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Very poor compression test, good leakdown

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Old 11-20-2017, 04:55 AM   #1
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Very poor compression test, good leakdown

So i have been trying to track down an issue with my rebuilt 22re in my 87 4runner and had some interesting test results yesterday.

i spent most of the summer testing different things and replacing bad sensors on my runner to try and stop a strange hard start and on throttle misfire and low rpm bog. It's a rebuilt motor, with all new temp sensors and double and triple checked tps and vafm, including wiring to the ecu and back probed voltage checks. I'm very competent with electrical and dmm use, all tests with my fluke 87v.

anyway, yesterday i decided it was time to vacuum leak check (found one small leak) and do a leak down and compression test.

my compression test numbers are as follows.

cylinder 1: 180 psi
cylinder 2: 85psi
cylinder 3: 180 psi
cylinder 4: 90 psi

test was done cold (i know should be warm but these numbers should be consistent regardless) with efi fuse pulled and at WOT.

now my leak down test, performed at 100psi had all 4 cylinders read 98psi on the same cold motor, so 2% leak down with the only air loss through the crank case.

i will re test both on a warm motor but can't wrap my head around these readings. The only thing i can figure is the intake valves aren't opening enough to allow the compression test to build.

i had the machine shop do the valve job, and inspect the cam, but installed the rocker arms at home myself after cleaning them and their shafts.

my valve lash is correct, engine runs nice cold and after fully warmed up and passed 2000 rpms. But falls on its face taking off and when shifting if it falls below 2500 rpms on the shift.

any suggestions on why my numbers are so off amd contradicting would be great
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Old 11-20-2017, 05:05 AM   #2
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One more thing worth noting, my head and block were milled .010 each. For a total of .020. So my cam timing is retarded about 2 degrees. I have considered an adjustable cam gear to correct this but not sure if it could contribute to the problem.

i suppose if my cam is worn , and my timing is off a couple degrees it may affect this, if someone could comment on that as well
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Old 11-20-2017, 06:24 AM   #3
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That's certainly possible. A compression test examines the action of the valves. With a leakdown test, you turn the crank to make sure the valves are closed on the cylinder you are testing.

Just a thought: the absolute number you get on a leakdown test (2%, 30%) is meaningless (the "leak" in the device isn't calibrated to flow). The consistency (between cylinders, and over time) is what you look for. But on my excellently running 3VZE with my HF leakdown tester, I get 30%. 2% sounds awfully low. and 100 psi sounds pretty high, for a leak down test.
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Old 11-20-2017, 08:00 AM   #4
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100psi makes the math easier. I suppose that the higher pressure could seal something that otherwise wouldn't seal. I could drop it to 50 psi and go again.

I also did it while cold since the problem is lessened after warmup. After warm the on throttle misfire goes away but the low rpm bog/power loss stays pretty consistent

also worth noting there is only about 500 miles on the motor

i remember the machine shop saying there was noticeable wear on the cam but it was still within spec. Due to cost i did not replace it but feel like maybe i should have.
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Old 11-20-2017, 10:15 AM   #5
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take a good cyl, mess up the valve lash and observe the effect on another comp test. (180 is really good. I think the factory spec is 170?)
I would definitely be more concerned about warm comp test numbers than cold. And squirt motor oil in, enough to seal the top comp ring to see if the number improves.
Could a sticking open EGR upset the test? Just a theory but I know from having one it will run like CRAP idle and low end and be way down on power. (Big vac leak)
Did you test with the throttle jammed open or closed- just curious, should be consistent either way but the factory manual specifies open.

Do the math on the cam gear and you may be able to just offset by one tooth instead of spending the money on the adjustable one. I ran an adjustable gear on a previous 20R and had it about 4* advanced and it really was more responsive in the low end. I run the cam in my 327 Camaro 8* advanced. It is great for small cube engines lacking low end power.
But all that said, If it's running crappy, there must be a reason.
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Old 11-20-2017, 10:31 AM   #6
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Have no egr. I thought about moving a tooth advanced but i would think that a tooth is about 5 degrees . So i would estimate i would have a 3 degree advance doing that. These are magic air numbers btw.

i would also think that if my cam timing was the issue then it would affect all cylinders but that would also make sense. Sometimes stuff doesn't make sense
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Old 11-20-2017, 01:16 PM   #7
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I'd look closely at the rockers on the low cylinders. Are they physically different in any way from the good cyls (new, 20R vs 22RE, different length on the adjusters) that could result in higher lift on some cyls than the other? think like the effect of a 1.6 ratio rocker to a 1.5 ratio rocker.
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Old 11-20-2017, 01:21 PM   #8
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36 teeth on the cam gear so each tooth is worth 10 degrees.
Then 2:1 on the crank, so half that 5 degrees wrt the crank.

Last edited by Melrose 4r; 11-20-2017 at 01:22 PM.
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Old 11-20-2017, 01:28 PM   #9
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I took the rockers apart for cleaning but did not compare them when i was assembling the motor. They were really gummed up, stuck to the shafts. The motor had an oiling issue due to timing chain guide parts being stuck to the oil strainer so it's entirely possible there is some damage

i also assume that all the intake rockers are the same, and exhaust are the same. I don't think i mixed any around but anything is possible
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Old 11-20-2017, 01:30 PM   #10
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Quote:
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36 teeth on the cam gear so each tooth is worth 10 degrees.
Then 2:1 on the crank, so half that 5 degrees wrt the crank.
math.

i still would feel foolish jumping ahead a tooth and going from a couple of estimated degrees retarded to a few advanced, especially blind. I think i would rather put an adjustable gear on and set it at 0.
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Old 11-20-2017, 01:53 PM   #11
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Quote:
Originally Posted by 92ehatch View Post
I took the rockers apart for cleaning but did not compare them when i was assembling the motor. They were really gummed up, stuck to the shafts. The motor had an oiling issue due to timing chain guide parts being stuck to the oil strainer so it's entirely possible there is some damage

i also assume that all the intake rockers are the same, and exhaust are the same. I don't think i mixed any around but anything is possible
Good question. I don't know off hand.
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Old 11-20-2017, 01:59 PM   #12
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Quote:
Originally Posted by 92ehatch View Post
math.

i still would feel foolish jumping ahead a tooth and going from a couple of estimated degrees retarded to a few advanced, especially blind. I think i would rather put an adjustable gear on and set it at 0.
Degreeing cams is fun!
You definitely do not want to run it retarded. It will result in poor low end, less snappy.
I bought an adjustable gear from TRD back in the 90s. I don't think they sell them anymore. But the LCE gear looks like a nice piece for $89.
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Old 11-21-2017, 07:30 AM   #13
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That's the one i was looking at. I won't be doing that right away though. The thought being, if it was that, all cylinders would show problems. First thing to do is fix the two cylinders i have problems with. Of course it will have to wait until I'm not at work.

I'll be taking the valve cover off and watching the valve action to see if anything sticks out to me.

thanks for the replies
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Old 11-21-2017, 07:54 AM   #14
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Yeah, keep going. I am very curious to see what you find out. My #4 cyl is low(100) compared to the others(138-140). I'll be doing some similar investigation myself.
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Old 11-23-2017, 07:15 PM   #15
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Figured it out. Turns out my harbor freight compression tester is faulty.

i double checked the timing, cam, valve lash and all was good. So i retested the leak down at 50 psi and all cylinders tested at 42psi
​​​​​
then i redid the compression test and cylinder 1 and 2 read 180, cylinder 3 read 85....what the hell. Turns out if i lay the compression tester a certain way the pressure leaks out, so i laid it the other way and boom cylinder 3 went to 180. So i have 4 cylinders at a perfect 180 psi with no deviation.

Yay, except, i still have this damn stumble.

i also check my cam to crank timing by eye and do not see any noticeable difference in my cam timing from what the fsm states. Cam dowel at 12, crank at 0. So even if my timing is slightly retarded from the machine work i don't see that being the cause of my stumble.

2 years ago i fixed my tps by re wrapping the spring inside, it still tests good to this day, but I'm going to change that since my issue is immediately on throttle or after a gear change, which is also an on throttle moment. I'm out of ideas

Last edited by 92ehatch; 11-23-2017 at 07:16 PM.
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Old 11-23-2017, 09:07 PM   #16
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your hard start and low rpm missfire a
is very likely a weak ignition problem. unfortunately the only real way to be sure is to throw money and parts at it.
I have found 2 ignition system faults with the late night water spray technique.
tonight when the car is cold, go have somone start the car, and as soon as its running spray a fine mist of water over the high tension leads and keep an eye out for any sparks. if u see a spark thats your problem. do this around the dizzy also.
A weak spark is most prominently felt under load and on cold start.
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Old 11-23-2017, 09:39 PM   #17
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I originally had the wire going from the ignitor to the dizzy corrode and swell and bust the cap. I replaced the rotor and cap with a new one and replaced the wire with an auto parts store unit (of course i had to buy the whole set)

i had the intention of replacing this cheap one with oem but haven't gotten to it.

I'll be sure to check the spark on the truck as i have not done that yet. And I've never heard of your method but i guess anything is worth a try
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Old 11-24-2017, 05:22 AM   #18
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Good deal on the comp test. Makes me wonder about my HF comp tester also. 180 psi is awesome.
i rechecked my #4 cyl yesterday and blew 115 hot. After spraying a few good squirts af WD40 down the hose it blew 125.
other cyls are 144. Looks like it could use new rings. I dont think the lower end has been touched and it has 182k on it.
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Old 11-24-2017, 07:33 AM   #19
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Even though one of yours is lower does yours still run ok?
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Old 11-24-2017, 04:31 PM   #20
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well if it has relatively new HT leads, and the mist spray shows nothing, check the coil specs are within range and that u have a sound 13.8 volts at the coil positive with the engine idling
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