Low Compression #5 Cylinder--Advice Needed

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Background: I've got 2.5 years and 4k miles on a complete engine rebuild that was done in preparation for the turbo kit. After the job was completed, I was not happy with the work due to the little details the shop missed. I took it back to them, it sat in their lot for a month, and eventually I said f*** it and picked it up. It left me wondering how the internals would hold up...

Three weeks ago I started getting a CEL for a #5 cylinder misfire (P0305) along with a pending random misfire P0300. Put in a new spark plug and new Toyota spark plug wires and nothing changed. The main symptom is a very rouge idle, I don't notice anything at driving speeds.

Since nearly everything on this rig is new, including the engine wiring harness, I decided to get a compression test kit from HF. From listening the to fuel injectors with a stethoscope, they sounded fine.

Compression Test:

#1 cylinder = 190
#2 cylinder = 185

#5 cylinder = 90 (tested 3x, including once with a teaspoon of oil and it read the same). I stopped testing compression here.

Next Steps:


The 80 is my DD. Will I make anything worse by continuing to drive as is? Should I disconnect the plug cable from the distributor cap?

I know the only correct answer is to start tearing it down, but I've got to find another drivable vehicle first. My Delta rear bumper was also delivered today lol 🤦🏼‍♂️
 
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Background: I've got 2.5 years and 4k miles on a complete engine rebuild that was done in preparation for the turbo kit. After the job was completed, I was not happy with the work due to the little details the shop missed. I took it back to them, it sat in their lot for a month, and eventually I said f*** it and picked it up. It left me wondering how the internals would hold up...

Three weeks ago I started getting a CEL for a #5 cylinder misfire (P0305) along with a pending random misfire P0300. Put in a new spark plug and new Toyota spark plug wires and nothing changed. The main symptom is a very rouge idle, I don't notice anything at driving speeds.

Since nearly everything on this rig is new, including the engine wiring harness, I decided to get a compression test kit from HF. From listening the to fuel injectors with a stethoscope, they sounded fine.

Compression Test:

#1 cylinder = 190
#2 cylinder = 185

#5 cylinder = 90 (tested 3x, including once with a teaspoon of oil and it read the same). I stopped testing compression here.

Next Steps:

The 80 is my DD. Will I make anything worse by continuing to drive as is? Should I disconnect the plug cable from the distributor cap?

I know the only correct answer is to start tearing it down, but I've got to find another drivable vehicle first. My Delta rear bumper was also delivered today lol 🤦🏼‍♂️
You need to do a leakdown test to determine if it is crankcase (rings) intake/exhaust manifold (valves) or cooling system (head gasket)

Since the oil in the cylinder didn't change the compression numbers, it would lead me to believe it is valve or HG related.
 
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Got the Leakdown kit from HF, input 90 PSI and cylinder holds 20 PSI. No air bubbles in radiator or air escaping from oil filler cap. I do hear air when I use the stethoscope down the oil dipstick tube. No air sounds are heard with the naked ear. So probably a bad ring? These were replaced during the overhaul and doesn't match with oil trick during the compression test.
 
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Verified #5 piston was TDC (piston all the way up) with an inspection camera. None of the other plugs were removed, if that matters.
 

White Sheep

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Recently my HG was blown between the 5th/6th cylinders. I wasn't losing coolant (that I could tell), and no smoke out the tailpipe, but it idled horribly when in drive and very lower 5th/6th comprehension.

20210903_105832.jpg
20210903_110926.jpg


I know your running a turbo and Im running a supercharger which may have help speed up the blown HG process.

It sucks that it happened, but it was also a good thing. I got the engine rebuilt and did some things in the engine bay which I wanted to do anyway.
 
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Got the Leakdown kit from HF, input 90 PSI and cylinder holds 20 PSI. No air bubbles in radiator or air escaping from oil filler cap. I do hear air when I use the stethoscope down the oil dipstick tube. No air sounds are heard with the naked ear. So probably a bad ring? These were replaced during the overhaul and doesn't match with oil trick during the compression test.
If you hear air through the intake, the intake valve is having a problem.

If you hear air through the exhaust pipe, the exhaust valve is having a problem.

There will ALWAYS be some air leaking past the rings, as they have a gap in them as they are staggered, but the leak by design. The percentage of leak coupled with the compression test will determine if the rings are a problem.

If you have a scope, what does the top of the piston look like on #5? How about the cylinder wall? Any big scratches on the cylinder wall?

Use the scope to look inside each cylinder to compare the look of one cylinder to the next.

Then decide to pull the head and get to the root of the issue.

Leakdown test procedure
 
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To clarify, the turbo is already installed. That being said, would this inhibit hearing leaking air through the exhaust?
 
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To clarify, the turbo is already installed. That being said, would this inhibit hearing leaking air through the exhaust?
No, you can still hear it. Literally go to the tailpipe to listen. However, you should do the other cylinders as well so you have a sound comparison for each cylinder, as some of this is subjective.
 

NLXTACY

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To clarify, the turbo is already installed. That being said, would this inhibit hearing leaking air through the exhaust?
Ugh. Sorry, I don’t recognize mud avatar to order name 😢

Yeah you’re not going to be able to hear anything because the turbo’s turbine wheel is spinning at a ridiculous rate
 
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Ok y'all bear with me as I learn about engines...

Inspection camera shows oil in #5 cylinder. I assume this is from the teaspoon of oil I put in during the compression test, however, it looks like there is some seepage on the side of the cylinder. This oil was put in ~75 miles ago, so I thought it may have burned off too.

5.plug.hole.jpg

5.cylinder.jpg


The #1 cylinder is completely dry.

1.cylinder.jpg


I redid the Leakdown tests of #1 & 5 cylinders.

1.leakdown.jpg


5.leakdown.jpg


At the time of the test pictured, the engine is cold (in conflict with the instructions above). I expect this to result in more leakage from the piston rings.

There is definitely air coming out of the PCV valve tube connected to the upper air intake plenum when conducting the #5 test. Not so when testing #1. It's not audible, but you can feel it with your hand.

I did remove the upper intake plenum when I serviced the fuel injectors (post rebuild). By my reasoning, if there was a problem with bolts being torqued incorrectly or a gasket issue the air would escape from that opening. I also wholeheartedly disagree this is turbo related, more likely the rebuild shop's screw up (which has now been sold and changed names). Could be a problem with my installation of intake plenum or exhaust headers, possibly?

In @OTRAMM rebuild video, he mentions having to re-shim a valve due to incorrect placement by a previous rebuilder. Pulling the valve cover is something I've done and feel comfortable with, and I already bought a set of feeler gauges just in case. What I don't want to do is unnecessary s***, but it seems like a logical next step.

However, if the cylinder is not perfectly TDC, would that allow air to escape through either the intake or exhaust valves? The instructions also mention the engine turning over during the leak down test, and that didn't seem to be happening (EFI and spark plugs disabled).
 
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Just to confirm, that’s a bit of oil in the top of the threads. What does the ceramic look like? Are any coated with oil?
#5 spark plug had a drop of oil or two on the flat washer, #1 was clean. The ceramic on both is still pure white. The threads are black from anti-seize.

Old #5 plug with 3k miles:

IMG_4540.JPG


New #5 plug with 200 miles:

IMG_4541.JPG
 

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