Cylinder not contributing ..

[justin_b31]

I personally think you just have low compression leading to poor combustion. 100psi is right at the threshold of rebuild time.

Based on your feedback, I decided to go back to basics and start from the beginning.

My previous compression tests were done in haste and I did not "go beyond" twist tight (the amount of torque the hose can apply to the fitting). I assumed that the plug threads were in good shape and finger tight was sufficient.

That said, this time around I bought a thread chaser and, with a liberal amount of anti-seize, ran all the plug holes. Needless to say, all plug holes had "stop" spots within a couple turns -not nearly sufficient for a good seal. The corrosion/rust was so much that it literally felt like I hit the end, but I figured that I would keep going as long as there was the slightest give.

cylinder -ave psi
1 150
2 150
3 150
4 138
5 140
6 123



Each plug port was sampled three times for the average PSI. Seeing the low number, I put in 10 or so drops of oil and re-sampled -no change.

So, what am I looking at??

1. blown head gasket (most likely?)
2. valve problems -not likely to affect just one cylinder to this degree?

My initial reaction is to think the head gasket on 6, but that doesn't really explain 4 & 5's lower compression compared to the other side of the engine. Would it be more consistent to have maybe bad valve stems or valve stem seals. Am I waay off base here?

 

[Facimeor]

based on those readings and the fact that you didnt see a gain with oil, I would have to retract my previous statement about compression. While you have a couple lower than the others they are now no longer down at the ragged edge of acceptable. They arent great, but they arent the problem either.

without going back and looking, did you replace the coil for #6? plug wires? how about a different set of plugs (different brand and type as well, I would recommend trying NGK coppers just because they are cheap and reliable.)

 

[justin_b31]

Coil was not replaced because it's a pack for all cylinders. Plugs are new, autolite coppers

 

[Facimeor]

ohh right sorry, OHV motor.

well...air, fuel, compression, spark. There really is very little more involved when you have most cylinders working and only one or two suspect. Sorry, I cant be of more help.

 

[justin_b31]

Decided to do a top-level tear down on the left bank by removing the cylinder head.

The problem in doing so were the other "might as well's".. ie, the A/C hasn't been working -I figured it needed a recharge so I "might as well" convert it over to 134a, and the steering has several degrees of play so I "might as well" fix the steering gearbox or at least adjust it, and well the power steering fluid was pretty nasty so I "might as well" flush that out too.

It simply amazes me how many side projects that have surfaced since starting this cylinder head pull on Saturday.

Anyway, I really am surprised that this engine ran at all. Considering this car was a donor from my brother, who in turn inherited it from mom and dad, who I believe are the original owners -it surprises me how little maintenance they did.

Ah well, here are some pics of the tear down

https://picasaweb.google.com/justin.broos/1993FordExplorerProject?feat=directlink



Now some questions:
1- cylinder six's valve is really recessed.. is this a quick fix by replacing valve or does valve seat need replacement (or something else)

2- what is all that ash deposits on cylinder 5? I can't seem to find anything on google -think I'm asking the wrong question

3- spark plug facing.. I seem to remember something about the open end of the spark needing to face the exhaust port for maximum burn or HP boost. Anyone have insight on this?

Well I'm off to bed, just got this tear down finished and I'm beat

 

[Roadrunner777]

Ash on 5 is because 5 tends to run lean because the intake manifold tends to get loose at that spot. When you install a new Ford dealer intake manifold and torque it precisely, you will have solved that.

 

[Turdle]

cyl 4 spark gap looks tight.

Looks like the best option is new heads. IMO

 

[Facimeor]

yeah I would attept to locate a set of low mile heads and just change em both out.