I have a friend who is having a problem with his Porsche 928S4. Basically, we have narrowed the problem down to the injectors not firing. This car uses the LH Jetronic, and the EZK ignition controller. Here are some tests we performed:
#1
Made sure that when the LH relay is on, injectors recieve a constant 12v
#2
Used that 12v source from the injector harness to sucessfuly fire an injector (by touching the other terminal of the injector to ground)
#3
On a 928S, i used the frequency function of my multimeter to determine the frequency of the injectors opening/closing. While my car is running, i recieved a 14. This number changes with RPM (makes sense). On the broken S4, the injector receives a frequency of 5 while the engine is cranking (probably 5 because the RPMs are very low while cranking)
#4
Verified that we reiceve spark. This is however irrelevant because the injectors are NOT firing.
We have performed other tests (all relays/fuses), but I believe the results above are pretty important. It appears as though one of 2 things is happening:
#1
The LH jetronic is not even trying to fire the injectors
#2
The LH jetronic is trying to fire the injectors, but a short in the wiring is screwing things up (We performed some tests to attempt to disprove this, and while it may be a factor, the possibility is slim)
Now, a couple questions:
#1
The injectors fire in batch mode. Does the LH Jetronic require some form of syncronization signal from the EZK to know WHICH side of the engine to open injectors for?
#2
Why did I receive a frequency of 5 when I checked the injectors? Does that mean that the LH is actually trying to fire the injectors? It seems like it... doesn't it?
Many thanks in advance!
#1
Made sure that when the LH relay is on, injectors recieve a constant 12v
#2
Used that 12v source from the injector harness to sucessfuly fire an injector (by touching the other terminal of the injector to ground)
#3
On a 928S, i used the frequency function of my multimeter to determine the frequency of the injectors opening/closing. While my car is running, i recieved a 14. This number changes with RPM (makes sense). On the broken S4, the injector receives a frequency of 5 while the engine is cranking (probably 5 because the RPMs are very low while cranking)
#4
Verified that we reiceve spark. This is however irrelevant because the injectors are NOT firing.
We have performed other tests (all relays/fuses), but I believe the results above are pretty important. It appears as though one of 2 things is happening:
#1
The LH jetronic is not even trying to fire the injectors
#2
The LH jetronic is trying to fire the injectors, but a short in the wiring is screwing things up (We performed some tests to attempt to disprove this, and while it may be a factor, the possibility is slim)
Now, a couple questions:
#1
The injectors fire in batch mode. Does the LH Jetronic require some form of syncronization signal from the EZK to know WHICH side of the engine to open injectors for?
#2
Why did I receive a frequency of 5 when I checked the injectors? Does that mean that the LH is actually trying to fire the injectors? It seems like it... doesn't it?
Many thanks in advance!