95 grand caravan fuel injectors wires

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  #1  
Old 06-16-06, 08:25 AM
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95 grand caravan fuel injectors wires

have a 3.8 motor, pulled wire off fuel inject still running rough.
before i change computer are there any ground wires and where
are they. checked the fuel inject wires for breaks. none. have had mice in engine compartment. did the whole tune up even change the coil box. thanks
 
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  #2  
Old 06-16-06, 01:20 PM
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why do you want to change the computer does it have injector pulse to the injector check with a noid light?
 
  #3  
Old 06-19-06, 06:24 AM
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one with no pulse one with very little the rest ok checked with noid light
 
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Old 06-19-06, 12:51 PM
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Check the outputs of the ECU before you replace it. get the pin out.
 
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Old 06-19-06, 01:37 PM
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this is where i get lost. do i need a special meter cause i heard you can blow the computer if u use the wrong meter. how do i test the ECU without blowing it?
 
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Old 06-19-06, 01:47 PM
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No you don't blow the computer using the wrong meter; analog or digital.

Plus a meter will do nothing in helping you to begin with. An oscilloscope will be the only useful way to check this, or bring it to a shop that can monitor injector signals. If you know what cylinder is doing it and you know you have good spark you can swap the injector with another cylinder and see if your missfire moves. You could have a stuck pintle or leaking injector.
 
  #7  
Old 06-19-06, 02:29 PM
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if you have tested the wires from pcm to injector and they are good and you have power out to the injector but no injector pulse then I would suspect bad pcm and would also check the injectors as one may be shorted that would of damaged the pcm driver circuit to begin with.
 
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Old 06-19-06, 02:44 PM
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Originally Posted by bejay
you have power out to the injector but no injector pulse then I would suspect bad pcm and would also check the injectors as one may be shorted that would of damaged the pcm driver circuit to begin with.
I am having trouble under standing a few things here.

Fyi when he says driver he means mosfet which is basically just an electronic switch that can respond very fast.

you have power out to the injector but no injector pulse

I am not following this statement as a response for bad pcm but as a response for a bad injector. If you have power to the injector, and the injector does nothing then the pcm is working. If you have no power to the injector then the pcm would not be working or you could have a bad connection.

I get it now he means the injector is tied high to battery voltage.


wether or not the pcm would be damaged by a short depends on the on the design of the pcm for the most part ecm's are pretty bullet proof from shorts especially obd2 series. In the case of the injector driver(mosfet), it depends on the algorithm used to switch the driver.

This would show up as the noid light staying on constantly and not flashing when motor is running.

The way you are describing your noid light test makes me lean more towards bad/corroded connection . I would check for shorts on the wires by unpluggin the ecu and then use a multimeter by putting one probe in the connector for the injector and measure to the battery terminals with car off and see if your resistance drops. You should get a nothing to either terminal and then from the other pin you should get nothing but an open either.

This is because the injectors are low side driven, and the power is supplied through a relay so there should be no connection to chassis or power when the vehicle is off.

Also if there is a short you could damaging the other ecu to
 

Last edited by scalar; 06-19-06 at 02:55 PM.
  #9  
Old 06-19-06, 06:44 PM
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i have no power to one injector and very little power to the one next to it, the rest are fine. are there any grounds that the mice could have gottten? i will try the meter, but what do i set it on. this part i dont understand You should get a nothing to either terminal and then from the other pin you should get nothing but an open either.
been out of work for five months cant afford to bring to a shop. any and all help would be grateful. thanks
 
  #10  
Old 06-19-06, 06:55 PM
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they should both be open
 
  #11  
Old 06-20-06, 02:59 AM
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yes when I was reffering to power it was positive battery voltage at one wire at each injector it gets power through the asd relay and will have power as long as a crank signal is being received by the pcm usually while the engine is running or while cranking over. if you dont have near battery voltage at one or 2 injectors with the engine running or cranking over then you have a wiring problem possibly broken wire or partially broken.
you said you checked the injector wires you should ohm them with the pcm and injector unplugged a good wire will be under 10 ohms resistance but generally the injector is what can cause the pcm circuit to go bad suggest checking each injector resistance and compare them, to low of resistance could cause the pcm to fail.
autozone has a wiring diagram for your van might be of some help to you.
http://www.autozone.com/servlet/UiBr...3d8010cca4.jsp
 
  #12  
Old 06-21-06, 11:03 AM
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i ran ohm meter from the injector all the way to the pcm plug.
there was power through the line. is there any thing else i shoudl check b4 i buy a new pcm?
 
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