Urgent Loud exhaust after 40 min of driving running really rough after same amount of time

[B_body beast]

Hey guys ive read posts on this site for just about everything i know about lt1s could say "grasshopper is learning" l but ran into a bit of issues tht stumps me now. I have 94 caprice the had engine swap with 96 lt1 with dual knock sensors and vented opti so pretty surre its the ss impala engine from 96...now when i got it ...i got it for a song cause the ppl had bought it with issues from the swapper..they had no knowledge so sold it ...got it home started checkin if everything was correct .......NOT by a long shot ..how he was capable of doing a swap and not capable of doin it right i will never know...upon inspection ..bad wires and plugs plus cylinder 6 and 8 were backwards..vacumelines to opti werent connected at all ..just sittin there evap hoses backwards steam pipe hose to overflowtank backwards ..egr clogged ...fixed all tht along with full fluids flush new plugs new wires new vacum lines ...ended up blowin from wheel bearings outa nowhere so replaced ....new evap soleniod plus valve..new fpr new o2s (both) ....wires to driver o2 were exposes so took pins out n fixed tht mess after popping a fuse from them touching..had exhaust leak cause by last two bolts broken off in head ..(both on drivers one on passenger..tried to extract didnt budge so got 1/8 in exhaust manifold gaskets..wich did the trick ran smooth ...after 40u min of driving check engine light came on(this is everytime the vehicle was driven more then 40 min) and exhaust got load as hell like exhast leak...but isnt ..checked it 100u timez so pulled. cleaned egr .solved check engine light...seafoam sprayed engine through intake just to give good clean ..anx still after forty min of drivin exhaust gets louder and loss of power ...like bad...heave replaced pcv valve and took of loose oil filler tube and replaced with new oem oil cap...did new fuel cap to oem sealed...well key vented..and new fuel filter seems to me like its my fuel oressure i know from testin while fpr change tht pressure bleeds off after fuel pump stopss...juat havent done tht yet (fuel pump) doin next weekend after seafoam fuel treatment as well as another oil change after seafoam treating crankcase for 100 miles... but i dont understand whats causeing the 40 min loud exhaust issue and the is nothing on other forums similar to my issue...so could it be caused by low fuel pressure or is there something im overlooking?

[B_body beast]

Oh and to top it off they didnt change obd1 plug ao i got an obd1 plug with obd2 engine back to the #$@#$ stone ages on that and only a few wires pluged into it plus evap system if u check on shoebox is set up as 93 -95 set up witout the open end vacuum switch witout the electrical connector for it(to purge canister vacumm from evap solinoid )which leaxs me to believe tht they used the engine wireing harnness from the 94 ( no idea what other issues this could cause if any) i know the pcm isnt getting the signal from that for sure ..but doesnt create a check engine or trouble code ...no idea why seein as thts how it knows if its workin properly...unless they tuned ot out ...but how could they do tht if alll tht list of other things were in dissarray wernt done ...i dont know if tht would cause and issue ...i dont think so...fixing what i could of evap got eid of the fuel fumes i smeelled so worked in my eyes.lol

[B_body beast]

Nobody has any insight?

[steveo]

loud exhaust after it gets really hot...

maybe bad lifter preload adjustment? valvetrain hits maximum heat expansion and you have some exhaust valves being held open?

just an idea, i remember when i had a couple burned exhaust valves it was pretty loud

[steveo]

4th Gen LT1 F-body Tech Articles

fyi

[B_body beast]

Not really hot just running temp not running hot or anything..i seafoamed it last night (spray..throttle body )n havent really checkeditit since lady got it in phx ..see how it sounds after all tht. But there is a slight tick on the same lifters as the original exhaust leak .would tht exhaust leak after long period start stickin from wrong back pressure? N not that the exhaust leak is fixed have to reset lash?

[B_body beast]

Thts the same bank tht getts loud

[steveo]

an exhaust leak would have nothing to do with valve settings

im just concerned your valves might be too tight (or maybe even binding in the guides) and you have some exh. valves sticking open

its just a theory

you should just set 'em, it's pretty easy

if you're unsure set them a bit on the loose side

valves that are too loose will just make a bit of tapping noise, wont cause major running issues

[B_body beast]

Ya i gotta do valvecover gaskets anyway so should just see if everything in order..wouldnt it do it when its cold too tho? Just cant hear it as bad till it expands?

[steveo]

not necessarily

the reason you have hydraulic lifters is that your valves get tighter as they get hot, and the lifters give it some cushion, so they aren't noisy when they're cold, and require less adjustment

if they're too tight, it might not be enough to hold the valves open when cold, but when things expand, the lifter might bottom out and stick some valves open