mazda626es

iTrader: (1)

My girlfriends car has been having issues(I made another post 2 or so days ago). Basically, her 03 Maxima, automatic, was throwing the P0420, P0455 and P0456 codes. I decided to try some things. Tonight, I replaced the PCV valve, front 3 spark plugs, and the ignition coil(the one off of my 2002 Maxima, 6spd) in the cylinder 1 spot, I replaced it because the one I took out of the car didn't want to seem to seat correctly, I would put it on and then it would push itself back up. The PCV valve didn't really rattle when i took it out, and it looks like the valve cover was leaking in cylinder 1 and 3, but 5 was dry. After doing the work, I pulled the negative off of the battery, and let it sit for 5 or so minutes to try and clear the code. I then hooked it back up, and went for a drive. I drove 3 miles up the road to walmart, and while going I reset the MPG gauge. I was getting between 15 and 17 mpg, mostly highway and driving normal. I stopped at walmart, put a quart of oil in the car, and then drove 3 miles on the highway home, but i reset the MPG gauge again, it bumped up to 47.9 and then came back down. I drove up and down our street at between 45 and 55 miles per hour, I did this for 17 miles. When I pulled back in the driveway, the MPG was reading 28.4. The car seemed to sound fine and drive fine. My first question is, is this normal? Is the car just "relearning" how to drive? The SES light is still on, but I don't have a way to test what the codes are at the moment, but i'd imagine its the same. Second question is, I'm not going to damage the car by doing just the front three plugs am I? I didn't think anything of it before, but now I'm questioning it. I plan on doing the back 3 this weekend, but I wanted to check the plugs, and since I already had them out, I figured, I would just do them tonight. Last question, I checked around and it looks like the ignition coil off the the 2002 maxima is the same as on the 2003 maxima. The coils are the same size, but the ending of one of the serial numbers is a G and at the end of the other one its an F. Autozone, advanced, napa, all had the same sku for the 02 and 03 ignition coil, but I just want to make sure.

tosheto

iTrader: (5)

02 and 03 have the same coils. You probably should do all 6 plugs at the same time. The front ones are cylinder 2, 4, and 6. Scan the codes and post here what they are.

Fakie J Farkerton

iTrader: (51)

I'll answer the computer mpg question for you:
The computer is never right about mpg.

maximasicilian123

Never do you say Anything useful. Ur probably the guy that leaves comments on **** videos.

Fakie J Farkerton

iTrader: (51)

GTFO with your oh so useful

The computer isn't ever right. Just like you.

dwapenyi

iTrader: (3)

The computer is probably right, but the reading its giving you is instantaneous. So for the OP's situation, there was an improvement.

02 and 03 Maximas are notorious for oil burning issues, so you'd bete watch the oil level carefully.

Fakie J Farkerton

iTrader: (51)

My mistake, I thought that total mpg's were being calculated, but with that said I have never seen an accurate mpg rating on any cars computer.

mazda626es

iTrader: (1)

Ya, I usually do all 6 at the same time. But since I had them out to check them, i just figured, why put the crumby worn ones back in? After that, I thought, now the car might be running differently on the two banks and cause it to damage the car. I am going to be doing the back 3 in the next week, more than likely this weekend. I just wanted to make sure the car wasn't going to blow up or anything, otherwise I would put the old plugs back in until I can do all 6. And ya, I was a little tired when I typed it, and I think I may be losing my mind, lol, but I meant cylinder 2, not 1. When the misses gets home, I am going to bring the car back to autozone and have them scan it again to see what the codes are this time. When she gets home, it should have about 60 total miles on it since I did the work, so I'm guessing that if what I did screwed anything up, the codes should show up.


Oh ya, I learned this one the hard way. This one in particular is our 5th Maxima between us, as you can tell, I love the car, but I wind up having to put a quart in, sometimes a little more, in between oil changes. I was just shocked at how much the gas mileage increased by just doing the front 3 plugs and the PCV valve. I will say, that PCV valve was pretty shot, as were the spark plugs, so I was hoping for an improvement, I just didn't think it would be that much. But when she gets home today, I'm going to check it again to see what it averages out now that it has about 60 miles on it since the work.

mazda626es

iTrader: (1)

I went from a P0420, P0455 and P0456 to a P0420, P0455 and P1456. I have absolutely no idea whats wrong. I'm stumped, I may bring it down to Nissan and just pay the diagnostic fee and have them figure it out. My car I was going to take the canister off and valve, but I'm getting the P0455 and P1448 code on my car now.

So bottom line, did all the work mentioned above, and now I'm getting a P0420, P0455 and P1456, and the gas mileage is now averaging out at 23.4 mpg now.

NSMO240

iTrader: (5)

you need a catalytic converter, if the is bad it will mess with what the front o2 sensor does, because it uses the rear o2 to adjust the front. find out if its bank 1 or 2, the canisters crack and create the p0455, and the P1456 is created by the purge valve on the back of the canister going back, i would fix all of these and see how your fuel mileage does

mazda626es

iTrader: (1)

Thats what I am starting to think. However, I did the work on the car, and the CEL has been off for 5 days now(I just have to do the back plugs) but the car seems to run much better. The canister isn't cracked(or at least anywhere on the outside) I took it off the car to do a visual inspection. But the vent control valve does look a little rusty, i haven't tested it yet but as soon as I find a 9 volt battery or get my volt/ohm meter up and running, I'm going to see if the vent control valve works. I just thought it was a very strange coincidence that all 3 lights popped on at the same time.

Also, after driving the car for a few days the gas mileage has even out to right around 24.

But NSMO, I'm going to do the vent control valve and more than likely the canister, because I have yet to take the valve off with out snapping those damn screws.