Can a bad MAF cause a misfire?

I have an issue that really wipes out the amount of fun I can have with my car. When accelerating and hitting the upper RPM range, I frequently get a misfire on cylinders #4 or #5. I thought it was the coils so I replaced those last week but the problem still exists. So I did some reading and found that someone once had some unexplainable CELs come up and found that it was their MAF. I tried to test this theory by disconnecting the MAF and trying to replicate the CEL. Without the MAF I didn't get the misfire anymore. Now my question before I spend another $300 on a MAF, could this potentially be the issue? I just find it strange that if it is I would only get errors on one side of the engine. This past weekend I did remove the entire air box assembly and MAF to clean it all out. It looked clean (even the throttle body) but I still sprayed it down - didn't make a difference. Any ideas anyone?

Did you clean the TB with a cloth and literally no dirt was on it?

Just curious, did you clean the MAF sensor as shown here? http://www.6speedonline.com/forums/9...sor-clean.html

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Yes and I also used "throttle body cleaning spray" that I found right next to the MAF spray at Advance Auto Parts. So in the case of the throttle body I used both the spray and a cloth. It had a slight film of grime on it but for the most part was pretty clean. I did. I took the whole assembly apart, checked the rubber hoses on the airbox to make sure I didn't have any leaks and sprayed the crap out of the MAF. The MAF was also clean but I figured just in case I would spray it liberally. The car ran very rough for the first 30 seconds or so after I put everything back together again but then it began to idle normally and I took it out on a test drive. On the drive all is well until I floor it and hit over 5000 RPM. At that point I get the misfire again on cylinder #4. So frustrating!

Are you getting any CELs?

I paid about $156. for a new MAF a year ago. I had previously spray cleaned my MAF but it still produced CELs after a couple of weeks.

egas MAFs are more expensive. $233 at autohauz vs $168. I replace mine every 2-3 years because of CAI oiling it up and its just not the same after. http://www.autohausaz.com/search/pro...0Mass%20Sensor

That's where I bought mine last year Chao. Non egas.

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If I rev the car up through redline I'll get a P0304 or P0305 CEL. Sometimes it'll clear up if I ease up on the gas quickly but other times it stays on and I have to clear it manually. Spark plug wires are in good shape and the coils have been swapped out so that's why I was wondering if maybe the MAF could be the root cause here.

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The answer is yes the MAF could *potentially* be the cause of the misfires. On another board I encountered a Boxster owner who reported misfires on just one bank. I forget the bank. He tried all the usual things: coils, plugs, 'bad gas', and I forget what else. He either disconnected the MAF or simply replaced the MAF and the misfires went away, AFAIK, never to return. I would not advise you to replace the MAF without more confidence that it was the source of the misfires. You disconnected the MAF. Did you clear the DTCs to among other things reset the fuel trims to their defaults? Then drive the car as you did before. You need to give the DME time to detect -- if there are any to detect -- misfires so just a quick spin around the block is not going to do it. If you give the engine every chance to misfire and it does not, then clear the DTCs again and reconnect the MAF. Drive the car again. See if the misfires return. If they do I have to say that this is not 100% proof the MAF is the cause. It could be with the MAF disconnected the DME varies the fuel or ignition timing or varies the valve timing (and if VarioCam Plus present the valve lift) of the engine in such a manner that the misfires are avoided. If at any time the engine gets sicker, makes any noises, behaves in way out of the ordinary, shut off the engine pronto and get the car to an expert for evaluation. Sincerely, Macster.

Maf sensor usually runs rough and gives a lack of power in my experience, i'd be looking at the solenoid for the cams first in case there is one off,or even swap side to side to see if the fault moves with it !

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Macster - Thanks for the response and help with troubleshooting. When I disconnected the MAF I ended up getting some PSM and ABS errors but no CEL codes. I didn't clear anything and figured these errors would continue as long as the MAF wasn't functional. I didn't like driving the car for very long without it connected so honestly my test was maybe 5 minutes at the most. I ran it through the same scenario and no codes appeared. But as you mentioned it is likely that I was now under a completely different fuel mapping scenario so perhaps the test wasn't really valid. Once I reconnected everything the PSM and ABS errors were gone and all instruments were back to normal. But when I floored it I ended up with the P0304 error. No other symptoms appear on the car and it runs great each day except when I go wide-open throttle and hit the upper RPM ranges. Based on what Ferryman states below about the cam solenoids, would that be a possibility? I try to do as much as I can by myself on this car but I might have to throw in the towel soon and take it to the professionals. The car runs fine so I'm not experiencing the rough running symptom. I'll do a search on that problem and see what else I can learn!

i have same thing what did you find out

In the original thread, I never responded again to the OP. Why I don't know. Maybe I can make it up some….. You say you have the same thing going on with your car? What model/year? Need more info. What have you done to the car? A bit of history on the car would be nice.

my car is a 2002 996 c2 with 33000 miles on it i use the car on the track more then the street. i changed the coils, plugs and the MAF and no change. above 5200 rpm it starts to brake up from idle to 5000 rpm it runs good. i get a code of misfire 4,5, and 6 most of the time but when i unplug the maf there is no change in the car but the code is not a misfire anymore but a maf sensor

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What are the cam deviations, FRA, and RKAT values on both banks?

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Easy one first. When you unplug the MAF the CEL might come on and rather quickly. This is the result of the MAF being unplugged. Just because the CEL comes on with a code related to the MAF you do not stop there. If the engine is otherwise not exhibiting any issues you should try to drive the car again like you were driving it before and it manifested the behavior that prompted you to unplug the MAF in the first place. It is not really a valid use of the MAF unplug test to unplug the MAF because the engine misfires at over 5K RPMs and then after the MAF is unplugged to drive the car around the block and hardly break 2K RPMs. I note you replaced the plugs and coils. I'll assume you used the right plugs. (I came upon one owner who used some other brand and style of plug (the center electrode was recessed in the tip ceramic.. don't ask me why I have no idea). I double checked and the plug maker's reference chart had this plug listed as being a replacement for the stock plug. Regardless, the replacement plugs proved to be so bad the owner was going to remove the new plugs and replace them with new stock plugs.) The coils must be securely connected to not only the plugs but to the engine wiring harness. When the old coils are removed, one should take note of the coil and its connection to the harness looking for anything out of the ordinary. Similarly when connecting the coil to the harness connector one must ensure the connection is a secure one and there is no risk of the connection coming loose. Last but not least, IIRC VarioCam kicks in at around 5200 RPMs. The intake valve timing is retarded (which is what I recall reading but seems "wrong" to me). If the VarioCam system isn't working right this might (I say might) account for the misfires. I was told when the VarioCam solenoid/actuator were bad on my Boxster that one symptom can be misfires as the DME adjusts fueling in an attempt to get the readings from the O2 sensors it expects. Because the VarioCam is not working right it won't and the DME can adjust fueling too far and misfires can result. In monitoring the short term fuel trims I was seeing some weird fueling taking place and told the tech about this -- which prompted him to tell me what I related above. The VarioCam solenoid/actuator failure was at that time though intermittent and the fueling didn't go off the deep end and the engine didn't misfire. In fact it ran rather well. You can I believe view the cam timing in real time with a Duramatric. If I'm right you could use this tool, well, have a passenger view/log data, while you are driving the car and to see if you can spot anything amiss with the cam timing. With just an OBD2 scan tool/data viewer you can view short term fuel trims in real time and perhaps spot something out of the ordinary. However, it will be more a stretch to blame the out of the ordinary fuel trim activity on the VarioCam acting up. Other explanations for misfires can be there is an intake leak,. An AOS generally doesn't cause misfires at high RPMs but I would never rule out an AOS until I have assured myself it is ok. There can be fuel supply problems or fuel pressure problems. Is the air filter and intake stock? Or have you gone aftermarket? I bring this up because in some cases some aftermarket filter/air boxes interfere with air flow past/through the MAF and non laminar air flow in the vicinity of the MAF can lead to all sorts of hard to diagnose engine behavior that is ultimately traced to the MAF being affected by unsuitable air flow.

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sorry i don't know how to check that. what are you looking for with that info timing problems?

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You need Durametric. Since your problem seems to be only on one bank, cam timing is a strong suspect to me at least. Air leak is less of a problem at high rpm. Fuel pressure and delivery rate should also be checked regardless but it should affect both banks if fuel delivery is the problem. Also, Durametric may retrieve other pending codes that a regular OBDII scanner may not be able to. If you don't have durametric, at least you can check the short term and long term fuel trims like Macster mentioned. Macster also raised some good points about MAF and aftermarket air intake but again your problem seems to be on one bank at high rpm...

Primary o2 will also cause misfires

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with the MAF unpluged i tested the car for miles in the full rpm range it acted the same as before no power over 5200 but no misfire codes just the MAF code the plugs are stock porsche from the dealer they were bosch super in a white porsche box with the 996 part number from suncoast porsche. the same for the coils they were the updated coils with a 997 part number from suncoast. there are no mufflers on my car so there is easy access. All the coil that came off had small hair line cracks so i thought i had it but no change at all. As far as the vario cam i don't know much about it or how to test it. any help in that would be appreciated. The AOS has been upgrated to a porsche motorsports AOS about 3 years ago some custom vent lines had to be done but it all works good. The kit from porsche comes for a boxter with a new vent line that needs to be customized for the 996. The intake is not stock it's from evolution motorsports it has been on the car for 3 years with no trouble. cleaned and oiled my fillter just befor i went to the track two weeks ago. At the track is were the problem first showed up so that is why i thought the MAF maybe the oil form the fillter got it. so i installed a new MAF from Pelican parts but no change in the car after a lot of test driving. I'm going to look for intake and vacuum leaks is there any place known to have a problem where i should start.

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i think you might be on the right track its never a misfire on 1, 2, and 3 do the cam solenoid good bad often.

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However, if the solenoid is bad, it should trip the CEL. One exception is if it's intermittent then you may get a pending code but not the CEL yet. If you're driving for a track session with sustained problem beyond 4.5k rpm, I imagine your CEL would be tripped. Durametric can show you mifire on each cylinder in real-time and it can also retrieve other codes that a generic OBDII scanner cannot. The hope is those codes will give you more clues. Without Durametric, you can still try to diagnose it in a generic way such as checking the fuel pressure and deilvery to make sure they are in spec., checking intake air leak after the MAF but as I said before vacuum leak will not make your engine bog down at 4.5k rpm...

thanks for everyone's help let me just put this out there the car has an IPD competition plenum with the 83 millimeter throttle body that has been on there for one season already worked fine. towards the end of last season I started to notice a little break up on top end at the end of the track day.so I believe this problem started intermittently.

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can you tell me your experience with the primary o2 sensor. I know my cats are not in the best shape.

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There's another possibility. If your cat on that side is deteriorating, it can (and will) cause misfires on that bank, and prevent revving past a certain point under load as it gets clogged and backs up the exhaust flow.

I have had my primary o2s go bad twice. It will act the same way when your cam timing tension fails. I think you can swap primary o2 from bank to bank if you want to see if the bank misfire changes. If not it's most likely your tensioner which is a ~900 part from Porsche

For me the solution was so easy yet ended up being difficult to diagnose because of the codes being thrown by the car. I ended up having a clogged catalytic converter on that bank! The way my dealer tested this was just disconnecting the cats and going out for a drive. After that the car ran perfectly fine. So I ordered up some a 200 cell x-pipe from Fabspeed and haven't had the issue since. Unfortunately the repair did cost much more than the $300 I was moaning about in the beginning of the post but the character of my car has changed and if anything it revs more freely so I'm happy again. Good luck diagnosing yours - it's probably worth looking at those cats and seeing if they are causing your pain as well. It appears cars on the track tend to kill the cats more often than pure street cars so yours might be doing the same thing.

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I like this theory as well. I just had my cat broken street driving 35k miles. The cat is fine functionally (the inserts look prestine and not melted) except the element inside has broken off fmo teh canister banging on the postcat sensor creating a horrible rattling noise. Just curious if your cat element failed the same way or physical it's fine just that it's not cleaning up the exhaust. Either case, one should be able to tell by comparing the postcat sensor readings of the two banks.

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Thanks for getting back to me i needed to change them anyway i just ordered cats and x pipe i'll let you know if it works.

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i ordered the durametric cable today 2nd day air that should help. Yes my cats are ratteling also at 33000 miles they have been like that for two seasons on the track. No cel but before the rattle i was using the gas from the track the high octane i always felt like the gas made the cats go bad do you think there is any truth to that.

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I think the stock cats are crap shots. Some last a long time, some not so much even for street usage. I'm pretty sure track driving is not helping with all the WOT fuel buring the cats. If your cats ae rattling, it's very possible they've melted inside (by the high heat) and blocking the exhaust. Of cource that would create misfires at high rev. Once you take off the cats, you can take a peek inside from the header end and from the postcat O2 sensor hole to see HOW it fails inside.

i took the cats off cut them open they are clogged i will post a pic soon. thanks for all the help

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not good

Oh yea, pretty clogged, especially the left one. The bigger one is the one closer to the header? Are they from bank2?

Now you can go sell the precious metals to a recycler and make a little cash on the side.

After cutting them both open they were about the same but the one that was giving me a misfire was broke lose inside and ratteling i think the inside was moving so much that it was acting like a cork. The one with no codes was still in place and had to be broke out. So i welded them back together empty put them back on and the car is faster than ever. THANKS

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Woo hoo...Success!

Good catch. A plugged converter is a rather rare problem. Takes some guts to cut one apart. I wonder why the #2 O2 sensor on that side was not giving a reading that would have flagged a problem with the converter?

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We have exhausted all options. New plugs and coils, new 02 sensors, tested the coils and the wiring. How can we test to check MAF? The codes are always #4

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@monnie's era have you checked the valve springs and cam lobes on cyl#4 ? If not you have not exhausted all options... I had a 3.4 once that had worn a intake Cam Lobe smooth/round......after swaping spark plug, coil, and injector from one hole to the next with same results, I pulled the valve cover and found the problem...,,The engine ran good at idle or anywhere you wanted to drive with no noise , except when you floored it and went past 5500 RPM it would set the miss code....With only one Intake Valve opening the miss would only happen above 5500 RPM.. A broken valve spring can act similar but also different depending on how much spring pressure is left after the coil breaks...