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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8420
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Wed Jan 02, 2019 9:23 pm    Post subject: What could be the cause of hesitation when accelerating? Reply with quote

I have been experiencing a bit of hesitation when accelerating and want to get to the bottom of it ASAP as I was hoping for a blast out on Sunday. I have changed spark plugs already and I have a set of coil packs to be fitted next but I wondered if it may be something else before I start chucking more money at it on parts that are not the cause, MAF etc. I had a misfire a month ago which turned out to be a coil pack, I wonder if more are on their way out?

I also thought fuel delivery may be another problem, I was going to check fuel pressure as it also seems to crank the engine longer before it actually fires, more than it did before this issue, this has been happening as long as I've had the hesitation in acceleration, probably for about 3 weeks but the car has hardly been driven in this time so not many miles to actually get a decent idea.
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kas750
Shanghai


Joined: 31 Mar 2013
Posts: 4526
Location: Chorley lancashire

2006 Porsche 911

PostPosted: Wed Jan 02, 2019 9:34 pm    Post subject: Reply with quote

Coil packs would be my first port of call for sure.
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8420
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Wed Jan 02, 2019 9:39 pm    Post subject: Reply with quote

kas750 wrote:
Coil packs would be my first port of call for sure.


Agreed, they are paid for and are an easy swap, just thinking ahead that if I need to order parts in advance to make sure they arrive and are fitted before Sunday so I can do that in advance. If there is a known problem this would help that situation.
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16809
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Wed Jan 02, 2019 10:17 pm    Post subject: Reply with quote

As soon as I saw the thread title I thought fuel delivery due to something not being right after your tank replacement.

Does the car live outside? If it's not being used much and we've had a lot of damp weather, could also be some water ingress with your coil packs.
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Ghianightmare
Spa-Francorchamps


Joined: 25 Apr 2017
Posts: 354
Location: Dublin


PostPosted: Wed Jan 02, 2019 10:18 pm    Post subject: Reply with quote

Since watching the videos in the below link, if I didn’t have coils ready to fit, I’d be bringing my car to someone with an oscilloscope and proper testing equipment as I had never realized how good they are at identifying misfires.

Worth a watch even if it only out of morbid curiosity

https://www.picoauto.com/library/videos
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8420
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Wed Jan 02, 2019 10:25 pm    Post subject: Reply with quote

My thought too with the recent tank issues but every chance it could be something electrical?. The 996 is locked away and has been for the last few months apart from a few trips, the 944 know's who's boss, that's on the drive under a cover.

I hate not using cars, they don't like it.
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Chris_in_the_UK
Estoril


Joined: 19 Mar 2014
Posts: 3586
Location: Harrogate


PostPosted: Wed Jan 02, 2019 10:31 pm    Post subject: Reply with quote

I would chase down the fuel system first Chris.
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Ghianightmare
Spa-Francorchamps


Joined: 25 Apr 2017
Posts: 354
Location: Dublin


PostPosted: Wed Jan 02, 2019 10:33 pm    Post subject: Reply with quote

That’s the beauty of the picoscope as it can map ignition, injection, compression etc simultaneously. It can check the MAF, TPS ETC ETC.

I did think of your fuel tank problem, but thought that had been solved...

I think the money spent getting it tested would give you peace of mind. Nothing worse than heading off for a long trip wondering if a problem is really solved or just hibernating.

The guy Frank Massy that does the videos really seems to know his stuff. If you don’t know someone with a scope, might be worth phoning him to recommend someone near you as he trains people too from what I can gather.

Best of luck solving it.
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Wed Jan 02, 2019 10:39 pm    Post subject: Reply with quote

Could be that replacing your tank has dislodged some shoite and caused a slight blockage in your injectors Dont know
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infrasilver
Fast & Furious
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Joined: 04 Oct 2010
Posts: 8420
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Wed Jan 02, 2019 10:48 pm    Post subject: Reply with quote

Tank was spotlessly cleaned before fitting but injectors are another thing for the list. The fuel pump that is now fitted is the one that came with the sender so I may swap that back to my original.
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Last edited by infrasilver on Sun Jan 06, 2019 6:56 pm; edited 1 time in total
 
  
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New997buyer
Fuji


Joined: 17 Oct 2010
Posts: 9150



PostPosted: Thu Jan 03, 2019 9:00 am    Post subject: Reply with quote

Fuel system and coil packs are the logical first choice as Chris, Adrian, Alex et al have mentioned.

If the problem isn’t these things, maybe look at the throttle system? Could there be a fault in the fly by wire system? Dont know
 
  
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Chuckmiester
Silverstone


Joined: 06 Dec 2012
Posts: 112
Location: South yorkshire


PostPosted: Thu Jan 03, 2019 9:22 am    Post subject: Reply with quote

Does it seem to be Rev related or pedal related. Mine hesitates slightly if you let the throttle pedal all the way up. If I keep slight pressure on the pedal it doesn’t seem to do it.
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ragpicker
Reims


Joined: 14 Apr 2013
Posts: 4029
Location: North East England


PostPosted: Thu Jan 03, 2019 9:29 am    Post subject: Reply with quote

As above. Also as per N997B, although if thinking about the throttle I'd be cleaning the throttle body. An old fashioned cause for hesitation which people seem to forget about these days is a gunked up throttle body.
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EGTE
Imola


Joined: 06 Jul 2015
Posts: 835



PostPosted: Thu Jan 03, 2019 9:38 am    Post subject: Reply with quote

Fuel filter blocked?
 
  
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Alex
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 16809
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Thu Jan 03, 2019 9:40 am    Post subject: Reply with quote

His doesn't get chance to get junked up. Its up and down like a brides nightie!! Grin
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Griffter
Spa-Francorchamps


Joined: 22 May 2016
Posts: 349



PostPosted: Thu Jan 03, 2019 10:25 am    Post subject: Reply with quote

I’d start by checking and cleaning every connector you can get to in the engine bay, and every inlet and vacuum connection. I can’t see it being plugs or coil packs to be honest. Why would they only misfire under acceleration?
More likely to be a sensor/signal controlling the spark or fuelling IMHO.
Also worth checking the fuel pressure and emissions and go from there.
Good luck. Hate these kind of things!
 
  
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wasz
Sepang


Joined: 28 Dec 2012
Posts: 2980


1999 Porsche 996 Carrera 2

PostPosted: Thu Jan 03, 2019 10:37 am    Post subject: Reply with quote

I could swear that using my homemade smoke machine to chase down any minor vacuum leaks fixed a bit of hesitation on my car. But I also changed the AOS, cleaned the TB and idle valve and changed the ancient fuel filter at the same time so it could have been that.
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thecarfixer
Monza


Joined: 03 Nov 2016
Posts: 166



PostPosted: Thu Jan 03, 2019 11:21 am    Post subject: Reply with quote

Have you got access to Durametric or PIWIS/PST2? I'd look at some live data - a good start is get the engine hot and compare the figures of ignition advance, injector pulse width and mass air flow against the nominal specs in the Porsche manual.

I had a 2.7 Boxster that was really quite 'fluffy' low down when cold, and started logging lambda faults, when in reality it was a failed MAF. It felt like I'd got 50hp back when I changed the MAF Grin
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8420
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Jan 03, 2019 11:34 am    Post subject: Reply with quote

Thanks for all the replies/ideas, I will try to get the coils swapped over as they are here and the history with my fuel tank leads me to maybe suspect something in there, maybe the regulator. There is no fuel filter on the 3.6 just a screen under the fuel pump which stops crud getting into the system, I'll pull the pump just to make sure there is nothing blocking it.

I will check throttle body, another easy old skool one to see and clean if necessary.

I'll plug my PC in and see what values I'm getting, I'm never 100% sure what I should be getting though or what deviations I will see. It does it when both hot and cold.

I do also wonder about the MAF, its never been changed and is now 17 years old and has done 125k miles, it seems to feel like it's low on power. I did unplug the MAF and ran it for a few miles but nothing changed so maybe not this?

I had a modified diesel Skoda Fabia annoying me a few days ago and I just thought I would power past him to get rid of him. He upped his game too and nearly caught me back up. This is what made decide I needed to sort this ASAP, that could have been embarrassing. Embarassed
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thecarfixer
Monza


Joined: 03 Nov 2016
Posts: 166



PostPosted: Thu Jan 03, 2019 11:48 am    Post subject: Reply with quote

If it's the original MAF I'd say it's very highly likely that it's shot..

I've got a pic of the exposed part of the MAF from my Boxster compared with a new MAF and the difference was quite marked..
 



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