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Discussion Starter #1
greetings--97 250 149k, absolutely stock. i am hearing a 'whump whump' noise from airbox entrance--not too loud, but definitely there. mpg is way down, 7-9-ish; truck starts and runs fine, but is somewhat slow off the line, and feels somewhat stiff and jerky between shifts and when decelerating. doesn't overheat, but reaches operating temp in 3-5 miles at 35 deg--definitely not normal. was thinking stuck ebpv, but it does move if i lever on it, with no change at idle. internet searches seem to rule that out and lean toward valve train issues. with lack of other symptoms i am reluctant to go there (denial, for sure) yet--could cat be clogged? time to open something up, obviously would like to start right place first...thanks in advance...
 

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Most likely a bent push rod or broken rocker arm ...
 

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Discussion Starter #5
ok--disconnected downpipe; ebpv was 90% open, and stuck. pblasted related parts and pivot points, put it back together and started up, saw the linkage to the ebpv moving, never did that before. sounded a bit better. took for spin, ran better; back home noticed blowby coming out the ccv and oil filler, took valve covers off, everything appears good, started engine; blowby coming from pushrod holes on rearmost passenger side cylinder only. took rockers off and pushrods out of that cyl only (so far) they look fine. is that cyl where problem is? will remove rest of rockers and pushrods unless this sounds like problem is deeper in that cylinder. blowby is not apparent when engine cold--strange... thanks again
 

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Don't know if that cylinder is the problem or not, but make sure the engine is in the 11 o'clock position when reinstalling pushrods and rockers. Having the engine in the correct position prevents lifter "jacking" and possible engine damage (it provides a drain path for the oil so the lifters don't pump up when the pushrods are out). Cheers!
 

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Discussion Starter #7
update--all pushrods and rockers are good. ebpv doesn't move now (when running), plugged, or unplugged. default position seems to be slightly closed, so it is going to get the axe. one of the widgets on the side o the fuel regulator is dripping, not going to drive it much 'til i get that fixed. everything on the top of the engine needs to come off for a cleaning/inspection--now is as good a time as any...thanks, k
 

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If the part (fuel restriction sensor) on the side of the fuel pressure regulator is leaking, just replace it with a 1/8 NPT plug. The sensor is anywhere from $35 to $50 and really isn't needed if you change the fuel filter regularly. Cheers!
 
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