Help! Misfire issue.

[JeffyJingles]

Hello everyone, so I have a 2004 ranger 4.0l sohc with 210326 miles on it. Two days ago I was driving in my neighborhood when my cel came one and began flashing. i ran the codes and got P0171 P0300 P0301. So i began to check my plugs, plug wires and coil pack. All were getting power to the plug and i even say spark. I decided i would have a check at the injector. I swapped the injector with the injector on cylinder 4 and still got the same three codes and trucks still running off one cylinder. Im guessing the lean code is all due to the misfire too. Anyone have any ideas on what else I could check?
Also, the truck was running fine until I decided to give it a tune up, by tune up I mean new intake plenum gaskets, throttle body gasket and IAC gasket. Along with the gaskets I cleaned everything real good with CRC throttle body intake cleaner. I have pcm scan tools checking stuff out but I can't pinpoint the problem.

 

[bmerr98]

What made you decide to replace the gaskets and all? I did read the other day that solvents should not be used to clean the IAC valve. Don't know what bad thing happens if you do though...

Lean code are often caused by a vacuum leak somewhere. New intake plenum gaskets...throttle body gasket...IAC gasket...all sealed to keep unfiltered air from being sucked in...possibilities...

 

[JeffyJingles]

I replaced the intake gasket because i had bad surging with the engine while at idle. Once i replaced the gasket the truck was fine for about a week before i started having misfire issues. i did use cleaner on the IAC but not a lot and not on the electrical components.

 

[JeffyJingles]

I did just find cylinder 3 plug wire was a little torn so im gonna replace the wires with an autolite set. although i have tried replacing one of the plug wires from a cylinder that is working to the cylinder 1 where the pcm is reporting misfire and I didnt notice a change or get a different dtc.

 

[JeffyJingles]

Quick Update: Check the gap between the spark plugs made certain they were all at .054 inch. and replaced the plug wires with a new set. Still misfiring, Now i will replace the fuel filter, just for maintenance purposes, and continue the search of why cylinder 1 is missing. I already know the ignition system is functioning properly as I am getting a blue spark from all plugs. after i check the fuel system, i will measure the compression on cylinder 1. Anyone know what cylinder 1 should be coming in with compression?

 

[JeffyJingles]

Giving up for today, checked fuel pressure - 65 psi constant when engine is on, injectors, replaced o rings on the injectors. The only thing I can think I haven't tested for is compression, maybe the timings off?? I just dont know anymore, probably will take it to the shop monday.

 

[RonD]

My guess, and it's only a guess, is that the intake gasket by #1 is leaking, only because that was changed recently.

My 4.0 OHV got a dead spark plug one day while driving it, plug just stopped working, looked fine but quit working, very odd.

Compression should be 160-170psi
But that is with all plugs removed so starter can spin the motor at a good speed.

 

[JeffyJingles]

My guess, and it's only a guess, is that the intake gasket by #1 is leaking, only because that was changed recently.

My 4.0 OHV got a dead spark plug one day while driving it, plug just stopped working, looked fine but quit working, very odd.

Compression should be 160-170psi
But that is with all plugs removed so starter can spin the motor at a good speed.

I did a compression check and cylinder 1 was reporting 25 psi. Then I followed that with a leak down test where It seems that the valve head is to blame. I believe the valve isnt sitting correctly or maybe bent ( since you can hear it tapping when the engine is trying to run ). Going to start taking it apart next weekend. Anyone have any suggestions on whether I should order remanfactured valve heads or just take the valve heads to a shop?

 

[RonD]

Pull the valve cover first, look at the rockers and valve springs on #1.

Rotate crank manually to see how intake and exhaust valves operate.

A Leak down test is when you set a cylinder to TDC(compression stroke), then you apply a known pressure, say 100psi, to the spark plug hole, and read the actual pressure at that cylinder, say it is 95psi, so leak down is 5%, which is fine, then add some oil to that cylinder rotate engine a few times and repeat leak down test, this time is comes up to 98psi, so you have 3% ring loss, 2% valve loss, which again is fine.

Metal to metal seals, like rings and valves should not be 100% sealed, not possible or wanted because of expansion and contraction.

So what were your results?
Could you hear air escaping from intake or exhaust valve?

Could be intake valve isn't opening all the way or at all, that would give low compression but good leak down %.

 

[JeffyJingles]

Pull the valve cover first, look at the rockers and valve springs on #1.

Rotate crank manually to see how intake and exhaust valves operate.

A Leak down test is when you set a cylinder to TDC(compression stroke), then you apply a known pressure, say 100psi, to the spark plug hole, and read the actual pressure at that cylinder, say it is 95psi, so leak down is 5%, which is fine, then add some oil to that cylinder rotate engine a few times and repeat leak down test, this time is comes up to 98psi, so you have 3% ring loss, 2% valve loss, which again is fine.

Metal to metal seals, like rings and valves should not be 100% sealed, not possible or wanted because of expansion and contraction.

So what were your results?
Could you hear air escaping from intake or exhaust valve?

Could be intake valve isn't opening all the way or at all, that would give low compression but good leak down %.

I could hear a a hissing sound and it was very apparent that it was coming from the top of the engine. When I applied the leak down test I only applied 80 psi to the cylinder at TDC and the actual reading from the cylinder was again 15 psi. I did a leak down test to cylinder 2 at the same psi as before and the actual reading was 70 psi, so just from those numbers I concluded valve heads are to blame. The sound of pressure escaping seemed to be coming from the intake side of the valve head but I'm not completely sure whether if its intake or an exhaust valve.

I turned the crank manually only to hear a click sound every time the engine made a rotation.

I have yet to take the valve cover off to get a visual inspection, but ill most likely end up doing it this weekend when I have more free time. This repair will most likely take me a while since the engine had to break down at a time where I am financially struggling but thats the way she goes, I suppose.

 

[70roadrunner]

I would recommend a pair of aftermarket heads, as 95% of factory heads that are available are cracked. as mentioned, I would pull the rocker cover and do a visual inspection. sounds very likely that you have a broken valve spring. if so, you don't even need to pull the heads to replace them

 

[JeffyJingles]

I would recommend a pair of aftermarket heads, as 95% of factory heads that are available are cracked. as mentioned, I would pull the rocker cover and do a visual inspection. sounds very likely that you have a broken valve spring. if so, you don't even need to pull the heads to replace them

Hmm, hopefully its a repair I can do myself, like you said valve spring, where I dont need to pull the motor to remove the valve head and replace them. Although Ill find out this weekend when i remover the cover and take a look.

What brand of aftermaket heads would be best for these 4.0 sohc?

Thanks for the suggestion too.

 

[RonD]

I could hear a a hissing sound and it was very apparent that it was coming from the top of the engine. When I applied the leak down test I only applied 80 psi to the cylinder at TDC and the actual reading from the cylinder was again 15 psi. I did a leak down test to cylinder 2 at the same psi as before and the actual reading was 70 psi, so just from those numbers I concluded valve heads are to blame. The sound of pressure escaping seemed to be coming from the intake side of the valve head but I'm not completely sure whether if its intake or an exhaust valve.

I turned the crank manually only to hear a click sound every time the engine made a rotation.

I have yet to take the valve cover off to get a visual inspection, but ill most likely end up doing it this weekend when I have more free time. This repair will most likely take me a while since the engine had to break down at a time where I am financially struggling but thats the way she goes, I suppose.

Hopefully pulling the valve cover will show an issue not involving pulling the heads.

The 4.0l SOHC has timing chains in the front AND the back of the heads, never pulled them but looks like a PITA.