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Old 11-30-2009, 05:32 AM   #1
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misfire 4,5,6

1999 boxster with 74000mls.has been misfiring for a while only when you put the foot down.just had major service last week(thought that would cure it but didnt) I changed all the coils on the plugs today but still the same,the plugs were changed last week.You guys got any idea what to try next?
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Old 11-30-2009, 04:42 PM   #2
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I am having the same issue. I have a 97 with 30,000 miles. Misfire 1&4. I have replaced the MAS and swapped coil packs. I can drive for months with no issues until I wind it out pass 6,000 close to redline. I did the 30,000 mile tune up two years ago and did it again hoping it would fix the issue. I am not that hard on it very often so its not that bid of an issue. However, I would love to know what to do to fix it without keep doing part swaps.
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Old 11-30-2009, 04:45 PM   #3
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I just read your post again. Since you issue is all on the left bank, try swapping the o2 sensor from one side to the other and see if the problem follows the sensor. Start with the ones behind the cats. If the problem switches side you kno wyou have an o2 sensor issue.
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Old 12-01-2009, 03:55 AM   #4
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Are you getting any codes?
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Old 12-02-2009, 01:55 AM   #5
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Hi codes are 304, 305 and 306 all cylinder misfire
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Old 12-02-2009, 02:38 PM   #6
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Have you tried swapping the left and right O2 sensors as an earlier poster below suggested? This is a 20-30 min project at most. Seems like the next logical step.
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Old 12-03-2009, 04:07 AM   #7
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what do the o2 sensors look like?where are they located and is it an easy job.thanks for the help guys.
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Old 12-04-2009, 01:13 AM   #8
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The O2 sensors look roughly like big spark plugs with about a foot of wire coming out of the top (photo attached). They screw into the side of the exhaust pipes near the catalytic converters; for a '99 I believe you have 2 per side. It's helpful if you have a special O2 sensor removal wrench (spanner) to provide good leverage without slippage. Such a tool should be available at any auto parts store. Attached is a photo. Notice it's usually meant to be used with a 1/2" socket wrench.

To access the O2 sensors you'll need get the rear of the car high enough to easily slide yourself underneath. A large floor jack along with a pair of high quality, stable jack stands will work well and should be safe. Slide underneath and remove the plastic belly pan closest to the engine. Look at the exhaust pipes and catalytic converters and the O2 sensors will be obvious. Carefully undo the clips at the end of the sensor wires, then use unscrew the sensors from the pipes. The sensors can be very tight so you may need to tap your socket wrench with a hammer or use a piece of pipe to get enough leverage to break it loose. Next, swap them left to right. Installation is the reverse of removal.

Invest $60 in a Bentley service manual. Use it for one project (like this) and it's paid for itself. And yes this is an easy project.

Let us know how the swap worked out.

Last edited by gschotland; 12-04-2009 at 02:28 PM.
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Old 12-04-2009, 03:52 AM   #9
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Hi today i disconnected the maf and the car ran superb apart from cutting out at idle.I then reconnected the maf and it was back to loss of power at 3500revs.Do you think a new maf is the answer,thanks Steven
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Old 12-04-2009, 04:26 AM   #10
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I believe there is a post about unplugging MAF sensor and it says if it runs better without then replace it. I believe the post is by Mike Focke. I appologize if i missed the last name. I do not have the link but its out their and is good info!! See if you can find it. You may try cleaning the MAF but i would suggest replacing it if you are sure its the issue. You may try swapping o2 sensors first since its and easy task.
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Old 12-04-2009, 04:30 AM   #11
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http://sites.google.com/site/mikefocke2/checkenginelightcausedbymassairflowsensor
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Old 12-04-2009, 09:48 AM   #12
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Sounds like your MAF is likely shot, but that doesn't rule out the 02 sensors. Mike Focke's MAF step by step is superb.

One O2 sensor in my '02 S went at just 64k miles (got check engine light) when my brother owned the car; 60-75k isn't uncommon. I read in this forum that it's best to change all four at once, so I changed out the other 3 at 68k miles even though I wasn't getting any codes. BIG improvement in idle smoothness and driveability. With 74k miles, your O2 sensors are likely on the way out even if they're not flashing CELs.

You might want to try ************************************************************ for the MAF, as they seem to have the lowest price. They show OEM type O2 sensors for the '99 for $100.97, and the air mass sensor for $161.48 or $217.22, depending on the part number you require. I imagine these prices are far lower than what you can get them for in Glasgow.

It's possible to get universal O2 sensors without OEM type plugs for substantially less, but I'd recommend against that in your case because if the connections you make aren't just right you'll have problems. "Plug and play" is the safe bet for the inexperienced DIYer (like me). Even with 4 sensors the savings isn't worth it IMO.

Last edited by gschotland; 12-04-2009 at 02:27 PM.
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Old 12-04-2009, 10:35 AM   #13
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Another great one courtesy of Mike Focke. All about O2 sensors.

http://sites.google.com/site/mikefocke2/oxygensensors
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Old 12-08-2009, 09:45 AM   #14
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Hi,took out maf and cleaned it with electrical solution,car now going great,thanks everyone for there help.
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