EGR Valve Stalling Issue

Hello,

I have a 1988 XJ 4.0L AW4, 190k on the odometer. This was an Ohio jeep that I'm now trying to smog in CA.

Here's my issue: It seems that my new EGR valve is causing the motor to stumble under light acceleration from a stop. If I don't let off the pedal or push down harder, the motor will stall. It idles in park without any problem, the problem only comes up when I put it into Drive.

The reason I believe it's EGR related is because the EGR is new, and this problem was not present before I put it in. The prior EGR valve did not function. I quickly tested it several time this evening by plugging and unplugging the vacuum input to the EGR. No stalling when the EGR vacuum is removed, stalling issue present when vacuum is connected.

Of course, this is probably how the EGR is supposed to work, and the real problem is elsewhere. Recently I've completed Crusier tips 1, 2 (actually 27), 3, 5, 6, 7, 8, 9, 10, 11 and 22 (replaced harnesses). EGR valve is new and O2 sensor is new. As I mentioned, I'm trying to pass CA smog. I failed the first time (high NOx). From a tip on this forum, I've put in colder rated plugs (Champion RC9YC) and a 180 stat as well.

I'm hoping to retest this week, but I would like to understand why the engine wants to stall with the EGR connected. Thank you.

The EGR should be closed except close to WOT ... At which point the EGR solenoid opens vacuum to the valve, opening it. I would suspect the solenoid as the source of the problem.

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Did you replace the base with a new gasket? There is a chance your new EGR is just bad from the box, and unlikely to get better by playing with it. Try another. Short discussion about EGR here: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

DId the box have a 'made in china' label on it? Recently I had to return a new-in-box ignition switch, (the switch on the GM column), and it was bad, causing me a lot of grief, (a few curse words, lost hours, 100 plus miles of travel, and many schedule screw ups). All due to the fact that those chinese factories often have low quality controls inherent in those typical Godless commie people's liberation army managed slave labor operations.

Thank you for your help. FSM says the EGR solenoid should be closed during warm up, idle, wide open throttle, and rapid acceleration/deceleration. That all makes sense, I guess.

The EGR solenoid appears to function correctly. I actually borrowed it off a buddy's jeep because mine is stuck closed.

Solenoid is open until given signal. I tested it with 9 volt and vacuum pump and it looks good.

It's not a case of the EGR solenoid being stuck open. I think the engine would just stall out even at idle. And it runs great, in the opposite condition, without vacuum to the EGR.

Thanks, Alaskan. I base nearly all my knowledge of the EGR valve from that link!

This a Duralast EGR valve with a gasket. I tested it prior to putting on, and after putting it on. If you give it vacuum, the diaphragm moves up and down, and given enough vacuum will cause the engine to stall.

I could replace it, it has a lifetime warranty, but it seems to work as it should.

I don't have anything to base this on yet, but maybe the colder rated spark plugs can't handle the extra exhaust. More research needed.

Have you checked your TPS voltages as you rotate the throttle(with key on engine off).

This will show you if your sensor has a glitch at the partial throttle area, which is where they usually wear out first.

If it was an EGR getting vacuum all the time due to faulty ECU or solenoid it would stall all the time,

So i would look elsewhere for the answer to your issue.

Good luck, let us know how we can help.

Good call. I'll try to check the TPS for a glitch sometime today. Thanks.

After doing some more research, I realize I did not test the EGR transducer separately. Perhaps it is not reacting correctly to exhaust back pressure?

I found this discussion enlightening:
http://www.cherokeeforum.com/f2/89-4-0-hesistation-stall-idle-drop-117961/

Specifically these transducer testing instructions:
I had the same problems, engine dying with light gas pedal application from a stop. Replace the EGR Valve Transducer. HOW TO TEST IT
This is used on 4.0L engines only. From the internet,,
Disconnect all transducer lines and remove transducer.
Plug transducer output port. Apply 1-2 pounds air pressure to transducer back pressure port (used compressed air adjusted to correct pressure). Apply a minimum of 12 in. Hg (kPa) of vacuum to transducer input port.
Replace transducer if it will not hold vacuum.
My findings,,,,, what I did,,,, with valve removed and outlet plugged, apply vac from a hand vac pump to the "VAC" side of the transducer, the black plastic thing near the EGR Valve. It should NOT hold vacuum. Apply air pressure to the bottom 90 degree molded hose on the bottom of the transducer, just blow into it, it should then hold vacuum when using the hand vac pump. Release pressure and vac should instantly bleed off. Another way to test the valve, with engine running and at operating temperature, look down into the EGR valve mount and watch for the shaft to move out and then back in. With slight gas pedal application there should be NO movement of the stem, at all. That stem should only be moving when there is substantial exhaust pressure applied to that bottom hose on the Transducer to allow the vacuum to get to the EGR valve, such as at cruise speed settings. What it does is when at low throttle settings, NO vac is sent to the EGR valve. That would kill the engine or cause stumble and hesitation. At higher throttle settings where the engine is up to speed, back pressure in the exhaust system allows that transducer to open and allow vacuum to go to the EGR valve. I have been fighting this problem for over a month now and last night I finally found out how to test the transducer. I replaced the EGR Valve Transducer ahead of the EGR Valve and the Jeep is running perfect now, no stalling off idle or any more hesitations !!!!

I think the transducer is the culprit. It appears that it may have been someone's first day on the assembly line because the transducer was connected to the EGR valve backwards. I took the transducer off tested it backwards (how it was assembled), and it doesn't work. Reassembled it correctly, and it tests fine.

I have to wait until tomorrow to reinstall, but I'll post final results afterward.

As old as that jeep is, it is doubtful it is the OEM transducer. Somebody about 10 years later goofed up putting in back on or replacing it is more likely.

Not all the Renix jeeps have a transducer. And they stopped using them in 1991.

Great info on that post on how test it, rarely ever been mentioned here much less how to test one. Most people have deleted them for off road....

I always wondered what the transducer was for.