Hi so ive been getting this random 3 second crank to start when my RX8 has been cooling down around 1-2 hours...

When I got the car back at 41k miles i believe the compession was Rotor 1: 8.1, 8.0, 8.1, Rotor 2: 8.0, 7.9, 7.9.

Now it has about 68k miles and i just had Mazda do a compression check again and im at Rotor 1: 8.0, 7.9, 8.0, Rotor 2: 7.9, 7.8, 7.9...

So im still good at compression i believe...not sure why Im getying that 3 second crank randomly...The car has good power still and no issues pulling and revving to redline and idles steady at 800rpm and dont fluctuate...I just changed the sparkplugs as well, battery is an Optima Yellow Top thats about a year old, still on Stock Coils.

Any ideas?

 

"stock coils" meaning those it came with from the factory? Because at 68k its kinda time for those. So that would be one point of preventative maintenance.

The other possibility is electrical, perhaps the battery isn't able to provide enough current to spin the starter up to full speed, or the starter itself is unhappy, or dirty battery terminals/grounds/everything in between.

Do you have the raw rpm number for both of those compressions tests? It'll tell you if the starter is in fact spinning slower.

 

But why does it only happen when the engine has been cooling down for more than an hour? and random?

 

After 2 hours the car should be basically cold. Pull the spark plugs and check for traces of coolant if you really want to be sure it's not that. I wouldn't focus too much on when the issue happens, especially since it's random, focus instead on what's required to not have the problem: fuel, spark, compression (which is a function of starter speed, which is itself a function of battery amperage and clean path for current to the starter)

Is it possible that you usually start your car after 1-2 hours of cooling, but it might also do it if you were to restart warm enough times? Does it ever do it when fully cold, like in the morning?

 

No, it doesnt happen when its cold...not when its still warm either...its specifically after 1 - 2 hours of cooling down when i experience the issue, but then when it fires up after 3 seconds of cranking it just starts normal without hesitation or strugling to idle...wierd.

I forgot to mention that the starter is brand new also from Mazda...my old one went bad about 3 weeks ago...but i had the issue even before the new starter

The coils are the only ones i havent replaced but then if its going bad why only during the cooling down time?

 

I highly recommend getting new coils. BHR if you have the cash. This fixed my warmed engine starting issues!

 

For reference, I occasionally get random longer starts, too. It's usually like 2 seconds at most. Happens with both BHR and OEM Rev C coils.

 

So this is normal?

Ima gonna go ahead and clean the throttle body and MAF and while im at it replace the ignitions coils with the rev c version see if that helps.

 

I can't say it's normal, but at the same time, it's unpredictable and not frequent enough for me to lose sleep over.

I cleaned the MAF and throttle body last summer.

 

Mine did this yesterday. I left my house and drove 15ish miles to a store. When I left the store it started instantly, drove a few miles to a friends house. The car sat for a few hours and then I got a long start when I left.

I've done this same thing 100s times where the car starts instantly too. The 2-3 times it has happen low compression gets in my head of course.

 

Sounds really close to my scenario...but i got the compression check and its still good.