2003 Boxter S - sudden engine miss
09-28-2018, 12:24 AM
#1
Racer
Thread Starter
2003 Boxter S - sudden engine miss
fellas - hope you can give me a few ideas! I bought this car about 3 months ago. it's a 2003 S, with very low miles (21k). I changed the oil and filter as soon as I got it; filter looked good. I drove it about 1000 miles since then and coming home from a nice 60 mile drive (it was dry and sunny out) the car went from running great to missing noticeably, especially at lower engine speeds with moderate to heavy throttle opening. drove it home about 2 miles (I was very close to home). no check engine light at all (which surprised me as it was missing very noticeably). the next weekend I took out the MAF and cleaned it with CRC MAF cleaner spray (it looked spotless even before the cleaning) and replaced the air filter with a brand new one (although it looked good too). took for test drive and still missing under load especially at lower engine speeds. interestingly it seems to idle fine and smooth. what's next? I ordered some new Beru spark plugs but haven't done the service yet as it's been raining too much to work outside. I read that it's possible that the coil packs might be an issue too? any other thoughts or things to try? anyone else had an issue similar to this and if so what was the fix? thanks so much!! Todd
09-30-2018, 01:30 PM
#4
Race Director
With no CEL the engine is not missing, at least in the normal meaning of the word. Did you check for any pending codes?
Could be a fuel supply problem. Don't know if the 2003 has a serviceable fuel filter. My 2002 didn't. The in tank fuel pump's housing was the filter. And even if the 2003 has a fuel filter 21K miles is not that many miles for a fuel filter. Still you need to 1) find out if the car has a serviceable fuel filter; and 2) find out what its replacement schedule is.
If you want to throw parts at the behavior then replacing the fuel filter is available to you.
Could be a fuel pump acting up. Again 21K miles is low miles when it comes to a fuel pump but a fuel pump can go bad at any time. Also, a 2003 to having covered just 21K miles in 15 years means a lot of time with the car sitting with the fuel level likely low and this can result in the hoses/fittings/etc in the tank suffering from being above the gasoline for long periods of time. If a fuel line/fitting is leaking internally in the tank this can result in insufficient fuel pressure to the injectors.
There is "bad" gas. Did you fill up the tank on your drive?
You can of course replace the plugs if you want. Be sure to use the factory plugs. Check the gaps. Be sure you install each plug correctly -- do *not* use anti-seize -- and properly torque the plug. At the same time you can replace the coils. Whether you reuse the old coils or replace them with new handle the used/new coils with care. Do not toss them around or bang them against each other. Porsche techs I have watched during a plug service are pretty gentle with the coils.
Whether you replace the coils or reuse the old ones bBe sure you connect the coil to the wiring harness securely and to the plug tip likewise. It is not unknown for the plus and coils to be replaced and the engine still manifests a "miss" or develops one later, in one case I'm familiar with in under 2K miles, due to a plug being left loose or what I found a plug wire left loose.
Another thing to look at is be sure the air filter air box is free of any trash. I'm not familiar with the 2003 air box but with the 2002 it is very easy, unavoidable in fact, for trash on top of the filter element to fall into the air box. This much be removed. One concern is it can get ingested by the engine but the other is the debris can come up against the plastic screen that sits in the intake air tube just ahead of the MAF and the presence of this trash can upset the air flow to the MAF and cause it to deliver incorrect info to the engine controller.
Could be a fuel supply problem. Don't know if the 2003 has a serviceable fuel filter. My 2002 didn't. The in tank fuel pump's housing was the filter. And even if the 2003 has a fuel filter 21K miles is not that many miles for a fuel filter. Still you need to 1) find out if the car has a serviceable fuel filter; and 2) find out what its replacement schedule is.
If you want to throw parts at the behavior then replacing the fuel filter is available to you.
Could be a fuel pump acting up. Again 21K miles is low miles when it comes to a fuel pump but a fuel pump can go bad at any time. Also, a 2003 to having covered just 21K miles in 15 years means a lot of time with the car sitting with the fuel level likely low and this can result in the hoses/fittings/etc in the tank suffering from being above the gasoline for long periods of time. If a fuel line/fitting is leaking internally in the tank this can result in insufficient fuel pressure to the injectors.
There is "bad" gas. Did you fill up the tank on your drive?
You can of course replace the plugs if you want. Be sure to use the factory plugs. Check the gaps. Be sure you install each plug correctly -- do *not* use anti-seize -- and properly torque the plug. At the same time you can replace the coils. Whether you reuse the old coils or replace them with new handle the used/new coils with care. Do not toss them around or bang them against each other. Porsche techs I have watched during a plug service are pretty gentle with the coils.
Whether you replace the coils or reuse the old ones bBe sure you connect the coil to the wiring harness securely and to the plug tip likewise. It is not unknown for the plus and coils to be replaced and the engine still manifests a "miss" or develops one later, in one case I'm familiar with in under 2K miles, due to a plug being left loose or what I found a plug wire left loose.
Another thing to look at is be sure the air filter air box is free of any trash. I'm not familiar with the 2003 air box but with the 2002 it is very easy, unavoidable in fact, for trash on top of the filter element to fall into the air box. This much be removed. One concern is it can get ingested by the engine but the other is the debris can come up against the plastic screen that sits in the intake air tube just ahead of the MAF and the presence of this trash can upset the air flow to the MAF and cause it to deliver incorrect info to the engine controller.
10-02-2018, 01:16 AM
#5
not going to be coils - that would cause a misfire cel. the key words here are 'under load' - car is in open loop when under load so o2 sensors not going to be providing feedback. since not spark then either air or fuel issue. won't be plugged air filter since car still using maf signal in open loop so would get cel if thottle position and maf signal not jiving. any air leak downstream significant enough to cause a misfire at open loop would certainly trigger a cel under normal operation or at idle.
so, fuel. looks like car can't deliver enough fuel under high demand. in your car the fuel filter is supposed to be a 'lifetime' unit and is unserviceable. it is part of the fuel pump. lazy fuel pump may not be able to deliver enough fuel on demand. probably not the fuel pressure regulator - they will fail to over-pressure - too much fuel. i wouldn't drive it until you sort this out - this is a high compression engine that requires the additional fuel under load to keep things cooler.
so, fuel. looks like car can't deliver enough fuel under high demand. in your car the fuel filter is supposed to be a 'lifetime' unit and is unserviceable. it is part of the fuel pump. lazy fuel pump may not be able to deliver enough fuel on demand. probably not the fuel pressure regulator - they will fail to over-pressure - too much fuel. i wouldn't drive it until you sort this out - this is a high compression engine that requires the additional fuel under load to keep things cooler.
10-02-2018, 09:50 AM
#6
Racer
Thread Starter
hi guys -- thanks for the advice (keep it coming please!). I've been at the track last weekend and preparing to go to the track this coming thurs (VRG vintage races at WGI) so haven't had a minute to look at the Boxter. I had put gas in it a few days earlier and it now has 3/4 tank. I can't say for sure if it has bad gas but i've used that gas station thousands of times and never an issue. the airbox was super clean no leaves (but i changed the filter anyway). i guess i should have tried running it with the MAF disconnected to see if there was a difference but I didn't think of that at the time. i don't have the porsche specific code reader software and no i haven't tried to check codes since there is no check engine light on. is it possible that there could be codes without a check engine light? hopefully after this coming weekends races I'll be able to at least change the spark plugs and visually examine the coil packs. is there a way to check the coil packs with a multimeter? thanks!
10-03-2018, 08:30 AM
#7
Captain Obvious
Rennlist Member
Rennlist Member
Does a misfire always trigger a cel code? My A4 would stumble on acceleration, but no cel popped up. I had it scanned, and it said there were misfires on cylinders 1 and 4...so I replaced the coils and the issue was resolved. This misfire was intermittent too...not always happening. Maybe that's why no cel here too?
Trending Topics
10-03-2018, 10:06 AM
#8
Racer
Thread Starter
Does a misfire always trigger a cel code? My A4 would stumble on acceleration, but no cel popped up. I had it scanned, and it said there were misfires on cylinders 1 and 4...so I replaced the coils and the issue was resolved. This misfire was intermittent too...not always happening. Maybe that's why no cel here too?
10-08-2018, 07:31 PM
#9
Race Director
Now the engine can be stumbling, suffering from some hesitation, generally not running right, and while this is real it is not misfires.
The cause of the stumbling/hesitation can be fuel (supply or pressure) related. Can be due to bad MAF. In my Boxster a slight hesitation proved to be the early warning signs of a failing AOS. Could be due to debris (leaves) in the intake air box which interfere with the air flow through the MAF. Could be an eGas issue (provided of course the engine is equipped with this system).
If equipped with eGas you can force this to perform a calibration.
With your foot off the gas pedal during the entire procedure, from an off state turn the key on and leave on for at least 60 seconds. Then turn the key off for at least 10 seconds. The next engine start will have the calibration complete.
After the calibration procedure one can also check for any error codes (these may not be OBD2 so a Porsche diagnostics computer or possibly a Durametric will be needed to retrieve these) from the eGas system.
Another possible explanation can be a failing VarioCam solenoid/actuator. Any pending error codes?