nomadic_addict

I finally did a compression test... the results from 1st to 4th cylinder in pounds per square inch:

#1 - 25 psi, #2 - 65 psi, #3 - 100 psi, #4 - 75 psi

Tried to do a cylinder leak-down test today, but my air compressor maxes out at 115 psi and could not keep up with how bad it was leaking. Once I connected everything, I then turned the regulator knob on my compressor in an attempt to get to the recommended 100 psi, but it would only get to about 70 before it would end up stabilizing at about 50 with the compressor running. So bascially, I had to test at 50 psi due to a small compressor and what seems to be really bad exhaust leaks on all 4 cylinders.

First question is: How important is it to test at 100 psi instead of 50 and could anyone possibly explain why as well? I could try again with someone else's larger compressor if readings at 50 psi really are far less accurate for some reason.

Here are my results from the leak-down test I attempted by regulating with my air compressor and attaching the air hose to a tee that has a pressure gauge on it before it connects to the spark plug hole with a fitting from a regular compression gauge:

Cylinder #1: reg. @ 50 psi -> held 25 psi on leak gauge
Cylinder #2: reg. @ 50 psi -> held 27 psi on leak gauge
Cylinder #3: reg. @ 50 psi -> held 28 psi on leak gauge
Cylinder #4: reg. @ 50 psi -> held 30 psi on leak gauge

That's about 40% leakage on all cylinders with almost all the air blowing out of the tailpipe on all 4.

So you know, I tested each cylinder with the piston at the top of its stroke but just barely starting to move downwards and with the distributor rotor pointing to that cylinder. To my understanding, this would be top dead center of the power stroke which is what is needed. I even tested one at both this position AND at top dead center of the compression stroke for comparision (tested cylinder 1 after testing cylinder 4 without turning crankshaft). It does seem obvious that it leaks more without being on the power stroke, but was still not a huge difference since I am leaking bad anyways.

By using a piece of hose for a stethoscope I could hear air making it to the crankcase through the dipstick hole, but I believe this is probably normal... and because I have never tried this before, I was probably taking long enough for the engine to cool even though I tried to get it to operating temp beforehand.

Leaking did not seem apparent out of the throttle body nor was the coolant bubbling in the radiator when testing any of the cylinders, however... I could feel it blowing out of the tailpipe like it was running except it was a steady stream of air. This was the result I got on all 4 cylinders... and I can't help but to wonder how much air would even end up anywhere else regardless, due to the exhaust leak being the path of least resistance.

Now to my main questions: Should I try this again with a bigger compressor that can hold 100 psi going into the cylinder? Are there any other diagnostics worth doing while the truck is still operational? I am thinking it is time to pull the valve cover... see what the clearances look like on the valves... then pull the head to actually see what the valve seats look like, as well as the camshaft lobes, pistons, and cylinder walls.

The truck still runs, but won't crank or idle due to such bad compression. I have to roll it and pop the clutch to get it going, but seems to drive fairly decent for running on 3 cylinders with exhaust leaks... I just can't take my foot off the throttle when in neutral or it dies.

The engine only has 30,000 miles on it and does not burn any oil, so I am hoping that all my problems can be fixed by replacing or servicing the cylinder head only. I suspect that I also have a blown head gasket, but the oil and coolant are not mixing. I recently saw that my radiator leaks and blows the coolant onto the front of the engine, which had me thinking it was leaking from around the water pump gasket at first. Radiator still holds coolant to where you can see it with the cap off, but will not stay full to the top of the neck. I already took the thermostat out suspecting it was stuck closed.

Also, does anyone know what would cause so much leakage into the exhaust? It does seem like there may a leak at the exhaust manifold, but wouldn't that just keep some air from making it all the way to the tailpipe? Surely, they didn't over-tighten ALL of the exhaust valves?! Is it possible that issues with the camshaft would keep ALL exhaust valves from fully seating? Any other scenarios that would give these same results? I also noticed they must have forced the spark plug into the fourth cylinder, because the threads seem messed up to where it gets tight way before any of the other plugs which thread in alot further before seating. What issues could that cause in itself?

Thanks to anyone taking the time to read all of this, and any advice or suggestions are greatly appreciated. I started to consider machining this head, but am now thinking it may be in too bad of shape to even be worth getting checked for cracks, warpage, etc. from a machine shop... probably gonna need to be helicoiled on the fourth cylinder as well. My main reason for the diagnostics is to know as much as possible, whether or not the block, pistons, cylinders, rings, etc. (bottom end) is at least in as good of condition as it should be. Can I assume the rings have at least seated properly if it is not burning oil?

Thanks again... and sorry... I really did try to sum this up briefly while also remaining thorough with the info given.

Airo Spade

Did you build this engine or did someone else and how far did you build it yourself. What did you reuse or not.

1styota4X4

just a heads up if the air is coming out the intake or the exhaust the valves are open or very poorly seated...what head work was done when the motor was rebuilt...You can pull the valve cover and make sure the cam is in position that the valves are both closed...also have you done anything else to the motor?? I would also recheck the rocker valve clearences....08 intake .12 exhaust if they are less that would keep the valve from completely closing.

when you have the valve cover off also check your timing chain and make sure the marks line up and u didnt jump a tooth or the chain has streched or the drivers side guide is broken

hope this helps and its where i would start to see how deep you need to get into the motor...

nomadic_addict

Thanks for the replies. I haven't done any work to this engine myself as of yet, but will be really soon for the first time. This engine was completely built and installed by yodaman in Santa Rosa, CA less than 3 years ago. I paid alot of money just to have such premature problems, which is why I plan on fixing it myself this time. This will be an ambitious project for me, but I no longer trust anyone else to care enough about my truck to do as good of a job.

The fact that the air leaks out of the tailpipe on all 4 cylinders seems to indicate exhaust valves not seating, but I am wondering if it may be either a camshaft or timing issue for all of them to do this. My biggest concern was to hopefully confirm in some way through diagnostics, before I dissassemble the engine, whether or not the block needs to come out as well. At this point, I am still hoping that a header rebuild or swap would solve my problems.

nomadic_addict

Oh yeah, as far as I can tell... other than having such poor compression, this truck still runs fairly well once I pop the clutch and get it going. Would this be the case if the timing chain were to skip a tooth? All of these parts were "new" with the long block that was installed and the chain has never and still doesn't rattle like I think it would if a guide broke. I'm starting to think either ALL the exhaust valves were left too tight.... or the camshaft lobes happened to wear on all of the exhaust valves. What else would cause them ALL to leak like that.

Anyways, I think I'll go ahead and pull the valve cover for a better look. Thanks again... and any further insight is welcome and appreciated.

nomadic_addict

I've reposted this in the classifieds since I've reached my 15 posts to allow me to. Feel free to use the following link if you would like to follow this thread there:

https://www.yotatech.com/forums/f116...n-test-230800/

Thanks