Check Engine Light when driving over 65 MPH
Thread Starter
4th Gear
Joined: Apr 2003
Posts: 4
Likes: 0
From: Great Mills MD
Check Engine Light when driving over 65 MPH
I have a strange problem that I have been chasing for almost two years. When driving my 1986 Vette, the Check Engine Light comes on within 10 - 20 minutes of driving the Car above 65 MPH (Interstate Speeds). I have ran the codes and it points to the EGR System. I have changed the valve and it still continues. The car performs fine, except for that stupid light. I would like to locate the problem vice ignoring it. Any ideas. The engine is the late year L-98 with Aluminum Heads. Over 102 K miles, runs great, doesn't burn oil and gets 24 MPG!
The only other thing I have found, and I am not sure if it is a contributing cause, the exhaust recirculating line between the Air Switch and Catalytic Converter is missing. Not sure if this would cause the problem. The car had a aftermarket exhaust sytem. I went back to stock and I discovered the line is missing. :nonod:
Any info or suggestions would be greatly appreciated.
CWM
1986 Coupe
The only other thing I have found, and I am not sure if it is a contributing cause, the exhaust recirculating line between the Air Switch and Catalytic Converter is missing. Not sure if this would cause the problem. The car had a aftermarket exhaust sytem. I went back to stock and I discovered the line is missing. :nonod:
Any info or suggestions would be greatly appreciated.
CWM
1986 Coupe
Burning Brakes
Joined: Aug 2002
Posts: 926
Likes: 2
From: chandler az
Re: Check Engine Light when driving over 65 MPH (cwmartin59)
On my 88 there is a metal tube that goes from the passenger side exhaust manifold to the intake manifold(then to the egr valve.) at the top of the tube there is a temperature sensitive switch. This is what the computer uses to determine that the EGR valve is functioning. If the EGR valve is operating the hot gasses go by the switch and cause it to close. on mine the center conductor unscrewed itself out of the switch. I just screwed it back in and JB welded it.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Re: Check Engine Light when driving over 65 MPH (cwmartin59)
Check vacuum lines in the area of the throttle body and solenoid, particularly at the splitter below the solenoid towards the alternator.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Check Engine Light when driving over 65 MPH (cwmartin59)
There is a method on my site to use available components to check the EGR valve, solenoid and temperature switch. You can jumper the EGR solenoid at idle to force the EGR valve to open and then measure voltage at the switch to see if it opens. This allows you to check both the solenoid & switch without special tools, other than a jumper and a DMM.
If it is the switch, the Grn wire from the switch goes behind the dist to a connector buried behind the engine. So you will likely have to cut the Grn wire and splice in a new switch.
If it is the switch, the Grn wire from the switch goes behind the dist to a connector buried behind the engine. So you will likely have to cut the Grn wire and splice in a new switch.
