EGR system

How do you tell if the EGR system is working and what happens when it doesnt work right. My wifes xj has a super mild lumpy idle that smooths out when you put it in gear. Thanks for any help. T.

If it smooths out in gear at idle then I wouldn't tend to suspect the EGR valve. On my '87 the EGR valve's diaphram was shot and the valve wouldn't open. If it does turn out that you need a new one, the one used in '89 will work on an '87 and cost about $60 less. Seems to be a dealer only part.

Whats the egr system do for a 4.0 anyhow? Will it change engine performance if its not working right? Its the only thing I dont think I can really test. I think my new fuel injectors are a bit too lean at idle and that might be the reason for the bad idle.

Hi,

I'm totally new here and it's awesome already. I have an 87 Cherokee with a 4.0L and major EGR valve problems. In fact the EGR is shot. I tried cleaning it, but it still doesn't move well. Problem is, trying to find an aftermarket one is proving impossible. And the dealer wants like $125.00 !

Anyone have an idea where I can get an aftermarket one? Also, I read PaulJ's post that I can use an EGR for an 89. Anyone know if that requires any modifications? He's right that it is much cheaper than the one for the '87.

Thanks!

Yosteroo said:

Hi,

I'm totally new here and it's awesome already. I have an 87 Cherokee with a 4.0L and major EGR valve problems. In fact the EGR is shot. I tried cleaning it, but it still doesn't move well. Problem is, trying to find an aftermarket one is proving impossible. And the dealer wants like $125.00 !

Anyone have an idea where I can get an aftermarket one? Also, I read PaulJ's post that I can use an EGR for an 89. Anyone know if that requires any modifications? He's right that it is much cheaper than the one for the '87.

Thanks!

Click to expand...

The EGR from an 89 should fit right on with no modifications, but it's a two-piece affair with a vacuum device separate from the valve itself. I would make sure that for the lower price you get both parts. The 87 had a single-piece unit that included a back-pressure valve in its diaphragm. You cannot vacuum test the diaphragm on this one, because it will always leak vacuum when that little valve is open (when there is no back-pressure).

When the EGR on my 87 died I noticed no difference. If it sticks open, it will stall, but if it stays closed it's hard to tell. In theory it should, in addition to controlling NOX emissions, help coll combustion and reduce knock. But since the egr-equipped XJ's have a knock sensor, they don't knock anyway.

My ex-wife's 88 had the newer style, and at one point wear in the valve caused it to hang open intermittently, a hard problem to diagnose unless you catch it red-handed.

EGR Function

The Exhaust Gas Recirculation Valve (EGR) is supposed to open at engine speeds above idle (lower engine vacuum condition), to let a small amount of exhaust back into the intake. The result is supposed to be lower emisions and a slightly lower combustion chamber temperature. If the EGR fails closed, you probably won't notice it. If it fails open, then it will run badly or stall at idle. My '90 died at idle when the EGR went out. My daughter's '90 is currently running with the vacuum line pulled from the valve and blocked (screw in it), until she has the $$ to replace it. My mechanic said that running without one could lead to slightly higher operating temperatures under heavy load (like big trailer up mountain passes), but ordinarly we wouldn't even notice if it was blocked off. It's easy to replace- I put mine in with no trouble (fight with the metal line from the exhaust pipe- leave everything loose until that pipe is connected, then it goes OK). Use antiseize compound on the connections if you work on it. If you have emissions testing, you will be checked for EGR valve. I don't have testing, but I want to breath decent air, so I replaced it. 4xBob

The EGR valve should be closed at idle, if it hangs open, it often causes the motor to stall (or when stopping or slowing for a corner). It has a solenoid in the circuit that shuts it off, at start up (high idle/timer), low coolant temp. or wide open throttle. If the solenoid is bad or the circuit is open, it will allow the EGR to operate when the motor is cold (not good).
This is what I learned, but darned if I know if it´s accurate or factual. The EGR helps reduce timing/octain knock. Helps when running regular gas and knock on hills.
If you get the right angle on a hot motor and blip the throttle you can see the rod move (sometimes need a mirror). I´ve plugged the EGR on motors (made a full gasket/plug out of tin) as a test, never noticed much difference in performance at moderate to high speeds. If it was hanging open a bit, a plug, sure cured the stalling and helped with the rough idle.
Most of my rough idle problems, usually turned out to be the distributor cap and/or vacumn leaks. Occasionally injectors or bad gas. Just for the heck of it, unhook your battery for awhile. Could be my imagination, but rebooting the Renix on my 88 seems to help with the idle some, for awhile. Think I have a fualty sensor someplace (garbage in garbage out).

I thought the EGR = reduced combustion temperatures was an Internet myth. Ran it through google and found more than one site that explained it does reduce combustion temps by diluting the air/fuel mix slightly, which has a little less to burn, etc.

Which is why it runs in the high vacuum mode, when you don't need power. Blocking it off can lead to higher chamber temps, and more spark knock, which reduces advance, which reduces power. So for more power, sounds stupid, but leave the EGR working. It's how science handles NOx, even in coal fired power plants.

As much as we spend on a few horsepower, it's worth it to keep it fixed, which might explain my stalling, too, unless it's the TPS or the C101 connection or the leaky fuel injectors . . .

I know. Fix them first. Can't afford too, can't afford NOT to -

Just FWIW my EGR has been disconnected for over a year now with the vaccume hose unplugged and has had no problems what so ever just a thought. We also don't have emissions test in Okla. heck we don't even have inspections anymore.
DIG IT!