Low compression numbers

2001 AC @403k
Compression test numbers:
1-89, 3-84, 5-65*, 7-84
2-96, 4-89, 6-98, 8-98

Been losing power over the last year or so, and was about to do a full TB & WP tune up to see if I could squeeze a little longer out of it, but thought it'd be a gamble without addressing the loss of power issue. Previously thought it was a clogged cat due to an o2 sensor tip rattling around In there for a few months. Also recently had a broken radiator cap fall down in and found a massive water pump leak from the weep hole and also the opposite side seal that caused the radiator to leak below the level of the pump and run dry. Was worried about the damage from possible over heating when that incident happened on a long drive home.
The compression test was done on a cold motor at 9 cranks of the starter. Numbers were not what I was expecting, especially after seeing that #6 cylinder looked fuel washed or, cleaner than all the rest. Turned out it was actually cylinder #5 with the lowest numbers..
Not sure where to go from here. Any advice on what to test next? Or if I should I look into swapping a used motor in, or do a full rebuild? I just recently got an '06 DC @212k to replace it as my daily driver, but the frame is so clean on the AC, i feel it's worth bringing back to life. Whatcha think?

 

Spec is 192 psi. Below ~ 140 is a sign of problems. Looks like you have a problem or two. Next step is a leak down test...

 

How does it run? Low compression in and of itself is not a big deal, more importantly is how consistent it is and your engine is actually pretty good. #6 is a bit low but nothing particularly crazy. Hell, it has 400k on it! If it runs fine and you're fine with the power why do anything? If you want more power, rebuilding it wont be a fast process since it's just worn out so you'll want to get it honed, maybe oversize pistons, new rings, get the valves and heads inspected, etc. since I doubt there's any one single thing that's particularly bad. Swapping a newer engine would be much faster snd probably cost effective. Personally I wouldn't do anything if it's running fine.

 

I’m curious what those compression numbers would be after taking a “wet test”?

 

Numbers look fishy. And remember, stuck valves can cause low numbers. Behind that, when was the last time you did the timing belt?

 

You mentioned a possible overheating- did it overheat? Apples to oranges here, but I killed a boat motor by overheating it. The pistons got hot enough to score the cylinder walls and compression went from 150 to 50psi.

You also mentioned that #6 looked fuel washed- did you look at the plug or were you able to see into the cylinder with a borescope? I'd personally be inclined to buy a cheap scope and check out what the pistons/cylinders look like inside.

 

It runs pretty good except the loss of power. It definitely needs new plugs and coils. The gap on the plugs is massive, but they all look like the same coloring. Several coils are cracked, but I haven't had any misfire codes, just codes for the rear o2 sensor and a cat code.
It got pretty hot on the freeway it's last road trip this summer when I went to go buy the '06 DC. I pulled over several times to cool down and then babied it home, but I know once coolant level drops, the temp sensor reads low, so I fear It may have gotten hotter than I thought (never did go into the red). I believe that's when the WP leaked all the coolant out and ran the pump dry.
Previously, the power loss got progressively worse over a year or two, to the point it struggled up the smallest of hills, so I started keeping it in town as a work truck. Recently it's been climbing In temp at stop lights (broken radiator cap fiasco), and is leaking most of it's coolant out the waterpump, so I haven't driven it since moving it. I know the water pump is toast, I was going to replace it this weekend, but the compression test stuff is throwing me off now.
I didn't scope down the cylinders, just shined a flashlight down to see if any of them looked steam cleaned from coolant, cause I was suspicious of a bad HG, and that's when I noticed #6 didn't look as dirty as the rest. Though the plug doesn't look any different from the others, and the low compression was actually on the other bank.
It doesn't really burn very much oil, maybe a quart every 6 weeks, but that's actually probably due to the valve cover leaks. The TB+WP & LBJ was last done when I got it around 280k I believe, so it's all overdue. I've neglected this truck for far too long. Also needs VC gaskets, plug tube seals, coolant bypass gaskets, injector o-rings, and a full front end refresh.
I started the TB job a few weeks ago while I was in the process of moving house (verified timing at that time), but I stopped before breaking the crank bolt loose, and had to reassemble to drive it a few miles to my new house where it sits in the driveway all sad. No temp issues noticed on that drive (refilled radiator with water and burped good+ new thermostat and radiator cap). Then I did the compression test yesterday and the numbers have me questioning if something more significant is going on. Or maybe I'm just dumb and tested wrong, or maybe he's just old and tired.
I'm tempted to do the TB & WP and just see if it'll run a bit longer and maybe make it through winter. I have all the parts plus a new radiator, but the '06 DC needs a belt and WP job too. (Me and my partner are down to just my DC, so I was considering getting a sequoia or 4runner with another 4.7 for her, or just seeing if my AC will take me to work through winter until we can get another vehicle. )
I'll do a wet compression test tomorrow and see if the numbers are different. Maybe I just do the TB/WP and run some cleaning products through it to see if I can clean up the rings and valves? Really just need to buy some time until we can get another vehicle. In the future I can dive in deeper and do a complete tune up.

 

I'd do the warm compression test and a leakdown test. See if you have compression leaking past the valves, especially if they've never been adjusted.

 

Agree with another compression test and leakdown test. It’ll be good to confirm your numbers and ensure that your numbers are correct. (Although I hope they aren’t)

I doubt that any cleaning product is going to get you much compression back.

 

If I were you, I'd probably do the following:

• Finish the TB/WP/tensioner/pulleys job.
• Seafoam the top end with their spray kit per their directions (video below) which involves a hot soak; consider doing one round now, one round in 200-300 miles
• Run either Liquimolly or Seafoam high mile thru the crankcase (full bottle) 2x @ 400-500mi OC intervals
• Run a bottle of ATP's AT-205 in the crankcase after the two above OC, just to refresh the seals, it's sold at any chain auto parts store, and is not a gimmick product

Why? In order of above points:

• Belt stretch could account for slight timing oddities lending to your compression numbers.
• Dissolving any sludge and buildup in the intake/top-end is worthwhile, you've got 400k miles of buildup in there.
• Running a very mild cleaning agent thru the top-end to help dissolve any buildups internally in a way that won't aggressively break things free is worthwhile.
• After cleaning things out, using another very mild agent to refresh seals and gaskets that isn't a "cure in a bottle" is wise
• (bonus) you're looking at another $60-80 to buy the extra stuff...

I genuinely suspect you just need a little cleanout, and there's nothing wrong with the engine itself beyond normal buildup.

https://www.youtube.com/watch?v=O5N_Z1W6mho​

 

And hey, I want to share this with you also @Gotta-Jibboo

This thread: https://www.tundras.com/threads/new-member-old-truck-dead-cylinder.96468/

Compression test showed a dead cylinder. Dude swapped in a new engine, and I'm not sure he could ever get it running. But he did do a teardown on the old, lo and behold: Stuck valve was the source.

While I would agree, if a head gasket was going to present in any way, the most-likely case would be lower compression on one - and potentially two - cylinders, when you look at the head gasket design. But that said, I don't get the vibe this is it.

Another thing I'd be suspicious of is your upstream a/f (O2) sensors and potentially your coil packs. If you have a OBDII scanner that supports realtime monitoring, it's easy enough to monitor the sensors and see if anything weird is happening.

We also know aftermarket coil packs cause problems with the 2UZ. And they seem to start getting flaky after 200k-300k miles.

 

Yeah I imagine this motor has never been taken apart except for a few timing belt jobs. And I've never run any type of cleaners through it since I've owned it, just occasional seafoam in the tank and some auto RX in the trans when I first got it.
I got the truck for $2k, and just drove the crap out of it for the last 10 years, so I'd say I got my money's worth! The only failures I've had is a fuel pump and an alternator.
I really like what you are suggesting shifty. I did read that thread you posted, earlier this week when I was researching, and it definitely makes sense. I will do a warm/wet test, leak down test, throw some new plugs in it, shrink wrap the coils to prevent arcing until I can replace the ones in my DC, then I'll reuse them in the AC. I do have one extra brand new up stream denso o2 sensor laying around I could throw on one side and maybe get a new one for the other side. Then I can drive it for awhile doing the cleaning treatments, and reevaluate in a few weeks after some miles go by. I'm not a mechanic, just a diy guy, so I appreciate your guys patience and input! Been lurking on this forum for a long time. Much respect to shifty, absolute legend.
I'll report back later with the wet test numbers.

 

Cracked coils in and of themselves won’t necessarily cause any problems. Replace any non Denso units with Denso. Post any codes thrown.

 

All coils are denso, and possibly even original. No misfire codes, but I know the clock is ticking on them. If they are the originals, they definitely outlasted their expectations. They all look the same age.
I'm planning to replace the ones on my DC, and use the old ones in the AC. Until then I'll shrink wrap them to keep them from arcing in the plug tubes.
Last codes:
Jan 31st - p0125
Sept 5th - p0125, p0135, p0161
It must have been low on coolant all the way back in January...
I kept the overflow full, but I'll admit I didn't look in the radiator itself until quite recently when the WP leak and "over heating"/ broken radiator cap occurred.
Since then I've replaced the battery, radiator cap, and thermostat. I kind of ignored the o2 codes cause I thought I had a clogged cat issue, that I was also ignoring. I'll admit I haven't been very nice to this truck, and I'm so thankful he never left me stranded so far away from pavement.
Thanks for your responses. I'll get back with wet test numbers soon.
Pic of '06 DC for fun. Getting 5100s and tires on this week.

 

Yeah, you probably have a couple of bad O2 sensors based on code history (although could be wiring of course) and should probably just replace all 4 with new DENSO “exact fit” units from a reputable source (not fleaBay, not scAmazon). It’s worth it for another 15 years of trouble free operation. Those codes wouldn’t be a cat clog problem. Factory cats are, apparently, hard to clog on these trucks, we rarely see it.

Coil packs swap with the old ones sounds like a plan. Though cracks in the tubes is semi normal, I wouldn’t bother wrapping them, just hold off ‘til you swap. I’d save the old ones as a backup, just in case.

 

Just finished the wet test.
Numbers were inconsistent and kind of a head scratcher. Some of the cylinders were lower than the dry test, so I reconnected the tester and got a higher number the second and third try. I added about 2 tablespoons of oil and turned the crank over 3-4 times by hand, then hooked up the tester. 9 cranks of the starter. Tested each cylinder 3 times.

1-105, 3-92, 5-60/90, 7-60/98
2-84, 4-102, 6-86/89, 8-84/90

I just finished putting it back together and fired it up. Smoked out the neighood like a 2 stroke whore! I grabbed the leaf blower to disperse it, but maybe I'll eat dinner and come back out to burn it off later, once the dog Walkers go to bed.

I'll throw in new denso upstream o2 senors, (I have one still in the package), and I have a couple trq downstream I'll consider seeing if they cooperate in the rear before buying more denso. The reason I suspected a clogged cat and ignored the o2 codes was because of the o2 sensor tip that fell down into the cat, and I let it rattle around in there for a few months. I put in a new denso on the upstream passenger when I fished the broken tip out.
I put the old plugs in just to burn out the oil I poured in for the test, but after that clears, I'll put new denso plugs in as well.
More to come.

 

Last week I was busy working on the '06 DC. I installed 5100's up front, on the 4th notch, got new tires (STmaxx 265/70/17), and had an alignment done by a 4x4 shop to DJ's specs. I had to cut off a stubborn strut bolt, but I was able to get a new one from a dealership. They only had one, so I re-used the other side. The ride feels good, similar to my AC also on the 4th notch. I'll be re-doing the front end on BOTH of my tundras soon with OEM LBJ's, JBA UCA, OEM LCA's, ome 2885/6 coil springs, fresh 5100's, OEM inner and outer tie rods, rack bushings, pathfinder or maxx links, etc..
I installed new plugs (Denso iridium) and coils (Denso) in the DC, and put the other ones in the AC. The DC coil packs were actually in worse condition than the ones in the AC, but the plugs were almost new.
Back to the topic, I finished up the timing belt and water pump job on the AC over the last couple days, and all went well. I used the Asin kit. It was my first time doing it, so I took my time, went slow, and kept everything neatly organized by putting the bolts through cardboard and labeling them. Spent probably close to 20 hours on this job! Most of the effort was cleaning up the years of oil leaks on every surface.
I replaced the cam seals and used a little Toyota FIPG on the outside, as well as grease on the inside of the seals (per Otramm). I opted not to do the crank seal because I didn't have anything to press it in squarely, and besides it didn't appear to be leaking, tho filthy from other leaks. I also used the FIPG on the surface between the water pump gasket and the engine block. It was pretty badly pitted I believe from the last pump being aftermarket (lasted 100k) with a paper gasket. I did NOT put FIPG on the other side of the gasket that mates to the water pump. So far no leaks.
It fired right up. No missed connections, no extra bolts. Sounds like it should.
I put a can of high mile sea foam in the crankcase and put in a new oem air filter as well as the aforementioned new plugs and the best of the coils I had leftover. The big job included TB&WP, tensioner, idlers, pulleys, new radiator, hoses, heater control valve, and fresh fluid, etc.
The plan next is to do o2 sensors, valve cover gaskets, spark plug tube seals, fuel injector o-rings, front and rear coolant bypass gaskets, and PCV valve. After that is the front suspension refresh. More to come. Freaking love these trucks.
(The lines on the belt in the picture aren't there because I had already turned it over by hand a few times).