Crank, but will not fire

Tiny
CODYMCCRUM96
  • MEMBER
  • 2004 MAZDA RX8
  • 1.3L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 120,000 MILES
Replaced coil pack, plugs, wires. When I plug into obd port, says unable to communicate with PCM. Not real sure what's going on. Just bought it, and want to get it running.
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Wednesday, June 17th, 2020 AT 1:48 PM

13 Replies

Tiny
KASEKENNY1
  • EXPERT
We can assume that the reason you can't communicate with the PCM is the same reason the engine won't start. This could be as simple as the PCM is faulty or the power and ground to the PCM is faulty. So we need to check power on the green/yellow wire and the grounds that are highlighted in the diagrams. If you have no power at the PCM with the key on then the main relay and fuse feeding the relay need to be checked.

Let us know what you find here and we can go from there. Thanks

https://www.2carpros.com/articles/how-to-check-wiring
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Wednesday, June 17th, 2020 AT 2:15 PM
Tiny
CODYMCCRUM96
  • MEMBER
Okay, I'll check it over tonight when I go to mess with it some more. Thanks!
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Wednesday, June 17th, 2020 AT 2:36 PM
Tiny
CODYMCCRUM96
  • MEMBER
Here's a video of it.
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Wednesday, June 17th, 2020 AT 3:30 PM
Tiny
CODYMCCRUM96
  • MEMBER
The man who owns it, said he was driving like normal, shut it off at home then all it did was what is showed in the video. I'm really wanting to buy it, because it only has 80,000 to 90,000 miles on it and figure it may be something simple.
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Wednesday, June 17th, 2020 AT 3:50 PM
Tiny
KASEKENNY1
  • EXPERT
Okay. I would start with a battery but it is not starting then we need to check for spark and fuel. If we don't have either of those, it could just be a failed PCM. However, I would not buy it if this is not fixed unless you get one heck of a good price as it sits. Basically the approach is, you may need a fuse, a PCM, or an engine. If he is not willing to fix it before he sells it to you then you are taking all the risk and risk needs to have a large dollar amount assigned to it before it makes it worth taking the risk.

Otherwise, tell him to call you when it is fixed and you will come buy it. Without really digging into this it is a large risk you are taking buying it as is. I don't see nearly enough to say this is going to be something simple or cheap.
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Thursday, June 18th, 2020 AT 7:54 PM
Tiny
CODYMCCRUM96
  • MEMBER
I have had a bunch of folks saying how it might be flooded out, and that they are very common to do so. But if it's flooded, it should still be able to communicate to the PCM, correct?
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Thursday, June 18th, 2020 AT 7:58 PM
Tiny
KASEKENNY1
  • EXPERT
Correct. Being flooded means there is too much fuel in the cylinders. That doesn't have anything to do with the ability to communicate with the modules. That is a wiring issue or module issue. If the engine is not starting, you need to check if the plugs are firing and if it is getting fuel from the injectors.

For the engine to start you need three things. Compression, fuel, and spark. So you need to check all of them starting with fuel and spark.

If you don't have either fuel or spark then I suspect the PCM is the issue.

https://www.2carpros.com/articles/car-cranks-but-wont-start
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Friday, June 19th, 2020 AT 6:34 PM
Tiny
CODYMCCRUM96
  • MEMBER
Thank you!
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Friday, June 19th, 2020 AT 6:50 PM
Tiny
KASEKENNY1
  • EXPERT
You are welcome. Let us know if you have more questions or how you make out. Thanks
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Saturday, June 20th, 2020 AT 7:07 PM
Tiny
CODYMCCRUM96
  • MEMBER
Will do.
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Saturday, June 20th, 2020 AT 7:16 PM
Tiny
CODYMCCRUM96
  • MEMBER
Bought a code reader, it popped up as crankshaft position sensor, the man I bought it from had put a new one on it, still won't fire up. I'm thinking that he didn't put it back in the right position, but I have no clue where it should be positioned.
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Wednesday, June 24th, 2020 AT 3:00 PM
Tiny
CODYMCCRUM96
  • MEMBER
That's the only code it showed at all. Nothing else.
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Wednesday, June 24th, 2020 AT 3:00 PM
Tiny
KASEKENNY1
  • EXPERT
I attached the info on this sensor and the process to replace it. I doubt the installation was wrong unless they just didn't tighten it. However, it should be checked. Then I put the testing there for this sensor.

Can you provide me the actual code that you are getting and I will give you the testing for that code? I suspect you have a wiring issue or control module issue. Thanks
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Thursday, June 25th, 2020 AT 8:19 PM

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