2003 Alero - Missfire Code

[pappyl]

I figured I'd post this in case anyone searches for the same problem...

Driving along about 90km/hr and check engine light goes on, engine revs jump up, then bogs, lose speed - run for a mile or so at 3000 rpm, then everything goes back to normal.

Use my scanner on it - got a cylinder missfire code (sorry forget the number). So first thing, pull the plugs. They look a little sour, little old, so I replace them. Car seems to be running fine for a few weeks after that.

BUT, it seems, every once in awhile, to "miss/hesitate/lose power" when going down the highway - very subtle though.

Next thing - I get a bad catalytic code p0421 - I scan and sure enough the rear o2 is jumping up and down in synch with the front (almost). Cat's shot. So I replace the cat $300.

Couple days later the missfire comes back (when I'm in town), car hesitates, then almost dies, no power, then surges and runs normal then dies again. I nurse it to the local garage because I live a ways away and wont make it back (time to cough up the $).

Well I had (2) ideas
1) Ignition control module
2) Coil

Mechanic hooks up his super scanner and sees 2 & 3 are misfiring, 1&4 are OK. Problem only comes up after revving it to 3000rpm up and down for 5 min as it runs normal when they pull it in the garage.

New coil pack was in stock, luckily. Note - on this one you needed to swap the little connector piece along with the black housing cover.

Running find now....

mechanic told me a missfire code can be caused by coil or the fuel injectors. This was definitely electrical given the way it was coming and going though.

Just in case anyone else has this same problem.

[jawa]

check your wires

[Shiwnath]

What engine do you have?

Edit: Never mind.. Saw your other thread.. 2.2L Ecotec.

[a.graham52]

never questioned plugs...

[pappyl]

Guys, Dont think I was clear on my little writeup there.

The problem was the coil pack.

It didn't show any physical signs of a problem.

The symptoms with missfire were made worse as the engine and coil back grew hotter.

Rare I am told, but I had a coil go one my bonneville (different setup but same behaviour)

[AleroB888]

Originally Posted by pappyl

Guys, Dont think I was clear on my little writeup there.

The problem was the coil pack.

It didn't show any physical signs of a problem.

Writeup looked pretty clear to me, I would not have suspected that, either.

[a.graham52]

i wsa just saying you never questioned the plugs. wouldnt have been hard to inspect them as part of your diagnoises.

[Hellfire5670]

After misfires its always good to change plugs and wires maybe a full tune up! This happened on my Acura and after i found the problem i checked the plugs and wires and they had a little damage and such... Just saaying a tune up would probably help a lot!

[03glgold]

Originally Posted by a.graham52

i wsa just saying you never questioned the plugs. wouldnt have been hard to inspect them as part of your diagnoises.

that would be covered by the part where he said he pulled the plugs, inspected them, thought they looked bad, and replaced them

[a.graham52]

Originally Posted by 03glgold

that would be covered by the part where he said he pulled the plugs, inspected them, thought they looked bad, and replaced them

oh you got me... guess thats what i got for skimming.

[pappyl]

I did forget one other thing...
The extended rubber boots/connectors - they can cause a misfire too. Check for carbon trails on the rubber, etc.

- One trick for test those - get a GOOD set of test wires - pull off the coil pack and plug wires from coil connectors directly to plugs, then put on a timing light to see if you get an erratic spark

Missfire causes in order of easy too difficult fix
- Bad plugs
- Bad plug connector (inside) and/or boot
- Bad coil
- Bad connector/wire to ignition module
- Bad ignition module (though usually it just will not fire)
- Bad fuel injector
- Timing due to bad chain tensioner - move a tooth (usually runs bad at idle)

* I am sure I am missing some other weird problem... BUT hope this helps someone