hey guys so i did my compression test today coz ive been having hot start problem... anyways, when i did the test, i used to top sparks plugs with the motor temp is about half of normal running temp... i got all 90's on all faces front and back... my question is does it make a difference being on normal running temp and using the leading or trailing spark plugs? coz i searched and i seen people using the top spark plugs and others the buttom??? which one is more accuarate? if somebody could lead me to the dirrection it would be great... im going to try doing the compression test again probably tomorrow, so if i could get some insights it would be greatly appreciated thanks

jeff

 

http://rotaryresurrection.com/2ndgen...ion_check.html

 

I would say the bottom (leading) would be more accurate.. It does most of the combustion, and probably sees the most compression. Also.. it is recommended that you are at normal operating temperature before doing a compression test. So, you are doing it correctly it seems.. maybe just in the wrong holes.

Another thing to try is remove the EGI Fuse (should already be doing this), Intake snorkel, and jam the throttle body open. This will let the engine breath a little better while doing the compression test.

 

thanks for the link, yeah, i just got my friend to press on the gas pedal all the way, but i shall try whatever is on that link thanks guys

 

ANY recommendations on a specific compression tester. I know that the ones for pistons you have to modify em slightly so they can read accurate for the rotarys.

Thanks

Jason NYC

 

Just Hold the Needle valve in to see that the Pulses are Consistent..then If you are "observant enough"(not bein an *** on that remark)you may be able to judge which part of the rotor face is giving you the reading once you Release the Needle valve..90's isn't That bad..Sort of an average,asuuming it is N/A..it will last you awhile.

 

yeah i just removed the bottom valve on my normal tester... and oh yeah mine is a turbo so i think that means i need a rebuild? would the compression change if its not on running temp? would the compression be higher on running temp?

 

# consistency is more relevant that actual #s. but for the highest numbers you need normal operating temp, and alot of other thigs done specifically

 

ok i just did the test again with the lower plugs on normal running temp and i got 90's all front and back... would a tII still be ok with this? or do i need a rebuild? also there are times when the hot start problem occurs and i get it to start it sounds like its only running on one rotor adn back firing alot? dirty injectors? i hope u guys can help thanks

 

Since turbo engines have lower compression than n/a's I would think you are fine.

 

If you got bounces in the 90's for all 3 faces of both rotors you're good for awhile. Mazda states the compression should be at least 85 PSI on all faces at an engine cranking speed of 250 RPM at sea level with less than 21 PSI difference between the chambers (faces). (Although I would worry with a difference of more than about 10-15 PSI.)

 

ok thanks guys, so im guessing i should get my injectors flow tested and cleaned?

 

so i need to get this clear before i spend the money to get my injectors cleaned... having 90's on all faces of the rotors front and back, normal for an 88 TII ? sorry for this noob question, its my first tII

 

Leaky injectors could be a culprit. However, an engine on the lower side of the acceptable levels of compression could still experience hot start problems without leaky injectors. Just wire up a fuel cut switch.

 

Your plugs may also be fouled...

 

when u pulled the spark plugs, theyre pretty black, should i go and replace then also?

 

See the attached picture. Look down into your spark plugs, with a magnifying glass if one is handy. If the center ceramic insulator (area in red in the picture) is a brown or tan color, the plugs should be OK. If the center insulator is covered in black material you should replace the plugs. Small amounts of black material ELSEWHERE on the plug is not particularly significant.

Keep in mind that fouled plugs (i.e., black on the center insulator) can be due to a weak or faulty ignition, over-rich air/fuel mixture in addition to bad spark plugs.

 

when's the last time you chaned the plugs? IF it's been awhile and you've flooded the engine several times since the last change....it might be a good idea to pick up another set.

 

weird my spark plugs doesnt look like that... and i just got the car like 2 or 3 weeks ago and i dont think the previous owner did change them so i might pick up a new set pretty soon

 

Your hot start problems are likely caused by your low compression. However, cleaning and blueprinting injectors isn't that expensive. I've never been a fan of the fuel cut off switch... it just fixes the symptom; not the problem.

As always, the FSM is helpful in this situation.

 

how would the fuel cut off switch fix the symptoms? coz i already have that

 

bump.. got another question... when i have the hot start problem... i try starting it and i would have to pump the gas to get it going... it sounds like its only firing on 1 rotor until i can get it rev up to 3500 - 4000 rpms then it would run on 2 rotors... wtf is going on?!?

 

I have a 88t2 and when its sounds like it wants to start I have to time it just right by pushing the gas pedal otherwise it wont start.

 

i have to do that too... but why does it sound like its only running on one rotors? coz i have even compression in all faces.... could it be dirty injectors?

 

Try change your plugs like someone said.
They should look like this:


(NGK BUR9EQ)