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Boxster 3.2S misfire - help needed please


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I have a 2000my 986 Boxster 3.2S with manual 'box and its covered around 130,000 miles. It hasn't seen a lot of use over the past couple of years - less than 1000 miles (yes I know, its a waste of a good car). In fact this has been bugging me, so a few weeks ago I decided to stop using my daily driver quite so much and use the Boxster a lot more. A couple of weeks into this plan, and after a journey of 120 or so miles, its started misfiring slightly and over the next couple of miles, got significantly worse. In fact it refused to rev over 2500rpm at all and when I pulled up at the next junction, predictably, it cut out. To my surprise, it starting up again instantly and ran beautifully - with no more misfiring. But then I tried to start it this morning and its misfiring like mad and will hardly tick over. 

 

However at no point has a CEL come on. I plugged in a generic OBD reader which gave codes P0300, P0301, P0302, P0303, P0304, P0305 and P0306. From what I can see, these are just telling me that the car has had a misfire problem rather than pointing to any possible cause. Last year - and probably less than 1000 miles ago, it had replacement spark plugs and coil packs so I can't imagine its that. I have a search on the internet but really I don't know where to begin.

 

One further point which may or may not be related: at first I thought it was my imagination, but I think I can detect a small hesitation when accelerating hard and shifting gears. Its occurs just as you change gear, say from third to fourth. This has been there for a while now and certainly before the misfire problem occurred.

 

Can anyone offer any advice please? 

Thanks,

Steve,

Northumberland, UK

 

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  • Moderators

Welcome to RennTech :welcomeani:

 

You have a simple misfire issue, literally on every cylinder, which is highly unusual.  I would start by putting the car up in the air and checking the coil pack wiring harness for rodent damage (for some reason, our little friends love to chew up the harnesses in these cars when they are left standing for a prolonged period).  I would also check the fuel system looking at delivery volume and pressure.  You may have some bad gas from it standing, or a plugged filter.  Time for some basic hands on diagnostics..........

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agreed with the above . possible too lean of a fuel to air mixture. could be sour gas. could drain the tank and add some injector cleaner. ive used acetone before which worked great on old hondas but that shouldnt be used until you test for fuel pressure and also measure fuel volume delivery


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  • 2 weeks later...

Thanks for the above. Time has been an issue recently so I haven't managed t take a further look yet. I'd like to think it isn't bad gas - the car had covered around 600 miles in the week before this incident. Is there any chance that a bad MAF would produce these symptons?

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I just started a thread about the same issue!

I have an vacuum leak witch i suspect caused my problem.

I only had it misfired a couple of times but it was on all cylinders and the car was shaking Alot.

Also when i tried to rev it hardly did so and the rattling of the car was worse, on stable rpm the shackin and rattling was less.

There is a Picture on were i have a leak, as of no its Ok but if so muck as look at the tube it starts to hiss.

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For future reference, please do not multiple post on the same topic in different threads.  It is against forum rules.

 

As point out in the other thread, you have a vacuum leak in your brake booster vacuum line that letting air directly into your intake and causing a lean miss.  Fix the leak, you problem will go away.

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  • 3 months later...

I just wanted to let you know how this ended...

 

...it was indeed the MAF sensor. It should have been an easy replacement but the two screws holding the sensor in place were rusted to hell and there was no way that they were coming out without a fight. The easiest solution appeared to be to removed the air filter housing and pipework and then have a good go at the MAF screws on the workbench. Of course it wasn't quite as straight forward as that. Removing the airbox is near impossible. However, in the end, the air box came out (in bits) and the MAF sensor was replaced and while I was at it, I replaced the existing air filter housing and filter with a rather more simple cone type air filter. I'm not sure that it adds any more power but it sounds terrific.

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