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Tracto-man

1998 k1500 5.7 missing and backfiring, like someone flipped a switch

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My old red trucks been missing on hot start up after it's been running for say 30 miles, (stop and the ag store for a few mins and start it it up again) but on cold start always ran smooth and after driving for a minute from hot start always smoothed right out. Then tonight driving along, running great, stopped at the RR tracks, went to go and it fell on its face. Missing like crazy, backfiring when letting off the throttle, goes 55mph but not easily.

 

Got it home, looked around for loose wires or anything somewhat obvious, wires are all still good, doesn't look like head gasket blew, no check engine light, but still always running like crap no matter what.

 

So could a basic tune-up maybe possibly help with this? Motor has 322k so kinda wondering if something internal might have finally gone wrong, new plug wires fuel pump, plugs cap and rotor, etc 44k miles ago, then new plugs, cap and rotor, and temp sensor again about 16k miles ago.

 

Kinda just wondering if it's worth $150ish on a tune-up again, or just call it quits and park it until I have a new motor ready to go in and the time to change it?

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You could be having a spider injector tube problem,they crack in the intake,leak is worse when warm, the crack expands(opens),you could pull the plugs,if some are blacker than others,it's likely

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Well on second realization the rotor tab got bent up, so I'm assuming the distributor has got just enough play that it got out of wack while at a low idle and hit one of the cap contactors. New rotor and it's running again, but looks like a new distributor is probably in order.

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on youtube there is a channel called scanner danner , he teaches others to be techs, i watched his video last night about a gm with cpi , the video is called, how to identify and repair a leaking fuel pressure regulator , its a 2 part video made 7 yrs ago , but it covers all your symptoms

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running good cold, the engine gets more fuel until 160F.

in live data, you may watch that switch to weird runtime you refer to.

could help

 

glad you found the disty problem.. I'd target injection/fuel

 

my own went goofy to find plugs all went to beyond .100 gap.

miles unknown.

I am at 375k odometer.. running beautiful. Oil is at 1200 miles (I full it back up in half quarts.)

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