I have a 1998 gmc savana 5.7 v8 vortec engine. I have a p0300 code for random multiple cylinder misfires. If the van has been sitting over night it takes 3-5 cranks for it to start. It has a new battery, fuel filter, new spark plugs, new distributor. I cleaned the MAF sensor , installed a new air filter.
Major update. I replaced my exhaust manifold gasket and my Check engine light turned off
Just replaced the ignition coil, pcv valve, and ignition control module. And the oil pressure sensor.The check engine light didn’t go away I reset it to see if I’ll come back, I’ll check the fuel pressure tomorrow.
Update: I just noticed my oil pressure switch is leaking oil. The switch has only 1 prong but the wire harness connected to it has 3 wires and 3 slots. Should I get the 1 prong switch or the 3 prong one?
Another thing I just noticed when it starts it chugs at the very beginning and then it catches wind and runs smooth
I have not changed the plug wires, when I did change the rotor when I changed the cap. I’ll see if I can rent something to check the fuel pressure. I have used a ton of fuel injector cleaners and they didn’t help in any way. Lol that’s the video that made me know about cleaning the maf.
Did you change plug wires? New Rotor? Random misfire code = running lean. What to rule out next: 1/ Weak Fuel pressure; 2/ Vacuum leaks; 3/ Clogged Fuel Injectors. Before doing anything, I'd truly start w/ this video (helped me so much, doesn't take long, always helps) using rags, old toothbrush & clean PCV Valve too while you're in there. Come back, let us know how you fare. There's a reason this video has nearly one million views:
The pictures is if the van idled