the way the spark looks like i would say some of your fuel injectors are leaking.

And because that you only have driven 700 miles on the sparks i would say act fast and don't drive too much with the car.

My recommendation is to uninstall all fuel injectors and bring them to specialized workshop. They can check if the fuel amount is OK, if the way the injectors spray is correct (german term = Spritzbild) and if one or more of them are leaking. Maybe the bad ones can be rapaired, maybe they had to be replaced.

Hope that helps.

Regards
Markus

If you are going to buy new coil packs, get the newer ones

best price I found was warehouse33auto.com
put rennlist in the coupon code and you get 10% off

I would think you should get your fuel pressure before going too much further.

@911monty:

Good idea, but if he would have a low fuel pressure i think all cylinders/sparks would be affected the same way. Please take a look at the picture of the sparks (i know you did): http://986forum.com/forums/494345-post17.html

But maybe it's a good idea to check the fuel pressure too, because fuel pumps on these cars tends to get fatigue and the sparks look more black and white than brown.

Just my 2 cents.

Regards, Markus

Marcus your expert advice is most appreciated! In your previous reply you mentioned leaky injectors, I also think this is possible. This would cause some cylinders to run rich, confuse the 02 sensors causing other cylinders to run lean correct? There appears to be soot on the electrode also pictured indicating possible rich/misfire.

Thanks everyone for the suggestions. I'll keep plugging at this when I have spare time.

Took it around the block, and got it to misfire - 4th gear up hill, 2500rpm,light throttle

Thursday,05,May,2016,17:59:57:42003
VCDS Release 15.7.4 (x64): Generic OBD2
Mode 07: Pending emission related fault codes

Address 11 (Engine): 1 Fault Found:
P0302 - Cylinder 2: Misfire Detected


So the #6 misfire must have been a fluke (or a sympathetic symptom). I'm going to swap 2 & 3 when I get a chance and retest.

Well this is embarrassing.

Went to take apart passenger side, got the wheel off, got the fender liner off.
Tugged on the #2 electrical connection... and I was able to pull it off. I must have not "clicked" it in when I did plugs 700 miles ago.

So, double check that the plug is set. Get that stupid rubber boot out of the way. CLICK it in, then push the boot down.