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Looking for max amp consumption on 930 fuel pumps

I may be getting closer to figuring out why my car suddenly went lean and lost power. I did all the recommended wiring checks topside and so far so good. Now I got under the car and supplied direct power to each pump. I purposely put in a 5 amp fuse to see how much current the pumps were using. Front pump sounds like a hair dryer on high. No issues with fuse and sounds ok? So safe to say front draws 5 amps or less.

On to rear pump. It blew the 5 amp fuse in less than 1 second. Put in a 10 amp, it ran about 1.5 seconds then blew it. Put in one more and same. It sounded sluggish but maybe it did not have enough time to get up to speed.

Should I bother to test with a 15 amp or is the pump shot? I need to rewire test setup to go upto 15 amps.

I searched and found a post that the Bentley manual states around a 4 amp draw??

I do not have a Bentley manual, so can someone post this info?

Thanks!!

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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"
Old 04-01-2012, 02:10 PM
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I've got the Bentley manual for 964/964 Turbo sitting on my desk here - but can't see where it mentions a 4A draw for the pumps...maybe that's a difference with my manual vs one for 930's?

I've checked in the Fuel section....it describes the flow rates and relay connections, and how to adjust pressure by shimming the valve.

I've also checked the Electrical section, but this only describes the pump locations, ground points and the fuse location/size.

For what it's worth, both the front and rear pumps on the 964 Turbo use 15A fuses, and are in positions 26 and 27 respectively. These are the only items supplied by these fuses, so I'd hazard a guess and suggest they draw more than 4A each...otherwise they'd have 5A or even 10A fuses, no?

Sounds a little like your rear pump is starting to seize and drawing excessive current....worth trying a pump swap, back to front to see if the problem "moves"?

HTH
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Old 04-01-2012, 02:52 PM
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My guess is somewhere around 10-12 amps. If the front pump is making a lot of noise, it's time for a replacement.
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Old 04-01-2012, 02:59 PM
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I checked the amperage draw on my fuel pumps last week. They are each on their own seperate blade fuse and 10 gauge power cables from the battery. They still go through the stock relays and are isolated.

I have a Bosch 044 pump in the front and stock 930 pump in the back. I think the 044 is doing all the work and the stock rear one is just there free wheeling in the fuel flow from the 044. The amperage draw kind of supports that.

The 044 is using a hair over 10 amps and the stock rear pump is using about 5 amps. System pressure is set at 98psi at the fuel head pressure regulator.
Old 04-01-2012, 03:41 PM
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I have never heard a pump before so I have nothing to compare it to. Sound is not too loud but has tone and speed of a hair dryer on high. That's the front pump.

The rear is the one that keeps blowing 10 amp fuses. I am going to rewire for a 15 amp set up and see. I left my amp meter at work so I will retest and post findings as well. I may try to post sound of pump on you tube and link back.

Thanks!
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"
Old 04-01-2012, 03:44 PM
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Quote:
Originally Posted by JFairman View Post
I checked the amperage draw on my fuel pumps last week. They are each on their own seperate blade fuse and 10 gauge power cables from the battery. They still go through the stock relays and are isolated.

I have a Bosch 044 pump in the front and stock 930 pump in the back. I think the 044 is doing all the work and the stock rear one is just there free wheeling in the fuel flow from the 044. The amperage draw kind of supports that.

The 044 is using a hair over 10 amps and the stock rear pump is using about 5 amps. System pressure is set at 98psi at the fuel head pressure regulator.
Those are the numbers I needed. So stock rear is around 5 amps, Do you think mine is toast at pulling over 10 amps?
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"
Old 04-01-2012, 03:46 PM
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Just retested with 15 amp fuse. Blew it in 3 seconds and heated up the wire as it ran. It sounded like a phone on vibrate.

Would running it direct as I did cause the fuel to pressurize and lock the pump up? It slowed down right before the fuse blew. It was really laboring before the fuse blew. To clarify what I am doing, I am hooking up a 12v fused source from another car directly my 930's rear fuel pump.
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"

Last edited by 1986911; 04-01-2012 at 04:05 PM..
Old 04-01-2012, 04:03 PM
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1986911 you might want to rewire your fuel pump fuses like this in the below thread. I did and think it was time well spent. I didn't do it exactly as that thread shows, I did not drill holes in the top of fuse box to run wires to the battery.



930 Fuel Pump Fuse Overload - The Solution
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Old 04-01-2012, 04:35 PM
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Thanks Oil, I plan on doing that once I sort out my pump issue. I looks like a great mod.

I posted the sound of my front pump, I would like others to chime in to see if it sounds ok since my rear pump looks to be toast.

Maybe we should have a sticky or thread to use as a baseline with known correct 930 sights and sounds??

MVI_1805.MOV - YouTube

Ok guys let me know how it sounds.............
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"
Old 04-01-2012, 04:50 PM
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"Those are the numbers I needed. So stock rear is around 5 amps, Do you think mine is toast at pulling over 10 amps?"

The amperage draw from the stock pumps can change depending on how hard they are working - the resistance to flow and pressure they have to maintain.
The fuel pressure is controlled by the fuel pressure regulator in the CIS fuel head.

Stock rear pump can be drawing up to around 10 amps but mine is using less now because I put the bosch motorsport 044 pump in the front and it is bigger and moves more fuel than either of the stock fuel pumps so the amperage draw from my rear pump is about 4-5 amps lower than it used to be before I replaced the perfectly good stock front fuel pump that only had around 30,000 miles on it with the bigger 044 fuel pump.

There is a pressure relief valve inside bosch fuel pumps and if pressure goes too high it opens and fuel recirculates around inside the pump housing so it will never seize or overload the electric motor too much.

Can't diagnose yours over the internet but it may be time for a new one.
If you're using the stock single ceramic fuel pump fuse that feeds both fuel pump relays and pumps it's supposed to be a 25 amp fuse. They are blue in color and that single fuse is not enough for both fuel pumps. It was a really lousy electrical design from porsche. The whole fuel relay, safety relay, and rev limiter relay under the driver seat and chain of relay grounds is a design from hell. Best thing to do after 25 years is strip it all out and throw it in the trash.

If you do the double blade fuse modification don't drill holes in the top of the steel fuse box and run the wires through it. Thats an incredibly bad idea.. the bottom edge of the stamped out steel frame for the hood goes right down into that area and will press down on the wires and fuse holders every time you shut the hood. That will eventually chafe the wires insulation and cause a short circuit and fire about a foot away from the gas tank fill pipe and rubber hose that connects it.
Just crouch down and look at the bottom of the hood in that area above the fuse box as you close it and you will see what I'm saying.

There's plenty of room to safely run the wires for blade fuse holders out either side or the bottom of the fuse box. Then tie rap the wires safely into place if you want.
Old 04-01-2012, 05:20 PM
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My guess is somewhere around 10-12 amps. If the front pump is making a lot of noise, it's time for a replacement.
Old 04-01-2012, 05:41 PM
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Thanks for the response J.

My test rig has the regular 2 prong ato fuses. That rear pump blows them like nobody's business. Did you measure your fuel pump amp draw with the engine on or off with the relays jumped. From what I can tell it seems like on.

I am definitely going to order a new rear pump. I can't imagine a good pump pulling more than 15 amps. Can you listen to my front pump on my you tube clip above to see how it sounds? Never heard one so don't know if I should change that one as well. Its sounds as if it was OK but what do I know!


Thanks!
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"
Old 04-01-2012, 05:49 PM
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I measured the amperage draw by removing the blade fuses one at a time and touching the leads of the digital amp meter to the spade terminals in the blade fuse holder while the motor was off and the pumps were on.
It doesn't matter if the motor is running or not because the fuel pumps move and deliver alot more fuel than the fuel injection can use and the rest is returned to the fuel tank. With CIS the tiny fuel pressure regulator in the side of the fuel head does that. All return line type fuel pressure regulators big or small work that way.

I listened to your video and it sounds like your fuel pump is dry or the rollers are worn and and chattering as they spin and buzz in the fuel pump race they spin around in. It's not accurate to try and diagnose it by recorded sound like that because whatever you used to record it will have an effect on the sound quality. I'd have to hear it in person with my own ears when it's stone cold and again when it's been running for an hour or so to make a judgment.

I did notice there was no voltage arcing or sparking at all as you touched the wire to the pump terminals. Mine spark alot when you do that because of the current draw. It's as if there is no fuel in your pump and no load on the pump your testing. And the way it slows down kind of slowly and lazily when you removed the wire also makes it sound dry inside. Mine stop real fast when you remove power from them.
It's just too hard to say without hearing and doing that myself in person. I'm not going to say you need new fuel pumps because they are expensive and yours may be ok.
They don't last forever but the origonal Bosch fuel pumps made in Germany from 20+ years ago are the best quality and usually are good for around 100,000+ miles. The newer current day Czech Republic made bosch pumps are pretty good I think but I really doubt they are as well made as the old German made ones.

Have you removed and cleaned the round fine screen fuel filter in the bottom of the fuel tank and after that changed your fuel filter in the engine compartment with the correct Mahle fuel filter recently?
Have you hooked up a CIS fuel pressure gauge to check system and control pressure and are you sure the fuel supply and return lines are not clogged or pinched anywhere?

Also check to see that you're getting the full 12 volts to the pumps when the motor is off and around 13 volts to them while the motor is running with the headlights on at idle speed, and about 13.5 volts while the headlights are off.
Old 04-01-2012, 06:29 PM
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Thanks for all the tips J. I am going to order a new rear pump to replace the one that keeps cooking fuses. You have me thinking now about fuel level. I should have around half a tank in the car. If its reading correctly then once I change that rear pump, I am going to drive it around till its low then check the screen in the tank. As far as I know its never been cleaned. Then I will check for proper pressure and flow on that front pump.

Thanks again guys!
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"
Old 04-02-2012, 06:16 PM
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Looks like I figured out what was wrong with my car. I changed the fuel pump and thought it was done. I started the car without getting in it and watched with joy as the car warmed up and AFR's were as they should be. I sat inside to turn off the car and restart to see if anything would change. So far so good. I got out to close the bonnet and look one more time for any fuel leaks before heading out on a test run. As soon as I get out, afr's jump back up to 19's and car starts acting up. CRAP. I sit back inside and car goes back to normal. Long story short the large black plug under the driver's seat was loose.



I pulled it out, cleaned it with electrical connection cleaner and adjusted (bent) the tabs on the box where it plugs in. Now its nice and snug. I could pull it off with my hand!

Search is truly your friend, it planted the idea to check and wiggle all connections and relays while trouble shooting.

Well, I got some CIS gauges and a spare rear fuel pump out of it so not too bad.
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MG---1986 911 TARGA, SSI'S, STEVE WONG CHIP, M&K EXHAUST, ELEPHANT RACING GOODIES + TRU DESIGN CUSTOM FUCHS
1989 930 FACTORY SLANT NOSE -- RARLYL8 EXHAUST, K27 7200, TIAL 46MM, 0.9 BAR SPRING, GARRETSON INTERCOOLER , LEASK WUR, WEGO IV AFM AND NHS BOOST GAUGE.
2012 DODGE RAM 3500 LONGHORN 4X4 "EVERYTHING BUT THE KITCHEN SINK"

Last edited by 1986911; 04-16-2012 at 05:09 PM..
Old 04-16-2012, 05:06 PM
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my pumps have been loud for at least the last 20K miles. I can hear both from sitting in the car very easily. Some of the old 80's Volvo and BMW pumps were loud for the life of the car. Don't think that is an indication that they are bad. I'd prefer them to be quiet though!

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Old 04-16-2012, 05:45 PM
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