In it's prime vs now
If this was an older truck, I would suspect a vacuum leak and/or transmission vacuum modulator valve.Hello, I'll try to keep this short yet descriptive. I've got a lot to say about this truck.
I'm not one to post in forums often but i'm running out of ideas.
Vehicle: The truck in question is a 1996 Silverado standard cab long box 350 5.7 Vortec automatic
Problem: The issue first developed on the freeway, many years ago. As i gave it more throttle the truck did not accelerate, more and more throttle and it actually kicked in and went somewhere. Initially, the problem was intermittent. Sometimes the truck would run fine. As time went on it became more pronounced. 10% to 75% throttle gets you very little repsonse, enough to putt around at 30 mph but extremely difficult to keep up with traffic. The engine does not continue to rev as you press on the gas pedal. rpms stay flat, stuck at like 1500 or 1800 rpms. When the gas pedal finally reaches 80%-100% the truck downshifts and revs to all hell. At first it ran normal at wide open throttle. it ran good. But now you can feel it fall in and out of power, the pedal is to the floor and the rpms are all the way up but it fluctuates between full power and like 50% power. It's very strange and hard to explain. P.s. It runs better when the engine is cold. Not good still, but it really runs like dog**** when it warms up.
Additional info: The truck revs perfectly in park. The throttle response in park is accurate. Because the truck runs so poorly it has sat outside for two or three years and the brake lines rotted out. I am currently working on replacing them, but can't drive it until then. I got this truck as a first vehicle when I was 16, 7 years ago. My Dad is..... "resourceful" so this truck has junkyard headers, salvaged true dual exhaust, (he welded in threads for the oxygen sensors, so i dont even know if i can get them off) 33 inch tires off of a jeep wrangler, nerf bars from who knows where, a brush guard from a 94' "custom paint" that's all peeling off. coil springs in the rear and cranked up torsion bars to "raise it" Etc. Etc. rolls eyes Also, (after it was running bad) someone got arrested in it and took the keys to jail so my dad took apart the steering column and put a piece of plastic behind the steering pin so the truck starts with a screwdriver. Nice, right.
Attempts to fix it: Before it ran bad we put a fuel pump in it but it wouldn't fit so someone bent the strainer so now it goes empty at a quarter tank. My dad insinsted for a while that the fuel pump wasn't grounded properly and he ran fuel pressure tests on it some time ago but i don't know the results. I have put in all new injectors, and it's got somewhat fresh plugs and wires, though this weekend i intend to double check they are ordered correctly. I've ran seafoam through it, I think i even replaced the MAF, in 2017 i was going through all the sensors but don't remember which ones i replaced. A knock sensor maybe? someone at o reillys told me it's the torque converter. I've done more but my memory fails me.
It's been a couple years since i've really looked at this project but i don't even know where to start. Besides brakes i suppose. Is there ever a time where i need to replace the entire distributer or just the cap? because i don't mind putting some extra new parts in it to freshen things up. Cap, wires, plugs, oil, radiator, sensors, are things ive considered replacing. Is a bad sensor enough to make it run THAT bad?
P.s. the obdII outlet isnt working and i dont know how to fix it. no check engine lights come on, at all.
p.p.s I've considered scrapping/selling this truck but i feel i owe it some effort first.
I just got thru with doin a lot to my truck too so I feel ya. I had to put a tranny in mine so I went ahead and changed my valve cover gaskets since she was gonna be down for a minute anyway. I changed the rear main, and my pinion seals. My head's were gunked up and had big chunks of crap, I vacuumed them out it seemed the safest way, then I poured some royal purple fuel treatment in them and let them soak a day or so and used a toothbrush to scrub some of the gunk off. Then I poured a bottle of marvel mystery oil in em and did the same thing-soak then scrub. I wiped em down with a microfiber cloth to get stuck on crap off then I vacuumed again i poured a quart of royal purple oil in em so the valves wouldn't seize up from where I had cleaned em and there no longer being any oil in em. I've been driving her for almost a week now so in a day or so I'ma do an oil change. I have discovered that I love royal purple products but they're expensive. But I'm finally getting to do the royal purple switch on my oil, I've slowly but surely been switching all fluids to that but some things are hard to find like the tcase fluid and tranny fluid. We also rebuilt my tcase and I put the valvoline tcase fluid cuz nobody around here carries autotrak2. I'll try to add pics of the products I mentioned when I post this. I don't know if anything I mentioned will fix yours I'm still slowly learning things as I go. I knew the basics but since I bought my truck last March I've learned so freaking much and done so much to my truck. I love it but it is super stressful sometimes, especially fighting the damn weather and cold. My truck is a 2000 GMC Sierra 1500 with a 5.3 Vortec and I love it. I hope you get yours straightened out. Also I use the longer oil filter cuz the other one didn't work well with my truck for whatever reason, my oil sending unit was also bad but it maintains good oil pressure now with the pf61e. If I think of anything else I'll let ya know. Keep us updated on your progress tho and good luck!😊 View attachment 168744