sweatyfox

Hello,

My 1999 Boxster 2.5 has a misfire when idling. The car starts and drives fine, but just has a slightly lumpy tickover due to 3 cylinders having a misfire on one bank.

The fault codes I retrieved were:
P0300 Random/Multiple Cylinder Misfire Detected
P0304 Cylinder 4 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected

I have trawled the internet and found many threads with the same or similar problems, but never with the solution or what the problem was.

From what I have found online, Im guessing the causes could be?

O2 Sensors
Variocam/Solenoid
Coil Packs.

As this is all one bank of cylinders I was thinking the most likely cause is a single item at fault that affects the whole bank, i.e O2 Sensor etc.

The car has 80k miles on the clock and regularly serviced.
Although at its last MOT it was very borderline pass on emissions, I think because the car spends quite a bit of time sitting in traffic possibly sooting things up.

So Im tempted to change the O2 sensors, but how many are there on an early Boxster? And where are they located? I have seen 1 on each side that a relatively accessible once the rear wheels are removed.

Edit: Since discovered waterlogged Alarm module under seat.

Thanks in advance,
Lawrence

Macster

You left off another possible explanation: MAF.

Don't know how many O2 sensors there are. Might just be 2 -- ahead of the converters or 4 -- 2 ahead of the converters, two after the converters.

Easy enough to find out. Just look.

With no O2 error codes -- did you read pending codes? -- I'm not blaming the sensors. I've gone through a few O2 sensors over the years in both of my cars and always there was an O2 sensor related error code with the CEL and never any misfires.

If you have a sophisticated enough OBD2 code reader -- one I bought way back in the late '90's is sophisticated enough although it cost around $250 then -- it should provide you with a menu from which you can initiate some O2 sensor tests. I have found that in some cases these tests can help ID a bad sensor. I kind of prefer to do this just to be sure replacing the sensors is the way to go.

When were the plugs last changed? Were the coil packs carefully inspected for signs of degradation?

If the VarioCam solenoid/actuator is at fault there should be at least a pending code. Also, with an OBD2 code reader/data viewer you should be able to monitor short term fuel trims in real time. When my 2002 Boxster developed what proved to be a solenoid/actuator problem on the passenger bank the tech told me that misfires can arise as the DME changes the fueling in an attempt to get the expected O2 sensor reading from the #2 sensor of the suspected bad bank. In some cases the fueling can go too far afield and misfires can happen. But what you would see would be at least one side's short term fuel trim reading wildly different from the non-misbehaving bank.

I mentioned MAF above. In one case a Boxster owner reported misfires on just one bank and after a number of things were investigated and checked and dismissed, and possibly a few things even done, what he found was the MAF was the cause of the misfires.

Sorry kind of all over the page.

Without knowing the history of the car a number of things could be to blame: Plugs, coils, contaminated fuel injectors (when was the fuel filter changed?), weak injectors, MAF, even rodent damage.

You can look for pending O2 error codes, run some of the O2 tests of you can, and possibly eliminate the sensors.

If plugs are due then there's plugs and while you are there at least carefully check the coils for any signs of degradation.

You can disconnect the MAF at the wiring harness and clear the codes and then just drive the car normally as you usually do and see if the misfires return.

Lots of possible explanations but it can get expensive if you throw parts at the symptoms and start on the wrong end of the list. But I don't think it a bad idea to at least address wear items that are due to be replaced that could possibly be the cause of the misfires.

Added: Was in a hurry this AM but there is another possible explanation. I do not think it that likely but one you have to consider and that is the AOS. I've been through 3 of these now with my 2002 and misfires have never been a symptom, but each failure was different, that is manifested different symptoms though they all ended with clouds of oil smoke just billowing from the exhaust. However, in the case of the first AOS this took a while. The engine was kind of hesitate off idle and idle was lumpy. The 2nd AOS was just a CEL -- accompanied by a bit of a stumble from the engine but the stumble was mild and short lived -- with an error code that had me suspecting the MAF. In the case of the 3rd AOS everything was fine until I spotted a huge cloud of what was oil smoke behind the car. Up 'til then no signs of the AOS going bad. Was only able to drive a mile or two before the smoking became constant then the engine started running very poorly. I knew it was time shut off the engine and call the cavalry (tow truck).

Frankly I like -- probably not the best choice of words -- the VarioCam solenoid/actuator for this. The misfires and confined to one bank. The lumpy idle. It kind of fits. But this repair is expensive -- and my experience is it is best to replace both the solenoid and actuator while one is "there" -- and you don't wont to go this route if there is no overwhelming evidence it is called for.

sweatyfox

Thanks for the reply Macster,

I've attached some screenshots from the engine at tickover.

Not really sure what Im looking for and Im guessing I only have two O2 Sensors? Or I have 2 knackered ones.

Is there anything else that would be of use at the moment?

Cheers

Macster

At first I was a bit puzzled by the #1 sensor readings of 0.410V and 0.380V. Normally these readings swing from very near 0.1V to around 0.7V every second or two -- at idle -- as the DME varies the air/fuel ratio slightly from rich to lean and back again. Readings in the 0.4V range is essentially a flat lined sensor, suggesting it is not functioning, possibly because it is cold. Then I looked at the data again and see both banks are in open loop mode.

That's kind of unexpected because I note the coolant temperature is 98C which is plenty warm. Warm enough that a healthy engine (well, an engine with healthy sensors) should be in closed loop mode.

Next based on the readings for Banks 1 and 2 #2 sensors these appear to be in the same non-functioning state as the #1 sensors. My reference -- the Bentley manual -- indicates for the earlier Boxsters there are 4 oxygen sensors: One ahead of each bank's converter and one after each bank's converter.

The other thing that caught my eye was the Bank #1 Long Term Fuel Trim reading of +18% vs. Bank #2 Long Term Fuel Trim reading of 0.8%.

My info is whenever long term (or short term) fuel trims get close to or more than +/- 10% from 0% that's a sign of some kind of trouble and a CEL is very likely.

If you observe the data longer and do not see the DME enter closed loop mode operation that's a problem -- I think it a problem now but I'd like to give it more time. But why the DME fails to enter closed loop model operation I have only wild guesses.

My best guess is if the #1 sensors (one or both) fail to begin that voltage swinging action I described above both sensors are either bad (if they are heated the heaters are not functioning) or there is something else going on the DME is unable to switch to closed loop mode. For the DME to operate in closed loop mode both sensors must be working properly.

I have to admit I don't really like both sensors failing at the same time. The two sensors are rather separate from each other and the only thing they should have in common is they both eventually connect to the DME via separate input pins.

To have both be bad concurrently suggests a common failure that based on my understanding would have to be at the DME. I don't like this as this is an uncommon failure.

Oh, forgot to mention: I checked the fuses and C2 is for the oxgen sensor heaters. But it appears this fuse is also for "fuel injection" and "ignition" so if the fuse was bad I think there'd be more going on than just cold O2 sensors.

I really wasn't expecting to have both banks with essentially flat lined sensors. Nor was I expecting to see the apparently "good bank" (#1) with the elevated Long Term Fuel Trim.

I'm not sure where to go from here. As I mentioned above there's giving the engine more time, the DME more time to enter closed loop mode but I don't hold out much hope. Based on the coolant temperature the DME should be in closed loop mode now. But give it a shot. Even though the coolant is hot the sensors need a bit of engine run time to get to their operating temperature, which is nearer 600C.

By way of comparison, though not apples to apples, from a cold start my 2002 Boxster will enter closed loop mode concurrently with the secondary air injection pump shutting off and the cold idle speed dropping to near hot idle speed. Coolant temperature is still way down close to ambient.

sweatyfox

Hi again, its all gone horribly bad! (Dont wory, not engine related now, but possibly connected)

Noticed the car alarm going off this morning in heavy rain, so tried to turn alarm off but not responding.
So keyfob remote not responding.
I put the key in the ignintion but it still wouldnt turn the alarm off!

So I just left the car unlocked and it eventually stopped.

Later today I noticed a fan/pump sound coming from the front of the car, cant I dentify what it is, but sounds like a fan or pump.

Now the big problem is I think theres water in the ECU or electrics.
I cant get the pump/fan thing to turn off.
I put the key in the iginition, turn to position 3, all lights come on but car wont start.
The key/doors locked light is on (red led illuminated but the key switch)
I cant open the boot or bonnet as the release levers are locked.

How can I kill the power to get the bonnet lever to unlock since everything is unresponsive?
Is there a fues I can remove to kill the power?
I've attached an image of my fuse box layout.

Ideally I want to disconnect the battery until I can check thouroughly under the bonnet.

Cheers

Macster

Probably not related but the water in the car is the bigger problem right now.

There should be a fuse diagram on the inside of the fuse box door.

I do not think there is a master fuse. Generally if one wants to cut power to the car one disconnects the battery.

My reference is for the alarm control module, DME control module, and Tip control module, fuse B8.

Horns is B3.

C3 is alarm control module and power windows.

C4 is fuel pump.

C8 is radiator fan motor right, and C10 is radiator fan motor left.

There are cable pulls at the front and back to let you manually open the rear and front lids. If the rocker switches or key module buttons don't work you'll have to find these cable pulls -- at least the front one for now -- and get that front trunk lid open and the battery disconnected.

Then you have to remove the water probably inside the cabin under the seats. In USA cars the right seat, the passenger seat, has the alarm control module on the foor under it and this is where water goes when it gets in the cabin.

You might have to remove the seat and then remove the water. Blotting it or using a wet/dry shop vacuum would work.

You have to find the source of the water. My money is on the water drains either the front ones on either side of the battery box. But check the rear drains too. There is one located under the clamshell arm on either side of the top. You'll have to put the top in service position and this requires battery power and and good battery.

Water can get into the doors and from the door run into the cabin too. Check the door bottoms for any signs of dampness. If there is any the door panel will have to be removed and the water removed and the door membrane glued to the door frame again or replaced if torn/damaged. (My 2002 Boxster had one of each: A torn membrane in one door and one that just needed gluing in the other door.)

Get the water out and get the electronics completely dry ASAP.

mikefocke

Some approaches to getting to the battery. Here.

Macster

Mike, I click on that link and get a Page not Found error message.

sweatyfox

Thanks for your help, I managed to get behind the emergency release cable behind the wheel arch, pop the bonnet and disconnect the battery, so at least the alarm wont be going off.

The reason I suspected water in the electrics was everything was going haywire.

So brief summary of all the problems I had yesterday:
Alarm went off in heavy rain in the morning (had quite a bit of rain the previous day)
The keyfob would not disarm the alarm or unlock door.
Some fan or pump had been going most of the day from the front of the car.
I put the key in the ignition, all lights came on as usual but car would not start.
The door lock switch on the dash is showing locked (red LED on) doors will not unlock when pressed.
Whilst I had the key in the ignition the windows started going down in steps, then got stuck down.
Its almost like the car is possessed!
I tried the OBD reader but it refused to connect.

So current status is windows stuck down and battery disconnected.

I had a quick check under the seats last night and everything seems dry, but I’ll check again today.
Any ideas where I should start looking or what the problem could be?
Any common places water can get into the electrics?
Or ECU gone bad?

I’ll check later today in the daylight and see what I can find.
In the past there had been some little puddles of water appearing in the bulkhead either side of the battery, this was caused by leaves blocking the drain holes.
I had a brief look and it looks wet, but definitely no puddles and I couldn’t see any electronics modules in these areas, although it was dark.

Cheers.

Edit: Just re-read your post Macster regarding places to check for water leaks, I'll see what I can find.
I'll definitly be able to check the front end out, but not sure if I'll be able to get the roof up the check the rear depending how things work.

Macster

If the floor of the cabin is dry, if there is no water under the seats, check along the door bottoms for dampness.

Water can get in the door and if the door membrane is bad the water can get where it shouldn't and affect initially the door lock and window behavior. If left unaddressed the electrical gremlins can start to appear at areas removed from the doors.

Less likely but still a possibility is check that the DME is dry. In the Boxster the DME is accessible from the rear trunk. You have to remove the trunk lining carpet at least along the front of the trunk to expose the module housing.

I don't think you need to open up the actual module housing unless you detect signs of moisture. If you do then you have to carefully open things up and dry everything out and of course find and fix the water leak.

Be sure the battery is disconnected. Be sure to watch for static discharge. That module is very sensitive to static and if you zap it a new one can cost like crazy to replace.

sweatyfox

Ok I found the problem! A bucket's worth of water under the passengers seat!!!! The Alarm Module has been swimming in water and I need to get it out ASAP.

Unfortunately I cant get the passengers door open to remove the seat.
Even before I disconnected the battery the passengers door wouldn't unlock.
The handle and inside door lever move the full range, but doesnt unlock.

Any ideas how can I get the door open?
I was looking between the window seals into the drivers door and could see the linkages moving, and everything that moved inside the drivers door was moving inside the passengers door but not unlocking.

I've mopped out all the water and the puddle is now gone and I've got as much water as I could out from the carpet, but need to gain access to the electrics to get it all out.

Its quite obvious the water has been peeing in from behind the seat.

Thanks again for all your help and advice

Pics below from what I found today......

Macster

'bout lost my cheeseburger lunch seeing that moldy blueberry muffin.

The door won't open because it is locked and there is no electrical power is my WAG. When the doors are locked if one pulls the outside handle the handle moves with no obvious resistance.

So does the inside handle the 1st time. But if one pulls it again one can open the door but this requires electrical power to disable the lock and engage the door handle to the door latch hardware.

With the alarm module wet not sure you want to connect electrical power.

Up to you: If you pull the alarm module fuse, or fuses, being sure to leave the door lock fuses in place, you can consider connected 12V power via the fuse box emergency power lug.

You connect 12V+ to this lug and then ground the negative lead -- the handiest place is the door latch catch that is exposed when the door is open -- and just long enough to work the inside/outside handle. If this is going to work it will work right away so no need to leave power connected any longer than you have to.

I would be reluctant to try to power up any of the car's electrical system with things still damp even with fuses removed.

Thus a safer way I think would remove the door panel and then opening the door by intelligent fiddling with the door latch once it is exposed.

I have a PDF of how to remove the door panel I can send you if you want it. Send me a private email with an email address that will accept a PDF file (not very big) and I'll send it along as soon as I can.

sweatyfox

Hi all, thought I'd give a quick update.

I managed to unbolt the passenger seat and get it out through the drivers side.
Wasnt sure if it was going to be possible, but it was

I've now removed the alarm module and its not looking good.
It was very much submerged in water and looking corroded.

I've cleaned it up and got it drying on a radiator, but I expect its knackered

I'll test it in a few days time and see if anything happens.

Pic below of how it was looking.

sweatyfox

Another brief update.

I have the alarm module back in and am able to start the car.
I've also been able to get the windows back up.

But the central locking and alarm will not operate from the key fob.
However I can put the windows down by holding down the unlock button and pop the boot with the remote.

So somthing isn't right with the alarm module and I can't unlock the passenger door, bonnet or boot from inside as the lock light remains on in the console.

Are there any tricks to getting this to unlock?

Im going to post a seperate thread related to the alarm for now.

I will update with regards to the misfire once I have this problem sorted.

Thanks for all your help

Macster

About all I have for you to try is it open up the key head and remove the coin battery and insert it with reverse polarity for a few seconds then remove the battery and turn it the right way 'round.

If this doesn't help then I think you have a knackered alarm module. That you managed to dry it and it works as well as it does I think is just luck.

Honestly, even if the key battery thing above does work I think the alarm module will just deterioriate over time. Once something like that has been submerged long enough for corrosion to set in the corrosion proceeds -- albeit at a slower pace -- even though the unit is dry. Moisture in the air is all it takes.