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5.7 350 Bucking/stuttering Under Throttle

Discussion in 'Chevy C/K Truck Forum' started by Mike350, May 30, 2014.

  1. Mike350

    Mike350 New Member

    Abridged version: Truck runs okay at start up, then once warm and given a little extra throttle something goes haywire and the truck starts bucking and losing power- starts gradually and worsens until I can't even give any gas at all without severe power loss/bucking/stuttering. Even idling sounds like its about to stall or something.

    If you need more info here's the full story:
    Tuesday I picked up a '97 K2500 5.7 350 auto with 160xxx miles on it. Everything ran great when I test drove it, and it ran like a top on the 45 minute drive home and 5 miles back and forth to school/other outings the rest of this week.
    Last night on my way to dinner after running fine for 10-15 minutes something felt weird on acceleration from a red light- almost felt as if truck went from 1st to 3rd.. Rpms were kinda high but truck wasn't moving fast, I let off the throttle and it bucked a little and then it seemed okay. 2 minutes later I started hearing the engine running unevenly and it gradually progressed over the next mile to having almost no power, bucking a lot when I gave it gas not accelerating well. Luckily I had just gotten to the restaurant so I parked and ate and let it cool down. After dinner i started her up with my fingers crossed and everything seemed fine, about 5-10 minutes into the return trip I gave a little extra throttle from a redlight and it started to go but then caught and the bucking and power loss started. Barely made it where i was going. Let it sit for an hour or so while i hung out. Then drove 5-10 miles home keeping the rpms under or around 2k and staying steady on the throttle. I made it with no bucking but towards the end I do think i was hearing some uneven running in the engine.

    Fuel pump was replaced by PO at 130xxx miles
    PO just recently did plugs, wires, cap, and rotor

    I thought maybe it was something trans related- when it was bucking I tried moving the shifter down to 1st gear to see if it fixed the bucking. But it behaved exactly the same as when in drive.

    The PO has the EGR port on the headers plugged with a bolt and the other end above the engine taped off with a plastic cap on it. (there's no EGR tube- throws an engine light with code 401- EGR insufficient) I thought maybe one of these plugs had fallen out but they're both still in there.
    Other code I found when I read them (Before this all started) was 151- 02 sensor circuit low volts bank 2 sensor 1. - however that code existed before all this issue and i'm not sure an 02 sensor would even cause this problem?

    I'm waiting for my brother to return home with his Code Reader to see if there are any new codes since all this happened.
    In the meantime my thoughts as to what could be the issue are along the lines of:
    -fuel filter (Bought one today gonna put it into tomorrow after codes are read, see if it changes anything)
    -IAC/MAF/02 sensors? dont know if any of these could cause this
    -EGR
    -Injectors (Bought STP injector cleaner- going to run after codes are read and see if it makes a difference)
    -Cat blocked up??
    -my drive belt is squeaking some and needs to be tightened, but dont think that would cause this
    -Timing chain
    -alternator?
    -bad ground?
    -intake manifold gaskets- i'm not leaking any coolant so i think that rules those out?
    -ignition coils?

    The symptoms are similar to what I'd imagine the truck would do with no gas or stalling.

    Any and all help would be much appreciated. Thanks guys
  2. kennythewelder

    kennythewelder Active Member 500 Posts

    it could be several different things. start the engine at night and look under the hood for a misfire in the dark, it much easer to see them like that. You can check for a clogged cat by removing your o2 sensors. If the ext. flow at the o2 sensor hole is about the same behind the cat as it is in front of the cat your ok. If the cat is clogged it be less behind the cat. I also have a 97 5.7 but 2 wheel drive. These truck only have 1 coil. No way to tighten serpintine belt. get a gates belt and it will quit squealing, but that wont cause a miss. Timing chain (don't think so but may be). I'm not saying that this is your problem but I would put the egr system back together. Get the computer back to where you have no codes. Once a code trips the computer goes into limp mode and you loose performance, and fuel mileage. Mine was tripping the o2 sensor code in my truck off and on. After trying several different things I changed the fuel pump , and it has not tripped an o2 sensor code since, but I'm not saying that's your problem, just saying some times its easy to get mislead by the code your getting. I would also pull the plugs and see what they look like. You can get a lot of info on what the engine is doing by what the plug looks like, Google it. good luck.
  3. Mike350

    Mike350 New Member

    Thank you! I actually just finished checking the codes and reading the freeze data and checking the system monitors etc. Codes are the same as before, i forgot to mention i actually have 4 codes. the two i said, and then the same two again but those ones are pending, I'm not exactly sure what that means but i think it just means the problem is continuous?
    The PO cut the exhaust and never got around to putting flowmasters on so its cut right now, after the cats and I dont THINK he cut off any 02 sensors but i'm not positive of that because i'm not exactly sure what the setup is supposed to be, is it 1 before and 1 after each cat?
    The freeze data shows a DTC of P0894- appears thats trans or torque converted. In googling the code it appears that the 4L80E is notorious for going through torque converters? Would that match up with my problem?

    Ill try to post pictures of the Freeze frame data and codes
  4. kennythewelder

    kennythewelder Active Member 500 Posts

    There are two o2 sensors per cat. one in front and one in back, 4 sensors total. I never had a 4l80e just 4l60e. If I could drive the truck I could tell you a lot more. I never had an issue with ether of the 2 trans I had except that I burnt up the first one I had but that was a different truck. Sorry I could not help more.
  5. Mike350

    Mike350 New Member

    Not a problem at all, I really appreciate the feedback and that gives me a place to start. I'm going to do my best to resolve the O2 and EGR codes. Here are the pictures of all the scanner data. Right now I'm thinking torque converter or something of the like, if anyone can chip in with opinions on the 4l80e and torque converters and DTC P0894 that'd be great. thanks! image1.jpg image2.jpg image3.jpg image4.jpg image5.jpg image6.jpg image7.jpg image8.jpg image9.jpg image10.jpg image11.jpg image12.jpg image13.jpg image16.jpg image15.jpg image16.jpg image17.jpg

    - - - Updated - - -

    Update: cleared all the codes etc. just let the truck warm up for 5-10 mins and it idled fine. I tried to drive it down the street and back. I didn't give it very much gas at all but I felt it starting to stumble/stutter so I turned right around and came back just coasting, pulled into driveway- sat there idling, I tried shifting into 1st 2nd 3rd. It didnt do anything weird but I didn't feel the trans shifting so part of me wonders if it shifted at all? Then I went to neutral and it started getting rough and stutter-rpms bouncing around, then I forget if I shifted to drive or was still in neutral but it stalked. Tried to started it back up a few times but just got the whirring of the starter and no catch-(it has done that occasionally when trying to start it and the second time it catches-but this time it just wouldn't start). Not throwing any codes or freeze frames. Help? Lol

    Attached Files:

  6. Mike350

    Mike350 New Member

    Wouldn't start today so I guess that kind of rules out trans. Really thinking fuel delivery system... Getting it towed tomorrow, sick of dealing with it and don't really wanna be throwing parts at it
  7. silverado002

    silverado002 Member

    Looks to me, if i am reading the pics right, like your fuel trims are way off. The ECM is trying to adjust and i'm wondering if the EGR being blocked off has the converters and ECM going crazy. I wonder if the converts are plugged now?
  8. Mike350

    Mike350 New Member

    By converters are you referring to cat converters or am I missing something? .. I had it in the shop today- Broken crank sensor... But the shop didnt road test it because brakes are so bad (was gonna do them last weekend and then all this happened) on my drive home it seemed to still be missing a little or something not quite sure. And still got some drips to worry about in drceshaft yoke, shifter lever thingy, and under trans.. Also need to replace the starter and possibly flywheel. So my agenda is brakes, road test, if all goes well from there then diagnosing an repairing leaks, starter, etc. Do you know if a broken crank sensor could be the culprit for the symptoms that I had described? Or was that just one face of a multifaceted problem?

    Really hoping this doesn't turn into a money pit
  9. silverado002

    silverado002 Member

    A broken crank sensor can cause a no start depending on severity. Did they say what caused the sensor to be broken? Was it a electrical failure or physical? I'm surprised that it ran at all but idle speed is so much lower than cruising speed. yes I was referring to the cat converters. Also, EGR systems perform several functions. It lowers cylinder temperatures as well as helps with emissions. If you have emissions tests where you are you need to reconnect the EGR and O2's. Looks like you have a bit of work to do yet but when all the brake work etc is done try to see if you have any more codes. Then work with the lowest numbered one first.
    P. S. I used to live in Pittsburgh but that was before the emissions deal got into high gear.
  10. Mike350

    Mike350 New Member

    Thanks, they didnt specify why it was bad, just told me they replaced it and it starts and runs now. We do have emissions here but it's inspected untill January so I have till then to take care of everything.. I'd like to reconnect the EGR but the little tube costs $100 lol.. I'll take the hit eventually though.

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