Bought a 1986 GMC 350day 1 started up good - idle was rough - idle really too low, when brakes where applied, it would backfire. (day 2) Changed oil which was really dark - oil filter too... ghanged spark plugs and wires. % 10 improvement... Engine lack power and vibrates but no more backfire.day 4 Changed Cap and rotor - % 30 improvement - day 5 Got the manifold gasket replaced. Same condition but silent... day 6 Changed coil in cap ... Changed fuel filter % 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's side... Engine lost lots of power, and vibrates a lot... doesnt heat up to much but oil pressure seems very low. (day 7) Start up the thing, and even when cold and choke on, oil pressure not as good as in the beginning. What went wrong
I never got to scan any coeds when I worked at AutoZone! There were a few colleges nearby that had plenty of them. Sounds more like you have some carbon built up around your idle air control motor, or the motor may be bad itself. It is located on the side of the throttle body. It is a small passage blocked by a small step motor that pulls away and allows more or less air past the throttle blade, thereby regulating the idle. Throttle position sensor can cause similar problems. Clean the motor and air passage, and test.
What went wrong? Bought a 1986 GMC 350. Solution? (day 8) buy a Ford
at first sounded like brake booster vacuum leak; the valve noise top end lack of oil ? if rod and crank bearings are good might be by pass spring on oil pump stuck or weak = low oil press
Sound like a blown intake valve. Do a compression test and if you find a bad cylinder, do a leakdown test. A leakdown test is where you pump compressed air into the cylinder with the bad compression. You need to make sure that both valves are closed which is determined by the crank position. If the air is leaking into the intake/carburetor, then you have a bad exhaust valve. Time to pull the heads, or do an engine swap. As for the buy a Ford guy, the GM blocks are the best out there. That is why almost all marine engines are GM blocks.
loosing oil pressure like that,it sounds like the oil pump.if the parts arent getting oil,it will loose power.also check the timing,it could be off and loosing power.if the timing is off,it will make the valves noisy.
