350 help

Bought a 1986 GMC c30 350, with supposedly 160 k on it last thursday (day 1). Motor started up good - idle was rough - engaged in drive , idle really too low, when brakes where applied, it would backfire. Exhaust
manifold gasket on left side was busted.
(day 2) Changed oil wich was really dark - oil filter too... changed spark plugs and wires. % 10 improvement... Engine lack power and vibrates but no more backfire (I set the idle a bit faster)
(day 4) Changed Cap and rotor - % 30 improvement - Obviously either badly maintained or the previous owner just let it go
(day 5) Got the manifold gasket replaced... The mechanic forgot to replug 3 spark plugs. Ran 3 miles and replugged the spark plugs wire... Same condition but silent...
(day 6) Changed coil in cap ... Changed fuel filter (had to cut the fuel feed pipe, was kinked, replace with flexible hose) % 60 improvement... The thing ran like new... Full power I started beliving again... Got full oil pressure 300 kpa - no valve noise
Ran 30 minutes on highway.... Valves started making noise especially on driver side... Engine lost lots of power, and vibrates a lot... doesnt heat up to much but oil pressure seems very low. made my trip 50 miles.... and leave it for a while
(night 6) I cry
(day 7) Start up the thing, and even when cold and choke on, oil pressure not as good as in the beginning. Put kleen flow lifter treatment ... At idle in park the ticking stopped, a bit better while in drive... As soon has motor gets hots problem persists... At 60 miles per hour, motor doesnt run great but vibration acceptable... But while trying to accelerate valves are really noisy, vibrates a lot especially at mid speed revolution... Made my 50 miles trip back very slowly and stopping often to try not to burn the thing
(night 7) i cry again
What went wrong from better to worst PLEASE
(ONLY OIL PROBLEMS !)
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Forgot to mention - oil is already blackened but not thick after 170 miles...
My opinion is - lifters unjammed explaining the clicking and oil filter clogged from all the gunk unblocking after full power oil pressure re-established
- Hope I'm right
Please help
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You took a severely gunked up engine and put fresh detergent oil in it and drove it without watching the oil. It dissolved that 100 years worth of gunk, blocked the filter so all the gung was bypassing it. You need to do some seriously cleaning of the engine and then do some compression and pressure tests to determine how much ring and other wear you did.

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I agree with you... Ttaking into account that I did not push the motor to hard and drove only 150 miles taking regular breaks, must the rings or other parts absolutely be affected ???? I'm trying to be positive.... Also how can the gunk bypass the oil filter ????
Thanks
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Soory, at this point I did not realize about the filter bypass valve
Respects,
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Hi, Perre, to really clean an oil pan and oil pump pickup tube/strainer, I've done the following several times and saved having to remove oil pan and oil pump strainer--where symptoms were the engine beginning to clack(lifters running dry) as soon as, or soon after, it reached operating temp & debris sucked up to oil pickup strainer and oil light comes on. Follow directions EXACTLY. Disconnect a battery cable so no one will attempt to start engine. Drain your engine oil as if you were doing an oil change. Replace filter. Replace drain plug. Pour into crankcase a gallon of carb soak/cleaner--the good stuff. Allow it to sit WITHOUT STARTING ENGINE for at least 2 full days, 48 hours or more. Now drain oil pan again as if you were doing an oil change. Let it drain out fully, until it completely stops dripping. Replace drain plug. *No need to replace filter again YET*. Fill crankcase(5 quarts?) with any decent oil--NOT synthetic; use something like Valvoline or Castro or Havoline 10-w-30. Re-attach batt cable(s). Start engine and drive it for about 20 miles, normal driving, allowing engine to fully warm up. Return to workplace and drain oil immediately while oil is still plenty HOT, AND change filter again. Let oil drain until completely stopped dripping. Replace drain plug. Re-fill crankcase with good oil that you plan to use--don't go *thinner* than 10-w-30 (personally I would run Castro 20-w-50 in an engine w/that many miles). ( If one were to drop oil pan at this point, he would see a squeaky clean oil pan and a bright & clean oil pump strainer on the pickup tube.) After 300 miles, change oil & filter again. Pierre, I've done this where several other mechanics have diagnosed a neglected oil-change history & their consensus was that pan would have to be removed & cleaned, and oil pump would have to be removed, cleaned, and re-installed(or replace old pump: personally, I would definitely replace oil pump w/new WHILE pan was off!). These were engines that would suck up debris and stop up the oil pump pickup and cause lifters to start clicking, unmercifully, and cause oil light to come on due to lack of both oil & oil pressure. After they sat overnite, most would pretty much behave until reaching operating temp. once again, after again sucking up debris to pickup screen. To some of my best mechanic-friends, I told them what I had done; none has ever criticized the procedure. I know of at least 3 others who now do this on a continuing basis, saving considerable labor and doing a nice cleaning job. I KNOW it works, and it is NOT a temporary patch job--it is a long-term solution(no pun intended!). I'm 63 years old and have been doing this since early 90's--I'm not a *theorist* who happens to have an idea, but rather a *realist* having gotten MY HANDS dirty for decades! I'll probably be flamed by ones who do not know; but from those who KNOW from EXPERIENCE, I might even receive some praise. Nonetheless, the proof comes when your oil-deprived engine revives after this procedure. Then, you can put in a fresh set of plugs, which is my preference, esp. when it no longer "lights up" but continues to skip. Good luck to you. Hope you can enjoy that GMC for 1000's of more miles. sdlomi2
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