tramphardrocker

Finally got my 87 Cherokee pioneer up and running ( 4.0, 208 K miles). Got new tuneup parts in it and new TPS, IAC, injectors. I eliminated the C101 connector and cleaned up the ground connections. Oil pressure is not as good as it is on my 90. The EGR circuit appears to be functioning normally. But... with the vacuum line connected to the valve the engine stumbles and stalls when I put it in gear and engage the throttle. If I disconnect the vacuum, the problem goes away. With it parked and running at idle I can see the valve open momentarily then close when I goose the throttle. My 90 xj doesn't do that. I've read that it might be getting a bad signal from the ECU. Before I put a new valve in it, anybody got any input?

cruiser54

Does the line that connects to the EGR valve have some kind of doo-hickey in it like a vacuum valve?

tramphardrocker

You mean that exhaust back pressure transducer doohickey? As I understand it, the doohickey regulates vacuum to the EGR valve based on exhaust backpressure. The research I've done says that most failures in an EGR circuit are caused by either solenoid or doohickey failures. The solenoid seems to be functioning as it should. Don't know how to test doohickey. Is there a spec. for that I can check with a vacuum gauge? Maybe I should just buy a new one. Another issue has popped up in the past couple of days..... parasitic battery drain. One thing at a time. My workload these days is taking up most of my time so tinkering with my clunkers is limited.

Oswalla

Egr system is easily testable with hand vacuum pump and gauge. Go here if you don't have FSM, https://xjjeeps.com/#ReferenceDocuments. EGR system is page 196 with the testing procedure.

ajpulley

My last ECM eventually failed to provide the ground to the EGR solenoid, allowing vacuum to always be present. And, most of the '87 model year 4.0s did not have the EGR transducer, so your symptoms sound very familiar. Use a voltmeter to determine if there is a ground at the solenoid from the ECM. It should be present during idle... if I recall, when a ground is present, the solenoid is held closed preventing vacuum from reaching the EGR.

tramphardrocker

My solenoid checked out OK. When I manually open the egr valve and plug the vacuum port, the valve closes. Shouldn't it remain open til I I unplug the vacuum port? Doesn't this mean the diaphragm is ruptured?