starting problem need help

pgs · 11-11-2001, 02:42 PM

I can not figure this out. my car will not start on the first turn but it will start on the second. have spent a lot of money and time on this. best I can figure out is it has something to do with my fuse block wiring. fuel pump fuse slot is not wired. fuel pump relay pin 30 is not hot while car is off is it suppose to be. someone told me the fuel pump needs to energized. what does that mean. is their some way to test this. also the previous owner did some creative wiring on the fuse block. can not figure this out based on regular wiring diagrams or buy looking at other 1978 911sc. please help.

Doug Zielke · 11-11-2001, 02:46 PM

Search the Pelican Parts technical site for the wiring diagram for your car, and see if that helps.

Jim Sims · 11-11-2001, 04:58 PM

Looking at an SC wiring diagram indicates that pin 30 of the fuel pump relay is not hot with the ignition key off. I suspect your problem is more likely a defective fuel pump check valve. A bad check valve allows the fuel pressure to bleed down and the pressure must be restablished by the pump and this takes a moment. Hence the starting on the second try.

Jim

pgs · 11-11-2001, 05:08 PM

had a fuel pressure check done everything was fine. i just checked my fuel pump relay with the power on and pin 87a and 86 are the only ones getting power. what should i do now.

Jim Sims · 11-11-2001, 06:20 PM

87a and 86 are the only pins which should show power with the key on and the engine not running. When you engage the starter an air flow contact switch closes (due to air being inducted into the engine by the moving pistions) and completes the circuit to the fuel pump relay coil and this will energize pin 30 which feeds power to the fuel pump. This air flow contact switch may also be faulty. However does your fuel system hold pressure after the pump has stopped running? Jim

pgs · 11-11-2001, 06:41 PM

when it is cold like in the morning it might take two or three times to start. but you can drive it for 2 or 3 hours turn it off and first time you try to start it will turn over and over and not start second time it starts. i was told the fuel pump was not getting energized i have been told starter, even fuel filter i have a new one now, i just know one thing the fuse block was rewired because thier are no wires or a fuse for the fuel pump slot on the fuse block

stormcrow · stormcrow's Garage

When you turn the key to the on position where the gauges will energize (not the start position), the fuel pump should run for a couple seconds and shut off via the pressure switch. When you turn the ignition to the start position, the starter engages and the engine fires up.

Check to see if your fuel pump is running when you turn your key to the on position. Also, there is the cold start selonoid that helps start the engine when it is cold. This energizes momentarily when the switch is turned to the start position. This could also be causing your starting problem. You may want to check it out.

Steve

Jim Sims · 11-11-2001, 07:29 PM

Terminal 87a of the fuel pump relay should be fed from fuse position 16 (a 25 amp fuse); terminal 86 of the fuel pump relay is fed by a jumper from terminal 87a. From your description of the starting problem is still appears you may have a faulty fuel pump check valve. A pressure gage should be connected into the system downstream of the fuel pump to monitor the pressure after shutting down the engine; if it doesn't hold pressure that may be your problem. Jim