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snoopster

Frustrating Misfire Problem

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I am a new Porsche owner who acquired a 996 Turbo with GIAC flashing running in the neighborhood of .9 bar. I had owned the car and had drove it hard for about 2 weeks when I swang around a corner and punched it in 2nd gear only to find out what a CEL looks like. I received a flashing CEL which yielded a P0301. I headed straight for the forums.

After some research into the history of the car prior to my ownership I realized it was time for a coilpack and sparkplug replacement time. I was only able to get 2 packs in from my local shop, but got 6 plugs. I tore the car apart, replaced drives side front two packs, I believe cylinders 1 and 2 and all 6 plugs. These coilpacks had hairline cracks whereas the others were not that bad. Plugs were FR 6 LDC - Bosch Platinum 2. I cleared the CELs after every change.

After a few drives @ wide open throttle I once again got CELs. This time P0301 and P0303 w/ P0300. I decided other coilpacks must be bad. I ordered in 4 more 997 part coilpacks, ripped the car apart again and proceeded to put in the new packs. I paid attention to the DIY guide here at RennTech and looked at the VarioCam brackets and they seemed to be ok.

Once again, @ WOT I received CELs. This time P0303 and P0304 w/ P0300. After digging in the forums, I checked my MAF voltage, 1.4V at idle using a voltmeter and then ordered a Durametric and did a data grab on the MAF voltage and it seems to be ok. As I have been running 91 Oct w/ ethanol I then tried a gas change.

I emptied the tank and put in 93 Oct. The car drove good for a bit, but yesterday once again @ WOT I got a P0305, P0306 w/ P0300 again.

The car drives wonderfully if I keep the turbos out of the picture. I have used the Durametric to verify that I get no cylinder misfires when tootling around town keeping the boost below .3 bar.

Does anyone have any suggestions on what I can do to fix this problem? I'm desperate for a working car!

I am a novice owner and barely know how to work the Durametric but am willing to post and gather all logs I can from the device to solve this problem. The nearest dealer is 2 hours from my place!

Thank you 6speed community for any input you can offer!

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*I have made this post @ 6speedonline forums as well*

The original plugs were Bosch with only a single ground electrode. The plugs in cylinders 1 and 2, closest to drivers seat, were fouled the most, where as 6 and 5, closest to the passenger seat almost looked new.

I cleaned the MAF following the instructions in the various forum posts twice.

I took the airbox out and blew it out with air, with the MAF out, and put in a new OEM air filter.

Today I took the car out and took 2 different Durametric logs. The first is with the MAF in.

The RPM has been divided by 100 and the Boost (in Bar) is times 10 to fit everything on the Excel graph. So 88 boost is really .88 bar and 50 RPM is 5000. The misfire counters are true.

In the first run I'm back to P0301 and P0305 errors. Cylinder 1 recorded 35 misfires, cylinder 4 - 1, and cylinder 5 - 8.

vxeosm.jpg

The second run I have unclipped the MAF sensor. This yielded only a P0301, but I didn't punch it as hard due to the fact the P0301 came on so quickly.

am8api.jpg

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My suggestions are:

1. Check for air leaks in intake air system. A loose or poorly fitted hose can cause all kinds of faults.

2. Check spark plug connectors. Approx 2k ohms.

3. Check ignition coils (again). 0.3 to 0.7 ohms (at 20 °C).

4. Get another set of factory spark plugs to test with.

5. Go back to the tuner that flashed the car and flash it back to stock to rule out the a bad flash.

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My suggestions are:

1. Check for air leaks in intake air system. A loose or poorly fitted hose can cause all kinds of faults.

Is this just the airbox to the engine or does this include the intercooler hoses as well? Is there anyway to pressure test these lines?

5. Go back to the tuner that flashed the car and flash it back to stock to rule out the a bad flash.

I have no idea who the original tuner was. I'm almost 100% sure it was in CA and the car is now 1800 miles from there :)

Edited by snoopster

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1. Yes, especially the intercooler hoses. They are know for poor fitting and collapsing under pressure.

Have someone rev the engine while you look and listen.

5. In the end you have to remove some of the variables - so in worst case scenario you need to find someone that can remove and store your flash. Then reflash to stock. Then after your problem is fixed reflash back to GIAC.

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1. Yes, especially the intercooler hoses. They are know for poor fitting and collapsing under pressure.

Have someone rev the engine while you look and listen.

5. In the end you have to remove some of the variables - so in worst case scenario you need to find someone that can remove and store your flash. Then reflash to stock. Then after your problem is fixed reflash back to GIAC.

hi there i too have these same symtons on 2003 996 turbo just seems to have this missfire hesitance at around 4500 rpm on boost or 3rd gear if you hang it out in the revs tryed new plugs;coils;air maf had engine out found 2 busted inlet buckets replaced them reset cam timing refit engine and drive now the light doesent seem to flash as long after i lift off gas but still same missfire jumps around cylinders but always on number 3 p0303 please anybody have any ideas

i did replace all the inlet buckets by the way

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1. Yes, especially the intercooler hoses. They are know for poor fitting and collapsing under pressure.

Have someone rev the engine while you look and listen.

5. In the end you have to remove some of the variables - so in worst case scenario you need to find someone that can remove and store your flash. Then reflash to stock. Then after your problem is fixed reflash back to GIAC.

hi there i too have these same symtons on 2003 996 turbo just seems to have this missfire hesitance at around 4500 rpm on boost or 3rd gear if you hang it out in the revs tryed new plugs;coils;air maf had engine out found 2 busted inlet buckets replaced them reset cam timing refit engine and drive now the light doesent seem to flash as long after i lift off gas but still same missfire jumps around cylinders but always on number 3 p0303 please anybody have any ideas

i did replace all the inlet buckets by the way

:welcome:

Have you checked for multiple fault codes or is there really just one?

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hi there i found a missing support ring inside one of the turbo feed pipes that stop it collaping when you tighten the jubilee clip so today we replaced the new hose and test drive still have same problem yes it does come up muliple fault codes p0300 p0303 p0304 and sometime p0306 very random boosts up to 0.6 then light starts flashing and if you keep foot down it bleeds off to 0.4 and hesitates and as you return to normal driving the light stops flashing . are the intercooler pipes renound for collaping then we have never experianced it is it quite common problem think i might try pump the systym up again see if hear any leaks thanks :help:

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Gents - any news on the misfire problems? I too am getting a CEL with codes P0300, P0306 and P0301. Mine seems to happen shortly after starting the car. (No boost - just idling in the garage warming up.) Not trying to hijack the thread but just curious if any progress. Thanks!

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My fault codes show misfires on cylinders 3 and 6 only. It has a 1 bar tune , unknown tuner, tubi exhaust, AWE headers. About every 200 miles, CEL lights up, I drive to indie who is an air cooled mechanic , and works on water cooled cause he has to, and tells me to come back when light comes on. 

I know mike schatz is at tre motorsports, so that is my next stop. 

The car runs very good, but I have nothing to compare it to. Not close to a 930.

i read articles on this forum and wished I lived around the corner from Loren. Read articles on rennlist, 6speedonline, call my indie, and ask him if this or that would cause misfires on 3&6.... no that’s not it. 

Hopefully it isn’t serious, but I’ve driven lots of Porsche’s, hot rods, etc and it doesn’t make any weird noises, runs pretty good gets to 1 bar pretty fast. 

Its very frustrating 

anyone else with a 3 , 6 misfire?

thanks , Kevin 

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