p0300 code bad ecu?

[383camaro]

ok so my setup is
98 trans am
408 lq9 swap
ls3 heads
248/257 .615/598 cam
patriot gold .650 springs
42lb injectors
vic jr intake with the low profile elbow
90mm throttle body
11.3 to 1 compression

now what im having problems with is a low rpm miss fire under load its not there at wot and runs strong but if I just baby it up to speed ill get a popping or a drop in power. Also im getting a surge but I think its mostly the misfire while cruising around town. Ive logged my runs and my spark table isn't jumping around. I have changed my plugs and plug wires which made it seem to have more low end torque. but when I pull the plugs I cant seem to find the one that's missing. I Bought a new coil pack and started moving it around to see if it made any difference on different cylinders and that didn't seem to help. So I moved on to see if moving injectors around while monitoring misfires and that didn't seem to help. when logging misfires it seems the most misfires are on cylinder5 and 6 so I did a compression check on the whole motor and everything is dead on give or take 5 numbers I also did a leak down test and found nothing everything looks good. pulled the valve covers and no broken springs everything is moving fine. Now my question is can my pcm be going out and this be causing my problems I will attach my tune file along with a log of my run from last night maybe theres something I missed when tuning for the bigger motor

[383camaro]

i forgot that when logging misfires the most misfires are on cylinders 5 and 6 but all of them will hit then go away then hit then go away so it coming and going i made sure that i was watching the data when i had the motor running its smoothest. I did do a crank relearn.

[Chevy366]

Don't forget injectors can cause a misfire event too.

[383camaro]

yea i did take that into consideration to so i moved those around and also logged the misfires and they didn't seem to move the misfire counts any

[joecar]

Inspect the harness wiring for damage (unravel it from the convolute tubing).

Disconnect the PCM, coils, injectors, and measure the resistance of each wire (end-to-end).

Inspect the pins in the PCM connector, and in the coil/injector connectors (look for damage or corrosion).


Measure voltage drop across each PCM power feed, and each PCM ground (e.g. measure voltage between battery and pin/wire at PCM) with engine running.

Measure voltage drop across each ground strap (e.g. between mounting bolts at each end).


What holds your battery down (is it loose)...?

[383camaro]

My battery is held down by the stock hold down. And today I pulled the harness out to inspect it and didn't see anything out of the ordinary so I said what the hell so I pulled the computer apart and right away I smelled burnt electronics. After tracing down the pin outs on the computer and splitting the two halfs of the boards away from each other I found the fuel sending unit ground pin has a chard mark on the board do you think it fried anything else on the board?

[joecar]

Yes, other stuff could be fried.

Question: what caused the over-current to occur...?

[383camaro]

My thoughts exactly I guess its time to pull the sending unit

[383camaro]

Well I pulled the sending unit and this is kind of scary this is what I found also here is what my ecu looks like

[joecar]

Those wires were shorting...? Wow...!!!