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89 chevy engine loping

Discussion in 'Truck & Equipment Repair' started by wiseguy479, Feb 11, 2010.

  1. wiseguy479

    wiseguy479 Junior Member
    Messages: 10

    I have a 89 chevy c1500 silverado. I tuned it up changed the oxygen sensor changed the nock sensor changed the egr. It still is loping and the services engine soon light comes on at speeds over 40mph for long distances. So i put it back on the computer it is coming back egr now what?
  2. jb1390

    jb1390 Senior Member
    Messages: 710

    It is extremely common for the egr valve port to become clogged with carbon. Did you clean the passage when you replaced the valve?

    A plugged EGR will act like a vacuum leak and make the engine idle poorly. You can test it by applying vacuum to the valve, and it should hold with the engine off. With the engine on - apply vacuum with a pump and it should stall the motor. Did you replace the gasket when you changed the valve?

    another very common problem is a plugged pcv valve-it will cause the loping idle. Also check all your vacuum lines for leaks and cracks.
  3. wiseguy479

    wiseguy479 Junior Member
    Messages: 10

    What would i clean the egr port with? How do i apply vacuum to the egr valve? If the egr is clogged how do i clean it or replace it?
  4. the_experience

    the_experience Member
    Messages: 75

    I agree that it sounds like an EGR problem. Have you checked for codes? When the check engine light comes on you can take a paper clip and jump terminals A and B (should be upper right two) on the ALDL under the dash and it will flash a series of numbers on the check engine light. I bet you get a 42.

    The egr valve on these trucks is pretty easy to test. First you're going to want to check and see that you are getting flow and that it's not clogged. An EGR valve that is stuck closed or not flowing will lean the truck way out at cruising speeds and cause all kinds of problems. With the truck idling carefully stick your finger up on the back side of the vacuum diaphragm for the valve and push it up. The idle should get lower and rougher. If it does you have flow.

    Next you need to check and see if it's working electronically. Put your finger again on the diaphragm, but don't push. Rev the truck up to about 2500 RPM with your other hand and you should feel it start to move. If it doesn't take off the vacuum line that leads up to the EGr solenoid. Repeat the test and see if you feel vacuum. In not you need to make sure it is routed to the correct port on the EGR solenoid. There is a vent and a vacuum port facing the firewall on the solenoid mounted to the passenger side valve cover. The vacuum line needs to go on the port closer to the intake manifold.

    Assuming that is correct you should pop the other vacuum line off the solenoid. This goes to manifold vacuum and should have a strong suction on it. If it does you're probably looking at replacing the EGR solenoid. No fears though, this part is cheap and easy to replace.
  5. Jack33

    Jack33 Junior Member
    from NH
    Messages: 22

    Bad EGR solenoid, just unplug it and drive it.
  6. the_experience

    the_experience Member
    Messages: 75

    Just unplugging it is illegal and bad for the engine. EGR cools the charge during lean cruise when it's at it's hottest and most prone to detonation. You will also lose noticeable mileage.

    It's not an expensive part so just replace it...after you diagnose that that's the problem for sure.
  7. wiseguy479

    wiseguy479 Junior Member
    Messages: 10

    Well i fixed the egr problem it was the solenoid. Now it needs injectors always something thanks to everybody who helped me figure it out wiseguy479.
  8. the_experience

    the_experience Member
    Messages: 75

    It's amazing what a little diagnosis can do. How much did the solenoid cost you?

    What makes you so sure it needs injectors? Injector failures on TBI trucks are not common. Even when they start dripping and don't have that perfect "bug fogger" spray they don't tend to exhibit a lot of driveability problems. Is this the same truck with the bad frame?