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What could be the cause of hesitation when accelerating?

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!
 
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:
 
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. :oops:
 
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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infrasilver said:
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. :oops:

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.....
 
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?
 
Yes I'd have thought the same.
 
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?
 
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.
 
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.
 
patpending said:
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.
 
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 :(
 
deMort said:
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 said:
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 said:
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 said:
No fault codes i take it ?

No fault codes unfortunately.

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

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

Yes, manual.

deMort said:
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 said:
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 :(

This search will continue.
 

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