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Serious Engine Mis-fire - Boxster S MY00


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Hey everyone,

I need some serious help.

My car has seriously started to mis-fire. It only started today but trying to think what caused it.

I took it in to have a vehicle check at a dealership yesterday and they told me that a few things need replacing.

First I need a new drivers side CAT cause it broken up slightly. This is also causing the O2 sensor to registar faulty.

Second, all 6 of my coils have cracks in them.

However, Porsche told me that they were not immediate issues and were not causing any problems, and its been running fine.

However, this major misfire has started, and the engine check light has come on. Its only in the lower rev's region, and it splutter badly when you try to pull away, but then all of a sudden it comes to life.

The strange thing is its only started to happen since I but some fuel in from this petrol start I have never used.

Does anyone have any ideas,

I was thinking of draining the fuel from it now and replacing it before I took it to the garage, what do you think?

Please help

Many thanks

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The first O2 sensor is used during part throttle driving only and adjusts the air fuel ratio slightly depending on what is seen in the exhaust. It's totally ignored by the computer at WOT during Closed Loop. The second O2 sensor is only to measure the efficency of the catalyst. If your cat converter breaks up or is no longer working both O2 sensors get the same reading and it sets off the CE light. Normally when the cat is fine the second O2 sensor would read way more oxygen in the exhaust as all the excess fuel is burnt in the cat.

These CE lights may put the car in "drive home safe mode" but shouldn't cause a mis-fire situation. Screwed up plugs or coils will be the culprit for that.

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Oh right, thats interesting, couple of questions if I may,

1) Do all Boxster S have the two O2 sensor per cat arrangement, even the very early ones (UK-Reg:99, US-MY00) cause I came from a 2.5 boxster which only had the 1 O2 sensor per cat arrangement.

2)Is the CAT damage system very effective, Cause the reason Porsche said my CAT is damage is cause there is a rattle inside the exhaust (which is not the heat shielding) and its more than likely pieces of CAT broken off. However, my CAT light is not on.

If the CAT light is not on, and the exhaust does not smell overly rich, might I be lucky and it could just be a little bit thats has broken off and the rest of the CAT is fine?

3)Have I understood correctly, that second O2 sensor (after the CAT) is not directly communicating with the Engine Check system and is part of the CAT check system. However, the first O2 sensor (before the CAT) is part of the engine check system and detects the air/fuel and burn characteristics of the engine?

A couple more things I have noticed.

First, my engine check light is not staying on now, instead it come on and then goes off. what happens is now and then when I try to accelerate away, the engine mis fires lots, then the engine senses a problem and the engine check light come one, HOWEVER, as soon as the engine check light comes on, it corrects its self and all the power come back and it runs OK'ish. Then once its settled the engine light goes off. What do you think?

Another thing, as the engine ticks over, I can here lots of "tickings" now I cant say its for definate, but might this be arching ticks?

many thanks

Russ

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Hi anyone, can anyone answer the question I posted.

Also, to try and fine tune in to what the fault is, not sure if this matters, but does the fact that it only seems to misfire at below 2000 - 2500 RPM.

also, just reading the report, its says that the O2 sensor ahead of CAT fualty - faults stored in DME memory. is this the sensor after the CAT, therefore should not have an effect on the engine management and only check the CATs efficiency....correct?

many thanks for all the help guys

Russ

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986Jim: The first O2 sensor... is totally ignored by the computer at WOT during Closed Loop. Normally when the cat is fine the second O2 sensor would read way more oxygen in the exhaust as all the excess fuel is burnt in the cat.
I see what you mean, but Closed loop Lambda Control falls into Open Loop at the greater throttle openings. The second O2 sensor would read practically no oxygen at all, as the excess oxygen molecules join with the Carbon Monoxide to form Carbon Dioxide and with the Hydrocarbons to form Carbon Dioxide and water.

Russ, is your car a UK car or US? In the UK, we have never had CAT lights and inherited CEL in 2001. The CAT can be damaged and require replacing for a number of reasons, including: erosion of the platinum cell coating (overheating or leaded fuel) core meltdown (excess fuel entering a hot CAT) core fracture (mechanical or thermal shock) and detached/dislodged core. Any of these can cause the whole thing to block your exhaust.

Are the 'tickings' just lifter noise or just the crackling of the hot exhaust?

... its says that the O2 sensor ahead of CAT fualty... is this the sensor after the CAT..?
No, ahead of CAT is just that, upstream of the CAT, before the CAT in direction of exhaust travel.

Loren, you said; "A bad cat could ruin the O2 sensor" the converse is definately true.

Russ, please post your trouble codes, as Loren said, if the Coilpacks are cracked like you say, your going to need to change them regardless if they are causing this fault or not, as they are exposed to everything the road can throw at them and the water (if you drive on wet roads) will be getting in.

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Hey 0586slb,

I will try and get the car booked in at the garage again and get they to write the codes down.

If its helps at all, the car is a UK car, and is the MY00 (its a 99 reg year in the UK, but MY99 do not exist in the US cause of there reg system)

I can tell if the cat is damaged, all Im getting is a rattling inside the exaust pipe, sound like after the CAT, which is more than likely a little bit fo CAT broken off, I guess if Im lucky the CAT might not of shattered and it just a little bit broken off, but this is probably rare.

The exaust does nto smell rich or anything, and it sounds fine apart from the rattling.

The tickings are engine speed dependant, so yes there could be tappets, but not exhasut system expansion. I thought they might have been arching cause of the coild being split.

So if the O2 sensor is the one straight after the engine, this could be effecting the mixture and might have an effect on the misfiring. However a damaged CAT wont effect anything then will it cause its after the damage O2 sesnor.

Also, surely, if the CAT is damaged the second O2 sensor up stream of the CAT will registar the damage, correct??

many thanks for all your help and advice on this guys and gals

Russ

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Hey all,

Well I fitted my new coils yesterday. All 6 of the old ones had verying size cracks in so the new ones were a good investment I guess.

Bad news though, Still misfiring alot.

One thing I noticed this morning as well, when I started it up from cold after a night of standing, is a huge puff of blue/white smoke coming out the exhaust, this then turned more to a white smoke as it heated up, then a few minitues later it calmed down.

Loren, Tool Pants, anyone, any idea's??

many thanks

Russ

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Hey all,

Well I fitted my new coils yesterday. All 6 of the old ones had verying size cracks in so the new ones were a good investment I guess.

Bad news though, Still misfiring alot.

One thing I noticed this morning as well, when I started it up from cold after a night of standing, is a huge puff of blue/white smoke coming out the exhaust, this then turned more to a white smoke as it heated up, then a few minitues later it calmed down.

Loren, Tool Pants, anyone, any idea's??

many thanks

Russ

Are you sure the connectors are all properly seated?

Post your fault codes please (all of them).

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Hi Loren,

I have just brought a OBD reader as per our PM's.

When you say are the connectors seated properly, do you mean the LT lead going in to the coils. When I was fitting them I triple checked they were in tightly

The smoke would not be an oil seperator problem, that I keep reading about, would it, causing misfire?

many thanks

Russ

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