Hello everyone, I have a inconsistent hotstart cranking time on my RX8. It has rebuilt engine with 5000 miles, new NGK coils and plugs. Sometimes it cranks for about 2s to hotstart and sometimes it starts right up in less than a second. The cranking speed is about 260rpm.
Here are a two starts:
https://youtube.com/shorts/WQcavB62nI8?si=icrTjSDpuu2P9Tlp
https://youtube.com/shorts/EJ63ZxmFeUM?si=9c05ZpBjq8UncldB

Is it normal for RX8?

 

Sounds fine. Is the slower start usually when the engine is warmed up?

 

Thanks for reply. It usually happens when fully warm up. Cold starts are usually consistent something in between cranking about 1-1.5sec. When hot it really depends sometimes it starts instantly as second videos, but sometimes it cranks more like in first video. Also letting it col down for a few minutes doesn't make a difference as far as I can notice. Judging by the cranking sound it seems to me it doesn't either have a fuel or a spark for a first second. I am curious if it is normal for a rotary as some people say because ignition is new and cranking speed of 260 rpm seems ok in my opinion.

 

Rotaries have lower compression at low rpm and when warmes up. Could be an early sign of compression loss, but the videos you posted sound fine

 

I know that low compression is problem on hot engine but I am curious why it is not consistent if my compresion is getting low. I also noticed that is starts also with about 2s cranking when it is half way warm (coolant temperature about 50-60°C) It is also weird because engine is at only 5k miles and it is premixed. In my opinion it is unlikely to get simptoms this early. Thanks for the answer!

 

It's probably fine. You can get compression tested and/or check the fuel trim data to see if there are anything out of place. But the starts in your videos don't sound bad

 

Check your starter speed (via OBD). A 2kw starter should turn at 300rpm, some of the earlier ones do about 250-260. Worn out starters do 200 or less and contribute to slow starts.

 

I checked. It cranks between 260-270rpm. I think it is revised series I starter. Also I checked my cold start ( summer ambient temperature about 30°C) it is almost the same cranking time as my longer hot start about 1.5 sec crank. To me personally and inconsistency between instant start and 1.5 sec crank is fine as long it is normal.

 

According to OBD my long term fuel trim settles at idle at 3.75% after a few minutes.