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


27 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?

  4. Hi Cruiser54, thank you for all the work you do… You are amazing for taking the time to help others with these amazing yet temoetmentemp 4.0 engines. I have an interesting issue occuring and I think it is all related to the TPS or very possibly the EGR. My TPS is only showing 1.94 volts no matter what I do. I have tried multiple TPS and still have 1.94 volts. I have grounded that directly to the battery and any other ground on the Jeep and it is still 1.94 volts. Most people that I see have 5 volts or just under, any idea why mine would only be pushing 1.94 volts?

    The issue I have is that once it warms up and gets out of the closed-loop it begins to want to die when you ease into the gas pedal. It is most noticeable if you are going uphill from a stop or if you want to test you can hold the brake and very slightly touch the gas. I am uploading a video now so you can see this. It runs perfect when it’s cold.

    When I unplug the EGR valve when hot it runs perfectly. Almost like the TPS is telling the computer to send the signal to the EGR solenoid allowing gases in that shouldn’t be let in at such low RPM. Does that make sense? I feel like if I can get to the bottom of the voltage issue on the TPS everything else should be fine. I have gone through and refreshed the grounds as I explained in the video.

    Any assistance you can provide would be much appreciated! Thanks again.

      1. Sorry for the delay. I didn’t get notified that you replied. And yes, 1.94V is what I get upon testing the voltage at the TPS.

  5. After reading this tip I’m wondering if the backpressure sensor diaphragm that is operated off exhaust system back pressure is specific to certain model years for the 4.0l engine? Mine is an 88 Comanche Pioneer. When I purchased it 2 years ago I checked the EGR using these instructions and it worked fine. Now the EGR diaphragm doesn’t move. The diaphragm on the EGR valve test out OK (moves when connected to a vacuum pump) and so does the EGR solenoid. This seems to be pointing to a defective backpressure sensor diaphragm (mine does have this). I have fabricated my own exhaust system and installed a high flow cat so I know the exhaust backpressure is reduced, this makes me question whether the backpressure sensor diaphragm is getting enough signal or if it has failed altogether. Is there a model year that did not use the backpressure sensor or is this only a difference between the 4cyl and 6 cyl models? If I bypass the backpressure sensor diaphragm and run the vac line directly between the EGR and EGR solenoid it does actuate the valve, I’m not sure that is a good strategy to pass emissions though. Currently failing on NOx, just slightly over the limit.

  6. my back pressure sensor has melted likely do to a clogged catalyst which caused its exhaust rubber elbow to blow off, which in turn allowed hot gasses to flow out onto the back pressure sensor plastic body.
    I cant find a replacement for this sensor nor its rubber elbow despite a web search. Where can I find one? I dont even have a part number.
    this is for a 1990 4.0 liter XJ, Calif emissions

    1. I have an 88 comanche with the renix and I’m failing nox by a hair, any idea where I can get a new egr valve for it? I have looked everywhere and can’t find the one for this model. I already cleaned it and replaced everything emissions related but this egr is toast. I live in AZ

  7. My egr diaphragm doesn’t seem to move when connected the following way. I have the transducer set with the egr label on top of the transducer connected to the EGR valve diaphragm and the Vacuum label connected towards the egr solenoid. However if I set the transducer in reverse, vacuum label towards the egr and egr label towards the solenoid it does move the diaphragm. Is my transducer failing or do I simply have it set in there incorrectly.

      1. I’ve been battling my EGR and CA smog. I have tested my EGR valve, and it is functioning correctly, applied direct vacuum, and from 0-15lbs you can see the diaphragm actuating. I have pulled my UFO (backpressure diaphragm), opened it up, cleaned/inspected and rein stalled. When checking vacuum from UFO to EGR I have 11-15lbs but its fluttery, which I’m assuming is from the UFO diaphragm sealing off the pintle hole (or should it be a solid reading?) Checked vacuum at the solenoid, 15lbs when disconnected, ramps up to 5ish pounds when connected, warm, and I apply roughly 1500rpms. Am I missing something? Smog tech says he isnt seeing EGR activation. Could my back pressure sensor be faulty? Or possible the smog tech isnt familiar with the EGR system on the Renix? I would prefer to just replace the components, but they are NLA…factory and aftermarket

        1. I say he’s not familiar with the system. You’ll never see the ECU give the solenoid vacuum at idle, and maybe not even under a light load. Does he have the scanner to even read the ECU’s outputs?

  8. Does anyone know where to buy an EGR valve? It failed the test and looked bad. I attempted a rebuild, not knowing much about what needs cleaned out. All the ports cleaned out easy with tiny drummels and sand paper. Not knowing if the circular housing for the rubber spring needed cleaning, I cracked it open, it was clean, but was tough to seal back up. It has a tiny vacuum link now I think. Can’t find one currently at local wrecking yards. Would really love a new one. I don’t like the idea of deleting the EGR. My experience with that was it made it more difficult for the ECU to figure out A/F mixture.

    My 89 XJ Pioneer runs rich. I just got a rebuilt motor installed and hot bathed the stock intake and TB. Exhaust has a new 02 sensor and normal cat. Vacuum tubing is all new, but i haven’t done the wider vacuum source off the IAT port over to MAP. Haven’t indexed the distributor, and don’t know if the mechanic who installed my 4.0 stock rebuild did or not. Better ask him. There’s Def not a window cut out. It’s got 60k miles on it (the distributor) Better just swap it. I did the big cables engine to chassis upgrades- the “big 7″ or whatever. I also a the high mount alternator mod with a 95 XJ AC compressor bracket and kit for big alternator – from a big dodge – using a voltage regulator renix seems to easily understand. We installed a new CPS but I haven’t checked voltage. I’m pretty sure I’ve eliminated all vacuum leaks. I don’t think the TPS and AW4 transmission interface is set to the right voltage. Jeep seems to shift too early. I’ll get the Bosch injectors and check the fuel pump ground.

    I’m gonna go through steps 1 through 5 firat, then CPS and TPS. With only a 3” lift and 31.5 x 10.5 tires I hope I can get 18 to 20 mpg on highway, eventually, if it weren’t running so rich. I’m going through the steps cruiser. Hoping I can get this XJ running better than new.

    1. Eliminating the EGR will have no adverse effects on fuel trim.
      60K on a stock distributor is just fine. I’ll bet your mechanic didn’t index the dizzy.

      As far as those mileage figures you’re hoping for, that’s a dream. The oxygen sensor won’t let it run rich as you’re saying unless it fails.

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