p0300 code bad ecu?

[383camaro]

Yep that was in the tank :(

[joecar]

Seeing that pic makes my brain skip a cycle :boom:

[383camaro]

Well I got a new pigtail for the sending unit and hooked it back up, installed the computer and wiring harness just got back from a test drive and still have the same problem when it throws the po300 code does it fire the injectors in batch mode? And since its a 98 ecu should I just upgrade to the 00 ecu since my computer looks like it took on a short circuit problem

[joecar]

It does not necessarily fire the injectors in batch mode when misfires are detected...

If the CMP signal is not detected during startup then it may run in batch mode...

but this PCM is able to determine the correct phase during startup from CKP response to ignition events (even if the CMP signal is missing).


The only way to tell is to capture secondary ignition kV waveforms using an oscilloscope... these will also show how the coil dwells/charges and how it discharges, and how the burn progresses.



You might try another PCM (and repin the connectors)... but we still don't know for sure... but there is the possibility of further damage on your current PCM.

[383camaro]

OK today I got off my butt and started to check for shorts in my wiring harness . I need a second opinion but I'm pretty sure I found the short just gotta seperate some wires in the harness if I ohm from the pink wire going to the ign coil 12v source to ground I get 2.1 ohms if I ohm the ign coil ground I get .03 ohms all test were with pcm unplugged and battery disconnected. I think the shorts in the pink 12v power wire any ideas were to start

[joecar]

I take it you had the coils unplugged also.


You have to unravel the split/corrugated loom (a seam ripper helps slicing electrical tape) and trace/inspect the wires by hand... follow the pink wire end-to-end.

[383camaro]

yes coils were unplugged. But after tracing wire after wire and finding nothing pinched or burnt I started unplugging fuses till it went away. I found that if I pull the fuse mark eng sen the 2.3 ohms I was getting finally went away. So I got the car manual out and it told me what sensors it powers which only thing I still had hooked up was the oxygen sensors. so I went under and unplugged them and the ohm reading went from 2.3ohms to 1.7....k ohms so I think this whole time I was just reading through the heater on the o2 sensors :( pretty much I think im back to square one

[joecar]

hmmm... this is where you try two things: different O2 sensors and different PCM.

[Chevy366]

Well I pulled the sending unit and this is kind of scary this is what I found also here is what my ecu looks likeAttachment 15861Attachment 15862

WOW, not good!

[joecar]

I'm thinking PCM has more damage than is visible.