Reply With QuoteDon't forget to release the gauge after each cylinder or you'll have a "D'oh" moment while you scratch your head wondering how every cylinder was exactly the same...
Compression Checking on a Small Block Miata
Well I was going to do the compression check last night, but I found out it was meet the teacher night for my kid. So I hope to do it tonight!
The Mazda Service manual says to unplug the coil pack and remove the plugs (duh). Then put Mark52's compression gauge in the #1 cylinder then turn her over and see what the gauge says, then repeat the process until I'm done!
Sounds easy! Am I missing anything?????
Don't forget to release the gauge after each cylinder or you'll have a "D'oh" moment while you scratch your head wondering how every cylinder was exactly the same...
OK so I warmed the car up, pulled the plugs (ouch, ouch, ouch, & ouch)
Hooked up the compression gauge and here are the results of the first test!So I'm pumped no low cylinders! Then I re-read the 'structions and notice where they say you need to fully depress the accelerator, which of course I failed to do on test #1! So I re-test and here are the results of test #2 with the accelerator fully depressed!
- #1 = 155 psi
#2 = 160 psi
#3 = 160 psi
#4 = 160 psiMazda Spec is compression is 192 psi, Minimum is 135 psi, and allowable differential limit between cylinders is 28 psi.
- #1 = 170 psi
#2 = 170 psi
#3 = 175 psi
#4 = 175 psi
So with 153K on the clock these numbers look pretty good to me! I'd like to run this same test on Sammm's '92 to see if he has more compression than my car!
Now I plan to wet test, but I have been called to dinner! BRB!
How much money ya' got?Originally Posted by POS Racing
I'd like to run this same test on Sammm's '92 to see if he has more compression than my car!
Any chance I can drop by and do the same test on my BRG??? I might even bribe you with the promise of beer and chicken wings......
Chris
OK so I did the wet test!
It states pour a small amount of engine oil* into the cylinders and recheck compression.
Three things can happen:So here are my numbers from the wet test.
- 1. If the compression increases, the piston, piston rings, or cylinder wall may be worn.
2. If the compression stays low, the valves may be stuck or seating improperly.
3. If the compression in adjacent cylinders stays low, the cylinder head gasket may be defective or the cylinder head distorted.So the POS falls under #1, which I expected with 153K on the motor! I actually anticipated lower numbers so all in all I deem this a successful test!
- #1 = 220 psi
#2 = 200 psi
#3 = 210 psi
#4 = 190 psi
*I was unable to meter how much oil went into each cylinder so I’m not so sure how accurate the readings may be due to differences in the quantity of oil being used. YMMV
word of advice, unplug the injector plug as well, we blew up a guage on sunday from doing a compression test on a hot motor with bad gas. just fyi. and iirc a brand new mazda crate motor puts out 185psi, we have had the best luick with 100k ish junk yard motors, have one with 200psi avg. a noticable power differnce in the two cars.
03 LS FM2ish TDR I/C
99 Disco, the go anywhere ride
That's pretty interesting about motors around 100k miles being the strongest....
So apparently, a motor has xx hp when new, and that hp goes up as it breaks in where it reaches a peak, until it gets old and starts to decline (A bell curve). We all assume the POS might be on the decline with it's higher mileage, even though it could probably go for years and many many thousands more miles...
I wonder where my engine (which feels great to me) is on that bell curve with it's 46k-ish miles, and if I would see a hp increase at 75k miles, then more at 100k,...
Just wondering out loud here....
SOLD: 92 silver w/hardtop, voodoo, Kosei wheels, pine tree air freshener, and some JR stuff.
SOLD: 99 silver; the old Goodwin supercharged car with gobs of power and everything else on it.
SOLD: 95 triple black; stock
SOLD: 99 black and tan; loaded and clean; just hit 50k miles.
SOLD: 2006 Copper Mica Red; stock.
FOR SALE: 2007 Galaxy Grey Grand Touring; stock; 38k miles.
That would certainly reflect some of what we saw on the dyno at ATS a couple of weeks ago. Out of the four C Stock cars there, mine had the highest mileage by a large margin (86k, while I don't think any of the other three have even broken 40k miles yet), and also made the most power (almost 4hp more than the next closest - Kestrel's, iirc).
Iain
"We don't stop playing because we grow old, we grow old because we stop playing." - George Bernard Shaw
And my '99LP just turned 30k...
Quick! Put on 56,000 miles and you can run with Iain!And my '99LP just turned 30k...
SOLD: 92 silver w/hardtop, voodoo, Kosei wheels, pine tree air freshener, and some JR stuff.
SOLD: 99 silver; the old Goodwin supercharged car with gobs of power and everything else on it.
SOLD: 95 triple black; stock
SOLD: 99 black and tan; loaded and clean; just hit 50k miles.
SOLD: 2006 Copper Mica Red; stock.
FOR SALE: 2007 Galaxy Grey Grand Touring; stock; 38k miles.
Sorry for the delay in getting back to you I wanted to ask the man who owns the gauge (Mark52) if it would be OK before I said OK!
I'd still like to test Sammm's but it seems as if he is scared! :P
If the compression is OK, then where do you think the power loss is coming from? I would say your car is well maintained and tuned, so I wouldn't expect anything obvious...
Maybe check the timing?
Is his one of the years that has TWO marks on the pulley?
Daily Driver: 2013 Club edition in Pearl White Mica
Lightness? What's that? I drive a PRHT!
I'd like to check another car to see if I'm that far off the norm on the compression numbers. It is well within Mazda's range but I wonder if it’s down from that of an average 1.6?
Nope 1 mark, timing was checked and then rechecked she is sitting at 14 degrees same as Sammm's car.
I can’t find any record of the O2 sensor being changed, but when I checked it with a meter it operates in the correct range. How much does it play into fuel delivery? If you look at the other 92’s that were dynod the only thing that is different is I start out pretty much the same then it starts to tapper off around 5500 rpm.
- Blue = POS
Red = m2rracing
Green = Sammm
So far none of my test have brought to light any drastic problems with the POS. I'm wondering if she just had a bad day on the dyno.
Or maybe I had a good day.
The ECU does not even look at the O2 sensor at WOT, so I would not suspect that to be a problem. I have heard that on the 1.6 cars that you can "modify" the MAS though. I had some spec guys tell me that they bought a few sensors and went to the dyno to see which one made the most power, after which they returned the other sensors. I can't remember the exact numbers, but I remember there being a pretty broad range in hp numbers. Maybe this is your problem? You could always swap sensors with Sam and see if it makes a difference, if so then you can accuse him of cheating
"Pain is inevitable, suffering is optional." Haruki Murakami
If your power is tapering off more drastically in the upper RPM range, that would suggest the possibility of a restriction in the exhaust flow. Based on the fact that your compression numbers came back good, I'd start thinking maybe a cloggedwas to blame.
Iain
"We don't stop playing because we grow old, we grow old because we stop playing." - George Bernard Shaw
I'd start thinking maybe a clogged
Don't you mean a clogged? That clogged
I just did a compression check on my 93 with 104K on it.
1=182
2=191
3=163
4=190
I did the test COLD, and I dunno what difference it's gonna make.... Do you folks think the numbers would change drastically?
Now obviously, I'm a bit worried by #3, and I'm gonna guess it's a valve because the plugs look identical across the board. I never bothered to do the oil in the cylinder trick.
But it's amazing the thing was running at all..... I dunno if the plugs had ever been replaced! Ground electrodes were cupped and the center electrode was rounded on every one. The gaps ran from .075 to .085
Yes, I replaced them along with the air filter that had sucked a whole sheet of paper towel inside the housing..... I wonder.......
I also tightened the throttle cable. Damn that thing was sloppy.
Hello, my name is OUTRACE and I'm a motorcyclist. It has been zero days since my last ride.
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