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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
Okay the way I understand it the Injectors get 12 volts constant from the ASD relay and the injector fires on the ground interruption.
I tested mine with a multimeter and i'm getting like 10 volts on each. The injectors open, but are they opening or (closing) correctly with weak voltage?
Correctly? No. Well enough to work? Maybe. There's a bad spot in either the wire or at a splice that will eventually get bad enough that the engine won't run. And just for correctness, the injector fires when the PCM grounds the injector, not interruption...
I tested mine with a multimeter and i'm getting like 10 volts on each.
How are you testing them? Are you doing injector to ground? Or the two leads to the injector while running? I think if you're doing the latter and your multimeter isn't measuring peak voltage then it won't be accurate.
How are you testing them? Are you doing injector to ground? Or the two leads to the injector while running? I think if you're doing the latter and your multimeter isn't measuring peak voltage then it won't be accurate.
I'm touching black lead to neg battery terminal and red to 12v line on injector plug while cranking.
Correctly? No. Well enough to work? Maybe. There's a bad spot in either the wire or at a splice that will eventually get bad enough that the engine won't run. And just for correctness, the injector fires when the PCM grounds the injector, not interruption...
cranking. Appreciate it. For correctness sake when the pcm grounds the injector it is interrupting the 12v circuit. 😷
Typically it is considered "completing" the circuit...
Plus, it's not a perfect ground. The typical mosfet driver in the PCM has around 0.1 ohms resistance when "on", so you'll see about 1/2-volt drop across the driver even when it is "grounding" the injector circuit.
An injector is like a solenoid - it's either open or closed. If you add power (9 volts will do) and hear a click, they are working. Your PMI dictates the timing and duration of an injector's open position. Usually. cleaning the muck out of the inlet end and spraying carb cleaner through them will return them to health. Measure the resistance between the injector's contacts - they should all measure the same - if the don't replace the odd one
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Originally Posted by Sean Tucker
For correctness sake when the pcm grounds the injector it is interrupting the 12v circuit. 😷
No, it is not. It does not touch the 12v circuit, other than telling the ASD relay to engage. It completes the ground circuit, and the voltage drop across the PCM will not alter the supply voltage measurement at all, the way he is measuring it.
10-25-2021, 02:03 PM
less than 12 volts at fuel injectors
