98 454 Temp Sensitive Misfire

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618 Syndicate

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98 C3500 454/4L80 107k
Had it tuned Monday tq management and downstream O2 sensors deleted. Timing was out 27° we were able to move the distributor and get it within spec for a successful crank/cam relearn.
As we leave the AC isn't cold at idle, but as you increase rpm (even not moving) it starts blowing cold. About 150 miles into the trip, the temp gauge climbs to 210, the AC quits blowing cold, and a few miles later the truck is running on 5 or 6 holes. Missing badly, won't take any throttle at all, just sputters and pops. Pull over, cools off, starts right up and runs fine. Any time it gets to 210 it repeats the behavior, each time it gets below 160 ish, it runs great.
Anyone got any ideas?
 

Frank Enstein

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Boil the T-stat in a pot of water to make sure it opens correctly.

Don't let the copper center touch the bottom of the pan or the thermostat can be damaged.

A candy thermometer to see what temp it opens can be helpful.

If it doesn't have a bypass drill a 1/16" hole in the non moving part to help bleed the system without slowing down the warm up.
 

618 Syndicate

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Pulled the thermostat Friday night, ran without one Saturday and today. Coolant looked terrible. Ran great yesterday, and stayed good on the way home up until we hit traffic on the interstate after about 200 miles. Got up over 210 and started missing. Shut it off, restarted it and drive the other 50 miles home with no further issues. I am going to thoroughly flush the cooling system, install the new thermostat, and go from there.
 
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