Another Misfire Issue

[Equalizer]

Hi,

 

I recently had the heads replaced on my 98 Leg. OB (ej 2.5) after the front gears on the belts broke and threw the belt. The shop replaced the heads w/used off of another car and redid two valves that were bent. It has 160,000+ mi. on it, has been well maintained, and I'd like to hold onto it until I can find full time work.

 

Since then, its been giving a Cylinder #1 and #2 misfire code. They happen intermittantly rather than at the same time. They replaced the plugs and the wires. It continued having the same issue. Today they replaced the wires and asked me to fill up with high test 93 octane gas and bring it in monday. If it was a gas issue after the engine work, due to say.....it being replaced w/a 96 top end, wouldn't it be giving signals on the other cylinders too?

 

There is no trend to the codes comming on. It can happen at idle, hwy speeds, or coasting down a hill. All dry weather. It doesn't smooth it out, or have any more power w/ the higher octane on top of a quarter tank.

This weekend, I'll mist the coil pack and wires in the dark to see if I get arch, (or idle drop off), but it didn't before the change, so I doubt its that. I've read some long threads on #3 & 4 misfires, etc, but still haven't come to any conclusions and need some help. Any likely possibilities/suggestions?

 

EQ

[Log1call]

The miss in question is probably almost undetectable driving the car. It there is a lean injector it could cause a weak firing just at certain throttle/load conditions and you would not notice.

 

A standard tune and inspection should in most instances cure these codes.

[Gloyale]

Check the routing of the new plug wires to make sure they aren't running too close to the injector wires. It helps to put some of the flexi-conduit (like for stereo wiring) around the section of the plug wires that run near the valve covers and injectors.

[unibrook]

Have you ever changed your front 02 sensor? An old sensor will give you misfire cel. Pay careful attention to whether the car drives fine when cold, but then misfires when warmed up? (if so, this is how a bad front 02 sensor behaves.) If it misfires equally when the engine is cold and warm, then probably a diff sensor or diff issue. Actually pay attention to this, and take notes! I did this, and it led me to figure out it was my front 02 sensor that needed replacing....many thx to others on this list who pointed my nose in this direction. You can change your front 02 sensor in your driveway in an hour...just like changing a spark plug.

[Log1call]

There is a better way to check the operation of the O2 sensor using a voltmeter.

[Equalizer]

Unibrook,

The misfire code usually comes up after only a couple of miles in the morning. The second does later on. After the first set of plug wires were replaced w/a used pair, the codes didn't come up for half an hour, or so of driving. Since then, they finally replaced the wires w/new ones.

 

First thing I'll do guys is put insulation, probably closed cell foam, taped around the plug wires. The new set of wires are too long and touch lots of metal on the body, per Gloyal's recommendation. Why foam? I just happen to have some in stock.

 

Log1call,

Would some injector cleaner in the fuel tank clear up a lean injector? I'm asking because some subie mechanics have told me conflicting things. Some say that the injectors don't/ can't get clogged. I don't know if they are too big, or what, but wondering if good cleaner w/do the job, or what will?

 

Guys, I'll ask the mechanic monday if he can check that O2 sensor w/a voltmeter.

 

The thing that made me wonder if this might be due to the valves is that the two valves that were replaced were hit by the piston when the belt came off. I don't mind replacing O2 sensor, etc. if that it, of course. The work that the shop did is still under warantee and I've already spent $ on unrelated stuff that wasn't under warantee. I guess the sensor will be an easy and reliable check w/out needing to buy a new one to find out.

 

Lastly, I can't reconcile needing to buy high 93 oct. gas for now on to keep the code from showing. One mechanic said that rather than doing another head gasket job on my existing heads, that the shop replaced it w/another set of heads off of another car. He said that because the heads are different, I might need to start buying 93 gas instead of regular. Do you guys agree, or see that this makes sense?

 

Thanks,

 

EQ

Edited July 12, 2009 by Equalizer

[Log1call]

Don't know if injector cleaner would help or not but it couldn't hurt.

 

That code is set at light throttle settings so anything that causes a miss under those circumstances could cause it.

In my experiance, and in the normal course of operation, having the plugs a bit too closed or opened can cause the sort of irregular idle/light miss that could cause it. The sort of miss-fire that you are normaly aware of, like plugs miss-firing under load, going up a hill or accelerating hard say, shouldn't cause the code. The other suspect, to my mind would be an air leak causing a slightly lean mixture. The slight air leak though should really show up more at idle.

 

Under your circumstances though, we would be foolish to disregard the fact it has just had some work done on it. You said initialy that two valves had been done. Was this because the new heads had bent valves too? Did they lap all the valves?

[nipper]

Replace the ignition wires. You have the classic symptons of silicon insulation that has failed in the wires. This failure occures either up top or down in the spark plug buckets.

 

 

Have you tired spraying the coil and wires with water in the early evening and looking for sparks?

 

 

nipper