83 sc fuel pump diagnosis needed

Flagstaff_911SC · Flagstaff_911SC's Garage

Hi,
I have an '83 911sc and I think Im having possible fuel pump trouble or I'm not getting voltage to the pump. Should I read 12 volts at the fuel pump terminals? I am not reading any voltage, with the key turned on.

I have swapped the red fuel pump relay with the horn relay and the relay still worked, so the relay is fine.

Any help would be greatly appreciated.

Thanks.

Jim Sims · 07-20-2004, 10:56 AM

If your system is in OEM condition and working correctly there will not be voltage at the pump when the key is in the on (run) position and the engine is not running (safety system). If you lift up the air metering plate under the air filter in the air box you will open the air flow switch which should then apply voltage to the fuel pump when the key is in the on position. Jim

Superman · 07-20-2004, 11:43 AM

True, but be also aware that this will spray fuel into your cylinders. Therefore, do not leave the airflow sensor plate displaced for very long.

On a side note, if your engine is running, so is your fuel pump. Fuel pump problems result in bad running conditions fairly rarely, in my experience. In my experience, fuel pumps either run, or they don't. And finally, if your pump is getting old and tired, it will draw increased amperage. This will heat up the fuse and the fuel pump relay.

vash · vash's Garage

what about a jumper from terminal 30 and 87 (or 87a depending on year)? i think this bypasses the safety switch at the air sensor. use a fused link (20amp)

Rufblackbird · 07-20-2004, 01:26 PM

Quote:

Originally posted by Superman
In my experience, fuel pumps either run, or they don't.

Yeah...no kidding. Mine died suddenly and without warning.

Flagstaff_911SC · Flagstaff_911SC's Garage

My SC just spins over and I can use some starter fluid and the car will start but of-course will die fairly quick after that, so that was what led me to believe my fuel pump is bad.

Glad to hear I won't read any voltage at the fuel pump terminals with the ignition in the "on" (run) position. That had me concerned since I did not read any there.

I might try what vash mentioned about the jumper, but I am a little cautious when it comes to jumping across terminals. Any other suggestions to check out 1st before I try this?

Thanks for the help

cowtown · 07:52 AM

If you're comfortable with using starter fluid, you should definitely be able to try the method Jim suggests of lifting the air plate (with the ignition switched on but not cranking), and checking for voltage and sound at the pump. Running it for a second or two will not hurt anything.

vash · vash's Garage

mr flagstaff, jump it! that is the way you have to do it if you ever hook up the CIS tester gauges. it is step one, in my bosch instruction book. if you are nervous, couldnt you pull on of the injectors, turn the ignition on, and then lift the airsensor bar to get the pump to run? i love seeing a nice atomizing spray to convince me that all is well upstream of the injector. as far as flooding things, i wouldnt worry too much about it, you need to lift that bar to bleed the system. keep us posted, i am very curious.

Westy · 07-21-2004, 11:59 AM

Cliff, you're smart, too. I don't need the book 'cause I got you.

vash · vash's Garage

yup, i can cook too. wait until you try my new tomato sauce! new trick: dry heat!.

Westy · 07-21-2004, 12:26 PM

Bring it up. I got noodles n bread

enolam · 07-21-2004, 01:05 PM

What I used to do with an SC was just reach around the back and unplug the connector at the air meter. Then the fuel pump runs any time the key is on. It's a little tricky to plug it back in when you can't see it.

Flagstaff_911SC · Flagstaff_911SC's Garage

Thanks for the help guys I appreciate it. I'm going to try the suggestions mentioned by vlad and jim and hopefully I will find out if it is my fuel pump or if I am not getting voltage to the pump.

thanks again.

Flagstaff_911SC · Flagstaff_911SC's Garage

I checked the fuel pump terminals while I had another person lift up on the air-sensor bar in the airbox and I had voltage there at the terminals, so that elimanted the issue of the fuel pump not getting voltage.

I pulled my fuel filter (needed to replace it anyways) and checked to see if I could get any fuel out, but nothing.

As I mentioned earlier I could spray some starter fluid and get the car to run for a few seconds, so I believe the fuel pump is just bad. Any thing else to check to be sure or should I just replace it with a new fuel pump?

thanks for the help