EGR Valve Test


Valve Opening Test

  • With engine at normal operating temperature and at idle, rapidly open and close throttle. Open throttle sufficiently to obtain at least 1500 RPM. Movement should be noticed in EGR diaphragm.
  • If diaphragm does not move, probable causes are: faulty vacuum signal to EGR, defective EGR diaphragm or defective backpressure sensor diaphragm (if equipped), or leaks in vacuum lines or connections.

Valve Closing Test

  • With engine at normal operating temperature and at idle, manually depress EGR valve diaphragm. RPM should immediately drop, indicating that EGR valve is not leaking and had been properly cutting off exhaust gas flow at idle.
  • If there is no change in RPM and engine is idling properly, exhaust gases are not reaching combustion chamber. Check for plugged passage between EGR valve and intake manifold.
  • If engine idles poorly and RPM is not greatly affected by manually moving diaphragm up, EGR valve is not closing off exhaust gas flow. Check for carbon between pintle, leaking EGR valve gasket or bad EGR valve.

Revised 1-31-2016


8 thoughts on “EGR Valve Test”

  1. My 87 xj won’t idle once hot. I recently put this jeep back on the rd after several years of pretty much sitting in the yard or occasional short trips. I have kind of went thru it. The injectors were all leaking so I replaced them . I put a radiator and water pump on. They were both bad. The fuel pump got very loud so I assumed it was bad and the no idle deal started. I pulled the tank and put a new one on and a new sock filter on the bottom( the old sock filter was full of rust) of a newer fuel pump I had with very few miles on it. I changed the fuel filter on the frame and disconnected the fuel line at the rail and blew thru with air just in case I had trash in lines. Figured this would take care of my problems. No. So I continue down ur list to clean the TB and idle air controller thinking this was the problem. Now when I crank up from cold it runs like a champ. However, once the motor is good and warm it idles like hammered crap and sometimes knocks off. When I crank it back up it usually is at a very high rpm, sometimes it slows down, sometimes not. I do have two parts jeeps and robbed a different egr valve and and idle air controller off one of the other jeeps. I changed out each part one at the time in case it fixed it then I would know which part was bad. Still has same condition though. Trying my best not to throw parts at this thing but, I am running out of patience and used parts. Lol. I am open to any suggestions u have. I have done all of ur tips that I feel mechanically competent enough to do. Feel free to call me if that helps. Don’t know if or when u might get this but, thanks in advance.

      1. Thanks for your help man. I have done tips 1-4. , 9-11,. 18, 28, 29, 31. I am just now getting comfortable enough to run a volt meter/ multi meter and I learned to solder last week. This has been over a period of probably 3 months. I know it is some little silly something because when it’s first crunk and not good and hot u can put a dime on the front of the valve cover and it purrs like a kitten.

        1. Thanks for the update. Great job of increasing your skill levels.

          Now you need to do Tip 5. Tip 27 if you wanna put your soldering and shrink tubing skills on a workout.
          After that is tested and repaired as needed, you can make a good adjustment on your TPS.

  2. Man knock on wood I figured it out this eve! Jeep still wouldn’t idle. Got to the point of not even when cold. ( At first it was only when hot). Anyway, I still didn’t trust my used fuel pump so I put a new one this eve. Still not idling. Next on my list was swap in a fuel pressure regulator off of my parts jeep. Still not idling. Next was another tps off the parts jeep. Immediately it ran good! So I was like ok maybe I just needed to adjust the tps. Aka my part is not bad just out of adjustment. Sure enough,. Went through ur steps on adjusting tps and it is running like a singer! Somewhere through the dirty fuel and switching out injectors it needed some fine tuning. Bingo. Thanks man.

  3. With the EGR Solenoid connector unplugged (engine running) I have no vacuum at the output on the solenoid. What would cause this?

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