vwjunkie53

Hey guys,
my girlfriends car has been having some problems lately since the weather here has gotten cold. When it first starts, it runs rough and misses if it gets below 20 or so and has trouble staying running untill it gets some temp. It will start, rev higher than normal, then die down and sputter, and sometimes stall. It did throw a code for "random missfire", but obviously that didn't tell me anything I didn't know. Also, her mileage is crap. She is getting around 15 on average, and 75% of her daily drive is highway. I just replaced the plugs, (the old ones weren't worn, and all looked like they were burning great). I also replaced the coolant temp sensor, as I know the PCM relies on that sensor pretty heavy for fuel mixture. Before changing the plugs, I ran a can of BG 44k through the tank, which did help it run smoother overall. Once the car is warm, it runs great. There isn't a hint of missfire when the engine is warm. I am going to throw a new fuel filter on it this weekend. Any other suggestions on what to try? Some people have suggested plug wires, or coil packs. You would think if either a coil or wire went bad, it would throw a code for a single cylinder miss, and it would do it all the time. Thanks for any help.

Jason

BLACK2001SS

spark plugs + wires make shure they are good, fuel filter is a good thing to replace. Cleen your maf with some crc maf cleener. The good fuel injection cleener is the stuff you get in a can and hooks right in your fuel rails, you have to unhook the power to the fuel pump and hook up the can and run the car till the can is empty.
Check for vacume leaks,
just some ideas hope it helps.

vwjunkie53

Thanks for the reply. I'll try cleaning the maf. BG44k is supposed to work as well as the direct to the rail stuff. I don't know how true that is, but I have seen it make a world of difference on a couple cars. I friend of mine had a LT-1 car with 200k on it and the 44K really woke it up!

Jason

ls1fst98

iTrader: (3)

Is that the only code its throwin? Mine would do that when my trans started to take a crap but it also would show a transmission component slipping.

01riceeater

iTrader: (4)

Seafoam it! Your on target with the fuel filter too, and the MAF cleaner....should add about 3-4 mpg if you do these three.

vwjunkie53

I'll try cleaning the maf. Thats the only code its showing...

Jason

wildn347

iTrader: (19)

same thing happend to a friend of mine check your coils he had a bad coil

WS6store.com

iTrader: (30)

Possible leaking intake manifold gaskets....Spray some carb clean or brake clean around the sealing area of the intake to the head on both sides and see if the problem arises.

Also, if you have a way to monitor the misfires when its happening, that would help nail it down to maybe misses on only one bank...then you can look at a possible O2 sensor problem. Say it is missing on cylinders 1,3,5,7, swap the front O2's side to side and see if the problem moves to the other bank. I see this problem quite often on the gen 3 engines. I wouldnt put my eyes on coils...they just dont fail on these engines.

I presume we're talking about an LS1...correct?

99z28monster

iTrader: (3)

have the same problem also but not as severe, it was a bad o2 sensor.

vwjunkie53

Yep its an LS-1. Thanks for the replies and suggestions. I thought if it was missing only on one bank the OBD-II would figure it out. Best it can come up with is random misfire. I don't have any way to monitor it. I did check for vac leaks at the intake, but found none. Like I said it only does it when really cold. You would think vac leaks or bad 02 would make it run crappy all the time! I'm pulling my hair out! If the fuel filter doesn't fix it (which I doubt it will, but I'm changing it tomorrow anway) then its on to 02s.

Jason

BLACK2001SS

I was throwing a missfire coed because one of my plug wires wasnt connected all the way and the thing about plug and plugs wires is the will decompose over time and use thats why when people get a tune up that includes plugs and wires.

vwjunkie53

Just did that... (plugs and wires that is) Thanks for the reply though!