I have a 91 L98 that has an EGR check engine light problem that i cannot get rid of. I have changed the EGR valve, and the EGR solonid. I purchased the EGR thermostat/switch but i cannot find where it goes Other threads in the forum say that it is at the top of the EGR pipe. Cannot find it. I am open to any suggestions on other locations.

The check engine light comes on after about 15 min of driving. No other symptom. If anyone has any other suggestions as to the cause of my probem.........

Thank you!!!!!

 

I believe it looks like a little O2 sensor on the top of the crossover pipe near the rear right valve-cover.

 

what code are u throwing? 32 im guessing?

 

I believe that '90 & '91 L98s did NOT use the EGR Temp Sw; not sure how the ECM got feedgack though.

Since you are getting the SES (code 32) after driving for a while, the ECM is calling for EGR and not sensing it.

One way to avoid the issue is to install a 160 deg T-stat & fan switch, as the ECM will not call for EGR till coolant temp exceeds 175 Deg F.

 

As far as I know - EGR temp switch was gone after '89. ECM is looking for a change in BLM'S when EGR is commanded. My guess is your valve isn't working. Need to capture data at cruise to figure it out, but you can return the switch or sell it someone who needs one.

 

take a vacuum hose that has full manifold vacuum and hook it up to the egr valve.the engine should stall or run very bad. if not then that new valve is not working or the egr port in the manifold is cloged with carbon. ive seen alot of egr valves not work right out if the box.the diagfram should move once vacuum is applied

 

In later years there is no EGR temperature switch. The ECM commands EGR operation and then looks for the O2 sensor going lean to detect that the EGR valve opened.

You have the classic symptom of EGR valve not working (SES light comes on after cruising for a while). Unfortunately it only happens while driving, so it's a little difficult to check things...

There is a vacuum hose that connects the EGR solenoid to the bottom of the throttle body. It is PORTED vacuum, so there will be no reading at idle. You need to get the throttle blades open to see vacuum on this line. The other side of the EGR solenoid feeds vacuum to the EGR valve. I recently found that the little plastic EGR vacuum line on my car had a hole melted into it and it was completely open, so check that out. The ECM applies a ground to the EGR solenoid to make it operate, so you can unplug the connector and measure (ignition on) 12 volts on one terminal (pink/black wire -- the gray wire goes to the ECM). While you're there, you can measure the resistance of the EGR solenoid coil, which should be around 28 ohms (my car).

If you have a Mity-Vac or similar vacuum tester, you can put a vacuum on the EGR valve and make sure the diaphragm is intact. I bought a new one from AutoZone that wouldn't hold a vacuum right out of the box, so that does happen. There's an AC Delco EGR valve on there now...

Your EGR passages in the intake manifold might be plugged up with carbon.

In the 26 years I've had my car I had a smog check guy check my EGR valve ONE TIME. He said most don't check it. He used a distributor wrench (the Z-shaped kind) to reach under the plenum and pull up on the bottom of the EGR valve. The idle immediately got rougher. You could also do this test with a Mity-Vac or otherwise get vacuum on the EGR valve while the engine is idling.

 

I finally have had the time to get back under the hood to work on my EGR (code 32) problem. I put a hand vacuum on the EGR valve and with the engine off i can pump the vacuum down and the valve will hold. As soon as i start the engine the vacuum drops to zero and it cannot be pumped back down. Do I have another bad EGR valve??
i have put two in so far - actually getting pretty good at it. Thanks for any suggestions or thoughts.

 

MY fsm ON CODE 32 SAYS that if the plastic vac harness is pushed into the solenoid too far it can plug end of vac line and cause 32. lots of info on the 2 pages. I am not familiar with it since I have never had to be.

 

with the engine idling. apply full vacuum to the egr valve with the vacuum pump and engine should stall or idle veryy rough. if it does not stall. remove the egr valve and check for a cloged EGR passage in the intake manifold or cylinder head. BUT ive seen many bad egr valves come right out of the box from autozone, so u need to make sure when your applying vacuum to the valve u will see the diagram move up and down if it does not u need to find a new egr valve that actually works. so best luck with be use a acdelco part.

 

For what its worth, when I replaced the injectors on my 1990, I bought a new EGR valve to swap in at the same time. The mechanic that I was helping to do the work, asked me for a can of carb cleaner and sprayed it in the EGR passages before bolting up the new EGR valve. When he sprayed the passages all this black junk came out. He wiped it down and sprayed it again. He kept repeating the process until the black stuff stopped pouring out. I would say that he used about a quarter of a spray can of carb cleaner to do the job. He told me that was the normal process when replacing the EGR valve to make sure that the passages are not clogged up.