Intake leak

[koda2000]

The throttle body has to be held open to allow air into the engine. Without doing this your measured compression will read lower. So there's no way to really know what your actual compression is. The compression test directions you referenced neglected to mention this step. It does mention that the engine should also be at normal operating temp before performing the compression test, but that may not be possible in your case if you engine wont run.

Your measured compression was low, but as you said not so low that it should be causing major issues.

More Importantly:
If your cat is clogged, it would also cause lower measured compression, backfiring through the intake and lack of power. Start with replacing the cat and then check your fuel trims. Something caused the cat to clog, so you should also replace your pre-cat O2 sensors and check fuel trims afterwards.

 

[David Kilmer]

huh, I had no idea about the need for air for compression check, I will see if there is a difference.

How could a clogged cat cause lower compression, intake backfire and lack of power? I am thinking something else is causing it to run rich hence the cat running hot...... what on earth would it be clogged with? Just trying to understand.
I should test sensors before replacing right? No CEL and no sense in wasting money on something that might actually be working, correct?

Thanks for your time btw

 

[koda2000]

huh, I had no idea about the need for air for compression check, I will see if there is a difference.

How could a clogged cat cause lower compression, intake backfire and lack of power? I am thinking something else is causing it to run rich hence the cat running hot...... what on earth would it be clogged with? Just trying to understand.
I should test sensors before replacing right? No CEL and no sense in wasting money on something that might actually be working, correct?

Thanks for your time btw

I've editing my previous post, so you might want to re-read it... In order to do a valid compression test the engine must be allowed to breath (both in and out).

Your catalytic converter can become clogged with soot, or even melted/broken pieces of the ceramic honeycomb inside the cat. Engines burning oil or running rich ruin catalytic converters. How many miles on your engine? Heated O2 sensors are only good for about 120,000 miles. In my experience malfunctioning O2 don't always set the CEL. Run your finger inside your tail pipe. It should not be black and sooty when you pull it out.

 

[David Kilmer]

I read somewhere it needed to be hot to do a compression test, and with this engine I don't know how to get the tester in holes without burning myself really good, I would imagine the compression would be lower (and more accurate) when hot. Tips on how to get the tester in there without burning myself?
I had all of the spark plugs removed, that doesn't qualify?

The cat is definitely clogged then, because I blew gaskets and it was burning oil and coolent, there is more than likely a ton soot in there. Replacing a cat is not something I could do?

 

[koda2000]

When engine parts get hot they expand, making for a better seal. A better seal will mean higher compression. That's why a hot (or at least a warm) engine will register higher compression.

I wouldn't worry too much about redoing the compression test right now. I'm more concerned about you red-hot cat. Before you replaced the heads were you having the same lack of power, intake backfires and red-hot cat?

 

[David Kilmer]

Before the head gaskets blew, I had power, no backfires and no red hot cat.

 

[David Kilmer]

Before the head gaskets blew, I had power, no backfires and no red hot cat.

 

[koda2000]

Before the head gaskets blew, I had power, no backfires and no red hot cat.

I know you don't want to hear it, but that sounds like a firing order problem. If a spark plug doesn't fire when it supposed to, you end up dumping raw fuel into the exhaust and when it burns the catalytic converter get's read hot. Something is wrong there. Forget the number on your coil, does you coil and wires look exactly to the pic below?

 

[David Kilmer]

It does, the coil has the same number, and the Haynes has the same diagram. I changed the Sparks and wires, and the plugs looked healthy and used when I pulled them to do the compression check.

Could it be my timing chain is stretched or jumped?

 

[koda2000]

It does, the coil has the same number, and the Haynes has the same diagram. I changed the Sparks and wires, and the plugs looked healthy and used when I pulled them to do the compression check.

Could it be my timing chain is stretched or jumped?

Very unlikely your timing chain would have jumped on the OHV engine. Other than the plug wires being on incorrectly, I can think of no other explanation for what you're experiencing. When I changed the plug wires on my daughter's 5.0L V8 a few weeks ago, it took us checking and rechecking the wires 3 times to find the problem (wires 7 & 8 reversed). It ran like crap, smelled of raw fuel and pinged. I'm sure if I let it run for more than a few seconds at a time the cat would have lit up bright red. The symptoms would be worse on a V6, because there are fewer cylinders to work with. Mix up two wires and a 3rd of the engine is effectively not running. I'm out of ideas. Nothing else you did would have caused the problem(s) you experiencing. IIRC, unlike on an older Chevy V6 or V8, Ford's valves have no lash adjustment and your compression isn't terrible, so you know the valves and pistons are doing their job. I don't think the wires for the fuel injectors are long enough to mix them up. IMO all that leaves is spark.

 

[David Kilmer]

I hope that was it, I will check once more

 

[koda2000]

I hope that was it, I will check once more

I just noticed that whoever came up with the color coding for the coil locations v the cylinders screwed up slightly. They have light green for cylinders 3 and light blue for cylinder 6, where the coil shows a kinda pink for cylinders 4 and 6. So go by the numbers and not the colors.

This image is better (color-wise)

 

[David Kilmer]

Verified, firing order is correct

 

[David Kilmer]

So after triple checking the firing order, I decided to turn it on and pull one wire at a time. At number 2, the backfire stopped. So I removed the valve cover and found the guide that is on top of the lifter, off and wedged between the rod and the header, preventing it from moving.

 

[Mr. Alligator]

Congrats! Mystery solved!!! Well done.