Well i have been chasing a miss in my bronco and finally had a chance to ck compression in it. Well it has like 25psi, wtf. Checked a few other and they are 150psi. I put oil in it and rechecked and no diference. Usually if rings are bad wont it go up? I know the engine has massive carbon build up and maybe some is stuck around the valves or something, but its just cyl #2. Dont feel like pulling it apart. What are yall thinkin?

 

Put a couple tablespoons worth of engine oil down the plug hole and test it again.

If it raises the compression considerably its excessive wear, if not its of a more severe mechanical failure, something broke.

Won't correct it but would give you a incantation of what the nature of the failure is and how to proceed.

If the compression reading doesn't come up at all with the oil test, pull the valve cover and make sure you don't have a bent push rod or broken or loose rocker arm.

Say like the intake valve, valve doesn't open, no air in, no air to compress etc, etc.

 

I agree valve cover is next. Do a good inspection if there's something wrong enough to cause that much of a compression drop, chances are you'll see it right away.

If not remove all the rockers on that side and put a strait edge across the top of the valves. When all the valves are closed they should be the same height. If one is low it's bent, if high it's sunken.

 

you could have a burnt valve and it would not be seen until head was removed.

 

Damn i just had the upper off, I just seafoamed it again and its gotten alot better, but still there. Ill have to pull the valve cover off when I have time.

 

true, but no way to know until the head is removed.

Another good trick is to move that cylinder to TDC of compression and apply compressed air through the spark plug. This will tell you if there is a compression leak where it is going.

 

in the long run, the head will have to come off to see and fix what is wrong.

 

Not if it's a problem with many of the other things that could cause low compression, cam, lifter, pushrod, rocker. And knowing what is wrong as early as possable can be very helpfull in deciding what to do.

95F350XL, it could very easy be as simple as a bad valve adjustment, make sure that the pushrods are loose enough to spin with a couple of fingers when the valves on that cylinder are closed.

 

we will just have to see.

 

Yea it will be a while as this is car #4 so it dont matter if its running good or not. I just drive it every once in a while. Guess thats what happens when you get it for free not knowing whats wrong with it.

 

Sorry missed the part where you stated you did the oil test already. I gotta sit closer to my monitor in the mornings! lol

Anyway when you say <i>Damn i just had the upper off,</i> what exactly did you have apart? Did you have the heads off?

And when you say

<i>I just seafoamed it again and its gotten alot better, but still there.</i>

coupled with

<i>Yea it will be a while as this is car #4 so it dont matter if its running good or not. I just drive it every once in a while. Guess thats what happens when you get it for free not knowing whats wrong with it.</i>

leads me to think this truck has sat for long periods of time.

The fact you put seafoam in it and it helped at all let alone a lot tells me the rings in that piston might just be stuck in the groves from sitting.

Remove that plug and turn the motor until the piston is down very near the bottom of the stroke, you want it near the bottom to take advantage of the slight cylinder taper. Put several ounces of clean tranny fluid down the plug hole and put the plug back in and let it sit a few days like that.
After 3-4 days when ever you next have a minute remove that plug, take the coil wire off and turn the motor over with the starter to blow out the fluid. Put the plug and coil wire back on, start it and let it get up to full temp, turn it off and let it cool all the way down, repeat this a few times. If the rings are stuck in the ring groves the tranny fluid and temperature changes may break them loose.
Worth a shot, slim one ya but it sound's as you don't "need" it right away anyway and have nothing to loose but a little time and 5 or 6 ounces of tranny fluid.

 

Ok here is full story. Truck sat for 1-2 years. Pulled it home, put in a battery and some gas and fired it up. Missed like hell which I did know. I did work for the kid and said give me the bronk as payment. So after a few days of looking I pulled the upper intake off to find that there was a mouse nest under the upper intake and it had chewed through cyl num 3 and 4 inj wires. So I repinned them and put it back together. Ran great but still felt a slight miss. Put new cap, rotor, wires, plugs in it and ran it for a day or so. Pulled plugs to recheck and the cyl #2 plug was black and wet. I know when I 1st pulled em the num 3 and 4 were black and all the rest were good. So that lead me to think maybe injector. So I checked with a noid light to make sure the inj wire for cyl 2 was pulsing and it was. So i pulled the inj while running and no diff. So I just changed that injector and it got better but still missing. Plug now worse with new inj then old inj. Sometime while doing all this I did seafoam it. Then today I decided to reseafoam it. Runs alot better. There was alot of carbon build up on the injector I pulled out, plus the runners were real bad also. Cleaned them up while I had the upper off. So as of last night I cked compression and its 25. Checked 1 or 2 others and they were 150. So I fig something with 2 has to be messed up.

Ill try the trans fluid in it and do as ya say. We will see how that goes. I did take it for a 20 min drive after I seafoamed it today and the miss is down alot so im guessin a piece of carbon might be stuck on the valve or something along those lines.

 

Just wondering, when you looked at the #2 plug was is a glossy black or a flat black?

 

I was under the impression the use of seafoam had increased the compression reading, that you took a reading before and then after using it.

The tranny fluid may still work, but it may not. Sounds like you got two cylinders back already and they might have had the same problem, really hard to say at this point.

I brought a old ALLIS-CHALMERS tractor back to life that sat unused for years with the same process, granted it was totally froze up and I had to pull the head first to free it up so it would turn over to start with. Got it to turn, put the head back on but very little to no compression on any given cylinder, used the same method with the fluid down the plug holes to free up the rings and got it back.

 

The plug is wet and smells like gas. So id say glossy.