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The Mighty Pieholio
 
Bob Kontak's Avatar
 
Join Date: Nov 2007
Location: North Canton, Ohio
Posts: 13,106
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Fuel pump down

After backing into the problem, my pals 89 930 has a fuel pump that will shut off intermittently. I think we have fixed this but we wish to run some data past the group.

Recent symptoms over last month, car warms, runs a little rough and emits black-ish, maybe a speck blu-ish smoke but does not stink like either oil or rich.

Today, both of in car, running an errand, car warms up fully - 85 outside. . Grocery store stop for 1/2 hour, car in sun.

Leave grocery store, within a mile or two, car hiccups and dies. Farted around poking stuff and looking at engine. A couple of minor attempts at firing from residual pressure then nothing.

Finally my pal asks "What about them fuel pump relays I got in the glove box?"

Replace both relays and we see the #6 fuse is cooked (Pump one and Pump 2) . Replace fuse. Runs like a champ for two hours. No smoke, no rough running, nuttin.

Question(s):

When one fuel pump goes bad what causes the smoke? Is it unburnt "stuff" because of a lean mixture?

What would cause the fuse to blow given the car ran "fine" recently with one fuel pump taking a nap. (we did find inconsistencies on the outside windings of on old relay - hoping this was the root cause)
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1981 911SC Targa
Old 06-15-2014, 02:00 PM
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Hi Bob, strange seeing you post in these here parts, my friend!

* The smoking when only one pump question; one pump means not enough fuel pressure at the fuel head = rich mixture during non-boosted operation . . . lower fuel pressure means that the 930 CIS metering arm piston has less hydraulic resistance, and thus, the arm moves downward (opposite movement to the non-turbo CIS variants) too easily (going rich). Under boost with one fuel pump = too lean, causing major misfiring and little to no acceleration.

* The blown fuses are a common problem, and basically, Porsche did a very poor job of designing the wiring circuit for the dual pumps (did not provide adequately for the amperage demands of the dual pumps). The following thread is an excellent fix for the problem -

930 Fuel Pump Fuse Overload - The Solution

I hope you are having a good day and that your daughter hasn't put any more scratches on yer purdy Targay, and tell her that Slipknot rulezzz!!!

Last edited by Ronnie's.930; 06-15-2014 at 03:03 PM..
Old 06-15-2014, 02:56 PM
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The Mighty Pieholio
 
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Quote:
Originally Posted by Ronnie's.930 View Post
Hi Bob, strange seeing you post in these here parts, my friend!
Thanks Ronnie. My pal says he understands what you are saying.

He also knows who you are and gives you a thumbs up. He is a silent member here but is more active on Rennlist with another car he has.

April says, "I like Ronnie. I am not so sure about Tim". LOL.

All I know is the one time I drove his 930 in anger, I peed my pants. He says, "Jesus, I wish I had vinyl seats. Really?"

Last time I drove it.
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Old 06-15-2014, 03:19 PM
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Yes i rewired my fuel pumps like the above link Ronnie posted. My single fuse would get too hot for my liking. Now that i have the two fuses when i check them after a hard drive they are warm to somewhat hot. The old one fuse system and that fuse would be very hot to the touch.
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Old 06-15-2014, 03:31 PM
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Quote:
Originally Posted by Bob Kontak View Post
He also knows who you are and gives you a thumbs up.
Cool, but just so's yer friend doesn't try to give me his "thumbs up" somewhere's errrr, inappropriate!!!! (no homo!)


Quote:
Originally Posted by Bob Kontak View Post
April says, "I like Ronnie. I am not so sure about Tim". LOL
I was fairly certain that April was a fine judge of character, and now I know for certain! Besides, how can a woman with any sense not be cautious of a guy who's hound sticks his nose into every nook and cranny it comes across (and farts a lot, too)!?!?

Quote:
Originally Posted by Bob Kontak View Post
All I know is the one time I drove his 930 in anger, I peed my pants. He says, "Jesus, I wish I had vinyl seats. Really?"

Last time I drove it.
Ha ha, yep they are quite good at triggering involuntary muscle activity in both the bladder and anus from time to time!!!!

Last edited by Ronnie's.930; 06-15-2014 at 03:46 PM..
Old 06-15-2014, 03:43 PM
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i wired mine a little differently.

if you cut the wire between the 2 relays closer to the relay, there is enough wire to run it to another fuse. i dont have fog lights so i ran the HOT wire to pin 30 of the relay to the fog light fuse. then ran a red wire from the top(?) of the supply voltage of the other fuel pump fuse to the the fog light fuse. that put the 2 pumps on there own fuses but kept the wiring looking original.

just be careful which wire and which relay you cut the wire at.
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Old 06-16-2014, 05:25 AM
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The Mighty Pieholio
 
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Join Date: Nov 2007
Location: North Canton, Ohio
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Quote:
Originally Posted by Ronnie's.930 View Post
how can a woman with any sense not be cautious of a guy who's hound sticks his nose into every nook and cranny it comes across
Dogs sniff. It's the law.

Quote:
Originally Posted by T77911S View Post
that put the 2 pumps on there own fuses but kept the wiring looking original.
This sounds like a good option if problem returns.

Not enough time with driving/normal operation to see if the problem returns. All that was changed out were the two relays (and the single fuse). We all know relays are a common problem. Maybe he hit the jackpot and it was just a failed relay? Mind you, the relays were installed after 1/2 hour of some serious (both of us) staring at the engine. Cooling of stuff? Brand new full tank of gas? Minutes before crapping out, filled tank with fresh petrol, "original" gas was at least six months old at 1/8th-ish tank.

New gas, new relays, at least 90 minutes of happy operation.
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Old 06-16-2014, 07:09 PM
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