I just got the compression test results back on a 94 FD that I'm was considering buying. The compression numbers seemed really low to me and I was wondering if someone could tell me what the 94 owners manual or the technical manual actually state as acceptable numbers (the page number this infor can be found on in either of the manuals would be great too). The acutal results were as follows:

-Test 90 psi on all cylinders
- No.1 top is 3.2 on all 3. Low is 3.0 on all 3.
- No. 2 top is 3.2, 3.1, 3.1. Low is 3.0 on all 3.

From what I remember the psi at 90 is pretty good but the rest of the numbers are crap. Aren't the recommended numbers from Mazda 590 kPa {6.0 kgf/cm^2, 85 psi} - 250 rpm? Please let me know what you think. I know most people seem to be getting 7's pretty regularly. The owner of the car said he's confused because someone in the service department showed him the 94 tech service manual that showed spec compresson for each "cylinder" to be 3.0 or greater.

Can anyone think of a reason for these numbers to be so low besides bad seals? Are there ways of doing the compression test or reporting results that could account for numbers this low? The car has a new engine with only 6k miles on it and the owner has stated that it has never overheated as long as he's owned the car (he's the one that had the new engine put in). The engine idels fine, pulls strong, doesn't blow any smoke, etc. I was going to call the mazda dealership where it was tested to ask some questions about how the test was performed to see if these results are accurate.

Other test results seemed fine. Control actuators and vacuum integrity were tested with the following results:

-With a differential limit of chambers 21 psi.
-Tested vacuum on turbos found to be dropping at specified air
pressure.
-Found no vacuum leaks in systems, turbo control and charge
control actuator are opening at recommended cycle.

Sorry for the long post but I wanted to include as much information as possible. I'm getting a fair price for the car but I want to know if the compression is as bad as I'm thinking it is. I'll pass on this car and look for another if this car has a bad engine. Any and all help is greatly appreciated.

Thanks,

Chaz

 

Who was running this test? (lame mazda dealers...)

-Test 90 psi on all cylinders
- No.1 top is 3.2 on all 3. Low is 3.0 on all 3.
- No. 2 top is 3.2, 3.1, 3.1. Low is 3.0 on all 3.

Those were the results you say you were given...

OK, what does Number 1 Top/Bottom and Number 2 Top/Bottom mean? Was someone actually attempting to test all four spark plug holes? That doesn't make much difference I don't believe. Was the person running the test leaving the other plug on the same rotor OUT while testing? This would create a large leak and lead to very low numbers.

I just don't think that a car that scored 6 readings of about 3.x would even START without ATF/oil/pushstart assistance. (even then I dunno)

If the car idles OK, my first suspect is that the test was done incorrectly. If you are interested in the car, I'd have it retested (preferably by someone else).

Brian

87 TII
93 R1

 

Thanks for the response Brian.

The test was performed by Les Marks Mazda in the Houston area. I advised the owner take the car to MazMax but he apparently decided to go with the MazDuh dealer.

I'm not exactly sure how the car was tested yet or what the results actually mean. That's why I'm going to look at the report itself and then call the dealership to find out exactly what they did. Any idea on what they could have been quoting to the owner from the tech manual that said 3's were acceptable? I'm looking for ideas on how this car could get those kind of numbers and not be in serious trouble. The owner drove the car to the dealership and has driven it to get it detailed for me and said the car is running strong (he's more than a bit confused as well). I also thought that comp. in the 3's would make it extreamly difficult to start the car and drive it around.

I think I'll ask the owner to have it checked somewhere else as well. I would like to compare results from a test performed at a rotary specialist rather than the mazda dealer. I paid for the test so if the dealership screwed up how the test was performed I want them to reimburse me in some manner for the cost of a test that was performed incorrectly.

Any other thoughts and ideas out there?

 

I think you need to double check the compression results. According to my 93' manual page (TD-2) the minimum compression should be 686 kPa or 7 kgf/cm^2 or 100 psi at 250 rpm. The maximum differential between chambers on the same rotor is 147 kPa or 1.5 kgf/cm^2 or 21 psi at 250 rpm. Make sure that you have the measurements right. I didn't see any units in the numbers you mention. 3 kgf/cm^2 is much too low, and it's pure BS if the dealership says that's OK. 3kgf/cm^2 is the lowest you can measure with the Mazda compression measurement tool (page C-10 in my manual).

-Mike P.

 

First of all, what were the test conditions? The minimum of 7.0 is for a cranking speed of 250 rpm and an altitude of sea level. The results must be adjusted for different cranking speeds and altitudes. Also, the engine must be fully warmed up before the test. A cold engine will give low numbers. It should be retested!

 

Thanks for the responses. I now have a better idea of what kinds of questions I should ask the guy who did the test. I'm still going to have the car retested somewhere else to see if I get any better results. Anyone know of a good specialist in the Houston area besides MazMax? Mazmax was recommended by another forum member but I was just trying to think of alternatives in case the seller doesn't live near that part of town.

 

None of you Houston people can help me out here?

 

The numbers lead me to believe the test was performed incorrectly or the units are different. This is because all the chambers appear to be the same, yet the numbers are too low for the car to even run if you're talking about kg/cm^2.

 

Do you have any Rx-7 Tuners in the area?? If so, I wouldn't even deal with the dealership anymore. Just bring it somewhere else and have them do it.