LB9, 44K miles. Went on a 250 mile non stop trip. At 200 miles out SES light comes on, code 45. It would always come on a few minutes after start up. Car got horrible gas mileage and idled rough.

Replaced o2 sensor. Car runs better, gas mileage improved. Idle might still be a little rough, Im not real sure. Code 45 still keeps coming.

What next?

 

You did disconnect your battery cable for a few minutes to reset the computer after replacing the sensor, right?

If that checks out start checking other sensors and relays starting with the MAF, something could be off enough to cause a rich condition but not enough to throw another code.

 

Do I really need to disconnect the battery? SES dosent always come on at the same time. Sometimes its after 5 minutes, sometimes 10, sometimes it wont come on for 30min. I have Speed Density, not MAF. Hanes manual says mabey evap can or faulty injector. How do I check those?

 

Check for a faulty fuel pressure regulator (leaking into vacuum hose).

On a side note, is this a stock engine. I had SD TBI that I swapped onto a L69 like engine, it had a little more cam than a stock 305 and a little better flowing heads (601s). I would actually get codes 44/45 on the same trip, just under different conditions/loads/engine speeds.

 

how??

 

I've never done it, but i'd guess pulling the vaccuum line and letting the pump prime, looking for leaks once it is under pressure..

 

no leaks

 

You can also smell the vacuum line for fuel, it definitely should not smell like gas.

FYI, ALWAYS reset the computer after replacing a sensor, or you can get weird phantom codes. I replaced my O2 without resetting it and got the same code you have, I reset it and it never came back.

 

Reset the battery, started it, let it idle for a minute, started driving, light came on. Stop to get gas, let it run for a minute, then drove home, no light.

 

I just got my new 1992 z28 and im having the same damn problem. It was surging pretty bad at low RPM's so we took it to a dealer and they found out it was code 45 and replaced the fuel pump, and the fuel filter...and i guess anything else that would be replaced with that repair. The surging is completely gone, but the car still throwing code 45 every now and then. It came on for 40 miles, went off for 350, came back on today. Difference is with me is that the car is getting great gas mileage (25-30 on the highway) and runs and idles pretty smooth (idle gets slightly rough at times, but i dont have any experience with TPI engines so it might just be that they idle that way compared to a TBI).

I dont really know what to do...where should i look???