Cylinder 4 misfire

[Subiedoobie]

Hi All, I’m new to This forum although I’ve been lurking around with no account for a while, but I need some help. I have been trying to figure out an intermittent misfire on my 1999 legacy Outback for over a year now and I am not having much luck. The car runs and I daily drive it, but it vibrates at idle, especially when in drive/reverse and I have intermittent misfiring when driving, especially at around half throttle and when going uphill. If I push the gas pedal down the misfire always goes away. It also misfired worse when using anything electrical (windows, ac, turn signals, headlights). I have a CEL for engine misfire cyl 4.

I have recently replaced battery, alternator, spark plugs, wires, and coil and it seems like I have a strong spark. 

I did a compression test and I have 165 psi on all cylinders with very little variation.

I swapped fuel injectors 3 and 4. Misfire stayed on cyl 4. I tried cleaning and then replacing with a reman injector #4. No change.

I’m thinking there could be a problem with my injector wiring, but I don’t know to test for this. Can anyone point me in t he right direction?

I’m going to try cleaning my grounds this weekend. Can someone tell me where the most likely culprit would be?

Any other ideas on what to check?

 

 

 

 

Edited June 4, 2022 by Subiedoobie

[1 Lucky Texan]

7 hours ago, Subiedoobie said:

cap and rotor

?????

I like the ground cleaning you have planned.

 

Throttle Position Sensor could have a 'dead spot' in its mid-range sweep. though I wouldn't overlook the possibility of more than a single issue given you symptoms.

could be battery cable is corroded under the insulation.

 

Possible bad Knock sensor - cheap easy to swap, if bad, often the plastic housing will be cracked.

automatic transmission? aftermarket axles can cause vibrations when stopped but in gear, goes away in P or N - seems weird, but it's a legit problem for some folks.

I suppose, if the car is missing at idle, you could squirt some ether start or even an unlit stream of propane from a handheld torch into the intake.If it smoothe-out, could be a fueling problem.  Have you measured the system voltage?

Edited June 3, 2022 by 1 Lucky Texan

[heartless]

13 hours ago, Subiedoobie said:

 .....spark plugs, wires, cap and rotor, and coil.....

spark plugs should be basic NGK copper cores, anything else is a waste of money on this car

wires should be OEM or NGK brand ONLY - anything else wont last and are known to be problematic.

cap and rotor???? your car does not have these items, so not sure what you think you replaced?

coil - pretty rare for an OEM coil to fail.. yes, it does happen, but not that often and when they do, they usually put on a show. Aftermarket are not nearly as good.

 

so, when did the misfire start happening? before all the work, or after?

have you pulled the spark plug on cyl 4 to check for fouling or other issues?

[Subiedoobie]

On 6/2/2022 at 10:38 PM, 1 Lucky Texan said:

?????

I like the ground cleaning you have planned.

 

Throttle Position Sensor could have a 'dead spot' in its mid-range sweep. though I wouldn't overlook the possibility of more than a single issue given you symptoms.

could be battery cable is corroded under the insulation.

 

Possible bad Knock sensor - cheap easy to swap, if bad, often the plastic housing will be cracked.

automatic transmission? aftermarket axles can cause vibrations when stopped but in gear, goes away in P or N - seems weird, but it's a legit problem for some folks.

I suppose, if the car is missing at idle, you could squirt some ether start or even an unlit stream of propane from a handheld torch into the intake.If it smoothe-out, could be a fueling problem.  Have you measured the system voltage?

TPS and knock sensor have both been replaced recently. The old knock sensor was cracked like you mentioned.

it is an automatic and I’ve heard of this. I’m not sure if the axles have been replaced at any point so I might try getting some oem ones. It smoothed out a little in P and N but the vibration is still there.

thanks for your suggestions. I’ll try the propane into intake and checking out the battery cable. I have have a charger that shows me the voltage constantly when I’m driving. It’s usually 14.1-14.5 when running and drops down to around 12.8-13 while I’m rolling down all the windows. I sometimes notice more vibrations when I use electrical components. Does that sound normal for voltage?

 

[Subiedoobie]

On 6/3/2022 at 4:21 AM, heartless said:

spark plugs should be basic NGK copper cores, anything else is a waste of money on this car

wires should be OEM or NGK brand ONLY - anything else wont last and are known to be problematic.

cap and rotor???? your car does not have these items, so not sure what you think you replaced?

coil - pretty rare for an OEM coil to fail.. yes, it does happen, but not that often and when they do, they usually put on a show. Aftermarket are not nearly as good.

 

so, when did the misfire start happening? before all the work, or after?

have you pulled the spark plug on cyl 4 to check for fouling or other issues?

Lol, you’re right there’s no cap and rotor, I’m getting my vehicles confused. The new coil made no difference so I’ll probably throw t he original back on to avoid any complications that may have caused. 
 

I think I went with NGK copper plugs and wires, but I’ll double check. 
 

I got it from a friend and he said this misfires just started randomly. All he tried was replacing the motor mounts and that didn’t help. The car had been bd tiring and there was lots of evidence of rodents u see the hood which is partly why I’m suspecting an electrical issue. The knock sensor wiring had be an chewed on.

All of my spark plugs looked fine when I checked the compression, but I’ll take a look again now that it has some miles on but he new plugs. 
 

I appreciate the help. I’ll report back with my findings

[heartless]

yeah, chewed wiring could be an issue. a big one.
was the wiring chewed close to the sensor?
was the sensor replaced?

motor mounts are totally unrelated to misfiring, so no, does not surprise me it made no difference.