Low Compression Numbers from Dealer - Feedback?
 

kpa readings they gave me

Port1 - 503.78
Port2 - 484.78
Port3 - 452.78

Is it correct that 680 is Mazda spec low before replacement?

Would these numbers really cause problems bad enough for my car to be consistently stalling when coming from speed to idle and having hard hot starts?

Dealer didn't even recommend anything. Of course, they gave me quotes on repairs and replacement, but only out of routine. Basically, they called me and told me the compression was low and come pick up your car. (I'm guessing not many people choose to replace or rebuild their Renesis after 160k miles)

Thoughts?

Those numbers don't mean much at the moment. Those might even be passing scores if your starter was only turning at like 180rpm. If your starter is up to the 250-300rpm then those are quite dismal, and probably nearly impossible to get it started when hot.

What about the other rotor? Should be an RPM and 2 sets of 3 numbers.


But yes, low compression will certainly cause low RPM problems, including hot start problems and idle problems.


If you want to replace and aren't looking for a custom built engine, Mazmart is your best and cheapest bet. Good engines that are usually lower than dealer prices.

I don't have the numbers for the other rotor.

Let me put this out there.
Last few times it died decelerating to near idle and died, I was in the middle of traffic that was slow rolling down hill. I tried restarting and it was having a hard time, and I roll started it from first gear and it started right back up. If it was low compression, would it restart like that? Or could the be a good sign of a weak starter?

Well, if it starts harder when hot than it does when cold, then it's a compression drop for sure. However, if your starter is old/dying, then you can probably get it to last a bit longer by replacing the starter. This will just help with re-starts though. You would still get it dying at the same points.

Dying at idle could be a number of other things, including vacuum leak, failing ignition, O2 sensors, etc. Of these, only failing ignition can also affect ease of start up.

So the two things that affect both problem points are compression and ignition. And with those compression scores, it's pretty clear that compression is at least one of the problem points. You might also have other parts failing though.

Ah I see now.

Well they did pull a code for the VSS valve. Which could be contributing?

They told me it could be a combination of those things, but that the compression was the main problem, and they don't really think replacing the VSS valve would necessarily help.

SSV, secondary shutter valve.

It's one of the intake valves that changes the length of the intake. No, it has nothing to do with low RPM or starting.