My rx8 was i was swapping engines out with a new rx8 engine and currently, I'm having issues with the spark for some reason it did start whenever I hooked it up as soon as I saw coolant was leaking from the heater core hose near the inlet by the brake booster I turned it off and since then it just didn't want to start again I check for spark and it gets one spark while cranking then stops very strange and another thing I noticed is whenever I'm cranking the rpms would look normal then it seems to drop to 0 as if it's unable to read the rpms anymore I did replace the sensor with an OEM replacement and ohms reading seems to be in range plus made sure to check the cables weren't shorting I'm not sure if something in the car is causing the car to short out or if I am having a bad PCM not sending the right trigger voltage at this point I'm very lost were to look with the voltage meter and would like some help to the right direction

 

Check that the grounds on the top of the engine are good.. they ground the coils and the PCM

 

I did check the resistance on my ground through the coil and I'm getting good continuity is there any other reason it would cause this issue

 

Tach dropping to zero sounds like it's losing the ESS signal. Since you replaced the sensor, did you do a profile reset? (20-time brake pedal press with key in ON until oil pressure gauge does a sweep).


The no start condition might just be flooding from the quick on/off you did. Dry off the plugs and start again, and perform deflood procedure as long as there is rpm signal. I'd hook up an OBD reader to check codes and also watch rpm and other signals in real-time, rather the the tach.
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Were the coils replaced with the engine? Usually engines die due to dead coils, and you don't want to put dead coils on a new engine. Is it actually new or new to you?

 

I have done a ESS reset and doesn't seem to fix it I will hook up my 0b2 scanner and check for live data but is there anything else that could cause this problem? It seems I could have a problem with the ECM since the way it's wired up it connects directly to the ECM you think I could have problems with other components one thing I noticed is that my ohmz on my coil from B-C has 800ohmz and as soon as I connect pcm connect F specifically the Black-white wire would cause my ohmz to drop to 400ohmz another thing I notice is when ever I check voltage I get 12 volts and when I start crank it drops down to 11 volts

 

And i have replaced all the coils brand new and the same goes for the sensor the old ones did work previously since I only swapped the engine out because of low compression and I can confirm the new engine started multiple times it's only as soon as I had coolant splurging on the engine is when it stopped sparking I checked for connections and made sure that none of the connectors are corroded together but I have feeling for a slight second this could of fried the ecu but I don't want to do anything before I can track down the actual problem

 

Battery voltage dropping under load is normal. Can't comment on coil terminal resistance, never tested it with the ECU connected. How are you doing that exactly? That could actually damage the ECU since to test resistance the meter has to put current through the circuit, so you're introducing currents to places it may not have been designed for.

The coolant leaked from the throttle body connection? So onto the coils? It should all be weatherproof, so I'd be surprised if that caused any damage.

Let's take it one step at a time. The main issue I see is the ESS signal drop. Without that nothing will work. Have you cleaned it? Are there ESS codes? Does rpm show at all times on OBD?

ECU failures are MEGA rare, it's almost never that, and it's a pain to replace, reprogram, etc.

 

The coolant was from the heater hose near the break booster it was shooting coolant on the knock sensor oil pressure sensor and maybe on the 02 sensor plug the way I was conducting the test was check the resistance from the connector for the coils and the connector (F) its what provides power to the coils its also provides power to DSC,SAS,Angle sensor and Coil for immobilizer I have another rx8 that is functional and that was one main difference between both