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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.
 

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ok. grab a obd2 scanner and plug it in. go to diagnostics and look for the tps test. the throttle position is simple to test and it kind of sounds like it could be the culprit. so it reads how far the throttle is open, which dictates how much fuel to spray and when to shift gears with correlated information from the VSS, vehicle speed sensor.

when the tps fails to report the correct data it reads as if the throttle is closed. and sends data that is incorrect, this messes with the computer which immediately compensates for the incorrect data.......

this can be read on an obd2 tps test in graph form. it should rise absolutely smoothly as you press the pedal. any breaks or missing data or anything other than a smoothly rising line and you need a new TPS.
 
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ok. grab a obd2 scanner and plug it in. go to diagnostics and look for the tps test. the throttle position is simple to test and it kind of sounds like it could be the culprit. so it reads how far the throttle is open, which dictates how much fuel to spray and when to shift gears with correlated information from the VSS, vehicle speed sensor
I have a zurich zr13 scanner which i'm not sure does throttle position but when i plug it in it does not recognize thats it's plugged into anything. It can't communicate. no fuses are blown as far as i can tell. I can order a tps it seems like i can get one for $40 on amazon ACDelco 213-912 it would arrive saturday but it's tricky to test it until i fix the brakes
 

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you dont need to drive anywhere, you dont even need the engine running just the ignition turned to "run." it will work on killing the battery without it running though.

shoot I cant remember which fuse is for the obd2 port, I think it might be the same as for the cig lighter, 12v aux plugs. but i cant remember off the top of my head.

Al
 

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I usually go with my gut instinct Ray. it dosent usually fail me. haha thanks for the confirmation!

Cheers!

Al
 

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al , question ,on these trucks i know the have a bad ground wire problem in computer going to trans , could this be a cause for his problem
 

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I usually go with my gut instinct Ray. it dosent usually fail me. haha thanks for the confirmation!

Cheers!

Al
Okay i will attempt this process tonight after work. Excuse me for asking but is AI one of the fuses? and is it A L or A i ? In the cab fuse box or under the hood? Thanks a bunch for your help so far.
 

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Hey Brian, the tranny dosent get its ground the way we would naturally think, through the case. instead it gets one positive 12+ through pin E. all other wires are switched grounds. they did this so that if something shorts out it operates instead of burning wires.... genius.
 
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Deon, that fuse in in the end of the dash, I'll take a look at a fuse cover but it might say, cig or Aux.

Al
 

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🤦‍♂️ Slap myself in the face.
I swear I'm usually somewhat intelligent.
When Ray said "it usually is Al" I thought he was saying "the problem is usually Al" so i got all mixed up. Thanks again for the help and respones guys. Hopefully this weekend is fruitful. I'll post with any updates. I will also be working on my gf's 12' grand cherokee so we'll see how much time i really get to tinker with ole rusty.
 

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BOOM there I go! LMAO. no worries I sometimes tell people to do something they all ready did just because what I read did not actually sink in completely, I was never really good with words. :unsure:
 

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I've been meaning to ask this for my own purposes, and Deon's situation reminded me. Is there a way to put the ECM into "base settings mode" or "default and stay there mode", maybe disconnect the O2 sensors or something? I know if you disconnect the battery for some number of minutes, the ECM will go back to default settings when you reconnect, but then it will begin adjusting when you run it.

Deon said he has 33" tires, so in addition to the previously suggested Throttle Position Sensor, the Vehicle Speed Sensor could be causing the issue if it's bad, and/or maybe the ECM has built up an adjustment if the tire size setting was not corrected. If the transmission output shaft RPM vs. Throttle Position readings are out of range and the ECM has already adjusted to its limit, maybe it's not changing injector pulses when he gives it gas. I'm wondering if he could get it into default settings and see how it drives.
 

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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 have a zurich zr13 scanner which i'm not sure does throttle position but when i plug it in it does not recognize thats it's plugged into anything. It can't communicate. no fuses are blown as far as i can tell.
It's going to be tough to perform diagnostics if the OBDII Data link connector (DLC) is not able to communicate to your scanner.
First things first. Get the DLC to communicate with your scanner.

These are the DLC pin assignments that you need to check with a meter or a test light.
Pin #4 - chassis ground
Pin #16 - Fused battery power.
In the absence of a fused battery power at pin #16 or a chassis ground, obtain a power distribution diagram or in the absence of one, you can temporarily bridge 12V+ and chassis ground to these pins and see if you can establish communication with your scanner.
 
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Hi guys, checking in after the weekend. I was able to get the scanner to communicate, some of the wiring under the dash was pretty rough. So I can get it to turn on, it has "no pending or stored codes" and as far as i can tell my scanner doesn't read throttle position. It has a live data page showing a bunch of sensor values that i dont understand like oxy and temp etc. I also started the truck and ran it for 5 or 10 minutes. I had to pull a boat out and get the old truck moved out of the corner so i can work on it. It stayed idling fairly well after it warmed up a bit. It was -29 degrees here in Minnesota this morning, and i'm more grateful than ever for a heated garage. Brake lines are coming along nicely, leanring as i go but i should have that wrapped after a couple more nights. I ordered an acdelco throttle position sensor so we'll give it a run up the road once I have brakes again. I'm picking up new front hoses, rear drums, and a battery tonight after work. Hearing the old girl fire over with headers and straight 2.5" dual pipes still hasn't gotten old.

Interesting information about the ECM, I can put lil baby tires (stock) on it and see how it rolls.
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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Hearing the old girl fire over with headers and straight 2.5" dual pipes still hasn't gotten old.
😎😎👍
 
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