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M5guy's Avatar
 
Join Date: Nov 2007
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Why two fuel pumps?

I re-wired the fuel pump circuit on my 930 yesterday. Now each pump has its own power supply wire and fuse, as well as Bosch cube relays.

So I was wondering: why does the car have two pumps? Redundancy, pressure, volume?
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86 930

x: 62 356, 64 356, 76 930, 84 911 Targa, 85 ROW 911, 00 996, 07 Cayman S.
Old 03-22-2019, 04:51 AM
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Crotchety Old Bastard
 
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Just my observation but the 930 fuel system appears to be a simple evolution of the 911SC fuel system. The front pump and fuse/relay setup is identical. The rear pump was added due to increase volume need. This may be the reason for the single fuse issue, the 930 added a relay for the rear pump but did not add separate fuse for the rear pump.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 03-22-2019, 05:29 AM
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If you go EFI you would only need 1.
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1979 911SC widebody conversion. 3.1 engine, 3.2 liter heads, carrera intake, Microsquirt V3 ECU, K27 7200 High flow turbo, Tial F41 wastegate, Evo X intercooler, Ford EDIS. .7 bar. 402hp 360tq
Old 03-22-2019, 09:31 AM
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Brando
 
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I drove safely on 3.0t cis with one 044 pump for years...
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Old 03-22-2019, 10:26 AM
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Quote:
Originally Posted by quattrorunner View Post
I drove safely on 3.0t cis with one 044 pump for years...
Brandon, based on a pic you recently posted of your car, I question the accuracy of, "I drove safely . . ."!
Old 03-22-2019, 10:35 AM
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Quote:
Originally Posted by Rawknees'Turbo View Post
Brandon, based on a pic you recently posted of your car, I question the accuracy of, "I drove safely . . ."!
It was never cracked up until I changed the engine to efi......
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Old 03-22-2019, 10:37 AM
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Quote:
Originally Posted by quattrorunner View Post
It was never cracked up until I changed the engine to efi......
Fookin EFI!!!
Old 03-22-2019, 10:39 AM
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Just a FYI-

Sometimes Two Fuel Pumps are desired when running a Club Endurance Race and a spare in-system pump is essential........



Len.Cummings at verizon.net

Old 07-28-2019, 07:48 AM
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Quote:
Originally Posted by BoxsterGT View Post


Just a FYI-

Sometimes Two Fuel Pumps are desired when running a Club Endurance Race and a spare in-system pump is essential........



Len.Cummings at verizon.net

Running pumps in parallel for redundancy is not the same as running two pumps in series...
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Old 07-28-2019, 09:58 AM
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Yes, but it is an interesting adaptation of "Dual Pumps".

Thought someone might like to see this application by Buckley Racing.

Len

Old 07-28-2019, 10:17 AM
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Quote:
Originally Posted by quattrorunner View Post
3.0t cis with one 044 pump for years...
Yeh, my RoW 3.3 ran just fine on the original (250K tub, receipts from the early 80's) 911 pump.

Swapped it out for an 044 because original was noisy, and upgraded turbo/headers etc. and thought more headroom would be good.

Made no difference; 044 just as loud (still is, 12 years later), and CIS fueling curve completely unchanged - not fuel pump shortfall, but tuning issue.

I even got a rear pump harness, mounting gubbins and another 044, but never got around to fitting - car dyno'd 370 at the wheels with a single pump, better things to worry about - like slipping clutches and breaking transmissions..

Some replacement pumps - like the 930 stock rear - are silly money. I'd replace both with 044's, or just run a single up front.
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'77 S with '78 930 power and a few other things.
Old 07-28-2019, 10:18 AM
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Crotchety Old Bastard
 
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Everything on the 930 was overkill. The engine was neutered for DOT purposes but the car was set up for racing. The dual pumps become more useful when the standard engine is set to race spec.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 07-29-2019, 05:29 AM
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I ran my '86 930 on one fuel pump for about 6 months. It ran ok but it had a high idle. I turned the idle screw in to adjust.

When I had the hose to the AAR valve crack and I replaced the hose, I realized the AAR was never closing. Took the AAR off and tested it and it closed. Put it back and realized it had no power. Schematic showed it was running off the one of the fuel pump relays. Looked in the fuse panel in the front trunk and a relay was in the bottom of the cover. The relay had backed out.

Plugged the relay in and the car ran great except now with the AAR closing, I lost all idle as I had adjusted the idle to make up for the always-open AAR.
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Old 07-31-2019, 12:01 PM
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Will it run OK on one 044?
Just trying to sort my fuel issue out (not enough at higher rpm). Not sure where to go with it right now.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 07-31-2019, 01:46 PM
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Quote:
Originally Posted by Alan L View Post
Will it run OK on one 044?
Mine did.

Quote:
Originally Posted by Alan L View Post
Just trying to sort my fuel issue out (not enough at higher rpm). Not sure where to go with it right now.
Alan
Unless your fueling issue is pump-related (mine wasn't), an 044 won't help you.

With it running nice and responsive in the mid-range, mine (k27/GHL/Kokeln) would get a touch lean over 5.5K. Really didn't seem to be much to do about it. About the only thing I could think of was to maybe tune the WUR for mid-range only and use the RPM pill to delay boost enrichment to 5K or so. Or FrankenCIS.

I didn't do that. Because with a 5 speed box, it didn't stay up there long (& power already dropping off with SC cams). And also a street driven car - so not like I was pegging it down a straight at those AFRs/RPMs.

I eventually went EFI, and it's a totally different car. But seem to recall you go racing in a class with rules, so....
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Old 07-31-2019, 03:54 PM
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Yes I need to stick with era equipment , and I don't mind CIS. Just need to get this working better. I will just have to plug away til I ind the problem.
Thanks
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 07-31-2019, 04:51 PM
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My 81 SC with 930 turbo power has always run on one front pump. The only problem I have had was due to a knockoff 044 pump purchased on ebay which only lasted a short time. After purchasing the real 044 from Pelican 2 years ago everything has been fine. These knockoffs are cheap and look just like the real one.
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1981 SC Steel Widebody, DP Lid, 930/51 to 3.2l, K27 7006 Turbo, DOD, P&P Twin Plug heads, Twinfire Ignition, Ruf Intercooler, Powerhaus headers, Zork, CIS Euro FD, 009 injectors, 044 pump, BLwur, 930 4 sp LSD, Mocal 44 w/fan, LM2, Brembo, Retroair, Euromeisters
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Old 08-01-2019, 04:36 AM
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Do to the Hi press needed in order to the cis system to work properly you need the second pump, it is matter of fact.
Old 08-02-2019, 06:38 AM
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Quote:
Originally Posted by Hot Euro View Post
After purchasing the real 044 from Pelican 2 years ago everything has been fine. These knockoffs are cheap and look just like the real one.
Curious; 10+ years ago, the knockoffs were easily identifiable as they had the wrong size electrical fittings (real 044's are both a size up from the 911 pumps), were shorter (I seem to recall) and came in (fake) Bosch boxes marked "Made In Germany" (whereas the real ones at the time were actually Czech-made).

Is that no longer true? Did they up the fake game?

It must also be said; just because its cheap doesn't necessarily mean its not a real 044.. Both of mine are - and I bought both (at separate times) for less than $200 US a pop. "Reputable seller" is the key...

The real ones are manufactured at scale, as opposed to being an obscure part they do a small production run for every 10 years and then have to put on the shelf until someone wants one...
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'77 S with '78 930 power and a few other things.
Old 08-02-2019, 06:42 AM
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I'm running dual 044s Alan and still lean out past 5.5k, sucks.

I've gotten good at modulating the throttle in the upper range - lifting a tad helps keep it from going too lean (like 12.5-13).

my shop tweaked some of my WUR pressures while doing the turbo job, so I'm hopeful when get it back maybe some of this will be addressed!
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Old 08-02-2019, 08:19 AM
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