Misfire problems

Hey guys, I have been having a continuing issue with engine misfires in my 02 impala ls and have hit a wall with the repairs. It broke down due to a plugged catalytic converter in December. It starting misfiring and loosing fuel economy and power before this. Since the breakdown I have replaced the converter with a factory model, replaced the coil packs, wires and plugs (regular maint.), fuel filter, fuel pressure regulator, O2 sensors, and EGR valve. None of this solved the problem.

I put a code reader on it an found that my fuel pump was very likely going out (pressure were well below normal at idle) so I replaced it and it solved the problem for about a month. Now I am back to misfires and an intermitent flashing "check engine" light whenever the engine is under strain (going up hill, entering the interstate, head wind, etc.)

The only other thing I can think to do is replace/clean the injectors. Does anyone else have any suggestions?

Jason

What codes are comeing up. Sounds like maybe a problem with the ingition module, located under the coil packs.

You said you put in a new fuel pump and that solved the problem for a while. What kind of fuel pump did you install? A friend installed one of those cheap chinese pumps in his Silverado truck and it failed on him prematurely. Not as soon as one month, but his completely quit. Maybe yours is not building enough pressure in the line...

Post back with the codes. A flashing Check Engine light could be a bad (or fouled) plug.

BTW, I've never cleaned injectors in my life. I think that problem is as rare as a $2 bill...

Thanks for the replies. I will have to run the codes again tonight because I can't seem to find where I put the list. The fuel pump that I used to replace the old one was taken from a 2004 ls and had only 400 miles on the pump. It checked out well electrically and was professionally cleaned before instalation.

BTW, I've never cleaned injectors in my life. I think that problem is as rare as a $2 bill...

$2 bills are actually quite common, most banks have lots that you can get if you want them, it's just nobody wants them. And I have seen many fuel injectors that needed cleaning. Usually only if low quality fuels are used, but I wouldn't rule that out just because only high quality fuel has been used.

Find a shop that uses BG products and have them do an induction flush on your engine. I have seen on many of the newer 3.8l engines that carbon builds up all through the intake and on the valves and causes misfires. The biggest cause of the cat going bad in these is the engine not running at 14.7:1 AF due to the carbon buildup absorbing the fuel and releasing it at a steady rate (runs rich on decel and lean on accel). I have done an induction flush on two of these that had the P0420 code (cat inefficiency), it actually fixed them both. It's expensive, but it's good stuff. Certainly not a gauranteed fix, but given what you've repalced, that's what I'd try next if the fuel pressure checks out good.

Well I ran the codes last night and it kept coming up with P0304 random misfire on cyclinder #4. I also pulled the throttle body and spacer and cleaned out the carbon. It amazed me how much crap was built up in there. Seams to me I cleaned this about a year ago and had a good amount of build up. Suppose it would be worse if I wasn't running the premium stuff.

Well I ran the codes last night and it kept coming up with P0304 random misfire on cyclinder #4. I also pulled the throttle body and spacer and cleaned out the carbon. It amazed me how much crap was built up in there. Seams to me I cleaned this about a year ago and had a good amount of build up. Suppose it would be worse if I wasn't running the premium stuff.

I would look at this problem as if it was a new issue. I have in the past recived broke plug wires and even dead spark plugs right out of the box from part stores here. While it is rare to have that problem it does show up from time to time. Make certin that the plug it firing proper and does not have massive amounts of carbon build up on the #4 plug. Carbon build up will make the tip and electrode of the plug solid black. Let us know the results.

Also I just got to looking and, Are you running Platium Plugs or Iridium Plugs? The 2002 Impala came factory with Iridum Plugs, they are 100k mile plug that fires at about twice the voltage of a platium plug. They burn hoter in order to insure that they burn all the full out of the cylinder walls. I have seen in the past were people have changed from Iriduim plugs to platium and start having premature failure of the plugs because the coil pack is pushing to much voltage threw them. Everyone thinks that there saving money buy putting in the platium plugs in there place but in fact there loosing gas mileage and causing un-burnt fuel to be diposited in the exhaust system.

Just A Thought

When I pull the #4 plug this afternoon I will check. I can't remember what I put in but I did change the plugs and wires at 100K. I do know that I put in the dual pronged plugs. Most likely they are not iridium.

So I went back and checked the plugs and I replaced the stock plugs with AC Delco performance plus platinums, not iridium. So I pulled all the plugs last night and replaced them all with a set of NGK iridiums. Still got the flashing check engine this morning entering the interstate. I think I am going to put some Seafoam or Miracle Mystery Oil to clear out the injectors some aslo. (I have been using about 4 oz. of Lucas injector cleaner every other tank.)