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Old 07-04-2011, 02:23 PM   #1
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Default Compression test results, anyone help me? have a really quick question

first:
1990 miata 1.6L
runs and drives fines, gets 28-33 mpg
adjustable cam gears and a few racing beat things under the hood
full adjustable suspension, springs
behind the seat metal panel on the corners are bent and you can get to the trunk like below where the top it, the carpet covers it but it sags down... i wasnt sure if a rollcage was once on there or what, havent looked into it yet. but i was wondering how usual rollcages are mounted on miatas


just doesnt have power, feels like it should have a good bit more.. never drove a car with this little power before lol

all cylinders are at 105-115 psi just removing spark plugs

and i tried the first two cylinders on a wet test and it was 148ish on both, pretty much on the 150 line



whats going on? piston rings shot ild assume, but anything else
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Old 07-04-2011, 03:34 PM   #2
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You want to get the engine up to operating temp, and remove all 4 spark plugs before running your compression test.

Have you checked your timing?

C
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Old 07-04-2011, 05:00 PM   #3
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Compression test should be done with throttle wide open in case you weren't already aware. What is your base timing set at?


BTW- Miatas are slow without turbos. Stock 1.6 ~95whp
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Old 07-04-2011, 05:31 PM   #4
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Hot compression on a miata should be between 180-200...
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Old 07-04-2011, 07:47 PM   #5
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ok, ill do a hot test and get back those results


havent checked timing, dont have a light. but ill borrow one and get those #s to you also
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Old 07-05-2011, 12:35 PM   #6
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IIRC the minimum spec for hot compression is 135psi, and it shouldn't feel TOO sluggish even if compression is getting low (mine's getting down there now).

I'd also check your ignition timing to make sure that's working fine as well.
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Old 07-05-2011, 01:01 PM   #7
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Not only does going WOT allow air to be ingested, it cuts off the fuel injectors.
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Old 07-05-2011, 02:10 PM   #8
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And make sure your tester is in all the way. I almost shat a brick yesterday when my gauge only read 105. Then I realized that the tester was in half way and slightly crossed on the threads. Fixed that and it was back to 170.
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Old 07-05-2011, 03:12 PM   #9
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test in all the way, brand new, oring is fine on tester

120psi on all cylinders and number 3 is at 105 or so


drove it around and temp gauge was in middle, and the tester was hot as hell after i screwed it out

the 105 cylinder when i put a little oil did jump up a past 120
and the 120 cylinders did jump up past 140 or so with a little oil


i dont have a leak tester to see if the air would come through the pcv valve/breather but timing will be next checked, whats easiest way to adjust timing on the miata?

Last edited by josh90miata; 07-05-2011 at 03:42 PM.
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Old 07-05-2011, 04:00 PM   #10
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typically when compression increases it's due to worn rings/walls.

that fact that 135psi is the min limit and that's all you can make with oil...
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Old 07-05-2011, 09:21 PM   #11
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Damn that is low.

How many miles on the motor?

Last edited by miatamania; 07-05-2011 at 09:41 PM.
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Old 07-06-2011, 01:39 AM   #12
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No idea man... odometer reads 211,000
but i found some paper work on the car today

bought at 144,000
1st rebuild at 146k
2nd rebuild at 146,935

5/28/97 front crankshaft seal/camshaft seal, timing belt, 115,527 miles
7/15/01 rings, oil pump, starter, rebuild - 145,975 miles
2/09/03 crank and bearings, water pump 146,935 miles


7/15/01 oil/filter 146k
2/09/03 oil/filter 146,935
5/29/03 oil filter 148,182
2/07/04 oil/filter 150, 282 1.5 qt low

have all original papers from roswell mazda in roswell, ga and this nice mazda book


has full suspension and handles amazingly, idk what the car was used for.. but a/c and power steering, and all accessories work, speakers in the headset too lol

but its a nice car and runs and drives fine, just doesnt have the power.. thats why i thought about compression and seems i was right... doesnt burn any oil at all though
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Old 07-17-2011, 06:45 PM   #13
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Where did you get the tester from? I have 2 Harbor Freight compression testers that both read a good 20 psi low. You might still have an issue with all the values not being within 5% though. Sorry
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Old 07-17-2011, 08:42 PM   #14
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Adjustable cam gears, is the cam timing correct? Poor cam timing can effect compression and power.
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Old 07-18-2011, 09:11 AM   #15
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My harbor freight gauge reads dead on.

However, I had a craftsman once read 90 psi accross all 4, I wasn't worried because it was consistent.

Try doing the test again with a different comp tester and see what you get
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Old 07-18-2011, 09:43 AM   #16
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engine should be warm.
make sure you are unplugging the CAS and running WOT so the injectors dont fire and you are ingesting all the air possible.
Crank until the gauge stops going up.
if you do a wet test, put the same amount of oil in each; you need very little like (1) teaspoon.
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Old 07-18-2011, 11:56 AM   #17
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Is the check valve in your tester in the end of the hose that goes in the cylinder?

Some cheapies have the check valve in the gauge itself, and they will read very low with small displacement engines.
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Old 08-23-2011, 07:48 PM   #18
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whatever became of this? I have a 1.8l 96 and also have 120, 105, 120, 120, this is warm, crank and WOT.

Putting oil in #2 brings it up to 120. I did not oil the others nor have I tried a second gauge. I can do that now.

Intake and Exhaust cams are 19 belt nipples apart (as it shows in the pictures on other links around here).

Could I have burnt all of the exhaust valves evenly? Hard to believe!
Yes, all kinds of sea foam and other products...no help. Car runs great but is amazingly slow. It did Dyno at 104rwhp before the turbo. 200hp with the turbo. Right now, no turbo.

Paul
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Old 08-23-2011, 08:13 PM   #19
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MAC Tools!

with the new gauge (MAC) now I have 210, 190, 207, 211
amazing what good tools can do....but why am I killing smog?
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Old 08-23-2011, 09:43 PM   #20
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Clogged cat, old O2 sensor, PCV valve, dirty injectors, emission system with leaking vacuum lines...

Do you have a AFM, move it a few clicks/ teeth so it sends less fuel, if I recall is CW.

Do a Sea Foam wash to see if it helps.
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