Hrm. So I checked the compression on my motor today, 1986 Base. Car does not run (from what I can tell, at least) because of bad fuel pump.

I used a regular compression tester from Harbor Freight in the trailing spark plug holes.

Using a decent battery and a starter, I pulled the EGI fuse and had a friend turn over the motor (at WOT) while I held the release valve at the top of the tester. To my suprise, I saw NO needle movement from either rotors, but I find this hard to believe for two reasons:

1) The car will run if I spray carb cleaner like crazy into the TB. After I crank the motor for some time, it will slowly begin to turn over faster and faster until the idle jumps up to 2K, but motor dies if I give it any gas. If there was absolutly no compression (like the guage says), the motor would'nt run at all (even on carb cleaner), right?

2) Even if the rotors had pratically no seals at all anymore, I would think that the needle would at least jiggle a little. Am I wrong to think this?

After a few tries, I tried testing compression without holding the release valve, with similar results: 0psi on front rotor and a 50psi total on rear.

Any thoughts?

 

try to compression tester on another car...make sure it isnt the compression tester...or you

 

It could be a temporary condition, excessive gas in the motor can eat off the oil film and you'll get blow by, just like when piston rings are bad. Poor 1-2 capfulls of ATF or marvel mystery oil, trickle charge the battery for 4+ hours, set the battery charger to start, and 15-90seconds of on and off cranking should start it. You should hear the compression pulses get stronger as you crank.

 

OK, I gave it a shot on my DD and it seemed to work fine. I listened for leaks when I tested on the Rx7 and didn't hear anything, but I wasn't really worried about that: I was sure to tighten it down well.


Alright, I'll try that tomorrow.

 

My old motor got 0psi compression in the rear rotor... It seems to be completely possible, although i still dont see how you can get absolutely no needle movement what soever like i did...

 

Screw the tester... take a plug out of each rotor housing, and stick your thumb over the sparkplug hole and have a friend crank at wide open throttle. Pull the EGI fuse... If it has enough compression to blow past your thumb, then your tester is crappy, or your not doing it right. If it cant blow air past your thumb, then there is little/no compression.

 

Shouldn't the Compression test be done in The LEADING spark plug Holes?..Just an observation..(sorry edit..also to be done with throttle wide open EGI and CAS unplugged)

 

You remove the schrader valve in the END of the compression tester, not depress the valve on the side. Look in the end that enters the sparkplug hole and see if there is a schrader type valve there. Remove it. Do not depress the relief valve on the side. end

 

speaking of compression if one were to forget holding it at wot and still gets 80 psi how much higher would it have been if it was held at wot?

i know that in a regular piston engine it doesnt make much of a difference

and also does alltitude make a difference?

 

usually it just takes several more cranks to get to maximum compression if you dont have it at WOT. readings shouldnt be much different.

 

but you wont build pressure because the schrader valve is not in you should just see pulses
when i did mine i forgot to hold it at wot and i got around 87psi on all three sides and on both rotors

but i am also at almost 2k above see level but i dont know if that matters on a rotory

 

Just for the sake of testing the tester, don't hold the valve button in. This will give you the highest reading from the combustion chamber, it will not give you the compression of each rotor face. If it is still zero then you truly have no compression.

 

No way the car would run with zero compression on BOTH rotors. It would be very difficult to start with zero compression on either rotor. And it would smoke like a grass fire.

 

You didn't happen to pull all of the plugs when you did the test did you?

 

this is probably your problem, when buying diagnostic equipment, its better not to skimp on it and buy the crap, hand tools, ok, for a one time use, but i wouldnt buy anything diagnostic wise from harbor freight and expect it to work properly

 

not all harbor frieght is bad

in order to sell their products it must work right to start with

just to let you know its the employees that are the ones who destroy the items

when it all comes in on pallets the just tip the pallet over to break it all apart



i go to college for automotive tech and because students like to destroy things for no reason most of our tools and testers are harbor freight and before students are aloud to use them they are tested and calibrated and to everyones amazement most of the testers are pretty accurate
the only diff between say snap-on and harbor freight is durability they just dont last to the rigures of constant use

 

I used this as a guide, and it said to use the trailing holes. Also, I did go WOT and pulled the EGI fuse (see my first post), but I never saw any mention of the CAS.

Also did that; see first post.

lol, no

I agree with not skimping on diagnostic equipment, but I happened to be there and I needed a comp. tester. Plus, it was only like $10.

 

If you are getting 0 and 50 then your engine is toast.

 

Bah. It was my compression tester.

I stole my buddy's tester and tried that. Got 30-30-45 on the front and 60-60-60 on the rear.

Oh well, I didn't really want this motor anyway; just something to play with for a while.

 

Pretty close to 0 and 50.

 

Blah blah blah. Who asked you?