P0300 misfire at idle on 5 & 8 stops when held at 3000 rpm

[mechanicalchic]

2001 4.0
Check engine light started flashing. Changed plugs, coil packs, valve cover gaskets, intake manifold gaskets. 
Borrowed scan tool from a friend and the code is P0300. Cylinders 5 & 8 are misfiring at idle and on acceleration cylinder 3 also misfires slightly. If I hold the rpms at 3000 the check engine light stops blinking and shuts off and the misfire stops. The car does not feel like it is misfiring at all when I drive it. The display on the dash tells me the coolant is always low and when it warms up, sometimes it displays low oil pressure. I love this car, but I obviously can't enjoy it with the check engine light flashing. Please help me fix my beast!

[mechanicalchic]

Also, the climate control has decided to not work properly. The heat works on passenger side, but only blows cold air to driver. Could all of this be related to a PCM issue?

[genedjr]

Check this out.

aurorah.proboards.com/thread/28582/2001-aurora-0l-misfire-help

I am still fighting this a bit.  Hopefully my experience helps.

From what you say I am thinking you still have a vacuum leak.  Also, can the scan tool do real time measurements?  That helped me alot.
...gene

[Randy T.]

Your climate control issue is more than likely separate from your miss problem, on the climate issue it sounds like you have a bad blend door actuator.

[genedjr]

Nov 9, 2014 16:50:56 GMT -6 mechanicalchic said:

Also, the climate control has decided to not work properly. The heat works on passenger side, but only blows cold air to driver. Could all of this be related to a PCM issue?

Check my post out here - aurorah.proboards.com/thread/28872/high-side-fan-kicking

You most likely have a (or a few ) bled door actuator broken.  They are a pain to get to.  But there are zillions of them at the junk yard.
...gene

[mechanicalchic]

Thanks for the information!
The scan tool does give real time information, but I don't understand it all other than seeing the misfires per cylinder. I am going to replace all the spark plug boots and change the plugs to AC Delco. I also have a new coolant tank on order.
I will change the actuator for the climate control and see if that does the trick. Everything on this car seems tough to get at
I will update after I get a few more things done.

[mechanicalchic]

I have been trying to find a diagram for the vacuum lines so I can check to make sure it is all routed correctly. Anyone have one handy?

[genedjr]

Nov 26, 2014 8:33:34 GMT -6 mechanicalchic said:

Thanks for the information!
The scan tool does give real time information, but I don't understand it all other than seeing the misfires per cylinder. I am going to replace all the spark plug boots and change the plugs to AC Delco. I also have a new coolant tank on order.
I will change the actuator for the climate control and see if that does the trick. Everything on this car seems tough to get at
I will update after I get a few more things done.

When you pull the actuators (there are a few in there) open them up (held together by screws) look at the gears, its fairly easy to see broken ones.  Also open up the junk yard ones, as these do break often.
...gene

[mechanicalchic]

Put in new boots, new AC Delco spark plugs and the scanner still shows misfire on 5 & 8.

[genedjr]

Did you try swapping the coil packs?  See if this issue moves with the pack?  That will point you to the coil pack or ignition controller.
...gene

[tigger]

Dec 1, 2014 15:50:17 GMT -6 genedjr said:

Did you try swapping the coil packs?  See if this issue moves with the pack?  That will point you to the coil pack or ignition controller.
...gene

Good advice, after you swap the packs miss will move from 5 & 8 to 1 & 4 if they're bad.

Couple simple things I didn't see mentioned;
MAF cleaner
Fuel system cleaner
Change PVC
Clean Throttle Body
Check Fuel Pressure

[mechanicalchic]

I did swap the packs, I forgot to mention that, and the miss does not move. I tried some Lucas fuel system cleaner, too. How about the camshaft or crankshaft sensors?

[mechanicalchic]

Also, I changed the coolant tank and the low coolant warning has stopped

[mechanicalchic]

Any diagrams available for where the ckp sensors are located on 2001 4.0?

[genedjr]

See my how-to for the crank position sensors.
aurorah.proboards.com/thread/28973/0l-changing-crank-positions-sensors

But, with the misfire being confined to 2 cylinders, I am thinking injectors.  Or (shutter) burned valves.  Have you done a compression check?  That would tell the tail if there are mechanical issues.
...gene

[sempar]

The FSM also suggests checking for vacuum leaks around the o-rings of the affected cylinder injectors and make sure the there isn't a vacuum leak at the same intake ports.

John

[mechanicalchic]

Checked the resistance of each injector and they are all between 11.2 and 11.8 ohms. So I think the injectors are ok. What would be the best way to check for vacuum leaks at the affected cylinder injectors?

[mechanicalchic]

I haven't done a compression check. Honestly, I don't even know how or what equipment I need.

[Randy T.]

To check injectors, sometimes people lift the rail and watch the injector spray pattern. Injectors are easy to change, I would recommend swapping your injectors to different spots, like the coil packs, and see if there is a change. I have not heard of your method of checking the injectors.

[genedjr]

Dec 3, 2014 9:32:13 GMT -6 mechanicalchic said:

Checked the resistance of each injector and they are all between 11.2 and 11.8 ohms. So I think the injectors are ok. What would be the best way to check for vacuum leaks at the affected cylinder injectors?

The injectors commonly have a little screen/filter at the top that can get clogged.  Removing the fuel rail and watching them spray is also good, but be really careful and do it with a cold engine.

As suggested moving 5 and 8 to different spots, and check the little screens when doing so.

An ohm check will tell you if the coil is bad.  If there is no continuity - the coil is shot.  But it tells little else.
www.youtube.com/watch?v=wi90kx32c10

You may also clean the injectors - this is a poor video, but shows how.
www.youtube.com/watch?v=rLuAVhVp44Y

...gene