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Surprising Compression Numbers

Old 04-18-2018, 08:06 PM
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Default Surprising Compression Numbers

93 vtec which I have owned for about a month. Changed the plugs and while out did a compression test. #1 = 190 #2 =190 #3= 215 #4 = 215. Engine was dead cold. Battery was charged for 30 minutes prior to testing. I drained the battery while installing an EL cluster -

Unsure of why compression is so high? As far as I know, engine is stock except a CAI.

Did notice the tip of the tester was covered in carbon mixture with fuel.

Unsure of mileage. VSS was out when I got the car and it had 238K.

Last edited by allmazda; 04-18-2018 at 08:07 PM. Reason: Forgot mileage info
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Old 04-18-2018, 08:37 PM
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Default Re: Surprising Compression Numbers

those are average usdm numbers, my jdm h22a has 260ish psi
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Old 04-18-2018, 09:05 PM
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Default Re: Surprising Compression Numbers

Originally Posted by holmesnmanny View Post
those are average usdm numbers, my jdm h22a has 260ish psi

So is the FSM incorrect? It is showing 185 PSI.
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Old 04-19-2018, 12:48 AM
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Default Re: Surprising Compression Numbers

Originally Posted by allmazda View Post
So is the FSM incorrect? It is showing 185 PSI.
having higher numbers than what is in the FSM is obviously not a bad thing
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Old 04-19-2018, 03:08 AM
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Default Re: Surprising Compression Numbers

True...lol. I was just surprised to see such high numbers on 3 and 4. The engine is new to me but I am guessing it maybe related to the EGR being on that side.
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Old 04-19-2018, 03:14 AM
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Default Re: Surprising Compression Numbers

I am guessing you tested the cylinders in order, 1 thru 4. So once you got to cylinders 3 and 4 you were getting higher readings. And you said there was fuel on the tip of the compression tester....

How did you disable fuel injectors during cranking? Unplug the injectors or ecu?
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Old 04-19-2018, 03:53 AM
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Default Re: Surprising Compression Numbers

First time I tested with fuel. Discounted injectors but maybe did not wait long enough for fuel to evaporate.
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Old 04-19-2018, 03:57 AM
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Default Re: Surprising Compression Numbers

Originally Posted by allmazda View Post
First time I tested with fuel. Discounted injectors but maybe did not wait long enough for fuel to evaporate.

Hmm. Just wondering if once you got to #3 and 4 the cylinders were starting to flood, increasing the compression numbers since it was essentially a "wet" test at that point.
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Old 04-19-2018, 04:07 AM
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Default Re: Surprising Compression Numbers

Originally Posted by 2x0 View Post
Hmm. Just wondering if once you got to #3 and 4 the cylinders were starting to flood, increasing the compression numbers since it was essentially a "wet" test at that point.

I could be wrong and since there was fuel I guess I am. I thought WOT would put the ECU in flood mode and not fire the injectors. I will retest again when I change the fuel filter.
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Old 04-19-2018, 04:26 AM
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Default Re: Surprising Compression Numbers

Originally Posted by allmazda View Post
I could be wrong and since there was fuel I guess I am. I thought WOT would put the ECU in flood mode and not fire the injectors. I will retest again when I change the fuel filter.
Either start the engine to let it burn off any fuel that may have flooded the cylinders, or let it air out for a decent amount of time. Make sure the injectors are unplugged when you crank it for the compression test.
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Old 04-19-2018, 06:51 PM
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Default Re: Surprising Compression Numbers

do a valve lash adjustment. I'm sure it needs it. But also because if lash is out of spec it'll have a pretty big impact on compression test results. looser lash increases compression test results, tighter lash decreases compression test results.
Also, just unplug the distributor before doing the compression test. All sensors related to rpm are in the distributor, so with it unplugged the injectors won't fire and the ignition won't spark.
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Old 04-19-2018, 07:12 PM
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Default Re: Surprising Compression Numbers

The valve adjustment will be done when I do the timing belt. I will pull the plug on the distributor when I test again. Like I said the Prelude is new to me so I am going slow. Engine starts and runs well. Suspension looks to be original.

Are Honda's picky about thermostats? Car will reach 1/2 gauge and idle that way all day long. Start driving and goes to 1/4 gauge. Turn on A/C it goes even lower.
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Old 04-19-2018, 08:43 PM
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Default Re: Surprising Compression Numbers

when doing timing belt new also water pump and all the seals what there is near (valve cover gasket set, cam seals, balance shaft seal, maybe even front crank seal)
+this: https://www.kstuned.com/products/h22-timing-tensioner

if you dont know when ignition parts are newd - get new ones there as well
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Old 04-20-2018, 03:47 PM
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Default Re: Surprising Compression Numbers

Originally Posted by allmazda View Post
Are Honda's picky about thermostats? Car will reach 1/2 gauge and idle that way all day long. Start driving and goes to 1/4 gauge. Turn on A/C it goes even lower.
Honda's are like any other car. put the correct thermostat in, of a reputable brand, and never worry again.
The problem is way too many honda owners put the wrong thermostat in their cars. It sounds like yours has a much lower temp "racing" thermostat installed. Which is not actually for racing, it's just labelled that way to make newbs think they need it and buy it.
Buy an OEM temp Stant brand thermostat with new gasket, and your problem should be solved.
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Old 04-20-2018, 08:28 PM
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Default Re: Surprising Compression Numbers

I figured as much. Thanks for the reply. I have ordered a new Honda one as well as most of the coolant hoses. I have an 02 Accord I am flipping that is funding the Prelude. The Accord needed a new ATX. Went JDM. Gearing was an issue but found a 4 lug Acura 16 inch wheel. Increased tire size to help offset gearing and the 16 inch wheels that came on the JDM car. It is slower now but more gas will fix that. Better than high rpms at highway speeds.
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