No power and bad backfire under throttle

[dweinhart]

I put another motor in after the machine shop shaved my last set of heads 3 times and still wouldn't seal. The new motor is throwing code 27 and backfires really bad under throttle with no power. While it's probable the sub o2 sensor wiring got messed up yanking exhaust, could this cause these symptoms? I thought sub o2 did not actually control air/fuel ratio.....

 

[dweinhart]

swapped sensor.No codes. new plugs, coils, injectors and verified 10 degrees advance with timing light. idles fine but misfires really bad under throttle

 

[dweinhart]

UPDATE: weak spark from ignitor appears to be culprit. Swapped ignitors and ran initially before doing the same thing....any way to get a stronger spark?I will see if adding grounds helps...

 

[Zuffen]

Could be a plug lead )or 2) braking down under load. These engines run quite well on 6 cylinders until you load them up.

 

[ivan129]

Pull the plugs out and see if they give you a clue. Good time to check gaps also. Stock ignition on those things would struggle to light a fire. Also those piddly little 5mm stocky leads are prone to leakage and cross firing if they are old and oily. Take a good look in the dark at them.

 

[dweinhart]

new plugs are all gapped. I traced it down to bad coilpack again