OT: fuel injection experts, L-jetronic?
29-12-2006, 10:01 AM
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OT: fuel injection experts, L-jetronic?
Does anyone know much about Bosch L-Jetronic?
I'm having real difficulty on this 924S (same engine/management as 944) in getting the injectors to work. I have meticulously gone through various troubleshooting guides to get the fuel pump working and I now have a spark but the injectors are still not working - I have the fuel rail pulled so can see the injector tips.
It appears that they are not 'clicking' as they should. I have the correct fuel pressure at the fuel rail and both position and speed sensors on the flywheel are providing a good signal to the ECU (or DME as its called on this motronic system) as I have tested these with an osciliscope.
I find it hard to believe that all 4 injectors would be completely clogged even if it has stood for 3 years - and even if they were I'd expect them still to 'click' as they attempt to fire?
My problem is i dont know what to look for on the feed wires. I've checked a few basic voltages on the 2 pin injector plugs:
1 pin has 12v when ign is on but drops to 9.4 on cranking, the other has 9.93v with ign on and drops to around 6.5 when cranking. Thing is I've no idea what these should be - I assume one at least should be a pulse? Can I check this somehow on an osciliscope? I have also checked the resistance of each injector and they appear ok at 2 ohms.
Sorry for the off topic and essay! I'm running out of options and the 924 forum is pretty poor in response....
I'm having real difficulty on this 924S (same engine/management as 944) in getting the injectors to work. I have meticulously gone through various troubleshooting guides to get the fuel pump working and I now have a spark but the injectors are still not working - I have the fuel rail pulled so can see the injector tips.
It appears that they are not 'clicking' as they should. I have the correct fuel pressure at the fuel rail and both position and speed sensors on the flywheel are providing a good signal to the ECU (or DME as its called on this motronic system) as I have tested these with an osciliscope.
I find it hard to believe that all 4 injectors would be completely clogged even if it has stood for 3 years - and even if they were I'd expect them still to 'click' as they attempt to fire?
My problem is i dont know what to look for on the feed wires. I've checked a few basic voltages on the 2 pin injector plugs:
1 pin has 12v when ign is on but drops to 9.4 on cranking, the other has 9.93v with ign on and drops to around 6.5 when cranking. Thing is I've no idea what these should be - I assume one at least should be a pulse? Can I check this somehow on an osciliscope? I have also checked the resistance of each injector and they appear ok at 2 ohms.
Sorry for the off topic and essay! I'm running out of options and the 924 forum is pretty poor in response....
29-12-2006, 12:21 PM
#3
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Injectors are switched to earth at the ECU. They will have voltage at the injector and the ECU earths the return wire to open the injector. You should expect to see 10v/ms on cranking with a scope. You could always use a LED at the injector terminal (disconnected) and see if it flash's when cranking. Try the LED in 2 ways as they are pos/neg. If no flash, the injector driver in the ECU would be suspect, because you are getting a spark at the plugs. I would tend to believe the they operate on the same input signal. If the LED flashes, the replace injectors.
Try some of the US site's on Porsche, as they can have a lot of info, but be careful of the wiring dia, as they will be slightly different the euro models.
John
Try some of the US site's on Porsche, as they can have a lot of info, but be careful of the wiring dia, as they will be slightly different the euro models.
John
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