Compression Test
 

I found this video on You Tube on how to perform a compression test on an RE using a conventional compression tester.

Is this the next best way to perform a compression test on an RE if an RE compression tester is not available?


I will be performing this test Tuesday, because my engine is idling low, is low on power, and stalls sometimes when I'm coming to a stop. Sometimes the engine does not restart after the engine is shut off after driving around. It will start after it sit for an hour though.

from what I've read ... yes. that's the way to perform the test.

Great, thank you for confirming :icon_tup:.

I'll post the results, praying for the best, I hope all readings are at, or above 90psi.

such a calm and soothing voice....almost put me to sleep.

Comression Tests
 

Here are the results from my compression tests I performed today.

I'm not too sure about the readings even after watching them countless times :scratch:.

What are your thoughts?

For the rear rotor video, it looks like the cranking speed might have dropped after the first ~10 seconds of cranking, which may explain why the pulses drop to around 60 psi.

Otherwise, both videos appear to show relatively even pulses around 75-80 psi. Was the throttle open, and was the engine warm? Having a fully charged battery is also important. Minimum spec in the manual is something like 85 psi, but there will be some variation between gauges. Length of the hose connected also plays a role.

Ah! I knew I was forgetting a step, I forgot to hold the throttle wide open. The battery is good, the engine was warm, but cooled down a little since I had to prep for the compression test. The connection/plug that was inserted in the spark plug hole was short like the one in the top You Tube video. It did not have the same length of threads as the spark plug threads, the hose is about a 1' to 1' 1/2" long.

Also I did not disconnect the CAS. Should I have done that as well?

I am about to do this test for my 90 vert and would like to know if you need to disconnect the CAS while performing the test as well? The manual says to, but some confirmation would be helpful. Thanks for this thread because I was using that first vid as a starting point also.

So I just did the test and yes you do have to disconnect the CAS. On a side note (this is my first time doing the test ever) I think my rx7 passed pretty good, even bounces at around 100-105 i think. Hope for your rx7 to be running great.

Awesome
 

You are welcome :icon_tup:.

Ok, thank you for the confirmation, because I was still wondering if it was necessary. Your vert is in good condition, I hope my retest has results in your range. You are out of the in need of a rebuild compression test results.

I will follow up again.

This is what my test looked like, you can tell me what you think and maybe it will help. First one was front rotor, sorry for the negative sound in my voice but i did not want bad results..still do not lol.

Your good man :icon_tup:. The two lower pulses followed by an above 90psi pulse is good :nod:.

I hope my retest with the throttle wide open and CAS disconnected will get me similar results :fingersx::fingersx::fingersx::fingersx::fingersx: :fingersx:.

I'd just pull the EGI fuse instead of disconnecting the CAS.
That connector is a pain in the ass.
You just don't want Spark ,or fuel,(haha!),when testing for compression...Ftt,fft,fftt..Woosh..(holy crap!)

maybe it's my hearing/vision getting old but to me the needle from both 'S4 Vert''s and 'Lonely Driver''s is not bouncing evenly on every pulse.

to me there is skeeping going on. I like to back off the schrader valve a bit to bleed off some pressure which minimizes the needle's tarvel. Makes it easier for me to see what the needle does on every pulse. I also suggest hooking up vacumm gauge to see where the #s are @ idle.

p.s. 'S4 Vert', notice 'Lonely Driver''s RPM is higher. That will give higher #s.

I recently had hot start issues on my rebuild that turned out to be a shit Autozone rebuilt starter that cranked slow. I got a Mazda rebuilt and now cranks on steroids (like 'Lonely Driver''s) and hot start is a thing of the past.

THANK YOU :icon_tup:!! I tried disconnecting the CAS and could not get my hands in there to pull the clips apart, DAMN MY MAN HANDS :ugh2:!! ha ha.

You are seeing correct, there should be two low pulses and one high pulse in a three pulse compression test. And LD's compression readings are better then my readings, so his compression is better then mine.

I will retest my compression, because I did not have WOT, and the ignition was not disconnected. Maybe then I will have either a better, or worse compression reading then my first tests.

I think the hot start issues might be from recent repairs I had done to my engine, because before the repairs my engine started on hot starts and did not stall when coming to a stop.

Thank you for the advice and tips, I will follow up this week when I have the time retest.

That top vid, the guy is like the Bob Ross of compression testing

[QUOTE=

I recently had hot start issues on my rebuild that turned out to be a shit Autozone rebuilt starter that cranked slow. I got a Mazda rebuilt and now cranks on steroids (like 'Lonely Driver''s) and hot start is a thing of the past.[/QUOTE]

I thought about what you said about your hot starting issues you had. Is it really possible that my starter could be causing my engine not to start on hot starts? My brother said he had the same issue with his dually, and a new starter had fixed his hot start issues too. My starter is the original unit, so it's possible a new starter may be needed.

The problem I am having on hot starts is the engine will not fire up, the starter cranks the engine and I smell gas instantly. However the engine will not fire up, so I figured it is a compression issue. Because when the engine has time to cool down the metal retracts and creates a better tolerance for the apex seals to create compression (imo).

The longer I drive my car, the idle gets lower and the power falls off and the engine dies when coming to a stop unless I blip the throttle once, or twice. I figured the hotter the irons get they expand causing a gap between the apex seals and irons. And that is where I am loosing compression.

Correct me if I am wrong, I am still trouble shooting and need any and all correct advise I can get.

Thanks

^^^^
make sure your battery connections are clean. Hook up a charger set to start assist next time you do the test. this will rule out insufficient voltage as the cause of low RPM.

let's say your hot start issue is low compression. low compression is a function of both mechanical (i.e., poor sealing) and RPM. cranking RPM should be 240-250 RPM. let's say compression shows >95 psi @ 240-250 then at 140-150 RPM compression might come in @ <80 psi. At 95 psi hot start should not be an issue (specially if less fuel than factory is being injected). At 80 psi it's a challenge.

If it turns out compression is pretty even but borderline w/proper RPM and hot start is still an issue, you should have luck by reducing the amount of fuel during cranking. You can do this by introducing a switch on the 12V start signal wire to the ECU (it's pin 3B on the S4 TII, might be the same for the n/a). By cutting the 12V during cranking, the pulse width is ~1/3.

You need to hook up a vacuum gauge. Cheap way to monitor the engine's health. The high compression n/a motor should be north of 18 inHg at idle.

I do have an AEM 320 Fuel Pump, I am not using an fpr to regulate the fuel pressure, and I am still using the stock fuel injectors and S4 TII ecu.

So now I am leaning towards too much fuel is being introduced. Which could be the cause of the hot start issues, stalling when coming to a stop, poor fuel mileage and performance??

I will try the measures you have advised me to do during my next compression test.

Thanks :icon_tup:

Thanks for the info OP

You're welcome.

Thanks for the info!

You're welcome.

Ah!!
 

Well after being tired of my car stalling almost every time I come to a stop, or let off the gas, I finally decided to adjust the idle. After let the screw out a couple of compete turns, my idle is steady at 900rpm and my engine no longer idles super low, my gas mileage is better and the engine no longer stalls.

Thus is such a relief, because I was worried that the problem was worse.