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one of the great unwashed
 
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930 Fuel Pumps ????

Being a non-930 guy, I would like to ask the real 930 guys how do the dual fuel pumps run? Are they both on all of the time, or do they stage up according to (whatever parameter) boost? Is there any form of pressure regulation on them?

TIA
Pat
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Patrick E. Keefe
78 SC
92 968 Cab
01 Boxster
RIP, Early_S_Man & RoninLB
Old 05-23-2008, 05:14 AM
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I'm a newb to CIS but these links helped me out. I looked but I don't see any specific info about the dual pumps on the 930, hopefully someone knowledgeable will chime in.

http://members.rennlist.com/jimwms/CIS/CIShome.html

http://www.auto-solve.com/mech_inj.htm
Old 05-23-2008, 06:27 AM
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sudo apt-get purge 930
 
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They run together. The front pump primes the rear pump so to speak. Both run continually so long as air is flowing past the metering plate. The only pressure regulation is the WUR. The front pump has a built in check valve and there is a fuel accumulator in the engine bay to maintain system pressure when the engine is off.
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Old 05-23-2008, 06:34 AM
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Quote:
Originally Posted by equality72521 View Post
They run together. The front pump primes the rear pump so to speak. Both run continually so long as air is flowing past the metering plate. The only pressure regulation is the WUR. The front pump has a built in check valve and there is a fuel accumulator in the engine bay to maintain system pressure when the engine is off.

What he said, here is another link, just cancel past the login prompts.

http://www.users.bigpond.com/interject/KSITEPLN.HTM
Old 05-23-2008, 06:39 AM
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Here is the diagram for the fuel pumps. The pumps are in the large square and the air meter contact is in the smaller one. The are a couple of other relays in the circuit as well as you can see. Pat, if you want to experiment with controlling pressure by varying pump motor speed I would only control the front pump as other things are in the circuit with the rear pump.

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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 05-23-2008, 07:04 AM
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one of the great unwashed
 
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Mark, thanks.
I have only one fuel pump on the SC. First step is turn down the fuel pressure at the head, and see if I starve at 6k RPM WOT. Then I may play around with the pump speed regulation.
Pat
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Old 05-23-2008, 08:14 AM
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930 fuel pumps

Front pump sends fuel through filter and accumulator to fuel distributer.

Front pump does not "prime" rear pump - has no connection whatsoever.

Rear pump scavenges excess fuel from system and pushes it back to fuel tank through return line.

Bad front pump results in not enough fuel to distributer - mine is 106 lbs.

Bad rear pump results in build up of excess fuel and fat condition.

Wire each pump on separate manual circuit with 25AMP fuses and proper quality toggle switches.
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Old 05-23-2008, 08:55 AM
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Quote:
Originally Posted by e p slick View Post
Front pump sends fuel through filter and accumulator to fuel distributer.

Front pump does not "prime" rear pump - has no connection whatsoever.

Rear pump scavenges excess fuel from system and pushes it back to fuel tank through return line.

Bad front pump results in not enough fuel to distributer - mine is 106 lbs.

Bad rear pump results in build up of excess fuel and fat condition.

Wire each pump on separate manual circuit with 25AMP fuses and proper quality toggle switches.
I stand corrected.
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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 05-23-2008, 09:19 AM
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Doug Siegel
 
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Quote:
Originally Posted by e p slick View Post
Front pump sends fuel through filter and accumulator to fuel distributer.

Front pump does not "prime" rear pump - has no connection whatsoever.

Rear pump scavenges excess fuel from system and pushes it back to fuel tank through return line.

Bad front pump results in not enough fuel to distributer - mine is 106 lbs.

Bad rear pump results in build up of excess fuel and fat condition.

Wire each pump on separate manual circuit with 25AMP fuses and proper quality toggle switches.


I recently put my fuel pumps on a separate fuse panel. Each pump has a fuse. ...

How can I test the pressure of each pump separately?

Should both be 106 psi?

Thanks.
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Old 05-23-2008, 09:51 AM
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Cis

Suggest Bentley Publications Bosch Fuel Injection & Engine Management book for understanding/testing/tuning of basic CIS. Look on Amazon and find a used book for $10.00 or so. Well written and a valuable addition to your library.

EPS
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Old 05-23-2008, 10:04 AM
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Quote:
Originally Posted by e p slick View Post
Front pump sends fuel through filter and accumulator to fuel distributer.

Front pump does not "prime" rear pump - has no connection whatsoever.

Rear pump scavenges excess fuel from system and pushes it back to fuel tank through return line.

Bad front pump results in not enough fuel to distributer - mine is 106 lbs.

Bad rear pump results in build up of excess fuel and fat condition.

Wire each pump on separate manual circuit with 25AMP fuses and proper quality toggle switches.
Good to know...thanks, slick!
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Old 05-23-2008, 10:07 AM
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It's been a couple years since I replaced all my fuel lines and installed EFI, but I recall that the two pumps are in series so the front pump does send fuel to the rear pump.
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Old 05-23-2008, 10:35 AM
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Quote:
Originally Posted by 125shifter View Post
It's been a couple years since I replaced all my fuel lines and installed EFI, but I recall that the two pumps are in series so the front pump does send fuel to the rear pump.
That's what I thought but who am I to argue.
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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 05-23-2008, 10:41 AM
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2 pumps

Don't know how others are set up but when I replaced all fuel lines and pumps on my 1979 930 earlier this year the lash-up was, and is, as described.
I'm no expert - just paint pictures and attempt to weld (It's a Frenchy Frog thing).

EPS
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Old 05-23-2008, 11:55 AM
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It's got me curious. I have my engine out right now so when I get home I'll check it. I wonder if it changed for different years.
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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 05-23-2008, 12:00 PM
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fuel line

Highly recommend replacement of all fuel lines if they are stock year application. I used AN line and fittings re-routed in more convenient manner than stock configuration. Replacing 30 year old lines gives peace of mind. EPS
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Old 05-23-2008, 12:52 PM
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They are in series... One pump is designed more for volume while the other increases the system pressure. The 930 CIS uses a hell of a lot of fuel to control the AFR. They will typically pump 1000cc in 15-20 seconds at the return line back to the tank, all while maintaining 6-7.5 bar of system pressure.
Old 05-23-2008, 02:19 PM
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pump

My rear pump feeds back to the tank through the return line. Turn off second - rear - pump and system runs way too fat with lots of black smoke.
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Old 05-23-2008, 02:59 PM
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Mine are in series too. When I converted to EFI, I removed the fuel accumulator, but remaining plumbing stayed bone stock. My system runs at factory pressure which is something like 6 bar (84 psi or so). I also eliminated the factory fuse/relay systems and installed my own wire harness. Now my ECU controls the fuel pumps. They come on when the ignition is turned on, remain on and do not alter their output - the fuel pressure regulator handles fuel rail delivery. This is probably too much info since mine is EFI, but the plumbing is close - no return pump, pressure is stock, delivery ample for 525rwhp, etc.
Old 05-23-2008, 04:40 PM
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I have seen 930 run rich when the rear pump quits. However, the reason for this is the front pump cannot force enough fuel through the inop. rear pump to maintain proper system pressure.

Considering the warmup regulator, or control pressure regulator, can also be called a differential pressure regulator, meaning it works by maintaining a pressure difference between the upper and lower halves of the fuel distributor. It is also designed to work with a higher system pressure then you get w/ a dead rear pump. I'll stop here at trying to explain the science behind CIS because, well, I can't. I can tell you that when CIS loses fuel pressure, it tends to run rich at times. Unfortunately, the lack of fuel flow can quickly lead to a lean condition w/ increased load which is why 930's are virtually undrivable w/ 1 bad pump and can do all sorts of weird stuff. I hope this makes sense.

Pat, let us know how your fueling issues go, if your using SC CIS, you should be OK w/ 1 pump...
Old 05-23-2008, 04:50 PM
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