Thread: Further to my car not going

Bob, It may be that your fuel pump is dying or your relay is not working as intended.

When you turn the ignition to "on" you should hear the pump start for about 3 seconds then a click as the fuel is turned off. AFAIR on the old L jets the relay has the timer in it. In a 3.9 the ECU controls the timer. So if it does not do it you may need a new relay.

The fuel then resumes as the engine starts. This is controlled by the flapper lifting as air passes through. You can check by having the ign on and lifting the flapper a little and see if you hear the pump start. BTW my memory of this is from installing an early "federal" system to my old 2 door but I am pretty sure it applies to all flappers.

The other thing to check is the inertia switch, which AFAIK is under the passenger seat. If the inertia switch is "up" then fuel is cut off. Maybe bridge it to see if it is the problem.

It also may be that the pump is just old and tired. My pump was noticably slower to prime the injection and sometimes took 2 goes. You can hear a change in pitch in an old pump when the rail is pressurised. A new Bosch pump from a Commodore will fix it, so see the project write up.
Regards Philip A

Originally Posted by PhilipA

Bob, It may be that your fuel pump is dying or your relay is not working as intended.

When you turn the ignition to "on" you should hear the pump start for about 3 seconds then a click as the fuel is turned off. AFAIR on the old L jets the relay has the timer in it. In a 3.9 the ECU controls the timer. So if it does not do it you may need a new relay.

The fuel then resumes as the engine starts. This is controlled by the flapper lifting as air passes through. You can check by having the ign on and lifting the flapper a little and see if you hear the pump start. BTW my memory of this is from installing an early "federal" system to my old 2 door but I am pretty sure it applies to all flappers.

The other thing to check is the inertia switch, which AFAIK is under the passenger seat. If the inertia switch is "up" then fuel is cut off. Maybe bridge it to see if it is the problem.

It also may be that the pump is just old and tired. My pump was noticably slower to prime the injection and sometimes took 2 goes. You can hear a change in pitch in an old pump when the rail is pressurised. A new Bosch pump from a Commodore will fix it, so see the project write up.
Regards Philip A

Hi Phillip, Cant find the inertia switch but found an ordinary toggle switch under the passengers seat and what looks like another computer there also. With the toggle switch in one position , will start and run good [ with the pump hotwired] but with the switch in the other position she wont start. This is just as an aside, though, as whatever the switch does is not affected by hotwireing the fuel pump. I believe that the pump is OK as it drives good with the pump hotwired. The problem seems to be that with the pump plugged into the normal wiring, the motor tries to start but just not making it.

So somewhere between the ign and the pump is not working as it should. A lot to check out, though, especially as I dont know what Im doing or what to check. Bob

Well, all you have to do is be thorough and systematic.

Start at the fuel pump and put a multimeter from positive to earth set at 12vDC, and see what is there. Then back to the next point , say the fuel relay. You measure power in and out. If you have power to the fuel relay but no power out then you have the problem. Maybe borrow a friend's and try it.

BTW if there is a toggle switch it sounds like a home made immobiliser. These are often the cause of problems so check the connections to it and where it joins the fuel pump wires.

Tell me what you hear when you turn on the ignition as I detailed above. That will give a clue as to the relay.

Lift the flap as I said and tell us whether the pump starts.

You have to help us to help you.
Regards Philip A

Originally Posted by PhilipA

Well, all you have to do is be thorough and systematic.

Start at the fuel pump and put a multimeter from positive to earth set at 12vDC, and see what is there. Then back to the next point , say the fuel relay. You measure power in and out. If you have power to the fuel relay but no power out then you have the problem. Maybe borrow a friend's and try it.

BTW if there is a toggle switch it sounds like a home made immobiliser. These are often the cause of problems so check the connections to it and where it joins the fuel pump wires.

Tell me what you hear when you turn on the ignition as I detailed above. That will give a clue as to the relay.

Lift the flap as I said and tell us whether the pump starts.

You have to help us to help you.
Regards Philip A

The wireing from the toggle switch goes over to the computer under the drivers seat. Once the car is running, you can switch the switch over, and no change to motor, it just keeps running good. Fuel pump runs fast at first [ maybe 1 sec ] then slows as pressure is there. Can also here the fuel being sent back to the tank via the return line. Changed relays and no difference. Bob

my money says dodgy fuel pump relay.

Originally Posted by Blknight.aus

my money says dodgy fuel pump relay.

Yea, thats what i'm thinking/hoping as it will be an easy and cheap fix. Will find out tomorrow for sure. Will post the answer/solution tomorrow. Thanks to all. Bob

G`day Bob ,

you won`t find an inertia switch and your Guru should be able to tell you about the common fault with the pump wiring ( at the pump ) may not be the problem though .

Cheers

In the 1st thread Car not going no more You said the fuel pump was flowing So It's pumping on start?