I haven't been getting responses so thought I would post here. I am getting my backside kicked and don't want to spend more money and time without some help.
I am getting a number 4 misfire code along with a noticeable miss espcially at throttle up from idle. To date I have done the following:
Replaced plugs, removed tested cleaned and swapped injector with another cylinder, swapped plug wires, replaced intake gaskets, cleaned carbon from intake ports, replaced coil pack, cleaned maf sensor, inspected for vacuum leaks by trying propane, wd40, checked for any jumping plug wires by spraying water and ammonia mixture, bought a code reader with scanning ability and confirmed o2 sensors are operating normally, cleaned egr valve, pulled my hair out, etc. The following is the freeze frame data and live data taken at idle.
P0304
RPM 1697
Load 58.0%
coolant 185
STFTRM1 .8
LTFTRM1 -2.3
STFTRM2 2.3
LTFTRM2 -7.0
MPH 45
Fuel Sys Closed
So then I decided to take some readings at idle:
ABSLT TPS 19.6
RPM 1054
Load 51%
MAF 1.12
Coolant 81
IAT 25
IGN Adv 15.5
STFTRM1 9.4
LTFTRM1 0
STFTRM2 4.7
LTFTRM2 3.9
02S11V .070
STFTRM11 1.6
02S12V .5
02S21V .75
STFTRM21 0
OBDII STAT CA

Any help is appreciated.

 

I would pull your plugs and check them for cracks. I changed mine trying to get rid of a misfire, never checked the new plugs for cracks, then figured it was something else. Couldn't be plugs right? They are new. Stuck a few other parts on it also. Finally got a misfire code, so I pulled the plugs and the misfiring cylinder plug was cracked. Either right out of the box, or I cracked it putting it in. Just check them, it might stop you from going insane.

 

will do. What I haven't got my arms around yet is when you get a misfire code as such is it truely isolated to that cylinder or is this just the luck that this is the one that is kicking? I think it should be isolated as other cylinders could give a code as well.

 

Mine was to the #3 cylinder and that one had the bad plug.

 

Replaced the plugs and wires tonight. Plugs on the left side of the engine were replaced for the second time. I know better than this as the way I troubleshot it should have revealed the problem. In desperation I have spent money and shouldn't have. I am bringing a borescope home from work tomorrow and going up through the plug hole to take a look at the valve and head area. I have access to a high def 4 mm scope so this should reveal any issues.

 

If its a sohc I d check for a broken valve spring.

 

Wanted to give an update and also looking for some advice. 04XLTFX was correct. Broken exhaust valve on #4 cylinder. So I have two questions...To remove the cam is it possible to pull the timing chain/gear assy from the cam without major dis-assy? It would seem that I might be able to pull the bolt and get it off though not sure. The second question is, can you get the piston on top dead center and pressurize the cylinder to get enough pressure on the valve to replace the spring without pulling the head? I have done this a lot on small aircraft engines though not sure if it would work in this case.

 

Dont pull the cam or sprocket. If you have a relationship with you Dealer. Borrow the valve spring compressor for the 4.0. It wraps around the cam and pushes the spring down till you can get the followers out.Then pull the keepers off with a magnet. Your right you have to blow air in the sparkplug hole to hold the valve up. the piston will go down to the bottom if you dont hold the crank with something. YOu dont have to be top dead center with the piston. With the followers out of #4 the valve are closed.

 

Thanks for the info 04XLTFX4. The only reason to get the piston at TDC is this will eliminate the need to hold the crank. Once the air is put to the cylinder it will stop any movement of the piston unless you try and pull it over TDC. The only kicker with this is if it is not tdc it will indeed push the piston. Not that hard to do though. I don't have access to a tool though if I could get a pic of it I can probably make one.

 

Final post and she is fixed. Couldn't find a lifter tool to use so with some assistance I was able to use a boxed end wrench for the particular spring that was broke. Wouldn't work on all cylinders though I got away with it.
Thanks for all the help and happy driving!

 

Cool,Where there s a will theres a way.