Cylinder 3 misfire

[PJB]

On my dad's '97 CS with a 3100 the SES light keeps coming on and off. Right now its staying on.

He had a mechanic check it out and it had a code for Misfire Cylinder 3. The mechanic replaced the plug wires and the car was fine for a week or two and then the light came on. My dad had Autozone scan it and it had an O2 sensor code. Then the mechanic he took it to before said to run a higher octane (89) gas for a tankfull and see what happens. The light went on and off periodically. Then it came back on and stayed on. He had Autozone scan it yesterday and it was the Cylinder 3 misfire code again. Today the car was stumbling on his way home from work so tonight he replaced the front 3 spark plugs (couldnt get to the back but #3 is in front anyway) and disconnected the - terminal of the battery but the light stayed on. The car doesnt stumble now though.

 

The plug wires are brand new and the old plugs only had about 15k on them.

 

What could be the problem? Other than today the car has been running fine. Its got 70k on it.

[manitcor]

I would say its unlikey your wires or plugs are bad, pull the plug on cylinder 3 and see if it is fuel fouled or shows signs of overheating. If its overheating then you are prob running lean on that cylinder indicating an injector problem. If its fuel fouled look at the coil packs and igintion module.

 

Test your coil packs with an OHM meter, measure the resistance between the towers on each pack, they should read between 5000 and 7000 ohms IMHO.

 

If you dont mind doing a bit of wrenching get a Haynes book, it can walk you through inspeciting the igintion system and fuel injection system. Its not very hard todo on the 3100.

[PJB]

The plugs just had some normal wear on them.

Ill have to check the coil packs tomorrow when its light out. Where do I check them though? I dont know what you mean by the towers.

Wouldnt the car run rough all the time if the coils were bad though? On another car I had it kept running like shit and dying due to a bad coil pack.

[94CutlassSLCoupe]

judging by the mileage, it probably has a bad intake gasket...what color was the plug when you pulled it out?

 

Chances are if it was a coil pack or ignition module, the companion cylinder (#6) would also misfire...wire being bad is still a possibilty

[PJB]

The plugs just had a little white on them. Theres no coolant in the oil like my truck had when the intake gaskets went and the car was running fine after replacing the plugs.

[manitcor]

when you remove the plug wire from the coil pack youll see what I mean by tower (metal contact).

 

94CutlassSLCoupe has a good point, check for oil or fluids around the area of cyl 3 (middle by the firewal) though it may not show its a good thing to check.

 

The car may run rough with a misfire though it depends on how bad the misfire is.

[94CutlassSLCoupe]

my sister's CS with the 3100 had a bad intake gasket which sucked enough oil into cylinder #5 to make it misfire occasionally...it leaked no coolant, and runs wonderfully now. It could also have a vaccum leak there.

[PJB]

Ok, so run the metter from the tower to what though? The other tower across from it?

I thought the odd numbered cylinders were in front on these cars. I know I cant really see anything around the back of the motor or change plugs without pulling the motor forward and I dont really have a way to do that at home.

[manitcor]

even numbers front, odd numbers rear

 

you measere across both towers on a single pack

 

you dont need to look back there, just reach your hand back there and feel for any oil running down that side of the block, both where the LIM meets the head and where the head meets the block.

 

Also check the sides as leaks will show there first normally.

 

Check your fluids for any inidcations of oil and coolant mixing.

[PJB]

I measured the resistance and all the coils were in the 6000 ohm range (car off).

 

I managed to get the #3 plug out and oddly it looks brand new and its a different brand than the front 3 were. Theres no white on it and my dad has never had plugs put in since he's had the car. They were changed around 15k ago.

 

Here's a few pics (not the greatest):

 

Also while back there I found this plug thats not connected to anything:

What is it for? It looks identical to another plug thats under the coil packs but theres only only hole for it to plug into.

[manitcor]

thats for your HVAC, the plug pics suck, I cant tell the condition of the electrode

 

if the ones on the back ar a different brand than the front you may want to cange the rears out

[PJB]

I couldnt get a good shot.

The plug looks like its brand new but its not. Theres no oil, grease or any kind of residue on it. Its not even white like the front plugs were (normal wear).

Where does the HVAC plug go?

[94CutlassSLCoupe]

looks like brand new sounds like there was coolant leaking in the cylinder...was probably steam cleaning the plug...and the piston...which would cause a misfire for sure.

[manitcor]

I couldnt get a good shot.

The plug looks like its brand new but its not. Theres no oil, grease or any kind of residue on it. Its not even white like the front plugs were (normal wear).

Where does the HVAC plug go?

 

sorry I ment evap, its a block that comes off the same studs that your coil packs are mounted 2, its has 2 vac lines going to it.

[PJB]

looks like brand new sounds like there was coolant leaking in the cylinder...was probably steam cleaning the plug...and the piston...which would cause a misfire for sure.

 

So it would seem like an internal intake gasket leak then? I didnt feel anything wet around the spark plug hole or the head.

[PJB]

I couldnt get a good shot.

The plug looks like its brand new but its not. Theres no oil, grease or any kind of residue on it. Its not even white like the front plugs were (normal wear).

Where does the HVAC plug go?

 

sorry I ment evap, its a block that comes off the same studs that your coil packs are mounted 2, its has 2 vac lines going to it.

 

I saw that part and theres already two plugs in there. The one in question has a red tab on it and it says Red 14. One of the plugs on the other part says Red 11.

[cutlassdude96]

[PJB]

Something looks different in that pic. I cant find a part like that near the power steering pump at all. Nothing that open.

Maybe its different from '96-'97?

[cutlassdude96]

its only if you have NV7 RPO VARIABLE EFFORT Steering, yours doesnt have it no need to wory about it

[DaveFromColorado]

okay, about the stumble problem - I know I'm a fan of damming fuel injectors, but if you have one injector hanging open a little too long (say in cyl. no. 3) you'll get rich exhaust codes, along with misfire codes after the plug gets too fouled out to spark properly - may be something to look into.

 

--Dave.

[PJB]

Its fixed. A replaced injector and intake gasket fixed it and its been running fine with no light for a week.