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Discussion Starter · #1 ·
I have just experienced one of these "difficult to diagnose" issues, that some 981 posts have been discussing parts of, but not quite to the extent that I have felt and seen it.
My car is currently seeing a series of misfires between 1000-3500rpm. It basically apprears much like several posters in here have reported; hesitation down low, shudders as coming from faulty plugs - and a marked improvement above approx.3500-4000rpm when the second stage of the varioCam kicks in. No error lights are thrown in the in-car displays, nor logged in the OBD. My local OPC has made several checks of the car over a period of days. As the car has only done 17' km, but is out of warranty - it is a problem I need to address on my own expense. The car is basically within its supposed to-be parameters in all the logged categories, but OPC can see comparable deltas on exhaust values between cylinder banks. As such and after consulting with Germany, the fix was to swap the HPFP (they stated to also be able to see white residue on some plugs - indicating a possible lean fuel mi. They felt this fixed the issue when performing the post installation run. But after having picked up the car and while driving back home, I could sense that the problem had not been totally cured. The following days the issue grew gradually worse, and the OPC was again consulted. A new 3 day analysis window was agreed, at which point they wanted to swap all 4 O2 sensors (still not being able to see any error codes in the OBD). At this stage, I did not buy their proposal at face value, and we ended up with a shared cost proposal where the OPC covers the cost of the O2 sensors and 6 new plugs and all labor, and I cover a new coil pack (which was also on their list of "potential fault sources" (but while being a 2016 car, I was unsure on this one as it could have the Borg Warner coil pack, but I just wanted to get this potential source of error out of the way, so I suggested to cover the swap myself). However after having discussed with the mechanic, I got the impression of a more general potential issue that no-one really like to talk about (from Porsche that is), and that points to the more general issue of emissions regulations and what producers need to do in order to comply, and effects of this in conjunction with carbon build-up on the inlet valves. He basically said that this could well be the issue, and something that you in the past could fix re-programming the CPU - but is something that Porsche do not allow anymore.
I think this sounds plausible, but want to hear if any of you have any thoughts?
 

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I have the same car and have not experienced this issue. If I did have the issue I would probably try the following (a in order):

1. Fresh gas / fuel system treatment / Italian tune-up
2. Plugs
3. Coils
4. Battery

I hesitate (ha ha) to put the battery last, but if your car was built in 2015 then the battery is almost 6 years old. Depending on where you live it could be starting to get weak. But you can get 7-8 years out of the Porsche AGM if it is treated well.

I don’t think your problem has anything to do with emissions control or the tune. I just replaced my entire exhaust system last Winter and also did a tune, and there wasn’t hesitation or misfires before or after.
 

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Discussion Starter · #3 ·
Thanks mate! I have to see I was surprised to see the battery suggestion since I never even considered it, but I think it is actually a very good one - since I guess the power supplied to the HPFP could come from the battery itself, and not from the alternator. If the battery is poor, then.....I did measure the volts of my battery using a std multi-measuring tool, and it read 8.7V, so - it could well be the culprit here:) I am now charging the battery, and will let the car rest post charging and see if the volts value drop again after a pause. I also need to find out why this was not on the check list of my OPC! Thanks!

JI
 

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Sounds like an opportunity for me to tell a story…. About 25 years ago I had a VW Corrado. I was working really late one night and came outside to find that I had left my lights on and the battery was dead.

The parking lot was abandoned. However against the building was a loading dock ramp. So I muscled the car over to the ramp and then pushed it up the ramp as far as I could manage, jumped in and popped the clutch near the bottom to see if I could bump start it.

I did this several times without success. Someone happened to come into the lot and upon seeing a madman repeatedly pushing his car up the ramp gave me a boost.

The next weekend I was telling a friend of mine in the car business this story over a beer and he just looked at me and said “Isn’t your car fuel injected?” It took me about 5 seconds to piece it all together and realize that there was no way the alternator was going to give me enough power for long enough to power up the ECU, the lift pump, and run the injectors to get the car started…

I recently helped a friend change the battery in her car and then next day she remarked that the car actually ran better with the new battery (less hesitation, smoother idle). The battery is a critical component of a modern vehicle for sure.
 

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Discussion Starter · #5 ·
Have done the re-charge now, and even though I quite obviously did an erroneous measurement yesterday (the selection wheel on my multitool was slightly off), I did a good 7 hrs re-charge with a CTEK charger incl. a "reconditioning" phase. After checking the voltage post charge (stable 12.85 v) with this morning (12.4v), the battery is clearly off its best phase in life. A new AGM battery has been ordered! I have to say I am pretty excited to see what the result will be. I will have my OPC do the swap.
Thanks again for a good piece of advise!

JI
 

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Discussion Starter · #6 ·
Just an update; new battery installed to no avail. Now schedullled for swapping of O2 sensors, spark plugs and coils - end of Aug.
 

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Just an update; new battery installed to no avail. Now schedullled for swapping of O2 sensors, spark plugs and coils - end of Aug.
keep us posted, mine does similar "roughness" between 0 and 3,000 until 2nd Vario Cam kicks in then fine above 3,000. Mine has 38,000m. I know its not the battery because I just had the dealer put in a new Porsche Battery for $600 !!! for battery, labor and programming??
 

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Discussion Starter · #8 ·
I know! The cost is "on the high side". I did it my self, just bought the battery (AGM with same spec), swapped it with the internal ECU terminal covered through a motorcycle battery hook-up.
I think there are many out there with similar issues, and this issue really puzzles me.....
 

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I know! The cost is "on the high side". I did it my self, just bought the battery (AGM with same spec), swapped it with the internal ECU terminal covered through a motorcycle battery hook-up.
I think there are many out there with similar issues, and this issue really puzzles me.....
Are you sure you aren't experiencing the well known torque and HP dip that these motors as well as the 911 variant has? It occurs right where you are claiming your symptoms are and has been discussed for years on many different forums. Just do a google search for "Porsche 3000 rpm hesitation" or similar and you will find many similar discussions and complaints as this is a "Porsche thing" it seems

Its typically more noticeable in slower city driving where you notice a non linear/jerky feel to the power delivery from a stop, and then this feeling that the car is "laying down" because it as it passes through the 3-4K range right where the torque/HP suddenly drops off . You can see this big torque/HP dip on any stock 981 dyno graph. Then it all goes away and the power suddenly comes in smoothly the rest of the way up the RPM range after the variocam kicks in. Using sport mode makes it a little better but doesnt cure it as I think the remapping of the throttle just mask the issue a bit since the source of the issue is obviously still there.

This can be tuned out for the most part with aftermarket high flow cat headers and a good ECU tune. In the attached dyno image you can see the original big dip in blue, then the steady improvement after adding headers and then even better with a custom tune.
 

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Discussion Starter · #10 ·
No, I am pretty sure this is something else. First of all, it appeares in a much wider rpm band (1000-4000), and manifests itself as misfires, not "torque holes". In addition, if it was like you're questioning, it should have been present since the very beginning (in some shape or form), which it hasn't. No - this is electrical related!
 

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No, I am pretty sure this is something else. First of all, it appeares in a much wider rpm band (1000-4000), and manifests itself as misfires, not "torque holes". In addition, if it was like you're questioning, it should have been present since the very beginning (in some shape or form), which it hasn't. No - this is electrical related!
Yes, good point if this is something that just started happening to you out of the blue. I wasnt sure from your OP if this car was new to you or not. Good luck on the quest!
 

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Discussion Starter · #12 ·
Just an update; the car in now with my local OPC where they will change 4 lambda sensors, all coils and spark plugs. The car is due back tomorrow, and will let you know the outcome.
 

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Discussion Starter · #13 ·
Have received the car now and test driven it, and the fix applied did not provide the cure wanted. This was also communicted to me by the OPC rep prior to receiving it. I have not yet spoken to the rep that will give me a run through of what was done and the status of the fix as seen by them, but to me we are now down to carbon build-up removal as the remaining cure with any credible effect. I will provide an update after the talk with the OPC rep.
 

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Discussion Starter · #14 ·
As promised; the OPC rep was of course sorry that the fix provided (even quite extensive) did not work as wanted. It has to be said that they did not give any guarantee going into the workshop appointment, but still. As we have now swapped both the HPFP, 4 lambda sensors, 6 coils and 6 spark plugs (plus a new battery) - the remaining list of potential areas of faults, is slimming down. Basically we seem to be left with faulty injectors and carbon deposits build-up on the intake site as the only remaining ones that is worth discussing. Anyway, narrowing it down from here will take time and effort, as we are talking of an "engine out" scenario.
We spent some time discussing what the he.. it is going on inside the engine, and why he is not throwing fault codes.
Their thinking is that there is nothing wrong with the engine as is operates well with the set tolerance parameters of Porsche, but there is a delta in the observed exhaust values between the cylinder banks. The engine tries to accommodate for this be different suitable compensating measures, and the end result is the observed and felt misfire/juddering in certain driving-/load conditions. As the engine is always well within the tolerance limits, the engine doesn't know "he is sick" - and no fault codes are thrown.
They think a natural step from here would include temp measuring devices in each cylinder to be able to narrow the faulty cylinder down, but for this the engine needs to come out. We didn't discuss the carbon build up scenario in great detail, but he indicated that a carbon deposit on the inlet side could well be a culprit that "steal" air/fuel mixture so that the observed flow by the engine is "off".
I will do a long journey this weekend and try to get a better feel with the engine.
 

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I’ve been concerned about the intake ports on mine as well, as these direct injection engines don’t have the benefit of fuel wash to keep them clean. I understand that the AOS is much improved on the 981, but I have no idea if that is enough.

To be honest I’ve been thinking of adding a catch can. Ha ha.

Edit: Another member on here has done an intake valve cleaning with the engine in and has a YouTube video of the procedure. I think I’d be trying that before paying for an engine removal.
 

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Discussion Starter · #16 ·
I completed a 650km (410 miles) trip this weekend, and I really can't see it being carbon deposits. Hence, I am leaning towards one or several injectors failing - or the injector wiring.

The misfires seem to be more frequent when the motor is warm and when abruptly leaning on the gas pedal. This could be in any rpm range below 4500. It is felt above this as well, but doesn't come across so defined. I drove the first half rather spiritedly, with a two day break before returning. The car felt worse going back.
The reason for why I am leaning towards the injectors are:
1. Sputtering behavior under load only.
2. No issues when cold start or at idle.
3. No rpm rush up or down the scale, only load issues (much like when engine knocking or pre-ignitions).
4. Soot build-up on tail pipes, but difficult to evaluate if excessive or not). I have the steel sport tail pipes, so any amount of soot is easily visible.
5. Very restricted fuel consumption, 7,4-7,8 L/100km (32-30 MPG), which I find just a bit on the lean side for (partially at least) spirited driving.
I would have thought that carbon build up would affect the motor behaviour differently?
 

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I completed a 650km (410 miles) trip this weekend, and I really can't see it being carbon deposits. Hence, I am leaning towards one or several injectors failing - or the injector wiring.

The misfires seem to be more frequent when the motor is warm and when abruptly leaning on the gas pedal. This could be in any rpm range below 4500. It is felt above this as well, but doesn't come across so defined. I drove the first half rather spiritedly, with a two day break before returning. The car felt worse going back.
The reason for why I am leaning towards the injectors are:
1. Sputtering behavior under load only.
2. No issues when cold start or at idle.
3. No rpm rush up or down the scale, only load issues (much like when engine knocking or pre-ignitions).
4. Soot build-up on tail pipes, but difficult to evaluate if excessive or not). I have the steel sport tail pipes, so any amount of soot is easily visible.
5. Very restricted fuel consumption, 7,4-7,8 L/100km (32-30 MPG), which I find just a bit on the lean side for (partially at least) spirited driving.
I would have thought that carbon build up would affect the motor behaviour differently?
From what I’ve seen, carbon build-up on the intake ports shows up most when the engine is cold and at low rpm. So I don’t think that is your issue.

I’m assuming you’ve run some fuel injector cleaner through like the Liquid Molly Injector Cleaner?

I’m also wondering about air. Have the air filters been inspected? Edit: I think this would result in a rich running engine, not lean so there’s that…

It just seems strange that the injectors would be failing this early in the cars life. It’s not impossible, it just doesn’t seem likely to me.
 

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Discussion Starter · #18 ·
Agree with you there; the only cause could be the fact that my car sits idle in my garage 4-5 months every year - hence the low milage.
I am contemplating getting a "second opinion" from a different vendor
 

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Funny thing, logged in here for first time in months (been hanging around lurking in the mean time) and this post was the most recent! I bought a 2014 981 CS about two weeks ago that I enjoy tremendously and that brought me here.

Thing is, I've been experiencing the exact same symptoms as you! I didn't notice anything during the test drive and I had a Durametric to read error codes - nothing. It probably took a week before I noticed the shuddering, not sure if it always was there but I don't think so. The car went through extended service in May and has had just a few thousand kms since then.

So far I've come to the conclusion that it's not dangerous since there is no CEL nor faults reported over OBD. I had a similar problem with a 996 I recently owned but that was solved by replacing a cracked ignition coil, on the other hand that was easy to spot via the fault codes. Only happens on partial throttle and lower revs, just as you. At first I thought it might be the clutch slipping a tiny bit but that would be visible in the fault log as well as being more prominent at WOT.

Please keep us posted on your progress
 

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Discussion Starter · #20 ·
On the effectiveness of injector cleaners in general, I have seen tests that serioisly questions it. You would have to run buckets of it to get any measurable difference. But yes, I did try it without any effect.
 
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