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New motor swap into my 2005 a couple of days ago. We have been running her intown and on the highway. when given full gas at about 85-95 MPH the codes for 0304, 0305, and 0300 happen complete with the flashing motor and VTM. there isnt any real sign of misfire (as in electrical) as she continues to drive smooth as silk not as though there are two cylinders not working... despite this I went ahead and switched plugs and coils. She does seem to like the brand new plugs HOWEVER the codes still drop at high speeds as before. Full throttle, 80-90 MPH.

Suggestions? fuel or air? sensor?

This does not appear to be an issue under normal driving conditions. I'm going to toss in some fuel additive as the old tank was 1/3 full of 2 year old gas. I do have another set of fuel injectors from my old motor. I'm not sure where else to look. Any suggestions would be appreciated. I understand that this could possibly be an exhaust issue and the old motor (when it died) had wrapped the serpentine belt around the crank and there was a ton of oil in the spark plugs so perhaps I have an exhaust issue. No other codes though.
 

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Congrats on the swap!

I’m thinking preignition at high load. Are you running 91 Octane? That’s what’s spec’d.

There’s also an ignition relay under the dash if I recall correctly. But not sure if it would blip at high rev, high compression.

Alt output at 2000 rpm with lights and AC on 14.5V ish (measured at battery terminals)?

Clean / good grounds at engine and chassis?

Maybe check the fuel pressure in case the pump can’t keep up or built in filter is starting to clog.

Good luck!
 

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With a junkyard engine, my first guess would be clogged injectors, and that would match the symptoms perfectly. You might get lucky and get them to clear with a bottle or two of snake oil, or just swap over the injectors from your old engine (it's the least it can do for you).

Or, you can drive slower. ;-)
 
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