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Porsche 924 - In tank Fuel Pump
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Tue Oct 27, 2015 7:36 am    Post subject: Porsche 924 - In tank Fuel Pump Reply with quote

Hey guys,

I have a Porsche 924 2.0L manufactured in 1985. I recently was running into the common issue of fuel management and hot starting issues. Recently I have replaced both the fuel metering head and the Fuel accumulator. Metering head was not working properly and was not distributing fuel very well. Fuel accumulator had been badly fixed by some previous owner, and was far off from working properly.

While I was testing it again, I have realised that the in tank fuel pump was failing, and at one point in time it just died and couldn't start back on. Therefore the engine is not having fuel to even start up.

Is the original Bosch in tank fuel pump, the only solution to fix this issue ? Are there any other alternatives brands or pumps which fit well in the fuel tank's hole?

In some posts I read that the recent models made by Bosch do not fit in the hole of the fuel tank. This really got me confused.

Thanks
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Tue Oct 27, 2015 8:33 am    Post subject: Reply with quote

Some of the US cars were "updated" via TSB to only use the external pump. The Internal pump just supplies the external pump, which supplies all of the necessary pressure for the CIS system.

I'd try bypassing the internal pump and verify the external pump works sufficiently.
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1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Tue Oct 27, 2015 11:46 pm    Post subject: Reply with quote

Thanks for your reply. Wouldn't this wear out the external pump much faster though ?

Or would I need to move the external pump to be at a lower level from the tank and gravitational wise, the fuel will be going down to the external pump ?
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11355
Location: PacNW

PostPosted: Wed Oct 28, 2015 9:10 am    Post subject: Reply with quote

ryanspud wrote:
Or would I need to move the external pump to be at a lower level from the tank and gravitational wise, the fuel will be going down to the external pump ?


924S has the same tank, and pump in the same place with no prepump, so I'd guess not.
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Wed Oct 28, 2015 7:22 pm    Post subject: Reply with quote

@Rasta Monsta

What do you mean they have no prepump ? I'm pretty sure that I saw the thin pump inside the tank, and the bulky pump exactly outside of the tank in my Porsche.
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Tue Nov 03, 2015 9:44 pm    Post subject: Reply with quote

I decided to buy an new In tank Fuel pump. Anyone has an idea if the rumour is true that the new Bosch in tank fuel pumps are wider in diameter, and therefore do not fit in the tank hole ?

Thanks
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Wed Nov 04, 2015 12:51 am    Post subject: Reply with quote

You don't need it. Remove it and bypass it completely. Drive car.
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1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Wed Nov 04, 2015 2:10 am    Post subject: Reply with quote

Wouldn't that wear out the pump ?
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Wed Nov 04, 2015 2:38 am    Post subject: Reply with quote

Nope. As has been stated previously, Porsche did away with it themselves.

Just add a good, generic fuel filter prior to the external pump inlet to ensure you don't get junk from the old tank in your pump and the CIS system and you'll be good. On a good, clean tank this wouldn't be needed, but most toofahs have rusty tanks by now.

Like I said, my 79 has the same tank, same external pump and no provisions for an internal pump and drove for decades that way before the pump died of old age a few years after I converted to EFI. Replaced it with a generic Walbro pump in the same location and kept on trucking.

Like Rasta stated, the 924S uses the same tank and runs a single external pump without issue.

Porsche made changes to the fuel system over the years based on feedback from the field, customers, Bosch engineers and their own testing. For example, they went from a dual accumulator setup to a larger, single accumulator. Similarly they went from a dual pump solution to a single external pump solution. For both of those, they sent information to the dealers to retrofit cars that come in for service for those systems.
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1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Wed Nov 04, 2015 3:16 am    Post subject: Reply with quote

Thanks a lot fiat22turbo.

I will check this out. So the fuel pump on a 924s and the external fuel pump of a 924 are identical the same ? Isn't the 924S one more powerful as a pump ?

Thanks
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Wed Nov 04, 2015 5:02 am    Post subject: Reply with quote

No, they are different, but more or less mount the same.

The 924 CIS system uses higher fuel pressure, so the pump is stronger on the 924.

The 924S uses EFI and a lower fuel pressure, so the pump doesn't provide as much pressure.

The flow rates are different and are controlled by the fuel pressure regulator in the engine bay and the extra, unused fuel is sent back to the top of the tank.

For your case, it doesn't matter. You've got a good external pump that is starved because the failed internal pump is in the way. Remove the internal pump as a restriction and your car will run again.
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1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Wed Nov 04, 2015 6:07 am    Post subject: Reply with quote

Thanks a lot for your reply once again. I will give it a go like this. Hopefully it will work also when the tank is half empty. Do I need to add some extra piping to the external pump? So as to reach the bottom of thw fuel tank?
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ryanspud  



Joined: 05 Jun 2015
Posts: 15
Location: Malta

PostPosted: Wed Feb 15, 2017 8:44 pm    Post subject: Reply with quote

I jsut wanted to let you guys know that I had removed the in tank fuel pump and my 924 has been more than a year running on the single external fuel pump.

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stv951  



Joined: 06 Mar 2005
Posts: 100

PostPosted: Sat Mar 25, 2017 7:49 pm    Post subject: Reply with quote

Am in the same position today with my euro 931 (1981)

About to blank out the internal fuel pump as per your guys suggestions and stick with the "external only" solution.

As i read above, i mount an good external one on the same location as the factory installed it.
But which pump do you guys use ?
I read about the pierburg 98154
Is it good enough flow wise ?
Any others ?

Any suggestions are quite appreciated
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931 81 177 bhp White
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stv951  



Joined: 06 Mar 2005
Posts: 100

PostPosted: Thu Apr 13, 2017 3:33 am    Post subject: Reply with quote

bump
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Steve
931 81 177 bhp White
931 81 0 bhp engineless Platinum
924S 86 stripped with cage for Track days Red
944 83 Auto Blk
924 84 project 924 CGTS with 951 running gear
944 S2 90 Convertible 3xBlack
951S 91 Vitesse stg 3 350 bhp
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