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Missfire under boost

My car started to missfire under boost, the feeling i have is like loosing some cylinders. I checked cis and all the pressure values are correct, the only value is out of tollerance is the fuel delivery to the wur which is 300 cc/ min. Spark plugs replaced and also spark plug wire. Any advise?
Thanks in advance

Old 05-14-2013, 11:27 AM
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Check your intercooler O'rings, as well as the O'rings on the turbo up-pipe to the intercooler. It's not all that uncommon for the o'rings to tear or become dislodged, and will cause a huge boost leak and poor running.
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Old 05-14-2013, 11:39 AM
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Thanks Mark, i don't have o' rings because i'm running a long neck intercooler, maybe has a cracked or the leaks is in one of injectors block
Old 05-14-2013, 11:58 AM
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Quote:
Originally Posted by Mario Motta View Post
Thanks Mark, i don't have o' rings because i'm running a long neck intercooler, maybe has a cracked or the leaks is in one of injectors block
Ok then. I thought long necks still had o'rings (??) unless you've gone completely over to silicone hoses coming up from the turbo as well as connecting to the throttle body. It's just the first place to look is why I mentioned it.

You might have had a vacuum hose pop off somewhere....simple culprit once you find it....but not always so simple to find it!

Could just as easily be a bad spark...I'm sure you've checked the coil wire, etc.
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Old 05-14-2013, 01:36 PM
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I have only silicone hoses between ic turbo and ic trottle body vacuum hoses chechrd already. You mean the two wires that go to the coil or the coil inside?
Old 05-14-2013, 01:51 PM
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Quote:
Originally Posted by Mario Motta View Post
I have only silicone hoses between ic turbo and ic trottle body vacuum hoses chechrd already. You mean the two wires that go to the coil or the coil inside?
I meant the main coil wire that connects to the top of the distributor. Unlikely that's your problem, but things can work themselves loose over time. I accidentally left mine disconnected once. It was still close enough to arch a spark across a couple inches, but the car ran like crap

There are so many things that can cause your symptoms. You have vacuum lines in several locations, or lines whose function isn't necessarily vacuum related but if disconnected will cause a vacuum leak - IC to the auxiliary air valve, IC to the wastegate, lines to the distributor (and where they connect to the throttle body), lines to the boost recirculation valve, and lines to the decceleration valve...unfortunately none of which are very easy to get to! The sad part is that these may - or may not be - the cause, but you have to look anyway to narrow the playing field. If all checks out ok, then perhaps your CDI is acting up and not delivering a hot enough spark when on boost. Also, do you know for certain that both fuel pumps are running?
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Old 05-14-2013, 04:32 PM
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That wire is new as all the spark plug wires. As you suggest I will check everything regarding leaks. I found the plug that connect the small wires coming from the distributor rotor to the main wire cooked and broken in few parts but the wires look good. Those wire look to be connected toghether in the plug so i don't thing can be the problem. How do they work?
Old 05-14-2013, 11:36 PM
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did you check your AFR's under boost.
cap and rotor?
like mark said, check both FP's


what i have found with my car is its tolerant of air leaks under boost. you just dont have the power.

you can also check to see if your WUR is dropping the control pressure under boost by putting about 15psi of pressure into it. it should drop around .8bar.

there is a spec for fuel delivery to the WUR? what should it be?
if you checked that, i would check system fuel delivery instead. and not to the WUR.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
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08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
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Old 05-15-2013, 04:04 AM
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I did the tests in accord with porsche manual. The fuel to the wur has to be between 140 to 240cc/min if i remember well i have 300cc/min
Old 05-15-2013, 04:29 AM
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a little hi? i dont see that as a problem.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-15-2013, 06:27 AM
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I had pinging and some break up as well. Turned out to be a faulty (newly rebuild) alternator!. We chased our tails looking at fuel issues thinking electrical was good due to the new rebuild alternator. WRONG! I swapped it with a 3.2 style (more AMPs), and problem solved. Check the voltage on your terminals with engine running. You are looking for more than 12V and probably in the order of 13-14V I believe (but don't quote me on this I am no electrical expert).

Last edited by 6771911esses; 05-15-2013 at 06:38 AM..
Old 05-15-2013, 06:36 AM
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T77911s sorry i did not say hello
Old 05-15-2013, 07:18 AM
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?
i am not one of those that goes off on others for not following the "newbie" edicate or if someone does not say hello.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 05-15-2013, 08:33 AM
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Hi All,

are you running the standard CDI or upgraded?

The reason I ask is that years ago, I upgraded my ignition system (not a Porsche) which produced such a strong spark under boost it fired to the distributer cap clips causing a misfire. I changed the cap and the problem was gone....... for a few months.

Cheers
Old 05-15-2013, 04:17 PM
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I'm running standard system. I hope i will fix it soon because i'm getting crazy
Old 05-15-2013, 11:22 PM
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Hello to everybody,
After the last two days in my garage problem is fixed! Injector number one clogged. I believe i should replace all of them but at the moment i cleaned them and the car run great again. Thanks
Old 05-19-2013, 05:04 AM
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Hi Mario,

Misfires from only 1 injector? I don't know... have a look when the weather goes bad...
I had exactly the same problem, I had new sparks and wires.... It turned out to be the new wires. So I bought original ones, you know with the iron thing around it.


If you drive slow all is right, ones you ask power you get misfires...

Last edited by klefroid; 05-19-2013 at 02:30 PM..
Old 05-19-2013, 02:22 PM
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I bought new wires too replaced directly problem still there. The injector number one was not completely clogged so i think under boost that cylinder didnt get the correct fuel.

Old 05-19-2013, 03:34 PM
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