s2Rick

Hi everyone, I have put new plugs, new coils, new air filter and new mass air flow sensor in that order on my 05 997. I'm still getting a misfire @ low rpm's. Seems to run great @ speed but it happens @ low speed but not every time. I have also ran different fuel treatments through the system. Any help would be appreciated. Thanks

Edgy01

Injector cleaner?

s2Rick

I have put in techtron and other additives to get rid of any water in the fuel. The misfires are random and in different cylinders according to the scanner. Thanks

997_rich

Is the car dead stock? No aftermarket intakes etc, right? Also are you throwing any other fault codes? Perhaps a cam position sensor failure? Or an oxygen sensor failure code?

The fact that it apparently happens on many differnt plugs leads me to think that it's something tripping up the computer rather than the actual act of spark creation itself.

Have you ever pulled the ground wire to the engine on the passenger side behind the tire (perhaps to change coils?). Better check to make sure that ground wire is still solidly mounted.

s2Rick

Yeah car is stock except for a cold air intake tube. Didn't know about the groung wire,can this cause problems? My indie seems to think it may be fuel related. If i take the car to the dealer can they plug into the diognostic machine and tell me exactley what is causing the problem? Thanks

jhbrennan

Cold air intake with oiled filter?? If so check the MAF for fouling ( I know you say the MAF was changed).

s2Rick

No to the oiled filter,installed just the orange cold air intake tube. Cleaned the old maf sensor before installing new one and no difference on either one.

997_rich

Ground wire can prevent a good spark... half of the electrical connection on a spark plug is the engine. One connection on the back of the plug and one connection is the threads (that connect with the engine).

Diagnostic machines can only provide clues... They may say "coil failure" but it could be the ground wire etc.

The first place to look is whatever you did before the problem started. If the problem started around the same time you changed the airbox, I'd set it back to stock for a while if you still have the parts and see if you still get the failures.

The only way that I know of that fuel can cause misfires is if the fuel is flooding badly. You should be able to see this as black powder residue on the plugs and you should also be able to put an exhaust gas analyzer in the exhaust pipe and see that the car is running rich.

Edgy01

Did you say that you forced an injector cleaner through the system?

s2Rick

No Just used tectron and fuel additives to dry any water in the fuel .I will try some fuel injector cleaner. Any other suggestions? Thanks

rnlarctic997

How many miles on your car? I'll suggest your mechanic looks at all 4 of your oxygen sensors...

Macster

I believe if I interpreted your earlier post the misfires are all over the engine, not confined to one cylinder or just the cylinders of one bank?

If all over this suggests a common failure. Air leak comes to mind with the mention of a cold air intake tube fitting. Any chance you disturbed something: wiring, vacuum hose, etc.; in installing the cold air intake tube? Also, you have to make darn sure this tube hook up didn't introduce any air leak.

Misfires have various causes: Plugs, coils of course. Air intake leak. If the CEL flashing this suggests a plug or coil problem. If the CEL not flashing this suggests an intake leak or a mechanical cause.

Probably not the case here but a burned exhaust valve for instance. Or a cam chain tension problem, or a VariOCam problem.

Fuel supply can also cause misfires. Your 'indie' thinks the symptoms fuel related? What did he advise you to do then? Or what does he propose to do about this?

However, I came across one instance of an owner reporting misfires on just one bank that ultimately he determined were due to a bad MAF. So one reasonable test would be to disconnect the MAF at the wiring harness, clear DTCs (even if there aren't any but in clearing the DTCs this resets all the learned fueling back to their defaults), then drive the car normally.

The check engine light might come on due to the MAF disconnect but the misfire symptoms might go away.

But all of the above assumes the engine is not making any noises, that it idles quietly and well, is not possibly in the early stages of some serious (maybe fatal if not caught in time) internal engine failure.

If the engine is not making any noises you can experiment, engage in some self-diagnosis. But at any time if the engine starts acting up above and beyond what it is doing now, shut the engine off and do not start it again. Your self-diagnosing time just expired. Now you have to rely upon a professional to diagnose the problem and his hands are tied by the fact the engine is at risk of serious internal damage if it is run any more.

Sincerely,

Macster.

s329

Excuse me if this is dumb question, but how does one actually know if there is a misfire? Is there a loss of power in certain RPM bands? A particular sound coming from the engine? Or is this something that can only be noticed when you run it through a durametric tool?

997_rich

at low speeds (like idle) you'll probably notice it as an uneveness.. almost like you're going to stall for just a second. At high speeds it's harder to notice but it sounds like a quick break in the buzz of the engine.

I beleive the OP is referring to some kind of durametric readout but I'll let him speak for himself.

aaks38

I recommend you remove your plugs and look for any difference amongst them to help isolate your problem. You may have cracked the ceramic insulator, have a bad coil pack or something not seated properly.

You can also try to run seafoam through the tank or intake..