I had a compression test done at a Mazda dealer today and it dowesnt make any sense to me. It is a 88T2 with 104,xxx miles. I need someone to tell me if this is bad compression. The service center said it was bad. The car starts right up and pulls hard til it hits a brick wall at 4000RPM. I have no idea what unit of measurement this is. Here are the numbers:

Front Rotor:
1st 18.5 / 18.5 / 08.1
2nd 09.0 / 18.1 / 08.6

Rear Rotor:
1st 18.4 / 18.4 / 14.7
2nd 8.1 / 12 / 7.4

 

i think the compression numbers are on the underside of your hood arent they? (im to lazy to check my hood) and yea its definetly not a good thing if it has trouble at 4k

 

Those compression numbers seem odd, try premixing a little, make sure the throttle is held open when this is done and the engine is fully warm. If the engine pulls hard until 4k it is a fuel issue, maybe you are overboosting, is the pump and filter known to be good? Are your 2ndary injectors clogged or hooked up correctly? 4k is when the secondary injectors switch on.

 

you know now that im thinking about it i think the hood only says spark timing...ahh i forget

 

Those numbers don't make sense. Maybe their tester was broken? Or the guy had trouble reading the display? You also need to know what rpm the test was done at. I would ask for your money back.

 

something is messed up. perfect compression is what, 8 on a mazda tester?

 

As usual the Mazda Dealership screwed up a compression test. I've had this happen to me 3 times. On one test they tried to charge me for removing the starter. They were unable to explain how they did a compression test with the starter removed. The other stories I won't bore you with.

My understanding is there are two compression testers, one analog, which provides a paper read out and a digital. Again, my understanding is on a digital test in kg/cm2 10.0 is perfect, 8.0s are very good, 6.5 is the bottom limit of acceptable (some say 7.0). Differential betweeen the chambers should not exceed 1.5 kg/cm2. The test results are adjusted for RPMs (which are provided in the read out) and altitude. Adjustment grids for both RPMs and altitude are in the FSM.

How they got readings of 18 +/- is ridculous. Demand your money back and if they try and stonewall, tell them to check the FSM for the correct procedure and explain how they got numbers higher than 10.

Sorry if the post is intense, but Mazda dealerships doing screwed up compression tests really pisses me off.

 

mazda dealerships are always screwing up...they broke my dashboard...

 

mazda dealerships are always screwing up...they broke my dashboard...those numbers don't make any sense at all...you need to go in there and crack some skulls..lol

 

I've tested engines with it and have some rare ones > 10(highest i've seen is 10.5 or so). The number is just a pressure reading, those 18s correspond to over 250 psi.

Rather, tell thim this: Since the highest compression rotary is 10:1, unless you live far below sea level or something the max reasonable possible compression is about 10.4 (10x atmospheric pressure, 1 kg/cm2 = 14.2 psi).

Can you ask to be in the room when they do the test? If the tester actually reads 18 then its most likely damaged.

 

The tester, not the engine.

 

Thanks for your input, I will get it retested somewhere else and watch them do it this time.

 

I'd go back to the first dealership and bitch at them.

 

I second that.

 

yeah dont let them get away with that go back demand your money back or that they do another test WITH u there so u can see how they did it and if there equipment is faulty

Dave