compression test, one low cylinder

So I just did a compression test on my 04 D2. I have a misfire in cylinder 4 with the code p0304. No other codes.
In addition i also performed a spark test (and replaced 3 mangacores as they broke whilst removing them, thanks mangecore).
All cylinders are getting good spark
PSI are average of three tries dry
Cyl1........185..............has oil on plug, is gummy and dark and there is oil around plug area
Cyl2........188.33.........
Cyl3........145..............WET..........152.33(ave of three tries)
Cyl4........178.33.........
Cyl5........171.66.........
Cyl6........170.............
Cyl7........175..............really clean plug
Cyl8........176.66........oil on plug and around the plug area, not as dirty as plug 1

I did not perform a wet test to the other cylinders as I felt that the compression was high enough that there was no indication of any issues.

So cylinder 4 is misfiring but cylinder 3 has low compression.
Am I missing something here?
Is my p0304 a result of a bad MAF? (I am installing a new one today, plus new plugs)

What about cylinder 3? I feel that since there wasn't a huge jump in compression that it's not the rings, but more likely the valves.

I have a leak down tester, and will run cylinder 3, but i'm seeing what everyone thinks before I go hand cranking the engine over.

Any help or suggestions would be great.

yup.
coils
87
65
43
21
fan

UPDATE : under acceleration the ses will flash. I'll show two tripped codes, p0304 and nothing else. no other code shows up. the engine seems rougher now. changed the plugs, new iac, maf tomorrow. what is up. I also found a leak at the exhaust manifold to down pipe.

UPDATE
installed new maf, no code for 15-20 minutes // ~4 miles, filled up gas and when restarted p0304 immediately tripped.

does anyone have any guess as to what is causing the misfire?

jymmiejamz said:

Did this happen randomly or after some other work was performed?

My guess would be an injector, injector harness, or injector o-ring.

Click to expand...

crap. crap. and crap.

today random. I'm doing everything I can think of on my way to the more involved things.
of chance, do you have any suggestions as to rotating the engine by hand for the leak down test.

squirt said:

Does the sparkplug in cyl 4 look lean or rich? If you leave the ignition on/engine not running with the plug out, can you see/hear/smell fuel filling the cylinder?

If it's not fuel and not spark, then it's mechanical. Do you have access to a borescope? If not, pick one up from Amazon or eBay that will connect to your phone for 15 bucks and have a look inside the cylinder..

That cyl 3 compression business may just be a red herring.

Click to expand...

the truck is running rich. when I pull it into the garage it smell of gas.
the boroscope is a good idea.
when you say mechanical, what are you suggesting..
ill try the plug out with ignition on/engine off

jymmiejamz said:

Getting to the injectors is pretty easy.

The easiest way to rotate the engine by yourself is to remove the fan and use a long ratchet on the crank bolt which is a 24mm.

Click to expand...

thank you

EricTyrrell said:

Ever been rebuilt or new cam/lifters? I've got a similar issue with misfires and rich mixture. I think it's either the incredibly shit cam, valve clearance, or valve sticking.

Click to expand...

at 60k miles, the engine was toast and they gave me a new bottom (i believe), but that was 66K miles ago.
All my O2 sensors went bad about 1-2 years ago, and it never really came back after that, usually running rich. I'm hoping on a sticky valve. I'll let you know what I find this weekend. I'm doing the leak down, I have a boroscope, and I'll try to get as much accomplished as I can without taking the top of the engine off as I have no gaskets yet.

so i just did the leak down test.
i'm losing < 10psi, but from around the spark plug hole itself.

I then just hooked up straight 90psi air into the cylinder and it pushed the cylinder all the way to the bottom, spinning the fan.

I am going to take this as a sign that there is no leak.

What am I missing?

What is throwing that code?

If I have vacuum leak, where should I look. I briefly tried just covering the hoses with my hands while running the engine but got nothing.

UPDATE:
I redid the leak down and got a proper seal on the plug hole. I went from 90psi to 70psi, a 20psi loss. so a 22% leak.

I then reinstalled straight air into the plug hole and heard the air in the oil filler neck.

I can hear the air without opening the oil filler cap. It just gets louder. Noise doesn't change with opening the throttle. No noise out the tail pipe, and no noise in the coolant areas.


A 20% leak still puts my in the green according to most testers.

Any suggestions?

I don't feel that the cylinder is dead, sure the rings might be worn, but would this be the cause of my misfire?

UPDATE to the update:

I noticed that when I attached the air line from the plug hole to the leak down tester, I lost psi.
I also failed to readjust the leak down tester after this.
So, with this in mind, I decided to test two cylinders, 4 and 6.
4.......LDT at 90psi, attach plug hole line, psi drops to 70, adjust back up to 90 and the difference is only ~5psi
6.......LDT at 90psi, attach plug hole line, psi drops to 70, adjust back up to 90 and the difference is only ~2psi.

I hope that I'm doing this correctly.

I can hear the air inside the engine on both cylinder tests.

So now I'm back to the rings are fine.

Maybe a vacuum leak?
Maybe an injector?

Thank you for putting up with me. I appreciate all your help.

squirt said:

Does the sparkplug in cyl 4 look lean or rich? If you leave the ignition on/engine not running with the plug out, can you see/hear/smell fuel filling the cylinder?

If it's not fuel and not spark, then it's mechanical. Do you have access to a borescope? If not, pick one up from Amazon or eBay that will connect to your phone for 15 bucks and have a look inside the cylinder..

That cyl 3 compression business may just be a red herring.

Click to expand...

Nope, cylinder 3 is leaking into the throttle body massively.
So that's a sticky intake valve.

So why no misfire code on #3?

I am correct that the D2 engine is laid out like this............Coil Pack
8 7
6 5
Passenger side 4 3 Drivers side
2 1
Fan

and i'm standing at the front of the truck looking at the engine from the top down