Blazer

I have a 1990 convertible with 21,000 miles. After driving with the cruise set at 75 for about 30 minutes, the SES light comes on. If I slow down, the light goes off. The Snap-On scanner says Code 45 (Oxygen Sensor Rich). I know it's running rich beacuse the BLM value is 108 and the integrator stays at 108.

I have replaced the O2 sensor with a new AC-Delco one. I replaced the cap and rotor, both were fine. I removed the sparkplugs, all were light tan, but I replaced them anyway. The fuel filter has been replaced. The fuel pressure stays at 42 psi, bleeding off to about 12 psi after an hour. I checked the injector resistance and they all show 18 cold, 16 hot on the digital meter. I checked the charcoal canister, it is fine. The egr valve passes a vacuum test, but I haven't removed the plenum to take it out. What am I missing here???????

I'm so frustrated with this stupid car, I may break down and take it to the dealer to get it fixed. :confused:

65Z01

Verify that the TPS resistance is changing smoothly with change in throttle position.

Also check the manifold vacuum with the scan tool. This could be very important since you have a speed density system.

How about coolant temp as seen on the scan tool, does it seem right?

Also is the ECM in closed loop when you're getting the rich condition?

Blazer

I did check the TPS, voltage is .54 volts and smooth all the way up to 4.48 volts at WOT.

The coolant temp is correct. When cold and using open loop, the BLM and integrator are both at 128. The minute the car gets warm and goes into closed looped, the integrator takes a nose dive down and the BLM quickly follows.

What should the manifold vacuum be? I don't have my Helms manual here at work, but I will look up that test when I get home.

Thanks for your response!!! :cheers: