Engine going flat between 3-5k rpm

[johne4]

Greetings

I have a 2000 Boxster with 54,000 miles, last week the engine started running flat between 3-5k rpm, the car accelerates great till 3k rpm, then goes flat, feels like fuel starvation, but when it hits 5k to redline it accelerates normally again.

Since it was close to the 60,000 mile service I went ahead in changed the plugs and air filter. That did not fix the hesitation.

I have not ruled out the possibility of some bad fuel, still got a 1/2 tank to go through before I can rule that out.

Just trowing this out to see if anyone had a similar problem and what the fix was since there are so many possible culprits from a clog fuel filter (on order) to pluged cats.

The check engine light does not come on.

Thanks in advance, any information/help anyone can provide will be greatly appreciated.

John

[BuffaloBoxster]

I had similar behavior when my MAF went bad, but my check engine light did come on.

[MNBoxster]

@ BuffaloBoxster

Good Call! I bet you're correct...

Happy Motoring!... Jim'99

[just_me]

That probably would nto throw a code, being hydro-mechanical........

Not much help beyond that I'm afraid, except to suggest you keep it about 5k :-()

[johne4]

Thanks everyone for the response, it appears that it was a tank full of bad/contaminated gas............I added a bottle of "Gumout" injector cleaner and ran the tank down, fill'r up with Sonoco 93 octane (at my normal gas station, the last tank I was on the road and filled up at a 7-11)........runs like new... :dance: I will keep my fingers cross and monitor.........

I do have a follow up question/issue I would like to here comments on; K&N air filter...........I have been using one since the first service, I do clean it and recharge it every 5k miles, never had an issue..............but i've been reading alot of tech articles against using them, specifically K&N don't filter the particles small enough and it damages the MAF......I would almost bet that the people having problems just install them and forget about them.......the box does say 100,000 mile filter...lol

Thought/comments

Thanks Again

John

[MNBoxster]

Originally Posted by johne4

Thanks everyone for the response, it appears that it was a tank full of bad/contaminated gas............I added a bottle of "Gumout" injector cleaner and ran the tank down, fill'r up with Sonoco 93 octane (at my normal gas station, the last tank I was on the road and filled up at a 7-11)........runs like new... :dance: I will keep my fingers cross and monitor.........

I do have a follow up question/issue I would like to here comments on; K&N air filter...........I have been using one since the first service, I do clean it and recharge it every 5k miles, never had an issue..............but i've been reading alot of tech articles against using them, specifically K&N don't filter the particles small enough and it damages the MAF......I would almost bet that the people having problems just install them and forget about them.......the box does say 100,000 mile filter...lol

Thought/comments

Thanks Again

John

Hi,

I'm glad you seem to have corrected the issue, but I wonder if the Gumout is just a temporary fix? Gumout can have an octane boosting effect and your DME may just be running a different MAP as a result.

Now that I know you're running the K&N, I suspect a little more strongly that you may have a masked MAF issue. I'm not a Fan of K&N's on any Car, but especially the Boxster. On other Cars, I believe that many of the reported gains are simple Placebo Effect or only show in Dyno results at the Top of the Power Band (often sacrificing some Mid-range performance), but generally, they do no harm. Not so on the Boxster, running one here has shown, somewhat conclusively, that they have a detrimental effect.

My suggestion is to keep an eye on it and ditch the K&N at the 1st sign of the symptoms returning and either clean (not always successful) or replace the MAF. Probably not what you wanted to hear. But, hope this helps...

Happy Motoring!... Jim'99

[BuffaloBoxster]

As far as the check engine light goes... My light came on at the very end of last summer. I took it in to the dealer, and it was running OK, so they cleared out the code and said if the light came back it would be because of a bad MAF. The light stayed off about two weeks, and during those two weeks the loss of power between about 3k and 4.5k started to occurr. As I was driving the car to storage the light came back on. It took another week after it came out of storage with the battery out for the light to come back on again, and the symptoms were still there.

So the point is, if your light isn't on it probably will be eventually. Mine took a while before the ECU noticed something was amiss.

[986Jim]

All it takes is for the air fuel ratio to be out slightly (and it alwasy goes rich when it does) and you will lose a lot of power. Normally at WOT the car will run 12.5-13.0:1 (air to fuel) which is great for a normally aspirated engine. When the maf gives wierd readings the ecu will compensate with extra fuel as it's the safe way to keep the motor from blowing up. A lean air fuel ratio is very hot and burns out pistons and valves. A rich condition really robs the engine of HP however the ECU may not consider that a fault as it's not out far enough to trigger a CE light.

Most CE lights are maily for emissions related items, as long as it things emissions are ok the light stays off. HP is not the computer concern, but it is ours and when the car is rich the CAT will take care of the emissions but hp is lost which the ECU doesn't car about. We sure as hell do, so thats a big problem.

Eventually the reading will get so far out that CE light will come on and you have your problem.

[MNBoxster]

Originally Posted by 986Jim

All it takes is for the air fuel ratio to be out slightly (and it alwasy goes rich when it does) and you will lose a lot of power. Normally at WOT the car will run 12.5-13.0:1 (air to fuel) which is great for a normally aspirated engine. When the maf gives wierd readings the ecu will compensate with extra fuel as it's the safe way to keep the motor from blowing up. A lean air fuel ratio is very hot and burns out pistons and valves. A rich condition really robs the engine of HP however the ECU may not consider that a fault as it's not out far enough to trigger a CE light.

Most CE lights are maily for emissions related items, as long as it things emissions are ok the light stays off. HP is not the computer concern, but it is ours and when the car is rich the CAT will take care of the emissions but hp is lost which the ECU doesn't car about. We sure as hell do, so thats a big problem.

Eventually the reading will get so far out that CE light will come on and you have your problem.

Hi,

I agree with you and this is what I meant by a Masked MAF problem. IIRC, the Bosch DME ME 7.2 has something like 27 different A/F Maps. So long as the DME can switch to a different, compensating, Map and the 0² Sensors don't throw an Emissions Fault at it, it's happy and won't trigger a CEL. But I still suspect there's more going on here than just tainted Gas...

Happy Motoring!... Jim'99

[Brad Roberts]

Fuel pump.

I would suggest having a volume test done on the car if this power issue continues. Your cleaner may have freed up the pump temporarily.

I have seen this 2-3 times this year on mid to high mileage cars.

The K+N stuff is myth. I sat with the independant 3rd party firm who tested ALL the filters. You can dunk the MAF in oil...

Bottom line: The dealers dont want to warranty the MAF. There is a VERY large lawsuit against the dealers from K+N right now.. and K+N will win.

Now.. if you want to chat about the "air boxes" available and how they can run up against the threshold for MAF failure...LOL


B

[oversteerdawg]

I had a similar issue with a comical ending. The car was idling at 1200 RPM, the ce light was on, and i had a big flat spot from 3-4k. Also, I had a lot of part throttle hesitation/surging. Turns out the celophane from a cigarette box somehow got past the filter and was blocking the maf. I think when it was last serviced it may have fallen in without anyone seeing it. Worth taking a look if you just had your car serviced.

[johne4]

Saw that my original post resurfaced, car is running great, took several long road trips since post, odometer shows 68,000 now, yikes. The only problem I had was when I spent a couple of week in Missourri, for whatever reason the highest octane I could find was 91, a bottle of octane boost help. I have been sticking to one gas company, Sonoco, they have 93 octane down here and the car runs great.

John

[Adam]

Originally Posted by Brad Roberts

Fuel pump.

I would suggest having a volume test done on the car if this power issue continues. Your cleaner may have freed up the pump temporarily.

I have seen this 2-3 times this year on mid to high mileage cars.

The K+N stuff is myth. I sat with the independant 3rd party firm who tested ALL the filters. You can dunk the MAF in oil...

Bottom line: The dealers dont want to warranty the MAF. There is a VERY large lawsuit against the dealers from K+N right now.. and K+N will win.

Now.. if you want to chat about the "air boxes" available and how they can run up against the threshold for MAF failure...LOL


B

"Dunk" the maf in oil and it will still run properly? Gimme a break. Oil on the maf will not allow it to properly interpret air flow. Oil and contaminates on the maf will compromise the system.

[johne4]

Since the air box subject as come up, what about it?

As anyone tried one?

I see one in the ******************************************** porsche catalog for about $380, seems to appear to be a alternative to desnorkeling.

Thoughts, comments, experiences.

Thanks