924Board.org

LeeXIX · Joined: 09 Feb 2006 Posts: 19 Location: Cleveland, Ohio

I just bought a '77 924 (build date 0f 9/76) and it has a strange problem. When it is first started it runs great....for about 15 to 20 minutes. Then I notice the tone of my fuel pump change and the idle drops down to about 300 rpm for about 15 seconds and then it quits. I can restart it easily and then it only runs for about 15 seconds the fuel pump tone changes and it drops to 300 rpm again and the same thing happens again. It doesn't matter if it is idling or at 1500 rpm or higher. It is always the same.
The guy I bought it off of has had two new fuel pumps replaced in it. The fuel pump relay fuse was blown. He replaced the fuse but not the relay. I have ordered a new one but am not sure if that will cure the problem.
I could use a few ideas so I am not wasting money on parts I don't need.
I am more familiar with air-cooled Porsches and VW's as well. So this is a new venture to me. I was a VW Porsche/Audi mechanic back when these cars came out (Yes, I'm over 50). But I first fell in love with Porsche when I took my first 911 (which had a pricetag of $13,000.00 new) thru a 25 mph onramp at 70 and the speedometer was still climbing. Now I own a 924 and I must admit; for a watercooled car it's great.
There are other issues I need to address as well like: should I take off the air pump and should I be using leaded gas since the car does not have a catalytic convertor on it. I just need a bit of feedback to let me know that I am doing the right thing.

Thanks
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I have a 924 (yellow) Porsche since I lost my 1971 914 in my divorce. She threw out everything except the shell of the body.

Ozzie · Posted: Sat Feb 11, 2006 2:29 pm Post subject:

sounds like the fuel pump relay is cutting out.
This could be a faulty relay or bad connection to the ign coil.
When starting the pump will run for a few seconds and then relies on the relay to keep going.
The relay will shut off the pump if faulty or it does not pick up a pulse from the coil.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Ozzie · Posted: Sat Feb 11, 2006 2:31 pm Post subject:

You can bypass the relay temporarily by jump wire in terminal 30 to 87 IIRC.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Smoothie · Posted: Sun Feb 12, 2006 1:43 am Post subject: Re: 924 Stalling problem

LeeXIX · Joined: 09 Feb 2006 Posts: 19 Location: Cleveland, Ohio

Thaks for the help. I thought that the fuel pump relay might be the problem. I ordered one from the nearest Porsche dealer and was told that the part is on national backorder and it would have to come from Germany.
I had a 91 VW Golf that was a California car and needed a throttle body that had to come from Germany as well. I guess I can wait.
But.....do you think that the bypass of running a wire from 30 to 87b (fused, of course) would allow me to drive it around. I hate to have to wait, but I do not want a pile of melted metal either.

Also, since this car came with no converter what are the odds that I should be using leaded gas in it? I can come with some lead substitutes so that is not really a problem. The reason I ask is I know that on the Bugs like the '66 I had, if you do not change the valve seats and use unleaded gas you will ruin the engine. I checked the gas filler neck and it looks as though it has the old style neck and not the newer type restrictive filler on it. But it also has a tab on the bottom of the neck that I am not sure about.

Thanks
_________________
I have a 924 (yellow) Porsche since I lost my 1971 914 in my divorce. She threw out everything except the shell of the body.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2745 Location: Sydney, Australia

you can drive with a bypass wire it's just a pain.

I'll probably get hammered for this but you can replace the fuel pump relay with a standard relay. That's what I did with mine after I blew the replacement relay (they cost over $100 down here). You could make up a couple of wires with spade connectors on one end to to wire the relay to the 30 and 87b connectors and then energise the relay from an ignition-switched wire (one which isn't disconnected when cranking). Your current diagram is your friend here.

Just remember that the without the real fuel relay you don't have the safety cut-out feature so no rolling the car and getting trapped inside.
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1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

macBdog · Posted: Thu Feb 16, 2006 4:11 pm Post subject:

I did this too. Supercheap auto $2 relay.
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1979 931 with a 350 chev
1973 911E with EFI

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

Porsche Dealers is not the best place to order relays from, mostly because they are the most expensive from them.

Buying a part from the Dealer gets you the longest warranty, but there are lots of places to get a replacement for much less.

Instead of waiting for one to be flown in from Germany, try contacting Performance Products in Van Nuys, CA or Mid-America in OH (formerly Tweeks), or www.stopshopanddrive.com All of those places should have the relay you need for less.

Paul · Posted: Fri Feb 17, 2006 10:55 am Post subject:

I'll have to do some research, but IIRC, the early cars did not use rpm to keep the fuel pump running, but rather used a switch at the air flow sensor.

I'd try running the car with the gas cap loose to see if the problem is related to the evaporative recovery system.

Also your fuel pickup might be getting clogged causing fuel starvation.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.