Ca. 258 rough idle

[Sasquach]

After just completing the TFI ignition upgrade and while that made a very noticable improvement I still had a spot just a crack above idle were it would nearly stop running if you held it there, I am talking with the hood up and manualy holding the throttle. So since I just passed my smog inspection I though I would see if dissableing? anything would make it right, tried messing with the air pump(smog pump) and that gave no real results, next I pulled the vacum hose off the EGR and JACKPOT! runs like an engine should. Capped off the hose and between torrential downpours I ripped down the street and back with a smile on my face, so after going thru my manual to see if I could better understand this contraption and if I really had to have it I decided NO but thought I would toss it out to the forum and see. I did find I had no delay valve between the vacum line and EGR valve but why bother with trying to fix it?

 

[TDHofstetter]

Lots of racing intakes don't have EGR setups on 'em... but if you leave it disconnected, it's likely to fail the smog test next time.

The EGR does reduce combustion-chamber temperatures, so running without it may make your motor run hot. It can possibly cost you an exhaust valve, even. Better, cheaper, and more reliable to just fix (or replace) that EGR valve.

Is there a plug someplace on that Jeep that you can remove & add at least a TCS to control the EGR? That'd help a bunch - it wouldn't be enabled unless the motor was warmed up.

 

[Sasquach]

As far as smog goes I just capped the hose and can reconnect as needed.

If it is going to cause other problems though that has to be concidered.
I thought it was missing a vacuum delay valve but after rereading the service manual I see that is for the 360 and 401 engines with 4v.
It has a the CTO switch to allow operation when warm only but
something must be wrong and not working correctly. the EGR valve looks new and per the manual test procedure it is operational.

 

[TDHofstetter]

What's the vacuum source? I'm betting it's getting vacuum too early in the throttle stroke - it SHOULD be getting vacuum only pretty late in the stroke, like around midpoint. You may have it hooked up where the distributor's advance hose should be.

 

[Sasquach]

What's the vacuum source? I'm betting it's getting vacuum too early in the throttle stroke - it SHOULD be getting vacuum only pretty late in the stroke, like around midpoint. You may have it hooked up where the distributor's advance hose should be.

That makes perfect sense but after checking it is coming from the correct port on carb. then goes to the inner port on the CTO then back outter CTO port to the EGR.

The EGR valve is mounted to or part of an integral back pressure sensor and it's job I now see is to limit EGR operation to certain engine loads etc.
Does not define how to test it but points to a restrictive or leaky exhaust system as apossible culprit, my system is new and stock in design.

 

[TDHofstetter]

Ah - yep, if it's a backpressure EGR, then it does sound a lot like exhaust restriction. Quite a LOT of restriction, too, if the EGR starts working only a little above idle! Got a plugged catalytic?

 

[Sasquach]

Ah - yep, if it's a backpressure EGR, then it does sound a lot like exhaust restriction. Quite a LOT of restriction, too, if the EGR starts working only a little above idle! Got a plugged catalytic?

Entire ehaust system is new plus I removed the cat after inspection and straight piped it. Manual also say's "exhaust leaks" can cause problems but I have no leaks either.

 

[TDHofstetter]

It's hard to imagine that an exhaust leak could cause a problem with a backpressure EGR. They only turn on (trigger the EGR) when exhaust backpressure pushes up the hollow actuator rod inside.

Is it possible you have the wrong EGR valve in it? One that doesn't need backpressure to turn it on? A backpressure EGR valve will look like a vacuum leak - you can suck air past the diaphragm all day long without drawing a vacuum. A conventional EGR valve will take & hold a vacuum.

 

[Sasquach]

It's hard to imagine that an exhaust leak could cause a problem with a backpressure EGR. They only turn on (trigger the EGR) when exhaust backpressure pushes up the hollow actuator rod inside.

Is it possible you have the wrong EGR valve in it? One that doesn't need backpressure to turn it on? A backpressure EGR valve will look like a vacuum leak - you can suck air past the diaphragm all day long without drawing a vacuum. A conventional EGR valve will take & hold a vacuum.

You hit the nail on the head!

I'm sitting here with the EGR in my hand and was thinking it must be a non backpressure unit--decided to see if any posts came up on it and Vola! did your test and it holds vacuum.
TDHofstetter to the rescue!
Thanks for the trouble shooting-I owe you one.