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Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Hi all,

So heres what happaned....I've been driving about 20/30 mins and doing between 60-70mph on the motorway.

All of a sudden while motoring along the car loses drive, and feels as if it has been put into neutral with my foot taken off the gas pedal. (even though I did nothing)

Pressing the gas pedal further at this point does nothing and the engine rpm slowly falls with the cars speed.

I can put the auto into neutral and rev the engine during this time, but when I switch it back into "D" the gas pedal has no effect.

I roll the car onto the hard shoulder, and the engine rpm will continually fall and as the car comes to a stop the engine stalls.

All electrics are working fine before, during and after this little interlude.

I can then start the car fine.... Select "D" and drive off without problem.

This happened the first time a couple of months ago, and I forgot about it...but as it's just happened again...here I am wondering what it could be....?

Any ideas guys?
Tiny

ps. I've had no other problems with the car for a while now....it starts and drives fine. I guess I'm due my next challenge.

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*****1981 - 924 - Auto - London, UK******

968rz · Joined: 21 Aug 2006 Posts: 537 Location: S. E. Wisconsin

That's not trans, could be fuel or plugged cat conv maybe.
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Rick
79 924 coupe Petrol Blue 3spd auto (wife's DD)
93 968 coupe Amazon Green 4spd Tip (my DD)

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Fuel delivery?
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Thanks guys,
Hmm well i don't have a cat conv. so it can't be that.

I have a new external bosch fuel pump fitted, and have overhauled the fueling and CIS system fairly recently. WUR and pressures check out ok.

If it's a fuel delivery issue, would I be able to put it into neutral and rev it freely whilst I've lost drive in "D"?

I wonder how to troubleshoot/eliminate possibilities on this?
Tiny
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*****1981 - 924 - Auto - London, UK******

968rz · Joined: 21 Aug 2006 Posts: 537 Location: S. E. Wisconsin

Paul · Posted: Mon Jul 07, 2008 8:58 pm Post subject:

If you don't know when your fuel filter was replaced last, replace it now and make sure the arrow is pointing in the correct direction.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

Ozzie · Posted: Tue Jul 08, 2008 2:17 am Post subject:

The car uses considerably less fuel to rev when in nuetral.
I'd say the fuel filter is a good guess too.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
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Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Ok I'll change the fuel filter and do a fuel delivery test as per haynes.

Last time I changed the fuel filter was about 2 years ago. I'd say it's done about 8000 miles or so since then. Arrow is in the right direction for sure.

Thanks folks, hope that's it.
Tiny
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*****1981 - 924 - Auto - London, UK******

Rich H · Posted: Tue Jul 08, 2008 5:13 am Post subject:

As Ozzy says under load the engine demands alot more fuel than stationary.

Check the air meter flap is clean and moves freely while you are in there, also check for vacuum leaks on all the boots and injector seals also check the idle air screw O-ring (A personal favourite for vac leaks).

On the motorway you are in cruise condition, high vacuum/high revs/low demand this will highlight any inlet manifold vacuum leaks and/or find new ones
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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Hi all,

I returned from a 430 mile trip to Manchester today....during-which I figured out it was the loose connections on the very hot fuel pump relay which was causing the problem. When I was mucking around with the CIS earlier in the year i must've worked the female connectors in the relay board loose. I squeezed em tight and she didn't miss a beat after that.

Having an auto and doing mostly town driving, I'd forgot the note of the engine between 4 and 5k rpm. Nice.
Tiny

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*****1981 - 924 - Auto - London, UK******

968rz · Joined: 21 Aug 2006 Posts: 537 Location: S. E. Wisconsin

Congrats, nice when it's an easy fix.
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Rick
79 924 coupe Petrol Blue 3spd auto (wife's DD)
93 968 coupe Amazon Green 4spd Tip (my DD)

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Well done, Tiny. I was starting to get worried for you there.

You were brave, taking what could have been a sick car on a journey like that! Still, all's well that ends well.
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

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