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Discussion Starter #23
Hey guys. Another update on the truck,

I took a side route and did a compression test just because I wanted to verify the motors worth it before I throw more money and elbow grease at it. Cold and dry results were

1. 200. 2. 200
3. 180. 4. 200
5. 195. 6. 170
7. 195. 8. 200

I then read through some forums to learn more about my results and realized I'm supposed to be holding the gas pedal to the floor so I retested 3 cylinders (it's getting late) and got
1. 188
3. 170
6. 150

Should I be worried about cylinder 6? The specs for this motor are 150 with a 20 psi variance according to a manual I read on and old forum post. I dont have an actual leak down tester but cylinder 6 dropped from 150 to 140 after 5 or 10 minutes. All cylinders lost pressure very slowly. I can do a wet test next time I get after it if necessary.

I did 6 cycles per cylinder because I couldn't consistently hit 5, but 6 or 7 cycles topped out every one.
I did the test cold because the headers are in the way for every plug hole and I didn't want to burn the crap out of me or my borrowed tester.

On a side note, I have brake lines again, and pressure on the pedal, so that's cool.
 

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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.
If this was an older truck, I would suspect a vacuum leak and/or transmission vacuum modulator valve.
 

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2000 GMC Sierra 1500
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Sounds to me like the throttle position sensor needs replacing and maybe the tranny is slipping, could be your clutches gone in the torque converter in a couple of gears. If it means something to you, then I'd start fixing things the right way and start with the obvious. Correct fuel pump, get a key cut for it by the dealer and remove the plastic , go ahead and replace throttle position sensor, do an oil change and tune up with new plugs(ngk ttr I believe someone on here told me to use and they're awesome), wires, air filter. Get some MAF cleaner and throttle body cleaner and clean those parts. Replace pcv valve, clean egr(carb cleaner or throttle body cleaner whichever you wanna use), run some techron complete fuel system treatment thru it, or you can get some marvel mystery oil that stuff is amazing(seafoam is too aggressive and messed my husband's s10 up years ago, I hate it), you can use marvel in the gas and also put some in the oil about 50-100 miles before you decide to change it, also get some shudder ease it's in a small red tube and I've seen it work miracles on tranny's that wouldn't pull up a hill. It sounds like a lot but it's just basic small stuff to try that can only help the truck and may fix it or at least help guide you in the right direction cuz once you do all that some of the codes may disappear and new ones pop up which means you're narrowing down the real problem. May just need to be driven some and get her parts workin and moving again. Sitting for a period of time is hard on vehicles and causes all kinds of problems. You should try to start it at least once a week and let it run for 10 or 20 minutes just to keep everything from seizing dry rotting or freezing up. Hope you find your problem and it's a cheap and easy fix and hopefully I helped in some way, even if it's just a little bit 馃し馃槒
 

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Discussion Starter #26
@Glen Spino I will inspect for vacuum leaks this weekend anyways. it's on my hit list.

@Keisha~Sue Thanks for the time to write that. I'll be putting a tps sensor in this weekend along with a 3 year overdue oil change, new cap, rotor, plugs, wires, fuel filter, cleaning maf and throttle body. I'll add pcv valve and cleaning the egr to my list. And I have a bottle of seafoam that I haven't used yet, I'll read into the alternatives you listed as well as the shudder ease. I have some other sensors and overdue cleaning i plan on getting to also, I've got a big weekend in front of me. If nothing else at least I'll rule out everything that isnt the problem lol.

Thanks again everyone who's offered advice.

On a side note, does anyone know the CORRECT fuel pump for my truck? I think I got the wrong one from o reillys I believe the long box has a different tank than short. Mines a standard cab long box. I would want the whole assembly
 

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2000 GMC Sierra 1500
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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!馃槉
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2000 GMC Sierra 1500
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I could've gotten my valves cleaner but I didn't wanna overdo it I just wanted the chunks out and to scrub the buildup off.
 

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Discussion Starter #30
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!馃槉 View attachment 168744

The only one i dont recognize is the shudder fix so I can order that and probably get the marvel local. I'll end up cleaning out my intake anyways while I'm in there this weekend and I'm considering blocking off my egr valve after looking into it. With my dual exhaust it's more than possible it doesnt have a port for it and my dad probably plugged the hose that's supposed to be connected to the exhaust anyways. I'd love to remove the whole system and clean up the engine bay. I plan on getting a tune soon anyways. and dont need more garbage/carbon/soot pumped into my intake. no concerns for mpg. Hopefully all goes well and I'll post again after it's maiden voyage.
Cheers
 

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The ECM (computer) uses the EGR valve to stop pinging (precombustion, spark knock). Supposedly it bleeds in exhaust gas in order to keep the timing advanced as far as possible. Maybe in actual operation, not having exhaust gas and having the timing lower produces the same or more power. You would probably need an aftermarket computer or tuning program added.

If your EGR is not hooked up, and if you get any pinging, like when accelerating hard, the computer has probably dialed back the timing and may even be reducing the fuel injector open time. That might be the root of your low power issue.
 

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Discussion Starter #32
Hey guys, checking back in after the weekend. installed TPS sensor, cleaned MAF, throttle body, replace cap rotor wires and plugs, changed oil and topped off coolant, added mystery oil in with 5 gallons of fresh gas. The truck runs good now with mild and moderate acceleration. I got it up to operating temp and when it usually would fall on it's face it kept running fair as far as i could tell. I couldn't go far, as the brake bleed did not go as well as i thought. the front end needs help, steering is all wonky. But the important bit is that the motor is proud to start up and I'll be able to safely keep up with traffic while i fine tune the rest of my problems. However, my WOT test was lacking at best, but to be fair to the old girl i intend to get a few gallons of gas ran through it and a 200 mile oil change before i start judging it too much. It DID sit for 3-4 years.

@TW97C1500 From what i have read i believe your statemnt is correct on how the egr works, but i believe the egr closes itself under WOT, which historically was when my motor would actually do something, but it would still fall in and out of power even at WOT. After the Tps and other things i'v done WOT seems to be the last issue area. I do intend to get a tune for this vehicle... Eventually.. I've been reading about the benfits of the newer PCM so i pulled one from a 2000 tahoe at a pull yard. $25 not bad.

TLDR - things are improving, but I still need to fine tune and troubleshoot as i drive the vehicle more.

THANK YOU EVERYONE FOR YOUR HELP.
 

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hell ya! thanks for the update!
 
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