924Board.org

bureau13 · Joined: 07 Sep 2017 Posts: 495 Location: South Florida

So basically, I was almost home, when I pulled up to a stop sign and the car died, dash warning lights on etc. I thought maybe I somehow just stalled it. Started it back up again, drove a little further, then it started sputtering and died again. Started it up again, very sputtery but got a little momentum and coasted most of the way home, pushed it up to the curb and parked it. Won't start at all now (it cranks, just won't catch). During the time when it was running rough, it gave a couple pretty loud backfires.

Any thoughts? I'm wondering if I have a fuel issue...one of the pumps maybe?
_________________
1982 931
1986.5 Silver 928S
2008 Volvo XC90 (Daily)

Past lives (I miss them all):
2007 Hummer H3 (Timing chain guide failure)
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

bureau13 · Joined: 07 Sep 2017 Posts: 495 Location: South Florida

Quick question about fuel pump behavior in this car: If I put the key in and turn it on (but not all the way to crank it) I hear the fuel pump (or something) hum briefly...maybe a second...and then stop. Is that correct? Under normal circumstances should it do that? Or should it keep running?
_________________
1982 931
1986.5 Silver 928S
2008 Volvo XC90 (Daily)

Past lives (I miss them all):
2007 Hummer H3 (Timing chain guide failure)
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

bureau13 · Joined: 07 Sep 2017 Posts: 495 Location: South Florida

I jumpered the relay (that relay box is NOT positioned for convenient access!) and both pumps appear to be running. In fact, it then started, and I moved it to my driveway.

At which time I noticed something else. Well, I noticed it before, but I'm dumb and it didn't occur to me. My fuel light was on, but the gauge was reading a quarter tank. I had been assuming the light was just coming on too early, because the gauge generally seems to function properly. Is there some sort of sensor that shuts off the fuel pump if it detects a low fuel situation? Not sure what the point of that would be, but given that it won't start with the relay (although the fuel pump stops and starts with key, which seems to be correct) but will with the jumper tells me that's the problem, or it's the relay somehow...like it briefly will connect and then can't hold it?

I'm going to order another relay just in case.
_________________
1982 931
1986.5 Silver 928S
2008 Volvo XC90 (Daily)

Past lives (I miss them all):
2007 Hummer H3 (Timing chain guide failure)
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

Overboost switch possibly... The brown wire I think going to the pressure switch on your intake just before your TB, ground that wire to the chassis, test that pressure switch for good ground on its contact..

I think that is the most likely, could also be that relays fault, or the tack signal to the relay..

Buzzing.. You sure you are talking about the pumps or the frequency valve? under the hood?
IIRC the freq valve will die along with the fuel pump when fuel pump power gets killed by the overboost switch, and tack signal, or relay fault, or bad grounds..
_________________
80 Turbo - Slightly Modified

Fifty50Plus · Posted: Mon Apr 09, 2018 4:47 am Post subject:

Before you go crazy chasing fuel pump cut off wiring, throw a few gallons into the tank. I'd trust the tank empty light just slightly more than the fuel gauge.
Sometimes the simple solution is the answer.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

gerben1986 · Joined: 13 Mar 2008 Posts: 232 Location: The Netherlands

Also check the ignition coil, I also have had the experience that the car died because the ignition coil was getting too hot, could restart and drive another 10 meters. But then the car quited and a couple of hours later it started again...
_________________
911SC - 1980

bureau13 · Joined: 07 Sep 2017 Posts: 495 Location: South Florida

Fifty50Plus wins the prize! I knew it wasn't the overboost switch, since that is already disconnected and the wire grounded. The buzzing to which I referred was from the back, the fuel pumps. I jumpered the relay and felt both the external pump and the tank near the bottom, both were vibrating a bit like the pump was working.

The gauge fooled me because I've seen it show almost empty, after the light had been on for a while, but I guess it's not that precise. And I'm still not really sure why jumpering the relay allowed it to start and run...but I added fuel and put the relay back in, and it seemed to run fine. I guess I'll have to keep an eye on it, but it seems I just need to trust that when the light tells me to get gas, I should do that.