P304 problem

[1up]

I have a miss and cannot figure it out.
Currently I have a miss at idle, but cleans up once I apply some rpm, and seems to have good power, I get the P304 on my code reader.

Engine is the 3.0 with the plastic intake manifold (no egr valve)
2002 Ranger XLT 196,000 miles

It started with a P104 (?) lean condition cyl 4, I did a smoke test and found smoke leaking in the crankcase, so I replaced the intake gaskets, and fixed that problem.

This then was followed by the P304, I thought it was possibly the fuel injectors, so I tested (ohm) and cleaned all of the injectors, I have replaced the coil,plugs and wires, idle air control valve and still have a miss at idle. I got a compression tester from Autozone and cannot get it to read (on any cylinder) I have an old compression tester and cannot get it to read either (I don't know why) the plugs look good the porcelain is white, no fuel build up and no chalky white either.
I did a live scan with my code reader and the long fuel trim bank 2 goes from 10% at Idle to 2/3% off idle (1500 rpm and up)
Mechanically I do not hear any excessive valve tapping/noises.
I have put 'sea foam' directly into the intake ports, also fed it through the intake before the throttle body, hoping to clean off the valves.
I am concerned about the PCV valve in the crankcase as there seems to be oil in the intake, I noticed it around the rubber gasket from the upper to lower intake manifold when I cleaned the injectors the other day, I did just replace the PCV valve and hose elbow about 8 months ago.

Am I missing anything? any tips would help.
Thanks.
Curt

 

[adsm08]

You need to figure out why you can't get a compression reading and then get those numbers. The 3.0 around that year had valve seat issues that caused misfires and compression loss.

 

[RonD]

Yes, +1 ^^^

Misfire code is generated by Crank and Cam sensors
Computer can time rotation of engine using both and can predict how much time(milliseconds) will passed before next cylinder fires and ADDS rotational speed to crank/Cam.
If a cylinder fails to fire or doesn't fire fully then speed is not increased, this doesn't set a misfire code instantly, it must be repeated a few times and at specific RPMs to set a code.

You can feel the misfire at idle so it is real and repeats so sets the P0304 code.

Does it misfire Cold or just after it warms up a bit?

Spark, at the right time
Fuel, in the correct mix with air
Compression, within 15% of other cylinders

These are the 3 things needed for a cylinder to fire, it's as simple and as complicated as that.

3.0l, 1995 and up, used Waste Spark system, so cylinders 3 and 4 share the same coil in the coil pack and both spark at the same time, at or about TDC.
You could swap 3 and 4 spark plug wires on the coil pack and see if misfire changed to #3, but since you have changed the coil and wires I doubt that would be the problem.

At idle computer will run engine Richer so it doesn't overheat, also when engine is cold it runs Rich(choke mode)
So generally a Lean misfire will show up under load, not when idling, but a dirty tip on an injector can cause lean misfire at idle.

Compression should usually be the first stop when you have a specific misfire.
Reason being is that compression is rarely "intermittent", like spark or fuel can be, it is black and white, bad or good, and once tested it can be taken off the table as the problem or found to be the cause of the problem so you don't waste time and money on non-fixes.

3.0l runs 9.3:1 compression ratio, so you would expect 165psi on tests
You should remove all 6 spark plugs first
Then test each cylinder #1 to #6 and write it down.
With all spark plugs removed you get good crank speed so good results
You need to get an average from the other 5 cylinders to see if #4 has a problem

 

[1up]

Thanks for the tips.
I'll work on getting good compression readings.
Strange thing happend today after I reassembled everything, I pulled #1,4,5, spark plugs for the compression test, after I put it all back togethe the missfire was very slight, I ran live data and fuel trim was at 3% on both banks, but after 1/2 mile it all came back,trim bumped up to 10% at idle. I also developed a PO301 misfire of cyl #1 and the 10% fuel trim at idle also.
I'ts done that a few times where it seems to go away but comes right back.
Curt

 

[B16racereg6]

Man just run that truck, it’s got a lot of miles and the cash value is low run that truck. It’s a daily work truck? over time lots of miles the motor is tired mine has 350,000 it misses lightly also. I think it’s just a combo of old age and high miles. Good luck man

 

[RonD]

Fuel trim should go high at idle, or engine will over heat