Hey guys

I watch a video on how to do a compression test with a piston tester.

You take the schrader valve out and hook it up to the top plug. Have someone crank and watch the gauge to see where it will bump to for each camber on the rotor.

Should see 3 bumps to 85 psi on each rotor.

What are your guys thoughts on this? Should be good enough to see how the apex seals are doing.

A lot cheaper then the stealer if you are just looking for low compression results.

 

Waste of time. Get a test done with a real rotary compression tester if you really want to know the health of your engine.

 

Im just looking to see if it has low compression.

The car wont start at all when warm. I mean not even a little bit. Sounds like it is misfiring when trying a warm start.

If it is that low for compression, I would think this method would show me if compression is truly that bad.

Doesn't matter how I get results. I just need results.

This is what I'm talking about.

 

This method will tell you if it is completely blown. But the results are not accurate and many things can cause low readings and hard starts are not always a blown engine, you need to properly diagnose it. Very common topic, Search.

 

Im going to try it real quick and post the results.

Its easier to try then not to try at all.

 

I have looked through everything other then a gutted cat or replacing the ignition.

Cleaned everything with MAF cleaner. Polished the ssv and camber. No codes. Live data shows everything is reading ok.

The car does start cold and runs. Dies when warm and wont start.

Its time to see if it is a blown engine.

 

So you didn't replace the ignition? Starter? Battery?

 

Been keeping the battery charged with a charger (12v @ 6amp). Starter seems to be spinning ok (could be an old version as it is an 04). Starts ok when cold.

Ignition has not been replaced but does look newer. Changed around the coils and wires to see if it changed anything. No, nothing changed.

I would thinking if it was that bad, a misfire code would come on.

I'm going to take a video of the compression results right now.

 

Man you really need to diagnose this properly before you assume the engine is toast. Seems to be spinning okay? Looks newer?

 

From what I have been reading and watching. A rotary starter spins faster then a piston starter. Mine seems ok if it was in my escort.

Could very well be the ignition. Waiting on funds and will be replacing coils, wires, and plugs.

Here is a video of the front rotor with a piston compression tester.

 

Dude, you can't tell if a starter is up to par by listening to it. Good idea on the ignition stuff. But I had similar issues and it was my starter (even though it was a brand new Denso unit and tested fine following the factory service manual procedure). Mazda upgraded the starter for a reason.

 

I had the same problem with hot starts it turned out to be my starter. After I changed the starter the car starts and runs like a champ. Mine happened gradually, as time went on my car was taking longer and longer to start when hot. If yours is doing the same it could be the starter. As for a compression test you need a real test. Take it to a shop that deals with rotaries if you need one.

 

As you can see in the videos my starter maybe the problem.

I have new coils and wires coming in the mail. I think its an spark issue as when I try to start warm, I can here it misfire. It could be just the way this setup is but I think its not. You can hear it try to start but then it misfires and starts all over.

The stater probably has something to do with it too. Both the ignition and starter would cause a big problem.

You can see the compression test I have done, both rotors seem to have the same compression. I highly doubt the seals are gone to the point where I need a rebuild for it to start warm.

I think its more of an ignition problem. I will post results when they do come in.

At least with the test I have done, I know the engine is not fried. From the VIN it only has 70k on it (140k on the dash).

At the moment I am doing everything I can to clean it up to my standereds. With a project car, I'm used to show quality work. Polished all the A/C and moving on to underbody paint. Whats a car when you put half the work into it. Put all your effort into it and you will hit gold when your done.

Sorry for getting off subject here, had a few of these at work.

 

isn't it a Schrader valve?

 

Idk if you know, but you are supposed to disable the ignition and fuel during compression test. I can see in your video, that the coil is sparking. You can fry the coil if its doesnt find a proper ground. Also, if the plugs wires and coils havent been done in the last 30-45k miles then id change that and the upgraded starter as well. also make sure your battery is up to par on CCA. Rotaries are low compression motors as it is and a weak electrical system won't bring it up high enough. components can also fail once it starts to get hot. i had the same starter issue on mine and countless other Rx-8s I work on.

 

disconnect the eccentric shaft position sensor to disable fuel and ignition.

and for an RPM reference disable the fuel pump and ground the plug wires, some DVOMs have an RPM magnetic pickup which you can use for a speed signal to see how fast it is cranking.

this test works fine to rule out the reverse, that the engine compression is good and has above 85psi while cranking, if it does then something else is problematic. to rule that the engine is bad you need a cranking speed reference. so for now you need to figure out exactly how fast the engine is turning to give a face to the numbers, slower cranking speeds will result in lower compression numbers.

 

I just pulled the fuse for the fuel pump.

At the time I didn't think about the coil arcing to the tester (saw that in the video to). It's not a problem though. Tomorrow new coils and wires should be here.

The point for this test was to see if a apex seal has failed completely. Where it would be the fault for not starting. At least I know both rotors have around the same compression.

I do understand that an actual test would give me better results. I just didn't want to buy new parts for a bad engine. Next will be a starter.

What starter should I look for? So I don't get the same poopy starter. I want to make sure I get the updated starter.

 

Can you search? the starter thing has been discussed like 50 billion times.

 

N3H1 A or N3Z1 is the upgraded starters. U can also let go of the bleed valve to see what ur max compression reading is for each rotor. But before u even do the compression test, change the starter, make sure ur battery is good and ur starter gets 12v with no voltage drop while cranking.

 

If you have a reader that shows live data, you can get the cranking rpms by pulling 1 plug on each rotor, plug in the reader, and set it up to show rpms, press the gas pedal fully and crank.
That's how I get my cranking rpms for when I do my home compression test.

 

Yes of course I can search.

Would be much easier just to ask and have someone give me a model #. I will search and find it myself. Should be easier then using the search for trouble shooting.

So far I have received great info from peoples responds on my questions. Al lot better then what I have been reading. 80% of peoples problems are "your engine is fried". Then the person comes back with the results of a bad ignition system or starter.

I like your sig

"Feel free to ask every single little thing on this forum. a lot of cool dudes will answer your questions accordingly "

Are you not one of them? Just playing, you set yourself up with that one.

 

Thank you for the model numbers. Saved me from searching it.

I took the valve out and will put back in to see what max psi is.
Could you please give me the numbers I should look for. I think I read somewhere that it should be at 110-120 psi?

Right now the battery is on a charger at 12v@2amp. When I run the test it is at 12v@6amp. Will be replacing it with a yellow top as more funds roll in.

Should be next weekend when I replace the starter.


This is a very good point. I don't know why I didn't think of it. Next test I will check starting rpm. A healthy starter should be at 275rpm right?

Thanks for the info guys

 

250 is Mazda's standard.

When I got my new upgraded starter it spun around 325rpms. I have it on one of my YouTube videos.

 

No problem dude. I'm not gonna be here everyday on these forums. I'm busy workin on cars everyday, but don't mind giving out some info. Anyways, 115+ is
Like new. U want a minimum of 85psi. Piston gauges wont give u the most accurate reading but the first compression pulse is what really matters and will let u know how equal each apex seal is at. The max gives you an idea of where of where they are at according to the max reading and difference between each tip. But like I said upgrade to the new starter no matter what before u continue on with the tests.

 

98psi@250 rpm is minimum spec.

Anything below that is low compression.