Feedback carburetor question

I have an 87 Dakota that uses the Holley 6280 feedback carburetor.

Recently the warm idle speed has been inconsistent. It switches back and forth between 2 distinct idle speeds. There is no in between, either too fast or too slow. When slowing down or stopping, the engine will stall if it is idling in the "too slow" mode. If in the "too fast" mode, it will jump off the line when I release the brake.

After researching the symptoms, I found that the duty-cycle solenoid in this carburetor alternately leans and enriches the idle mixture, depending on a signal that originates with the oxygen sensor. I disconnected the solenoid and the problem vanished.

Since the problem does not occur until after the engine warms up, likely culprits that I can think of include the engine temperature sensor that informs the Spark Control Module (SCM) that the engine has warmed up, the oxygen sensor or the SCM itself.

I checked the engine temperature sensor and the resistance varied between about

1000 ohms when fully warmed up to about 6000 ohms when cold. The Haynes manual does not spec the range of values for this component so I don't know if it is operating within the correct range, but it does change with the temperature.

I have not been able to discern a pattern to the change in idle speed. It appears to be completely erratic.

Does anyone here have any experience with this condition and, if so, what suggestions do you have for isolating the source of this problem?

Thanks, Jack

Reply to
Jack
Loading thread data ...

these can be tested. auto parts stores sometimes have testers. on the printout of one I had tested it shows tests for Crank-rpm, Low-rpm, Idle-rpm, and High-rpm. a parts store tested mine for free.

formatting link
is the website of a manufacturer of testers

--

------------------------------------------------------------------------------ William R Watt National Capital FreeNet Ottawa's free community network homepage:

formatting link
warning: non-freenet email must have "notspam" in subject or it's returned

Reply to
William R. Watt

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.