Deon Mohs

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.

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.
p.p.s I've considered scrapping/selling this truck but i feel i owe it some effort first.

Gumby22

1) The torque converter won’t stop the engine from responding to throttle. Don’t expect working at a parts house means someone is experienced and knowledgeable unless you personally know otherwise. There’s nothing wrong with selling parts but knowing parts is not the same as knowing principles of operation.

2) Is it misfiring, either at idle or while driving (at least as best you can recall from the last drive)?

3) Is your code reader not powering on, or not communicating with the PCM? If it’s not powering on, check the auxiliary power fuse (25A) in the instrument panel fuse block - that’s what provides power to the OBD port.

hanky

One of the most difficult problems to find and correct is the list of what someone who had no idea what they were doing , did it anyway and now you need to start from scratch . That can take some time and $$$ and can get very disappointing. I admire your determination, just read up and learn the right way to do some things and eventually you may get it to where you are somewhat satisfied. Let's hope your funds hold out .

Chris94

I would suggest getting a good repair manual and a digital multimeter first, then doing a compression test and inspecting your spark plugs. This should give you a good idea of your engine's health before tearing into everything else.

Deon Mohs

Thanks for the responses guys, I was able to find some rough wiring and got the OBD port working! but, the scanner says "no pending or stored codes" so that wasn't much help. I do not have a check engine light on the dash.
. @Gumby22 glad to hear I can ignore the 19 year old at O'reillys. He claimed to have experience with this model truck. When the motor gets real warm it idles down too low and starts to get grumbly. not sure what i can classify as a misfire under acceleration, it mostly refuses to accelerate at all.

@hanky I've owned a couple other vehicles that i didn't let him touch so I at least know how to turn some wrenches and diagnose SOME problems. I feel like i'm bringing this truck back from the dead. So far I'm focusing on brake lines so i can stop and go down the street to see how it is acting again.

@Chris94 I have a digital multimeter and I would really like to do a compression test. I'll swap out the plugs anyways, they're like $3 a piece on rockauto. I'll do some research on compression tests, that'll be a first for me.

westcoasterbc

Check your catalytic converter for an obstruction. Definitely the age to be an issue with back pressure.

Deon Mohs

@westcoasterbc It has straight dual exhaust with no cats.

Got the rear brakes on so wednesday the front will go in then i can doa compression test and start installing parts and testing more thoroughly