93 RX7 Compression Test
09-25-10, 02:35 PM
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93 RX7 Compression Test
After just completing an 1100 mile round trip to Riegelsville,my car seemed down on power a bit.Vacuum at idle was down at -480mm Hg although idle was still a smooth 750rpm,I was unable to boost over 0.78bar and the car seemed to run out of breath as it were over 6500rpm.I also noticed that manifold vacuum drops quicker with throttle opening than before
The engine is the original,has a mileage of 105,000km(or 65k miles) and burns no oil.I have BNR turbos,PFC,HKS downpipe,factory cat and RB muffler.
So because I pounded it a bit on my way down and on the cruise I thought I may have broken a seal spring or something.So my first move was to perform a compression test---I was really happy with the results which are really good for a 17 year old motor!
My thinking now is that the factory cat has started plugging up--probably some melting.
The engine is the original,has a mileage of 105,000km(or 65k miles) and burns no oil.I have BNR turbos,PFC,HKS downpipe,factory cat and RB muffler.
So because I pounded it a bit on my way down and on the cruise I thought I may have broken a seal spring or something.So my first move was to perform a compression test---I was really happy with the results which are really good for a 17 year old motor!
My thinking now is that the factory cat has started plugging up--probably some melting.
09-25-10, 04:03 PM
#2
After just completing an 1100 mile round trip to Riegelsville,my car seemed down on power a bit.Vacuum at idle was down at -480mm Hg although idle was still a smooth 750rpm,I was unable to boost over 0.78bar and the car seemed to run out of breath as it were over 6500rpm.I also noticed that manifold vacuum drops quicker with throttle opening than before
The engine is the original,has a mileage of 105,000km(or 65k miles) and burns no oil.I have BNR turbos,PFC,HKS downpipe,factory cat and RB muffler.
So because I pounded it a bit on my way down and on the cruise I thought I may have broken a seal spring or something.So my first move was to perform a compression test---I was really happy with the results which are really good for a 17 year old motor!
My thinking now is that the factory cat has started plugging up--probably some melting.
The engine is the original,has a mileage of 105,000km(or 65k miles) and burns no oil.I have BNR turbos,PFC,HKS downpipe,factory cat and RB muffler.
So because I pounded it a bit on my way down and on the cruise I thought I may have broken a seal spring or something.So my first move was to perform a compression test---I was really happy with the results which are really good for a 17 year old motor!
My thinking now is that the factory cat has started plugging up--probably some melting.
Also sounds like a boost/intake leak. First thing that comes to mind is the y-pipe to intercooler pipe coupler. It is attached to the bottom of that cross pipe going from the turbo side of the engine to the intercooler. They split open and leak boost pressure.
09-25-10, 04:34 PM
#4
Oh. For future reference, if you put you year and model with major mods in your signature people can look at that when trying to help diagnose.
I'd still check for a boost leak in addition to cat. Basically anything after and including the compressor outlets can be a leak. That includes all those large hoses and their respective valves. Like the air bypass (blow off) valve and hose.
I'd still check for a boost leak in addition to cat. Basically anything after and including the compressor outlets can be a leak. That includes all those large hoses and their respective valves. Like the air bypass (blow off) valve and hose.
09-25-10, 11:56 PM
#5
If you suspect that your cat is clogged, unbolt it where it connects to the downpipe & take the car down the road. Yes. It will be loud. I had a plugged cat & upon unbolting the exhaust from my downpipe, boy, did the car really come alive. Your boost may go to 12 PSI or more so watch that. Would be a quick way to determine if it is your cat or not.
09-26-10, 06:39 PM
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I'd pull that sucker and rebuild it before it throws an apex out the exhaust port. My engine was sitting at about 90k miles and I was stocking up on stuff for the rebuild, my compression results were similar to yours, when it shot an apex seal out the exhaust port 
Anyway glad to hear it was a resolved
Anyway glad to hear it was a resolved
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09-26-10, 07:07 PM
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Glad you resolved the problem Gerry 
Those numbers certainly aren't horrible, but keep in mind mazda spec on a comp test is 250 cranking rpm (which you probably are well aware, lol), so you're about 10% high most likely due to having a strong battery. If you take that into consideration, that rear rotor is looking a little weak. Not atypical given the mileage, but food for thought.
Those numbers certainly aren't horrible, but keep in mind mazda spec on a comp test is 250 cranking rpm (which you probably are well aware, lol), so you're about 10% high most likely due to having a strong battery. If you take that into consideration, that rear rotor is looking a little weak. Not atypical given the mileage, but food for thought.
09-26-10, 08:11 PM
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Hey Rich--how are you?I am not too worried---I have a rebuilt motor sitting on the shelf.It was a low mileage JDM motor I was able drive before I bought it.All it really needed was the oil control O-rings.
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