"cyl 3 misfire"

[2001ExpSport]

Ok....I'll try to explain.

For the past..oh....8 months I have had a rough idle. I ignored it for a while figuring it was bad gas. Once it started to get worse I decided to run a few tanks of injector cleaner which didn't help. I ignored it a little more(hoping it was a phase), but it persisted. So I tried higher octane fuel which didn't help, I knew it wouldn't, but I tried it anyway. Last week I got a check engine light, which gave me a "cyl 3 misfire" code. I bought some new plugs and wires, changed them and the PCV valve I had sitting around for months. Still does it! I cleaned the TB and the IAC valve. The only reason the check engine light came on is that the rough idle was really bad, shankingly bad. It is almost as if the cyl is not firing at all. BUT it is, because if I pull the plug it shakes even worse. It will do this up to 2000 rpm and the run smooth. Drives great and smoothly under normal conditions, just the idle sucks my ass .

Now, it's really bad when it's cold, but it does this all the time. It is not specific to engine temp, just the intensity is.

I have had the 00M12 recall done as well as new intake O-rings.

It has 84k, original 02 sensor(maybe the issue?)

Any help is greatly appreciated.

Matt

 

[Critical_Level2]

Sounds like an ignition problem. What brand plugs and wires, if the wires are lifetime warranty, take them back and try some new ones. Another thing to test would be the coil pack, maybe it isn't sending enough voltage to fire the plug. Have you checked the MAF sensor, it could have mung built up onm the sensor wire causing the computer to think there is less air coming in and retarding the spark and/or fuel.

 

[2001ExpSport]

BTW, when I pulled the old plugs they were all in excellent shape.

It can't be the wires and plugs, it's doing the same thing it was with the original wires and plugs. It just runs better, but the misfire is still there....if that makes sense.

I am going to check the coil tomorrow.

Matt

 

[2001ExpSport]

One thing I don't understand is, why would it only have a misfire issue at low rpms and run smoothly @ 2000rpm and higher?

 

[2001ExpSport]

.

 

[Critical_Level2]

If it only happens at idle and not higher rpms. It could be the IAC. At idle your throttle blade is closed and the IAC lets air into the motor to maintain idle, when you open the throttle blade (Press the pedal down), it lets air in and the IAC does not control air flow into the motor. It could be the IAC has build up on it or is not working right, hence it runs like crap at idle cause the motor is not getting sufficiant air flow, but at higher rpms the throttle blade is open providing the motor with adequate air flow.

 

[Brain]

I think all of the suggestions above are valid and good, but the IAC would probably not favor making cylinder #3 misfire more than the others. There are only a couple of things that would make a single cylinder misfire:
1) bad ignition timing (computer controlled) / spark -> seems like you've eliminated this issue if you've check the plugs, wires, and coil
2) bad compression (bad rings / valve) -> can be easily tested with a compression tester
3) bad fuel delivery (fuel rail / injector / injector signal) -> I'm thinking this is the issue, but you can't test for it easily. It requires replacing the fuel injector for that cylinder. It takes about three hours (removing the upper intake manifold and the fuel rail plate that holds all the injectors).

Here's the thought process: If the fuel injector for #3 isn't closing fast enough, it will be rich at low speeds (and run rough). When the RPMs increase to where it needs more gas, the symptom will decrease. A rich mixture would run rougher on a cold engine than a warm engine. Seems to be what you are listing as symptoms.

Bad O2 sensors don't typically list a cylinder in the trouble codes, they list a bank (set of cylinders) that is indicating rich or lean.

 

[2001ExpSport]

Update

A rich mixture would run rougher on a cold engine than a warm engine. Seems to be what you are listing as symptoms.

I haven't tested the coil yet, but I started it up tonight and the cylinder absolutely would not fire. I drove it around the block and she was very reluctant, letting out a few internal pops, but nothing substantial enough to be called a backfire. The check engine light flashed a few times and went out. Once warmed up the cylinder started to fire, but still had a rough idle.

I like the clogged injector idea because this whole issue has been gradually getting worse. It wasn't a sudden failure.

I am going to retest my IAC as well.

Thanks Brain

 

[goliath]

I drove it around the block and she was very reluctant, letting out a few internal pops, but nothing substantial enough to be called a backfire.

Assuming you verified the coilpack is not sending spark at the wrong time...

Burnt valve, fuel injectors dont cause pops they just flood or dont work at all. pops are caused by obstruction in the engine like a bad valve causing the gasses to back up in the engine(exhaust valve burnt closed, or intake burnt open) or explosions to escape out the exhaust(exhaust valve burnt open). Check the compression on that cylinder. Its proably very low when cold. Other things can cause valvetrain problems, but i would start here.

-joshua

 

[Brain]

I would definitely check the coil pack first just to eliminate that as a possability. Coils can go bad gradually just like fuel injectors, and they are a LOT easier to eliminate as a potential issue. Good luck.

 

[cjpwalker]

Just a thought, but if the computer is throwing a misfire code for a specific cylinder, doesn't that make you think spark? Or can it tell if there is a bad injector or stuck valve?

 

[goliath]

Just a thought, but if the computer is throwing a misfire code for a specific cylinder, doesn't that make you think spark? Or can it tell if there is a bad injector or stuck valve?

Car computers are exceptionally dumb. all it knows is that when it sent spark to that cylinder the spark didnt jump the plug gap correctly. I would think a good tune up or crossed/shorted wire would be the place to start too, but he allready said that he verified the spark plugs, wires, and coil. That leaves mechanical problems as the possiable cause. i am trying to save him hundreds spent on throwing parts at the problem, when a simple compression test can be very enlightening.

-joshua

 

[2001ExpSport]

but he allready said that he verified the spark plugs, wires, and coil. That leaves mechanical problems as the possiable cause. i am trying to save him hundreds spent on throwing parts at the problem, when a simple compression test can be very enlightening.

-joshua

I have yet to test the coil, I have been quite busy. I will be on it tomorrow.

Matt

 

[2001ExpSport]

Update

Started it up today and it ran smooth as silk during the initial warm up, but once the idle dropped to normal it started to spudder. It just gets worse when put into gear.

Tested the IAC for the hell of it and it checked OK

Tested the coil connector: OK

Tested the coil resistance:
Primary is .7 ohms

Secondary
1-5 is 14.04k ohms
2-6 is 13.98k ohms
3-4 is 14.04k ohms

Haynes parameters for secondary are 6.5 to 11.5k ohms

Tested a new coil at PB and the resistance was 11.3k down the line.

If the Haynes numbers are correct and the stated resistance value is critical then this looks like the problem.

Comments?

 

[captTelescope]

Secondary resistance is inconclusive, since they are all so close. I'm thinking #3's companion, #4, would misfire too, if it were the coil, since this is a waste spark system. Anyone have an opinion on that statement?

I think Brain is on the right track, #3 injector or something mechanical with that cylinder. Put a vacuum gauge on it and see if the needle is steady. If it is, that tends to eliminate the mechanical.

 

[2001ExpSport]

Put a vacuum gauge on it and see if the needle is steady. If it is, that tends to eliminate the mechanical.

That's going to be my next step.

 

[captTelescope]

Another thing you can do, since you can obviously measure resistance, is check the Fuel Injector coil resistances. If #3's is out of whack with spec (or the other FIs), it's a bad injector. good resistance doesn't rule out a plugged injector. Disconnect the FI wires before measuring.

 

[2001ExpSport]

Another thing you can do, since you can obviously measure resistance, is check the Fuel Injector coil resistances. If #3's is out of whack with spec (or the other FIs), it's a bad injector. good resistance doesn't rule out a plugged injector. Disconnect the FI wires before measuring.

OK, I'll try that...thanks.

 

[captTelescope]

Hi 2001ExpSport,

We're hanging on pins and needles, here. Any news?

Anyone: What clue is this giving us that the engine runs OK at startup? (See post of 11-07 @ 1:01.) 2001ExpSport, does the engine run OK until it warms up, or just for a short time after starting? Brain, Goliath, are you still there?

 

[goliath]

waiting to hear from 2001expsport about his current diagnostics progress before adding anything. I would like to know the outcome when he does get it fixed.