Looking for suggestions

[Jmclendon]

No dramas. Thanks for the advice. I'm going to try to buy a test kit today or tomorrow, then I'll see how I go.

If I understand the process correctly, it's just a matter of disconnecting the battery, unhooking the leads to the sparkplugs, removing the sparkplugs, reconnecting the battery and then going through each cylinder with the gauge while someone turns the engine over a few times with the throttle down all the way? I've found some tutorials online. But, like lots of things on the internet there are some contradictions.

Sorry for all the questions. My issue is that I understand a lot of the basic theories, but I have almost 0 practical hands on experience. My father was a mechanic (one of those magical types that just seemed to know everything about cars), and he spent a great deal of time talking to me about a lot of this stuff when I was growing up, but there's obviously a vast difference between thinking you know how to do something and actually having the experience of doing it.

[bobdylan]

If you find you have low compression on a cylinder, squirt a little oil in the cylinder, if the compression goes up the you know it is rings, cylinder wear, if it does not go up the it is a valve problem.much easier fix.

[TJ's GMC]

Originally Posted by Jmclendon

No dramas. Thanks for the advice. I'm going to try to buy a test kit today or tomorrow, then I'll see how I go.

If I understand the process correctly, it's just a matter of disconnecting the battery, unhooking the leads to the sparkplugs, removing the sparkplugs, reconnecting the battery and then going through each cylinder with the gauge while someone turns the engine over a few times with the throttle down all the way? I've found some tutorials online. But, like lots of things on the internet there are some contradictions.

Sorry for all the questions. My issue is that I understand a lot of the basic theories, but I have almost 0 practical hands on experience. My father was a mechanic (one of those magical types that just seemed to know everything about cars), and he spent a great deal of time talking to me about a lot of this stuff when I was growing up, but there's obviously a vast difference between thinking you know how to do something and actually having the experience of doing it.

All you have to do is pull the plug wire off the coil and you can leave the rest. Pull one plug at a time and do the test. You don't HAVE to be at WOT as with mine I was pulling 120 PSI without the wot. lol I'd do it with and without for the heck of it. Nice thing is you don't need someone to use the key switch either. You can take a screw driver and touch the power lead of the starter solenoid to the Purple wire terminal on the right side of the solenoid that will kick your starter on so you can do it all in the bay.

[Jmclendon]

Is the fact that I've got an electric fuel pump that kicks on straightaway going to be an issue?

Trying to think about it logically, if the idea is to test the amount of pressure generated in each cylinder, then I would think that I need to leave the pump alone. Otherwise, there won't be any petrol in the cylinder, which I'm assuming would cause a false low reading?

But, if I leave the pump alone, I would think I risk frying the points and flooding the engine?

Not sure if I'm over thinking this (wouldn't be surprising if I am, it's what I do).

[James]

Originally Posted by Jmclendon

Is the fact that I've got an electric fuel pump that kicks on straightaway going to be an issue?

Trying to think about it logically, if the idea is to test the amount of pressure generated in each cylinder, then I would think that I need to leave the pump alone. Otherwise, there won't be any petrol in the cylinder, which I'm assuming would cause a false low reading?

But, if I leave the pump alone, I would think I risk frying the points and flooding the engine?

Not sure if I'm over thinking this (wouldn't be surprising if I am, it's what I do).

As far as safety is concern I would disconnect the electrical wire to the electric pump. If you did have a spark and there is fuel vapor around it could light off.

As far as other servicing I recommend changing the rear axle and transmission oil.

Did you get a front end alignment? If you do one be sure it is performed as per the instruction in the GMC manual. Most shop will place it on the alignment rack and adjust away, big mistake. These truck you need to measure the frame angle and the ride height to get the camber correct. On my truck someone had aligned it like a car with too much camber. With manual steering it was everything I had to turn the wheel while going around the corner. Once I corrected it the steering was still hard but I able to turn the wheel without King Kong helping me. On my truck the spec says -0° 15' to 0° 45' with a 2" ride height. I don't remember what my frame angle was but the manual will tell you how to calculate it in.

[WE7X]

You are testing cylinder compression (basically rings, valves and head gasket sealing), so the fuel pump should not enter into the discussion.
Disconnecting the electric fuel pump will not hurt anything, but is a bit of extra effort.
The fuel pump only refills the carburetor float bowl. If all is working as it should. the only fuel being taken from the float bowl will be as a result of the air being pulled into the engine as a result of the piston and valve action ( the engine is basically a large air pump, to which you add fuel and a spark.....hopefully at the correct volume and time).
By having the throttle wide open, it reduces the vacuum in the manifold and carb, and will draw somewhat less fuel into the manifold and cylinders while cranking. That should not make any significant difference in your compression readings. In general, having the wide open throttle might make readings a bit higher, because there will be less restriction in the air passage. In practice, it is not particularly important, because most of the time you are looking more at relative readings between cylinders; and different compression gauges and procedures will give slightly different results also.

Try to run each cylinder through the same number of compression strokes to be consistent. Usually five of six compression cycles is plenty in a decent motor. Some guys do more, looking for the absolute highest reading. Personally I like to see what happens by the time a motor has gone through three or four compression cycles. Hopefully by four, you will be very close to the maximum pressure. If it is still climbing significantly by the end of four cycles, I would suspect weak rings; but there are a lot of other variables involved.
If you suspect weak rings, the common test is to add a teaspoon of motor oil and retry the test. That helps to temporarily seal the rings an will usually result in higher readings. If the readings go up a lot, then there is likely a ring problem, but just very minor increase could be attributed to the added oil taking up a bit of the combustion chamber volume.
It is all relative, so don't hang your hat on any specific numbers. If it starts OK, and runs relatively smoothly, does not burn a lot of oil, and seems reliable; you should be good to go with it for quite a while.
There will likely be other things to take up your spare time and provide more 'education' on big American iron.

Rod J
Issaquah, WA

[AZKen]

I think you are playing with it too much. You are going to poke your eye out, cause leaks or get paranoid. Drive it.

[Jmclendon]

Originally Posted by AZKen

I think you are playing with it too much. You are going to poke your eye out, cause leaks or get paranoid. Drive it.

LOL point taken. I do have a tendency to go overboard. Thanks!

[TJ's GMC]

Nothing wrong with being cautious. I've almost been stranded for just Driving. lol If you use the screw driver method I mentioned you won't have to disconnect the electric pump, unless it get's its power from the cranking side of the solenoid which I doubt. If you need a picture of what I am talking about I will post one.

[Jmclendon]

I'm too clumsy and scatterbrained to not be cautious. If you've ever met someone that could brake an anvil with a rubber hammer, that's me.

A picture would be awesome. At least then I'll know what I'm looking at is similar to what I've got.