Failed CA smog

1989 4.0L Aw4

Recently had a Fuel Pressure regulator leaking through the O-rings and back into my Vac. lines. I got a new FPR and a complete new vac. Harness that was replaced because I noticed my EGR not working. EGR is working by visual inspection now. Here are my smog numbers.... Any idea where to start?


Oh btw a complete tune up was done on my jeep about 20k ago. Plugs,wires,cap,and rotor

Catalytic converter.

I had similar looking numbers. New cat and it passed.

While this is vague, it's somewhere to start. You're looking for sources of high combustion temperatures. Possible causes to high nitrous oxide:

Lean Fuel- check O2 sensor and closed loop operation (including O2 heater), check for vacuum leak, hard plastic line to MAP and MAP operation (including ground), and engine coolant sensor operation.

EGR System- check vacuum solenoid operation (ECU controls the ground), check vacuum line, check valve operation. 89s had a pressure transducer which my 87 does not. My original Renix ECU failed to control the ground of the EGR vacume solenoid some years back. It took a while to figure it out, but I eventually traced it back to the ECU itself. When I obtained a later model ECU out of a '90, I opened the old one up and found a few fried components. I made sure that the circuit was clear, installed the new one, and the EGR worked again.

Catalytic Converter- mileage and overall condition? Mine burned very clean after I had it replaced years ago.

Engine Compression- higher compression than usual, causing higher cylinder temperature?

Cooling System- though unlikely, is your engine running at normal temps? Higher than usual temps may cause higher cylinder temperatures.


My 87 originated in CA with CA smog certification for what it's worth.

I had to replace a intake gasket to get my numbers down on my 94.I also found a crack in the exhaust header when i removed it to fix the gasket.Couldn't hear it leaking by the way.

Anybody got a good site that will give me the numbers I need to check the EGR or transducer vac. Pressure? Also how can I trouble shoot the MAP sensor?

Warm the engine to normal operating temperature.


Operate engine at idle speed.


Check vacuum at solenoid vacuum source.


Disconnect the hose and attach a vacuum gauge to it.


Vacuum should be at 15 inches.


If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.


If vacuum is ok, remove gauge, reconnect the line and proceed to next step.


Check vacuum at solenoid output port.


Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid.


If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.


Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port.


If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:


Leave solenoid electrical connector disconnected. Note the engines idle speed.


The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step.


Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.


Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid.


If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.


Vacuum Transducer Testing as follows:


Disconnect the transducer vacuum lines and back pressure line. Remove transducer.


Plug transducer output port. Apply 1-2 PSI air pressure to transducer back pressure port. Air pressure can be supplied with a hand operated air pump or compressed air (regulated to correct pressure). Apply a minimum of 12” of vacuum to the input port.


Replace transducer if it will not hold vacuum.

Joe_Peters, awesome post. Thank you.

Your problem is probably not the Cat converter looking at that data. That data shows that your engine is running way too lean. Pull the plugs and lets see what they show, is it all the cylinders running lean or not?

The common problem is carbon fouling in the combustion chamber and clogged injectors which is usually helped (if not solved) by using injector and intake manifold cleaner like Gum out to clean them.

This thread is a good source of data, and a good place to post you before and after, and what fixed it later!!!

http://www.naxja.org/forum/showthread.php?t=966054&highlight=emissions+test

Just wanted to give an update, I followed the trouble shooting steps post by Joe_Peters and found that I have a bad vacuum transducer. I've got a new one on the way along with a new egr, once I smog it again ill post up some numbers for comparison