Major Problem Need help fast

[924Sracer]

I'm having problems with my 87 924s it will start but dies after a few seconds the injectors stop firing and the fuel pump stops, but if you unplug one injector any injector it runs. It sounds to me like the DME is bad. What do you guys think?

Jason

[924Sracer]

how would that explain it running on three injectors but not on all four

[Zero10]

Because when the fuel pressure goes up, it takes more current to fire the injectors. Eventually the current required gets high enough that the DME can't supply it. The injectors are fired in pairs, so if you unplug one, that one pair can fire, usually lowering the fuel pressure enough to allow the others to fire too.

[924Sracer]

Thank you so much for your explination that makes complete sence. I'll let you guys know how it turns out.

Jason

[Makis]

Originally posted by Zero10
Because when the fuel pressure goes up, it takes more current to fire the injectors. Eventually the current required gets high enough that the DME can't supply it. The injectors are fired in pairs, so if you unplug one, that one pair can fire, usually lowering the fuel pressure enough to allow the others to fire too.

They may be wired in pairs but I think they are fired at the same time, so removing one injector will reduce the load to the DME by 25%.

I still think the DME should handle any small extra load that may be caused by excess fuel pressure. I would check all the wiring before condemning the DME.

Probably a faulty ground which when loaded with 4 injectors in parallel will cause less voltage to go to the injectors and more to the faulty ground connection. If you remove one injector the voltage to the other three increases while the voltage to the faulty ground decreases causing the 3 injector to appear to work normally.

[Zero10]

I'm not condemning the DME, let me make that clear first. That's a very expensive little box to change unnecessarily. I'm pointing my finger at the Fuel Pressure Regulator. First, check the vacuum lines to it. If they are disconnected, it will cause high fuel pressure (although it shouldn't be that high). If they are disconnected, try hooking them back up. You need a fuel pressure gauge to accurately diagnose this problem. If you can't find one that will fit the end of the fuel rail, you will need to drill a spare end cap to accept a normal fuel pressure gauge.

I don't believe all 4 are fired each time. I think they are fired in pairs. I believe the injectors are wired in pairs, in paralell. That's why disconnecting one works, if they were in series, the pair wouldn't fire, and it wouldn't help anything. If all 4 were to be fired at the same time, they would all be wired in paralell, from the same place.

[Zero10]

*sigh* those crazy germans.... very counter-intuitive.
I guess I'm wrong on this one =)
Although, it does explain why it doesn't matter which one you unplug.

just wondering if you've fixed the problem yet. it turns out that my 944 is having the same problems right now. When I unplugged one injector the car would continue to run instead of before when it just ran for 30 secs. Let me know what fixed it. thanks

[SoCal Driver]

Originally posted by Jameson
just wondering if you've fixed the problem yet. it turns out that my 944 is having the same problems right now. When I unplugged one injector the car would continue to run instead of before when it just ran for 30 secs. Let me know what fixed it. thanks

How long before you can restart the car? Does this happen again right after you restart it?

How long before you can restart the car? Does this happen again right after you restart it?

I have to wait 1-2 minutes until I can start the car again and with all 4 injectors in, the car will only run for around 30 seconds until it just dies. With an injector pulled, it runs rough, and will keep running rough.

[DannoXYZ]

Put a fuel-pressure gauge onto the end of the rail and measure your fuel-pressure. Too much pressure locks up the injectors.