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toohey
Monza


Joined: 22 Jan 2009
Posts: 184
Location: Naarfolk


PostPosted: Thu Jan 03, 2019 12:14 pm    Post subject: Reply with quote

infrasilver wrote:
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


If there was no change in performance when the MAF was unplugged then its most likely toast - Pretty sure the ECU has a base map in it that the cars drops back onto when the MAF misbehaves or packs up(all other vehicles i've messed with have). They are usually pretty conservative maps to account for different environments (think arctic to bahrain!) Its was a difference of about 20bhp on my 109bhp diesel vw van! MAF cleaner is a possible alternative but if its on the original MAF then it certainly wouldn't hurt to change it.....
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Jan 03, 2019 1:09 pm    Post subject: Reply with quote

The MAF is old and may need changing but I thought that unplugging it will send it back to its default setting (as you say) and it should run better without the MAF connected, if the MAF is faulty, as this didn't change the way it ran I assume it is something else?
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alex yates
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 15565
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Thu Jan 03, 2019 1:27 pm    Post subject: Reply with quote

Yes I'd have thought the same.
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wasz
Sepang


Joined: 28 Dec 2012
Posts: 2869


1999 Porsche 996 Carrera 2

PostPosted: Thu Jan 03, 2019 2:29 pm    Post subject: Reply with quote

I changed my MAF on my 3.4 somewhere around 115k miles. I was having idle problems, I think I unplugged it and it idled better, with a new MAF it idled properly and ran much better afterwards, better mpg too. I bought mine based on the BOSCH part number (beware lots of fakes around). You will find a date stamped on it - mine was replaced before.

My car doesn't run quite as well when I unplug the MAF. The car will drop to an open loop base map that estimates air flow. It will do the same if it decides the MAF is giving bad values. If your car runs better or exactly the same MAF plugged or unplugged I would think its faulty. Got any mates to swap with?

Of course vacuum leaks can cause similar but less obvious symptoms, exacerbated off idle or when accelerating hard (hence my other experience), any vacuum leak will allow unmetered air (that has not gone past the MAF) into the intake leading to imperfect fuelling and hence hesitation.

Have you ever run an aftermarket air filter?
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Last edited by wasz on Thu Jan 03, 2019 2:44 pm; edited 1 time in total
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Jan 03, 2019 2:43 pm    Post subject: Reply with quote

I've just bought a MAF from Euro Car Parts to eliminate fakes and collect it tomorrow. It can't hurt to try that along with everything else I have planned, its probably due a change.
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alex yates
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 15565
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Thu Jan 03, 2019 5:31 pm    Post subject: Reply with quote

Take MAF readings with a code reader for both and see if they differ (at tickover). Might be worth another member with a 3.6 taking their reading at tickover and see what it's saying.

TBH though I doubt your problem has anything to do with the MAF as I'm led to believe they're pretty useless (above 2k rpm) except for trying to get your tickover right.
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patpending
Nürburgring


Joined: 11 Jun 2018
Posts: 402
Location: IoM


PostPosted: Thu Jan 03, 2019 6:38 pm    Post subject: Reply with quote

When it plays up try running it (carefully and in a safe place) with the fuel filler cap off.

Obviously not with a full tank !

If the hesitation stops you have a breather issue.
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Jan 03, 2019 8:09 pm    Post subject: Reply with quote

patpending wrote:
When it plays up try running it (carefully and in a safe place) with the fuel filler cap off.

Obviously not with a full tank !

If the hesitation stops you have a breather issue.


I have been running it recently with the tank venting to atmosphere (tank vent disconnected) and with a sealed system, it just passed its MOT last week like this (with a sealed system). I have also been through the EVAP system with a fine tooth comb but nothing changes to the hesitation whatever way I have run it.
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6178
Location: Brighton


PostPosted: Thu Jan 03, 2019 8:11 pm    Post subject: Reply with quote

Basic test for a maf with a tester .. ignition on but not running .. the sensor voltage should be 1.0 volts.

Running on a warm engine with a/c on and it should read about 17 kg/h .. if above 25 or below say 12 then it might indicate a problem .

Bear in mind an air leak after the maf will give a low reading as air is bypassing the maf .

A misfire .. say a coil pack .. very lumpy at idle but better when driving it .. kinda an obvious fault and your description doesnt sound like a coil pack.

From previous converstaions it does seem like your car is running weak .. this could be to do with the tank vent or a possible air leak ..

Simple check .. is the oil cap sealing .

No fault codes i take it ?

Fuel adaption figures if you can get them please .. Rkat , frau , frao .. or tra / stft depending on the tester .

Fuel pressure .. pretty hard to check under a load but basic symptoms would be a lack of top end .. holding back after about 5k rpm .. which is also similar to a faulty maf sensor im afraid .

A long crank before starting would indicate either low fuel pressure , fuel draining back to the tank .. thinking the rail pressure reg here .. fuel filter if fitted or a crank / cam sensor problem .. this is at the bottom end of what it might be though .

The car is a manual yes ? ive never actually asked that !

Tip can have torque convertor issues .. lock up clutch.

Gut feeling .. the tank fault and this are related .

BTW i looked at an early training manual for the tank vent system .. even though we are UK we got taught the USA spec one .. there still is no info on our market for this that i can find so far Sad
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Jan 03, 2019 8:54 pm    Post subject: Reply with quote

deMort wrote:
Basic test for a maf with a tester .. ignition on but not running .. the sensor voltage should be 1.0 volts.

Running on a warm engine with a/c on and it should read about 17 kg/h .. if above 25 or below say 12 then it might indicate a problem .

Bear in mind an air leak after the maf will give a low reading as air is bypassing the maf .


Will give these a check, but will most probably have a new MAF before then so will be just easier to fit it and eliminate. If I get time I will get the figures even if just for future reference.

deMort wrote:
A misfire .. say a coil pack .. very lumpy at idle but better when driving it .. kinda an obvious fault and your description doesnt sound like a coil pack.


I had a single faulty coil pack last month so I thought if one was on its way out others may not be far behind, these again will just be fitted to eliminate, I'm sure this isn't the problem.

deMort wrote:
From previous converstaions it does seem like your car is running weak .. this could be to do with the tank vent or a possible air leak ..

Simple check .. is the oil cap sealing .


Yes, oil cap is sealing.

deMort wrote:
No fault codes i take it ?


No fault codes unfortunately.

deMort wrote:
Fuel adaption figures if you can get them please .. Rkat , frau , frao .. or tra / stft depending on the tester .


Again, will check as soon as I can, tester will be Durametric.

deMort wrote:
Fuel pressure .. pretty hard to check under a load but basic symptoms would be a lack of top end .. holding back after about 5k rpm .. which is also similar to a faulty maf sensor im afraid .

A long crank before starting would indicate either low fuel pressure , fuel draining back to the tank .. thinking the rail pressure reg here .. fuel filter if fitted or a crank / cam sensor problem .. this is at the bottom end of what it might be though .


I have a feeling both the hesitation and the long cranking are related as they started at the same time.

No fuel filter as 3.6, as is the fuel pressure regulator is on the tank sender on the 3.6 and not on the fuel rail like a 3.4 is. I will pull the tank parts out again and see what I can swap back from my old working parts to see if something is eliminated.


deMort wrote:
The car is a manual yes ? ive never actually asked that !

Tip can have torque convertor issues .. lock up clutch.


Yes, manual.

deMort wrote:
Gut feeling .. the tank fault and this are related .


Me too and if I swap my old fuel pump and fuel pressure regulator back onto my car, it may be the fault but things are never that easy frustrated

deMort wrote:
BTW i looked at an early training manual for the tank vent system .. even though we are UK we got taught the USA spec one .. there still is no info on our market for this that i can find so far Sad


This search will continue.
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kurlykris
Indianapolis


Joined: 30 Jun 2014
Posts: 2329
Location: Warwickshire


PostPosted: Thu Jan 03, 2019 10:54 pm    Post subject: Reply with quote

I`ve just had a watch of some of the videos of the Pico Scope, that looks like a really usefull tool and will come in handy with work too, thanks Ghianightmare, a 2 channel version is available at RS components for £100, no brainer really Thumb

Chris, having watched those videos, particularly one on how to read the MAF, it does look like a likely cause for your issue, a mass influx of air on WOT that the ECU can`t see if the MAF is faulty Confused

I`m having a slight issue on the 996.1, idling was all over the place the other night after not using the car for a month and fitting a new battery due to a dead cell, car was jumping from 600 rpm to 1200 almost as though I was blipping the throttle Sad

I shall be watching this thread with interest Thumb
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Thu Jan 03, 2019 11:00 pm    Post subject: Reply with quote

I hate not using them as much as I did, they love to be used, I've had so many niggly issues with the 996 in 2018.

New Years Resolution, drive it more often.

That Pico Scope sounded like a good bit of kit but I forgot to check it out after I'd read about it in that thread.
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wasz
Sepang


Joined: 28 Dec 2012
Posts: 2869


1999 Porsche 996 Carrera 2

PostPosted: Fri Jan 04, 2019 10:47 am    Post subject: Reply with quote

kurlykris wrote:


I`m having a slight issue on the 996.1, idling was all over the place the other night after not using the car for a month and fitting a new battery due to a dead cell, car was jumping from 600 rpm to 1200 almost as though I was blipping the throttle Sad
:


Whip your idle valve off the throttle body, it should snap open either way with a 9v battery. I dismantled mine to clean up, it was stuck after 3months of no use. Just push the little roll pin out, care not to crack the plastic like I did.

Also usual check for vacuum leaks.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Sun Jan 06, 2019 7:37 pm    Post subject: Reply with quote

I manged to get some garage time today and it seemed the easiest thing to do it just swap the MAF over as it was in my hand. I was going to do each job I intended to do and test drive it between so I knew exactly what I had done to cure this.

I fitted the MAF and it fired up fine, I let it warm up a little and took it for a spin, it seems the MAF was the problem. It didn't hesitate at all, I did feel it wasn't 100% as it should be but this may be down to the coil packs being quite old as I recently had one fail. I'll run it from stone cold to make sure 100% but I'm sure this has been solved with a new MAF Thumb
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Sun Jan 06, 2019 8:30 pm    Post subject: Reply with quote

This is the old MAF and looks a similar condition to the picture thecarfixer shows of his old one although it's not quite as discoloured as his.


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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6178
Location: Brighton


PostPosted: Sun Jan 06, 2019 9:01 pm    Post subject: Reply with quote

Whist this is good news i want you to drive 20 miles at least then give me some readings from your durametric .. obvioulsy sort the tank issure first on your other post .

What im after is maf readings and fuel adaption figures plus any fault codes .

You may have to clear the codes then do a 20 mile r/t and recheck for codes though.

When you clear a fault code it also resets the adaptions .. this is for basic wear and tear so the car needs to relearn these before it will run correctly , you will have the odd air leak or rich mixture that the car will adapt to so you always clear the codes then give it a good run before rechecking for faults .

lambda faults take 5 - 10 days to re occur ... you just have to wait before checking for these faults ... see my boxster thread !!
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Sun Jan 06, 2019 9:16 pm    Post subject: Reply with quote

Will do, will take a fewvdays before I am back with the car but will run through everything you have pointed out.
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kurlykris
Indianapolis


Joined: 30 Jun 2014
Posts: 2329
Location: Warwickshire


PostPosted: Mon Jan 07, 2019 5:10 pm    Post subject: Reply with quote

I was home really early from work today, so decided to have a play with the 996.1. I popped the MAF out and it looked brand new, clean as a whistle and the green o-ring looked like brand new, I had a poke around the Idle Control Valve and wiggled the plug a bit, but I couldn`t get my torx driver on the back screw as there was a plastic pipe in the way and I didn`t want to have to start stripping half the engine bay down on a school night.
I warmed the car up on the drive, turned the engine off and then plugged the iCarsoft 960 in, started the engine again. Revving the engine from the throttle cable Very Happy I heard a distinct click from the ICV. When I had the problem the other night, I noticed that if I turned the Aircon on and off, there was no change in RPM at idle, which now there is Grin all seems to be back to normal, maybe having sat out in the cold for a month she was just having a strop and just jealous of me using the Boxster over Christmas Laughing

Unplugging the MAF with the engine running, the RPM dropped to almost stalling then picked up to a lumpy idle

Anyhoo, I took a photo of the Airflow at Idle and up to temp.
4.99 g/s equates to 17.964 Kg/h at idle thumbsup


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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6178
Location: Brighton


PostPosted: Mon Jan 07, 2019 7:13 pm    Post subject: Reply with quote

Maf is spot on were it should be .

If you have the early IACV .. black box on the side of the throttle houseing then a remove and a good clean out is always a good idear .. like the old Bosch ones they can and do stick.

Is the last reading on your gauge the post cat lambda sensor for bank 1 ?

Its only that the reading is spot on what a dead sensor would read .

You tend to do a quick stamp on the acc and it should rise and then fall to prove its ok .

Something people also forget these days .. clean out the throttle butterfly .. i did a Boxster last week .. i ended up removing it as it was that bad .
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kurlykris
Indianapolis


Joined: 30 Jun 2014
Posts: 2329
Location: Warwickshire


PostPosted: Mon Jan 07, 2019 8:43 pm    Post subject: Reply with quote

Yes it is the Lambda demort, I`m sure that is the one that was changed last year for the MOT, I`ll stick the code reader back on tomorrow night and look for some sign of life and compare to bank 2 Thumb
I`ll most probably pop the throttle body off at the weekend and give it all a good clean, I did open the butterfly and it looked a bit grubby inside Grin
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