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Solenoids 101: What they do and how to diagnose them

by Bob O'Neill and Bob Lincoln

In Chrysler cars, a solenoid is a plunger valve which is opened and closed electrically. When power is applied to the solenoid, a magnetic coil is energized which moves the plunger, opening a valve to redirect or apply vacuum or boost.

The solenoids on the Chrysler cars have three vacuum hose ports. There is one which is the vacuum or boost source port, and one which is open when no voltage is applied. The other port is closed when no voltage is applied; vacuum or boost is redirected to this port when voltage is applied.

When voltage is applied to the solenoid coil, it energizes an electromagnet which then pulls on the valve piston to direct air from the source to the 'other port.' Sometimes the ports are connected where vacuum or boost is routed through the normally closed port and other times it's through the normally open port. So the 'other port' is, well, the other port.

The port which doesn't have a hose connected has a foam block over it. This is to filter dust and dirt from getting into the solenoid. Many times these foam filters fall away to nothing due to age. If the port which doesn't have a hose connect also doesn't have a foam filter, replace the filter as these filters should always be attached. These filters could be made from open cell foam and cam be made from any dense form which air can flow through. If a 'new' foam filter attached to a drinking straw can flow air, it can be used. Any filter which will not flow air should not be used.

Where replacement solenoids can be found

The solenoids used on the Chrysler cars in the '80s and early '90s were very robust, so finding a replacement solenoid should as easy as a visit to the local pick-n-pull junk yard. MAP solenoids can be found on the firewall and other solenoids can be found on the passenger side inner fender. These are also available from the auto parts store and the dealer. Be sure to get the right type solenoid. Some have only two ports. These are basically on/off valves which will either close or open based on type.

Diagnosing and Repairing Solenoids

The Chrysler solenoids are sturdy and rarely fail, so most of the time a 'solenoid' problem is probably a wiring issue. But the solenoid which controls the wastegate for turbo applications sees a lot more action then the others. This solenoid opens and closes many times per second when the engine is producing boost. If there is no air flow because dust and dirt has clogged it, actuation can fail. Remove the solenoid and test for flow with voltage and without. The following steps can help decide if the solenoid has failed or is not functioning beyond repair.

  1. Remove the solenoid from the car.
  2. Test for air flow through the common port. Air should flow through the open port but not flow through the closed port.
  3. Close the open port with your finger and test for air flow again. There should be no air flow through either port.
  4. Test the solenoid for electrical function. Put 12 volts DC across the terminals and listen for a click. You can (very carefully) use jumpers and the car battery.
  5. Test for air flow again with the voltage applied; air should now flow through the previously closed port.
  6. The solenoid is OK if it passes the tests above.
  7. If the air flow test failed, the solenoid may be clogged. If the solenoid did not click when voltage was applied, the coil which generates the magnetic field may be open. If either of these tests fails replace the solenoid or try to clear the clog.
  8. To clear the clog, (carefully) flush the open port with solvent such as lighter fluid or throttle body cleaner. Once the solvent has dried retest with step #4. If the flush fails replace the solenoid.

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