Electronic or mechanical ?

[Ed H.]

I have a ghost in my L98, 1990. While traveling along at highway speed (55-75) after approximately 10 miles the "CHECK ENGINE SOON' light comes on. If I drive the car depressing the throttle and releasing same, I can drive it all day and the light will not come. I was told by a young mechanic who, after placing a diagnostic computer into the ALDL location under the dash, stated the problem was in the EGR system (code 32). We then looked into his computer for photos of the system. In computer photos, we observed an Exhaust Gas Temp sensor on the back, right hand side of the engine near the distributor. When looking at my engine in the same location, no sensor or wire was observed. I checked my 1990 service manual and was unable to find an Exhaust Gas Temp sensor. Was there a change from earlier L-98 engines that were not incorporated 1n the 1990. Since my car is a convertible, I understand there was a change in the HP from 245 to 250. Any help would be greatly appreciated.

[Joe L.]

Re: Electronic or mechanical ?

I have a ghost in my L98, 1990. While traveling along at highway speed (55-75) after approximately 10 miles the "CHECK ENGINE SOON' light comes on. If I drive the car depressing the throttle and releasing same, I can drive it all day and the light will not come. I was told by a young mechanic who, after placing a diagnostic computer into the ALDL location under the dash, stated the problem was in the EGR system (code 32). We then looked into his computer for photos of the system. In computer photos, we observed an Exhaust Gas Temp sensor on the back, right hand side of the engine near the distributor. When looking at my engine in the same location, no sensor or wire was observed. I checked my 1990 service manual and was unable to find an Exhaust Gas Temp sensor. Was there a change from earlier L-98 engines that were not incorporated 1n the 1990. Since my car is a convertible, I understand there was a change in the HP from 245 to 250. Any help would be greatly appreciated.

Ed------


1990 does not use an EGR temperature switch. 1989 and earlier do.

My guess would be that you have an EGR valve problem. Sometimes you can get by with just removing the valve and cleaning the orifice which will likely be carboned-up resulting in sticking. However, if it were me, I'd replace it. These things have a rubber diaphragm and they're subjected to a lot of very high heat. GM #17113456 or GM #19210674.

[Edward J.]

Re: Electronic or mechanical ?

Ed, There are a few checks you can do easily, one is make sure you have a vacuum at the solenoid you'll find the solenoid I believe drivers side just slightly under intake runner. If good there just take a 12 volt test light and ground the terminals one at time one is power the other is ground I am going from memory but believe its a pink wire for power (key should be on), if power is good, next start car and let idle, pierce the other wire with test light, this will act as a ground and the solenoid will activate and the vacuum will be applied and if the EGR valve is working, this will cause the engine to stall when you ground the wire. Let me know how you make out.

[Ed H.]

Re: Electronic or mechanical ?

Thanks guys, right now I am baby sitting my two grandsons, 5 and 7. Takes all of my attention just to keep them from injuring one another, very active. I love it.
There is nothing better than papa teaching them about corvettes. I will go to the man cave tomorrow AM and check it out. Joe and Ed very good info and advice.

[Bill H.]

Re: Electronic or mechanical ?

Ed, do the checks Edward suggested.
The symptoms sound like it's the EGR Valve itself, doesn't light the check engine around town but does after some highway miles.
If your mechanic didn't clear the code, it's stored I the CCM as "history" but every time the ck eng. lite comes on, it will throw a 32.

You can check the codes yourself, all you need is a paperclip. I think on a '90 you can clear the codes with the dash buttons.
The procedure may be in your FSM (it is for 92-93). You can also clear the codes by disconnecting the battery but I'd do another code check first.