Hi I've got a 2005 Ranger edge 3.0 5speed. I have been having lean codes for both banks as well as misfire codes for cyl 4 and so I did compression test. Results are as follows 1-173 2-160 3-169 4-138 5-125 6-178. I figured this is the notorious valve seat recession problem so I did a leak down test to confirm. Plugged my air compressor to the compression tester with about 120 psi. Opened the throttle body to see if I could hear any hissing and put my hand over it-no pressure build up. Opened oil fill cap put my hand on it-nothing. Went back to the tail pipe and I couldn't hear anything and put my hand on it- no pressure build up. I did this procedure on both cyl 4 and 5.

I have had this issue for a while and can almost guarantee it is not a vacuum leak. I feel like this compression test is leading to the right answer, Is the next step a wet compression test? I do not want to redo the heads if that is not what is going to fix this.

Thanks,
Sam

 

Is there actual running issues, misfires under load, rough idle?
If so does it do it more with cold engine or warmed up engine?

What were/are the "codes for both banks"?
Misfires tend to set Lean Codes

The compression numbers do show #4 and #5 as for sure having problems, and #2 on its way
Is it burning any oil?
Do spark plug tips look blackish?
Or is the PCV Valve getting very oily very quickly?
That would indicate "blow-by"/ring issues
If not then its for sure exhaust valve issues, so head issue

Exhaust valves are the reason most people have heard the term "Valve Job", lol, any engine with valves will at some point get burnt exhaust valves if they are used long enough
The 3.0l Vulcans seem a little more susceptible to this, and the 2004-2006 models especially

No sure why applying air pressure to #4 or #5 at TDC didn't result in a definitive leak point
What was the Leak down %?
i.e. 120psi IN, what did pressure hold at

Yes, a wet test would confirm which are leaking, Rings or Valves
Compression will always go up on wet test but if it doesn't come up to your 160+psi average then its not a ring issue

 

There is a little misfire at idle even when cold. I have noticed that the power is not great under about 2500 rpms, but definitely drivable . It intermittently will get really bad misfire that shakes the whole truck and the CEL will start blinking because the computer is aware of it. When this happens there is severe power loss and I can barely get the truck rolling in first gear. I have noticed this happens a lot when I have been driving on the highway and then when I come to a stop and let it idle at a light and it will start missing pretty bad. I should mention that I have never had power loss driving down the highway at higher speeds, it always starts happening at idle. Sometimes when it is doing this and I can barely get going in first it's like a switch turns on and I get full power back all of a sudden.

As for the codes I am getting P0171 and P0174 I believe as well as cyl 4 misfire code and random misfire on start up (dont remember exact number for code I can look it up after work if you need)

Spark plug tips do not look black and the truck is not really burning oil at an alarming rate for a truck with 165k miles. For example I maybe have to top it off once between oil changes(every 5k miles)

I was really surprised with the leakdown test, I let the compressor run until it reached 120 psi then turned it off and it held at that psi for several minutes while I looked for any possible leaks

I really think this is a head problem but, I do want to rule out the rings before I make any assumptions so I will be doing a wet test

As always thanks Ron

 

Just a heads up, the 3.0l Vulcan has its highest torque/power at 3,500 to 3,900, other engines do that at 2,500-2,900
It was specifically designed as a high RPM engine
3.0l specs seen here: https://www.therangerstation.com/tec...nger-3-0l-v-6/

Flashing CEL means "back off the gas", "damaging misfires detected"

Yes, no doubt heads will need to come off and be serviced

The main issues with misfires and fuel injection is the way the system works
Computer calculates air/fuel mix based on RPM, it already knows its running a 3 Litre engine so it knows exactly how much air is coming in at any RPM, its just math
And it knows the size of the injectors and "fuel pressure"
So it can easily calculate the 14.7/1 air/fuel ratio

It then looks at the O2 sensor on that bank after its calculated mix has be "burned"
O2s can ONLY see oxygen, not fuel
If a cylinder misfires then no oxygen was burned up............................and that oxygen is dumped into the exhaust
High oxygen in the exhaust is interpreted as Lean(low oxygen Rich)
We tend to think Lean means too little fuel and Rich is too much fuel

So O2 shows too much Oxygen, Lean, and computer then adds more fuel, and more fuel and more fuel until the firing cylinders on that bank are now also misfiring, lol
So a misfire can propagate other misfires in some situations, by skewing the Fuel Trims too far
Computer is doing its best given the data its getting from sensors

The reason we need compression is to vaporize liquid gasoline, can't ignite liquid gasoline with a spark, yes the movie guys take liberties with that one, lol
Only gasoline vapor/fumes can be ignited with a spark, spark plug in the gas tank doesn't actually work to blow up a car
Compression heats up the gasoline and instantly vaporizes it, if its high enough
Static compression of 150psi, is about 80psi when engine is running, so about 40% less
When static compression drops into the 130psi range you start to run into issues, you get partial misfires, incomplete "burn" so that cylinder doesn't add as much power to the crank and you can feel it, especially under a load
And complete misfires you really feel, no ignition at all