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Chris
Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 9872
Experience:  ASE and Chrysler Certified Master Tech
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1987 dodge truck: spark..the reference voltage..swich

Resolved Question:

1987 dodge truck 318 no spark. the reference voltage at the hall effect swich is .31
Submitted: 4 years ago.
Category: Dodge
Expert:  Chris replied 4 years ago.
Chat Conversation Started
Chris :

Hello and welcome to just answer. That is not enough. It should be more like 5 or 8 volts. Are you checking it with the hall effect switch disconnected or connected?

Expert:  Chris replied 4 years ago.
Chat Conversation Ended

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Expert:  Chris replied 4 years ago.

Get back to me when you get a chance.

 

Chris

Customer: replied 4 years ago.
the reference voltage mis .31 with it connected or disconnected
Expert:  Chris replied 4 years ago.

Ok, then there are a couple of things that may cause this. 1 another sensor that is shorted internally, or 2 a failed voltage regulator in the PCM. Do this: disconnect the map, tps, and the speed sensor one at a time and recheck the reference voltage at the hall effect switch. If the voltage comes back up after disconnecting a sensor, then that sensor is shorted and should be replaced. If the voltage does not come back up, then suspect a faulty PCM.

 

Chris

Customer: replied 4 years ago.
where is the map sensor and the speed sensor
Expert:  Chris replied 4 years ago.

I am sorry, I just realized that this truck does not have a map sensor so ignore that. Now the speed sensor is in line with the speedometer cable and should be around the left side of the engine compartment.

 

Chris

Customer: replied 4 years ago.
chris, I asume the PCM is the computer hanging on the left fender it was checked and they said it was good. there is no throttle position sensor and no map sensor and I found the speed sensor but disconnecting it does not do anything for the reference voltage
Expert:  Chris replied 4 years ago.

You may have a short in the reference voltage circuit between the PCM and the Hall effect switch. Try this next: disconnect the PCM's connector (yes it is on the left fender) and disconnect the connector at the Hall effect switch. Then use an ohm meter to see if that circuit is shorted to ground. Put one lead of the meter on the reference voltage terminal at the switch end, and the other lead to a good engine or chassis ground. There should be no continuity (no reading on the meter). If there is then you will need to find and repair this. While the PCM's connector is off, inspect the terminals for corrosion, damage, etc.

 

Chris

Customer: replied 4 years ago.
chris there is not a short in the circuit
Expert:  Chris replied 4 years ago.

Can you check continuity on the reference voltage circuit between the sensor and the PCM's connector? It should be the orange wire at the PCM connector.

 

Chris

Customer: replied 4 years ago.
chris i have been a mechanic for over 45 years. i checked the voltage at that pin a long time ago and it was the same as the other end but i checked continuity and they are hooked together.
Expert:  Chris replied 4 years ago.

You know what? I just realized that this truck does not have an actual Hall effect switch, but an old style pick up coil (2 wires correct?). Do this next. Measure the resistance of the pick up coil itself. It should be 150 to 900 ohms.

 

Chris

Customer: replied 4 years ago.
chris your right two wires i measured the voltage along time ago and it fluctuated but then the dodge dealership told me it was a hall effect switch and the voltage should be 7 volts. so thats how we got here. any way the coil measures 250 ohms. there is 12 volts at the terminals on the coil.
Expert:  Chris replied 4 years ago.

Ok that resistance appears ok. Try this next: disconnect the pickup coil connector, and with the ignition on. make and break connection on the pickup coil connector with a jumper wire and see if you can get the coil to spark by doing this.

 

Chris

Customer: replied 4 years ago.
chris no spark
Expert:  Chris replied 4 years ago.

Then that sounds like another bad ecm, unless you are missing a ground or battery / ignition feeds. Any blown fuses or fusible links?

 

Chris

Customer: replied 4 years ago.
chris there is 12 volts on the two plugs to the ecm two times on each one. i think the ecm is bad
Expert:  Chris replied 4 years ago.

It is starting to look like it huh?

 

Chris

Customer: replied 4 years ago.
chris can you tell me which terminals are suppose to have power and the ground ones
Expert:  Chris replied 4 years ago.

Sure The J1 Pink wire on the larger connector should have 12 volts all the time. The J2 dark blue wire on the smaller connector should have 12 volts only when the ignition is on. The ground will be J9 which is the black wire on the smaller connector.

 

Chris

Chris, Shop Foreman
Category: Dodge
Satisfied Customers: 9872
Experience: ASE and Chrysler Certified Master Tech
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