Macster

If you want send me your email address via a PM and I'll respond by sending you a copy of a PDF file that details the 996 Turbo diagnostic/trouble-shooting steps to pinpoint the cause of a P0300 misfire error code.

I'm not sure how compatible the steps that rqeuire a PST2 are with the Durameteric tool.

Sincerely,

Macster.

Bryce

Hooked up the Durametric and recorded misfires on all cylinders while I was driving. The data show that when the engine increases load, Cylinder 3 goes bonkers first and hardest, with also a lot of misfires on 1-2. So, I hope that it's just a bad coil or plug there. We'll see. Took it in.

Kevin

Please be aware that IF you are getting low RPM misfires on most of the cylinders. You might have a fuel pump issue.

Bryce

Thank you, Kevin. I hope we can rule out the fuel pump for the following reasons:

1) Misfires are worse at temperature. To me signifies thermal expansion / poor connection in coil.

2) Misfires occur at all rpms when accelerating. This also rules out variocam as the book says that's only going to occur around 1500 threshold.

3) The misfires occur on 1-3 only. (I might be wrong on this one as the cams are so weirdly spaced on the driver bank that that problem could just surface there first because it's more sensitive).

Bryce

Well guys, I am about to give up. Been in the shop for 3 weeks now and they are still scratching their heads over it. Their PIWIS isn't doing much for diagnosing the problem, but a problem remains. Under load the driver's side misfires.

They said they hear some IMS noise and some oil pump noise, but can't correlate that to misfires in any case.

Sheesh, seems I am having some bum luck on my car. Do you think it could be the GIAC software? It's had that flash for 3 years or so without a problem until a couple months ago. Doesn't seem likely.

raineycd

I breifly read through this again but did not see a definitive if you have done these things yet:

1) - new plugs (I think the ones you have are copper and could need changed in 9k)
2) - new coil packs
3) - new MAF
4) - boost leak test (pressure test from turbos)

That is the order I would attack...

Bryce

Well, all the simple stuff has been tried. We're tearing it down and going inside! Mechanic says he thinks he hears weird sounds coming from the lifters.

Not a fun prospect but even if it costs $15k to rebuild, at least I have a Porsche Turbo at the end of the day.

Since we're going in, I need to think about what else I should do in there so that I don't have any reason to go back in anytime soon. Plan on keeping the car many years, so I can swallow some costs.

IMS replace with GT3 part? (He said he heard noise along the shaft). Or I saw there is a kit here: http://www.lnengineering.com/ims.html

Weld coolant flange?

GT3 oil pumps?

Update lifters to new part number (even if they aren't the problem so as to prevent scoring from back-out of pins)?

What else should I be considering?

jpflip

WOW! Another engine overhaul...Amazing. Please keep us inform of the findings....The IMS kit you mention is not for our TT engine it is for normally aspirated engine. For the coolant pipe there was a guy on Ebay selling the pipes but I don't see any adds anymore but his name was "racing-chip-pros"

OOPS just found it: http://cgi.ebay.com/ebaymotors/ws/eB...#ht_668wt_1165

There is another badlucky guy atisvt99 who's overhauling his engine, may be a good reading for you : http://www.6speedonline.com/forums/9...ing-chain.html

Bryce

I'm not sure overhaul is the right adjective, because there is a chance I could wind up like the guy on 6speed who had lifter scoring and just needed to replace the lifter housing and the lifters. That wouldn't be all that bad. I doubt very much there is anything wrong at all in the bottom half of the engine.

jpflip

Agree with you I just choose a bad word because of my limited english grammar. The pipes (welded instead of glued) will keep you away from the coolant lost happening frequently lately.

AndyMc

Can I ask a question? How does the ecu know a cylinder is misfiring,what is it that it detects?

Say for example the engine is at 3k rpm and one cylinder is misfiring occasionally, how does it know?

cheers Andy

PS hope your problem doesn't turn out to be too serious,

Kevin

Bryce, I think that things will become more clear when they remove the camshaft. I wouldn't have the shop split the engine case to address a IMS. The link that you posted is for the 996NA. It's a different design. The thread that Joel started might prove to have a similar outcome.

AndyMc, the engine is fitted with sensors to hear the knock or detonation. As the engine rotates the ECU knows exactly where the crankshaft is, and can pinpoint the firing order. Thus knowing which cylinder is knocking.

Bryce

Thanks Kevin. If you were closer I'd have you work on the car. We all appreciate your presence here. I am eager to find out what is going on.

Macster

The Ecu constantly measures the speed of the flywheel and can detect the slight variation a misfiring cylinder causes. Too many of these in a row for a particular cylinder (or cylinders) and one (or more) misfire codes are stored and the MIL is turned on.

If the misfires are of the type that the Ecu decides the converters are at risk of being overheated it will flash the MIL.

Sincerely,

Macster.

Kevin

Andy, I need re-clarify my answer. Macster answer was spot on for the "general" reply.

Typically, there are 3 causes of engine misfires.

1) Electrical> coils, spark plugs, and wiring

2) Fuel, lean misfire or incomplete combustion> oil fouling (bad rings)or fuel fouling..

3) Mechanical > worn camshaft lobe on one cylinder, broken valve spring, burnt valve, or a broken lifter.

Bryce misfire most likely have a "knock" picked up. I have datalogged the ECU pulling timing on the same cylinder that is misfiring.

The ECU can "see" the crankshaft rotation acceleration and deceleration "difference" When there is a cylinder deviation a misfire is tripped (when it has been sustained for a certain amount of time/revolutions) This also means that we can have a misfire, but not sustained> it will not trip a CEL.

My "opinion" is that it is a failed mechanical-valvetrain issue that will trip the misfire CEL AND a "knock" >> the frequency from the valvetrain chatter simulates detonation. One could argue a "false" alarm.