Toofer89

Hi Everyone,

I will be conducting a compression test on my 1987 series four Turbo II this weekend and wanted to be sure I have the procedures correct for my application. I will be testing with RotaryCompressionTester.com’s RCT-V5 unit from the cabin of the car. I have searched and done a fair amount of reading, but the steps and methods seem to differ. After comparing info from popular vendors and rotary builders (Racing Beat, Bonzai Racing, Rotary Compression Tester.com, and this forum I have come up with the following procedure:

1) Have a fully charged battery
2) Bring engine up to operating temperature
3) Turn the vehicle off
4) Disable the fuel and ignition*
5) Remove trailing (top) spark plugs*
6) Connect tester
7) Crank engine with gas and clutch pedals fully engaged until readings are complete*
8) Repeat for each rotor housing

A couple questions:

I have found some discrepancies in step four “Disable the fuel and ignition”. Across the board it is said to remove the EGI fuse, simple enough. EGI is fuel correct? Is disabling the ignition as simple as removing all of the ignition wires from the spark plugs? I have read a couple sources that say for the FC the CAS (crank angle sensor) should be disabled by disconnecting the CAS’ electrical connector (described as “white clip with four wires running out”). Is this true? Will cranking the car with the CAS disabled require it to be fiddled with or reset after?

I have also found some variation in step five “remove trailing spark plugs”. Some say remove trailing and other said remove leading. I have determined this does not make a difference. I chose the trailing (top) plugs because they are easier to reach. My real question about this is do you remove both of the trailing plugs at the same time (cranking engine with one plug hole being tested and the other totally open?) Or one by one – remove housing #1 plug, test housing #1, replace housing #1 plug, AND THEN remove housing #2 plug, test, etc.

I want to make sure that I have step seven “Crank engine with gas and clutch pedals fully engaged” correct as my RX7 is a series 4 Turbo II. From what I have read series 5 ECU’s work a little differently in that are made to clear flooded engines by depressing the pedal and cranking while the series 4 does not have that luxury. Does this difference come into play or affect my compression test?

As for the results should I go by these standards for each rotor face? :

Best: 110PSI
Normal: 85PSI or more
Minimum: Anything less than 85PSI

I know the series four cars have lower compression rotors, should I be looking for different tolerances of PSI as a result?

Thanks for help, this will be my first time performing a compression test and I want to be sure I am doing it correctly for my particular vehicle. Being that it’s a turbo 87’ with over 100,000 miles I’m expecting low numbers. But the car starts up and drives fine, no smoke when heated up so fingers crossed! The motor looks stock/original and I have no paperwork for a rebuild but who knows. This will dictate whether it gets a rebuild this spring or a new turbo setup. Either way I’m excited to see how it goes and have a plan for my 7 once the snow is gone.

-Mike

FührerTüner

iTrader: (5)

Never heard of holding the gas pedal down.

Are you using a standard compression tester, or a rotary compression tester?

If youre using a standard tester, you'll need to remove the schrader valve, and watch the gauge for 3 even bounces over 90psi.

EGI is fuel, and you could also unplug the CAS. It wont hurt anything or throw anything off. No fiddling required.

You should only need to remove 1 plug from each housing. I personally would use leading because the hole is bigger. Probably doesnt matter tho.

Like i said above, Ive never heard of holding the gas pedal down. Maybe youre supposed to???


85 is getting pretty tired. I'd say anything above 90 with the schrader removed is good.

DankestKush

iTrader: (4)

i found this bit of info quite useful on aaroncakes Is My Engine Blown?

ACR_RX-7

iTrader: (1)

He is using the electronic rotary compression tester that calculates RPM and all three faces. The tool is on sale in the vendor section for $399, I believe.

Toofer89

Thanks for the responses guys. ACR is correct; I am using the electronic tester. For the most part I think I have these procedures in line. My biggest concern really is the few places that said the CAS should be disabled on FC's. What would disabling the CAS accomplish? Holding the throttle open was almost universal but as Fuhnortoner pointed out there are people that do not do this. I am also pretty curious about removing one plug at a time opposed to removing both plugs before starting the test, this was probably about a 50/50 split between people who do it one way and people who do it the other way from everything I read.

Again, thanks for the help, any input is appreciated. Getting correct readings is very important to me.

ACR_RX-7

iTrader: (1)

Me personally, I unplug the CAS. The CAS controls spark AND injection. No need to pull fuses and such. Holding the throttle open allows the air to travel into the engine unimpeded. With it closed, you can have inaccurate numbers. The engine will work harder to produce a vacuum.

I remove both leading plugs when I do it. The trailing is fine, but I prefer to have the larger opening. At the end of the day, pressure is pressure. The tool will calculate the RPM and each rotor face, so you shouldn't have any issues. The reason for the RPM measurement is to reference it to the FSM.

I also hook up a battery charger when i run the test. I work in a shop, so i set it up on 40A continuous. This is not to supplement the cranking, but is more to give the battery a boost after cranking. This will also help keep the readings even from rotor to rotor.

You very much have the right idea, but holding the throttle has zero to do with fuel cut and everything to do with allowing air into the engine. Unplugging the CAS accomplishes fuel cut.

Toofer89

Great info! Thank you ACR!

misterstyx69

iTrader: (142)

Pulling the EGI will disable fuel and spark..so think of that as #4.
..and having the Throttle Fully opened when cranking and testing gives you the True reading..

RotaryEvolution

iTrader: (30)

holding the throttle open does make a slight difference, i always hold the throttle WOT when doing compression tests.

scathcart

I think this is not such a great idea. Disconnecting and reconnecting electrical connectors causes them to wear out and fail. On something as critical as the CAS, one already prone to connector problems, this seems pointless when pulling the fuse in the engine bay accomplishes the same this with less risk.

ACR_RX-7

iTrader: (1)

Over how many cycles? A fuse in a holder is the exact same thing. A connector.

The terminals in the connector should have life for about 20-30 connection cycles without any risk. The plastic is brittle and that is what fails. On most of the RX7s I get my hands on, the fuse cover is missing. I'm lazy, so I pull the CAS connector since I know exactly which one it is. I work on just about any make and model on the road from BMWs to Fords, so I don't have the fuse locations memorized on every car.

Either method accomplishes the exact same thing. Disables fuel and spark. You can do it either way. If the connection at the connector is bad, you replace it. Simple as that. Usually the tabs break off, so it will not stay fastened. Nothing a weather-pak connector can't fix.

scathcart

Meh. Connection points for a fuse are on the fuse; if the connection loosens, you just replace the fuse.
if you think diagnosing a bad connection at the CAS and then crimping on a new connector is easier than pulling a fuse in an out, more power to you. Not sure busting on a 'scope to diagnose readings on the VR terminals at the ECU is as easy as a DMM at the fusebox.

Then again, the fuse connections rarely go bad.
CAS... all the time.

To each their own.

RotaryEvolution

iTrader: (30)

pissing into the wind.

i've used both methods and disconnecting the cas or pulling the fuse never resulted in any issues. if you break the cas connector, it's probably best you did while the car is in the garage anyways, instead of it going south on the road, on a rainy night.

ACR_RX-7

iTrader: (1)

If the connection is that finicky, then the connection will be bad down the road. Better to catch it in the shop. Scoping can be done at the component, not just the PCM. I have never seen an FC CAS fail, only the connector itself.

I agree. I already stated above either way works. After touching thousands of vehicles with hundreds more connectors per vehicle, the only ones that fail are the ones that were bad already. You just end up finding it in the shop.