bruce987

Hi All,

I have a base model 2006 Boxster with 155,000 miles on it. I'm the original owner and have taken good care of it over the years. It was track for a couple years by me and later my wife tracked it. It has several types 1, 2, 3, 4, and a few 5 overrevs, but the delta between the type 5 and number of hours on the engine is several years. When the pandemic hit and both wife and I started working from home, the Boxster sat in the garage (climate controlled) for about 6 months without driving it. I believe the gas tank was about 3/4 full. It was on a battery tender. During this time, I mainly drove my Cayenne to run errands. Once the pandemic was over, I took the car into town, I live in the suburbs and went on the toll road doing about 70-80 mph. During this trip I got my first check engine light. When I got home, I pulled out my OBD reader and it gave me the P0301-P0306, misfire on all cylinders. After discussing this with various people at the track I was advised to put some engine gas cleaner in the gas tank (STA-BIL). I cleared the codes, drove the car and the misfires came back. It should be noted that it doesn't happen immediately, but in some cases on the way back from my destination. When it does happen there is no noticeable change in engine performance; no studder, no hiccup, nothing, just the check engine light. Next, I replaced the ignition coils and spark plugs. Cleared the codes and took the car out. The same thing happened, usually on the way back from my destination it throws the codes. Next, I took it to the dealership. The dealership had their mechanic do his thing and said it was my ignition coils. Of course, I explained that I had already replaced them with OEM parts from SunCoast. They insisted, so I had them replace the ignition coils under warranty since I bought OEM parts (they also gave back my coils) - this was done with no charge - parts or labor. Of course, the same thing happened. I returned it to the dealership and the mechanic pulled the overrevs and said that was the problem, I needed a new motor. I can clear the codes and drive the car to do errands and no problem, it only happens when it's taken out on the freeway.

In summary:

1. Boxster sat for a period of time > 3 months in garage during pandemic with 3/4 full tank of gas, with battery tender.
2. When eventually taken out on the freeway it throws the misfire codes.
3. Tried to add gas cleaner (STA-BIL) and of course fueled the car up.
4. Drove it on the freeway it eventually throws the misfire codes.
5. Replaced ignition coils and spark plugs with OEM parts.
6. Drove it on the freeway, throws the misfire codes.
7. Took it to the dealership, they replace the ignition coils.
8. Drove it on the freeway, throws the misfire codes.
9. Take it back to the dealership and they determine it's because of overrevs, even though the overrevs occurred years prior. Recommended a new/used motor.
10. The car was driven by my wife 100 miles each day for several years with no problems until it sat during the pandemic.
11. Keep in mind that when the misfires happen, there is no discernible change in the performance of the engine. The only way we know for sure that something happened is the console warning light.

There's the problem. I don't really want to spend $7500 for a used motor, plus expense of having it put in.

Thanks for any help in solving this problem.
Does anyone have any other suggestions on what to look for, what else to replace. I have some ideas, but I would rather not mention what I think so as not to influence anyone else's suggestions.

Schwinn

I agree, the overrevs don't make sense as the cause here. I have a few range 6 in my car when I bought it... and it runs fine (granted, it's a 2010 as well).

First thing I would suspect is the battery. Battery tenders help, but they don't solve problems. Even the ones with "conditioners" in them. How old is the battery? I might suggest replacing that anyway, as it's a much lower cost proposition. These cars are VERY sensitive to weak batteries.

For the supposed "new engine" call, I'd send an oil sample for analysis if you can do so. See what that shows. If there really is an engine issue, you should see it there.

Lastly, I'd also suggest just running the fuel out on the car, and then refilling with fresh gas and some fuel injector cleaner. I'm not sure it's possible to "re-stabilize" gas that has gone bad... so running that through the car likely didn't help matters. I would suggest Redline injector cleaner or Techron - both of which have the recommended chemicals for cleaning the injector.

All of these are far lower cost versus a replacement motor. Fact is, I'd stop going to that dealer at all - they don't seem trustworthy, to me.

harveyf

Very simply put, the biggest risk from an over rev is bent valves. I too have a hard timing believing that over revs are the problem but I would think a compression test would settle that argument.

Sta-bil is not much of a fuel system cleaner. There are other better products. I like Techron and a lot of folks like Seafoam.

But I do agree that if you can't remember the last time you replaced the battery, that might be a good place to start. Because of exactly this sort of thing and fitment, I usually pony up for the official Porsche battery from the dealer.

hueyhoolihan

i'd take it somewhere else. it's clear the dealership is clueless, they've proven themselves to be embarrassingly wrong once already, even though insistent. . clues are that it is fairly high mileage, been tracked, sat for some time and, thus far, only rears its ugly head when fully warmed up. not plugs, or coils.

BTW, if there is no significant oil consumption, the chances of catastrophic engine failure necessitating a major rebuild are minimal. a compression test may prove useful.

TMc993

As mentioned previously, battery (Replace if marginal, weak or older than five years)...Then, I'd be looking at alternator output at higher RPM...

jesseellington

I’ve been in two caymans that had similar symptoms and in both cases it was a bad engine. Kinda no easy way to diagnose or prevent at this point IMHO. My car eventually spun#6 rod bearing to end things. My students car just got trailered home and I never heard. Just drive it and I’m interested to hear how things go. Maybe the rod bearing can somehow cause codes to flash. All coils??? Why I think it’s gonna be something else bad.
Oil analysis might detect something coming apart inside. I had messed with coils and O2 sensors near the end. Maybe coincidence.

harveyf

I'd be really curious to know what Porsche is measuring to determine a "misfire". If I knew more about that, we might go beyond guessing.
Two broad possabilities are:
From an upstream standpoint, the ECU knows when a signal/voltage/resistance to the coil pack deviates from a set pattern.
From a downstream standpoint, there is a disturbence in the O2 sensor readings. This one is problematic, as I don't see how it could distiguish a particular cylinder.

I just finished tearing down my 07 CS and I am pretty sure there is no dedicated "misfire" sensor. It's got to be something they can determine using existing data required to operate the engine.

Schwinn

Apparently, most ECUs use the crank sensor to determine misfires. The timing to each cylinder's sense tells the ECU what the speed is, and if the speed isn't "correct" it calls it a misfire. Interesting. See https://mechanics.stackexchange.com/...tect-a-misfire

I also thought that you could watch by checking the coil voltage (one of the commenters there said this as well)... basically, if the spark doesn't arc, you'd see a very different voltage profile on the supply-side of the coil. But I guess either/both could be used?

harveyf

@Schwinn Good stuff. Stackexchange may be another website I'll have to check out.
I am back to over revs causing damage that the OP can't even feel. Again, I think a compression check would be in order. I just did this on my 07 Cayman S and got 225 to 235 psi (throttle closed, cold engine). The OP's car is a base and maybe doesn't have such high numbers but I would think the compression would have to be pretty horrible to cause the fuel/air mixture to not ignite. With a noticable loss in performance.

XuTVJet

Before going down the gloom and doom path of a bad engine, consider the more likely stuff first. Seeing that the car was fine before sitting for 6 months and you're seeing misfires across all cylinders and the car runs fine, it makes me think it's a fuel quality issue. Gasoline will go bad after 3 to 6 months. If the fuel has ethanol in it (most have 8-10%) then it becomes worse as the ethanol will take on water. Adding Stabil and the like after the gas has gone bad won't help. It's too late. Seeing that you live in humid Texas and it's winter, I would imagine that a lot of water vapor has built up in that tank because of the temps rising/falling a lot (big vapor pressure swings) and a considerable amount of water is in the fuel now. I'd drive the car softly (no heavy load, under 4500prms) until you can get it down to 1/4-1/2 tank and then fill it with fresh stuff.

Try that first and see where that gets you.

hueyhoolihan

if the problem only occurs, and only occurs consistently, after the car is fully warmed up, it will usually indicate that the temperature and probably expansion of something is the root cause.

XuTVJet

Could be, or could be because the car is coming out of its rich, warm up, running program and once the DME starts to lean things out as the motor comes up to temp, the misfires start happening. Meaning, the potentially bad fuel has just enough water in it to throw a misfires when in the leaner running condition vs the richer warm up condition where there is a higher percentage of fuel to offset the water content.

Bruce987 - Does the car still have much of the old fuel in the tank?

jesseellington

I hadn’t paid attention that the car is the base model maybe vs the 3.4. If so my info is that engine is extremely less likely to have oiling problems. The cayman rental at Kaizen at VIR is the 4 cyl engine, guy there said he wouldn’t rent it otherwise. Just one data point.

bruce987

Since it has been about a year or so since this problem has occurred, the fuel has been cycled several times. Currently, I have the tank almost empty (30 miles to empty). The battery was replaced on 6/2020 by AAA. As for using Porsche specific batteries, I've used aftermarket batteries for over 35 years of driving Porsches without any issues. My plan of attack is to replace the fuel pump and filter (which I believe is part of the pump). I also plan to put some Techron in the tank for good measure. The oil analysis is also a good idea. I used to do that with my 996 GT3. I would like to see what kind of wear the engine does have (or not). Also, the leak down test would be another good idea. So many good suggestions.

Julian_KCMO

I have an 06 Boxster S that also has random misfire codes and it’s an “issue” that I’ve been chasing since I got the car (car has 153,000, mine are 23,000 miles) I do all my own mechanical work (not a mechanic!)

What is the exact situation yours starts flashing the CEL? Mine only starts flashing the CEL under a very specific circumstance and that is when at speed (45mph and up generally) when going down a slight hill and I’m on such light throttle (or cruise ctrl) to maintain speed that the car is basically coasting. If it starts to flash and I dip the clutch or give it a little throttle fore a 5 or so seconds the light generally stops flashing. Occasionally I’ll be too slow to catch it and the light will stay on. Only twice in 23,000 miles has it ever changed the way it runs and actually sounded like a misfire. I pulled over, shutdown the engine and restarted, all running fine again but CEL on.



I change my oil every 5k and send it to Blackstone each time, engine seems healthy to them. I have done plugs/coils when I got the car, also replaced the battery a while back.



Only other “issue” with my engine is that my bank 1 cam deviation values are at the top end of the spec range and I’m seeing little pieces of chain guide plastic appear in the filter and in the oil pan when I take it off. I’m going to tackle the chain guides soon, need to start ordering parts (and a brave pill) to get that underway. I bring up the cam deviation and chain guides as if the chain guides are starting to go away then perhaps that can affect/cause misfires? I have also changed bank 1 chain tensioner (under the engine, easy), AOS, cleaned MAF and intake etc in order to try and rectify the misfires. I have also scoped the cylinders (though only from the spark plug holes) and all is OK.



Cheers,

Julian