96 geo mpg and 420 code

got a 96 metro with the 3 banger and am getting anywhere from 35 ri 39 on the hwy with three people and lunches inside, a buddy has a 90 and gets way better than this, I also have been getting a 420 code which is the post cat o2 sensor out of spec?? replaced it but still getting it, found a leaky egr valve and blocked it till I can get another but still kicking the code, it only has 80 k and seems like the cat should still be good??? the idle was also surging but the egr block cured that, runs great now other than the code.... any ideas,, just put all new tune up stuff on and used split fire plugs,, the guy said they were the best,,, any advice would be great,,, thanks dave

Tune-ups are always a good idea. Use some Bosch Platinum +4 plugs, and a new cap and rotor. Also try replacing the manifold o2 sensor too, it could be giving a false reading causing the cat o2 sensor to appear out of spec. Blocking the EGR will also create a lean mixture and cause the computer to run open loop rich, which could make it run crappy, and burn more gas. I would fix the EGR, replace the manifold o2 sensor, and tune it up. Also, you won't get much better than 40mpg on the 96+ metro cause of the OBDII software set makes the car burn a little more gas, to help the cat converter. Cleaner emissions, but more emissions.

I just did all the tune up stuff but ran it 150 miles today and was about 40mpg with it loaded so and it seems to run way better with the egr blocked maybe cause of the vacuum leak it was creating,,, well I will run it a few more days and see how it reacts,,, thanks

dave



Tune-ups are always a good idea. Use some Bosch Platinum +4 plugs, and a new cap and rotor. Also try replacing the manifold o2 sensor too, it could be giving a false reading causing the cat o2 sensor to appear out of spec. Blocking the EGR will also create a lean mixture and cause the computer to run open loop rich, which could make it run crappy, and burn more gas. I would fix the EGR, replace the manifold o2 sensor, and tune it up. Also, you won't get much better than 40mpg on the 96+ metro cause of the OBDII software set makes the car burn a little more gas, to help the cat converter. Cleaner emissions, but more emissions.

got a 96 metro with the 3 banger and am getting anywhere from 35 ri 39 on the hwy with three people and lunches inside, a buddy has a 90 and gets way better than this, I also have been getting a 420 code which is the post cat o2 sensor out of spec?? replaced it but still getting it, found a leaky egr valve and blocked it till I can get another but still kicking the code, it only has 80 k and seems like the cat should still be good??? the idle was also surging but the egr block cured that, runs great now other than the code.... any ideas,, just put all new tune up stuff on and used split fire plugs,, the guy said they were the best,,, any advice would be great,,, thanks dave

You need to get the EGR fixed. With out it you will burn up the head.
This could also be seting your code.

The split fire plugs are a wast of money. I've tried them in several engines. Thay are good plugs but not better. Just use a good AC Delco the next time. Platnams don't even do much in these cars.

I have replaced the egr solenoid and the valve itself and it is now operating like it says in the book, the code is still coming up but I am inclined to think the cat is not up to par and the cause, the mpg has been around 38-39 with three people and bags, from what I here that is the best to expect out of the obd II models.. thanks dave

Did you check and see if the EGR passages were blocked?? They often get filled with carbon. They run right through the head, there's no external lines. A pipe cleaner, screwdriver, and some de-carb solution should help open them up.