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Acceleration issue / No top end

911_DRE

New member
Joined
20 Aug 2013
Messages
16
Hey guys,

After following advice on this forum to a prior issue (now resolved), I replaced the coil packs, spark plugs and MAF.
This stopped the hesitation it once had. All was fine and dandy.

However, my car has since developed a new fault, this time I believe it to be fuel pressure related, as all my electrics are fine in this respect.

The problem is when I am accelerating the car is fine pulling away so long as I do not go full throttle - if I go full throttle, it kind of stops all power, it hesitates and won't go completely through the rev range.

I have recently changed the fuel filter hoping this would alleviate the issue, it did for about a day then went back to normal.
I also pulled out the fuel pump and cleaned off some gunk at the bottom of the small round filter, but the problem still remains.

I was hoping someone could help me identify what exactly it is that is causing this hesitation / full throttle starvation issue... and what I can do to fix it please.

Many thanks in advance.

DRE
 
Presumably no fault codes to work from?

What makes you think it's fuel feed and not the DME pulling timing? If you've got a diagnostic kit, try getting some live data on the problem.

Has the car ever been remapped and are you running it on 95RON or higher octane?
 
Hi eca02apc,

I have had the car checked over, no stored codes, no warning lights on dash.

I use shell v power all the time and it is still... spluttering / hesitating.
As for Re-map, I cannot say for certain, but I would assume Not.

I can replicate the fault every time I drive, it is exactly as I described, as soon as I apply 100% foot to the floor, it will hesitate further up the rev range, if I drop a gear and accelerate hard, it will repeat it.
The only way I can describe it is as if there is not enough... oomph! or pressure to give it the full power, it just feels restricted, not like a 911.

Any more advice greatly appreciated.

Thanks guys.
 
STILL sounds like a MAF issue to me. Not exactly failed enough to fire up a code, but failing enough to cause an issue.
Does it hunt for idle?

I know in several turbo'd cars I've had, when experiencing similar issues, the MAF sensor was on it's way out.

Just a thought.....

Dan
 
Does your car have e-gas? (Early 996s did not).
I believe there were sometimes issues with the potentiometer contacts deteriorating. :dont know:
 
I may have missed something in thhat I don't know if yours is aTurbo. If it is Turbo you need to eliminate boost pressure leaks from your list. You may initially see little boost pressure on the display - it should boost comfortably to 0.7 - 0.8 bar.

That's my contribution.
 
Hey Guys, thanks so much for your input, please see below:

ScoobyDoo555 said:
STILL sounds like a MAF issue to me. Not exactly failed enough to fire up a code, but failing enough to cause an issue.
Does it hunt for idle?

I know in several turbo'd cars I've had, when experiencing similar issues, the MAF sensor was on it's way out.

Just a thought.....

Dan

Hey Dan,

Thanks for the response,

I don't think it's a MAF issue, reason being I've had it out, inspected it, it is immaculate cond. it's the original BOSCH one and I have no idle issues, it fires up perfectly and the revs do not fluctuate... Moreover, I also borrowed a friends working maf and the issue still remained...

It's so irritating trying to pin-point what it is..

Red993C4 said:
Does your car have e-gas? (Early 996s did not).
I believe there were sometimes issues with the potentiometer contacts deteriorating. :dont know:

Hey Red,

Thanks for your response,

I am not sure what e-gas is or how to check for it – my car is a 2001 model, so it May have it?.. I would still like to check if you can point me in the right direction?
Cheers.

maor said:
PSE kicking in ??

Hey Maor,

Thanks for input,
PSE... I don't think mine has the Sports exhaust. It has a 'sporty loud exhaust' not sure of make or model, but it definitely isn't the Porsche upgrade – thanks for input though.

cheshire911 said:
I may have missed something in thhat I don't know if yours is aTurbo. If it is Turbo you need to eliminate boost pressure leaks from your list. You may initially see little boost pressure on the display - it should boost comfortably to 0.7 - 0.8 bar.

That's my contribution.

Hey Cheshire,

Thanks for your response,
I have the 3.6 N/A, it's definitely not a turbo, but if it was I would also have suspected a pressure leak. Which is why this is such an annoyance and hard to pinpoint, for example this morning I was driving on the motorway, switching up gears, as soon as I begin to press down hard on accel. You can feel as if it's not getting enough surge to pin me back in the chair, it just gives a slight jolt, then holds back and won't rev beyond wherever it decides to stop, usually above 4k revs sometimes 5k the only way I can gain more momentum is to gear up and drop revs and build up that way... or I just rev about 70% throttle to take me through the rev range, even then it can be temperamental...

I aim to check it over this weekend and see if I can see anything obvious.. But again, thanks all and any more advice is always greatly appreciated.

DRE
 
Surely there comes a time when even the most avid home mechanic really should take their car to an expert. :dont know:
 
911_DRE said:
Hey Red,

Thanks for your response,

I am not sure what e-gas is or how to check for it – my car is a 2001 model, so it May have it?.. I would still like to check if you can point me in the right direction?
Cheers.

E-gas = electronic throttle control. Instead of a mechanical linkage between the throttle pedal and throttle body on the engine, the system involves measuring throttle pedal position with a potentiometer and transmitting an electrical signal via the electronic control unit to an electric motor which operates the throttle valve. IIRC, the contact surfaces of the pedal potentiometer were sometimes prone to pitting and giving out an intermittent or incorrect signal (voltage).
Any Porsche workshop (OPC or indy) should be able to check for this easily, or indeed for any other possible cause of your car's problem.
As T8 suggests above, having it looked at by a specialist would your best course of action.
 
Clutching at straws a bit here because you've already done all the usual suspects, but it could be a vacuum leak. Although that usually gives you fluctuating revs when accelerating hard, rather than just a bogged-down feeling.
 
I had the fuel pump actually fail on my 986 - you say you cleaned it but I guess its still possible its on the way out.

Chris.
 
T8 said:
Surely there comes a time when even the most avid home mechanic really should take their car to an expert. :dont know:

Mmmm thanks, I think?...

Now then,

a) It had been to a Porsche Indy / 'expert' - who really couldn't do anything other than make suggestions, considering the car is throwing up no fault codes via OBD check & given the symptoms I described, he concluded it was most likely the fuelling system, potentially cured by replacement of, but not limited to: Fuel filter & inspecting fuel pump for clogged filter / swirl pot and possible replacement.
b) This forum is frequented by experts, so by describing the exact same symptoms and sharing my experiences on here, I may be given extra pointers to consider (which I have done thanks to all those who replied with useful suggestions) and you never know, if this happens to your car.. you read it here first on how to come to a speedy resolution!

:)
 
You could always find a shop with a rolling road and run the car through he revs with a fuel pressure guage attached, they should be able to check fueling for you and print a graph out with AFR v RPM etc, thats what I would do anyway :D
 
Have you got standard induction or an upgraded induction? K&N Kit etc , or are you bog basic?

Sometimes if you improve the induction too much [loads of air flow] the standard MAF cannot cope with the air volumes and your engine effectively drowns out with air as you increase the throttle.. to cure you have to fit a MAF from the next engine size up and use Super Unleaded all the time.

I had a Eurocup twin intake fitted.. You can hear the air sucking through the grill in the engine cover.. The engine was flat as anything once you applied more than I would say 60 to 70 pc throttle. Right Maf and right fuel BINGO! BONGO!


:thumb:
 

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