98 Silverado 5.7 Vortec running rough

Discussion in 'GM Powertrain' started by lightemup, Jan 9, 2011.

  1. lightemup

    lightemup New Member

    Bought this truck a month ago and it's had quite the misfire since i bought it. Checked the plugs which looked great. Pulled the codes (someone pulled the check engine lightbulb so i thought it was throwing no codes) Came up with multiple knock sensor, multiple 02 sensor codes, and 2 camshaft/crankshaft correlation codes. Ive also noticed my tach is very jumpy, it doesn't make smooth transmissions as the RPMS climb or fall. Crank sensor? Cam position sensor? both?
  2. Magna86

    Magna86 Rockstar

    First of I'm sorry to hear that is sounds like your were scammed! Hopefully you got this truck for little as it had a miss when you got it. Either way I would question the seller about the check engine light bulb being removed and maybe threaten legal action for fraud. Now on to the truck sounds like you have a mess going on there. I'd start with cam/crankshaft sensors as the engine doesn't know what to do with out these working correctly. Which maybe setting off your knock sensor and the engine is reacting that causing the O2 codes. yes check all the basics plugs, wires, clean TB and MAF sensor. If the knock sensor codes go away but O2 show up still you may sensors that are failing and the computer will tell you which ones to replace. Though I'd just replace them all to save future replacement. How many miles are on this truck? Thats the best I can give to start and I'm sure others more wise than me will chim in!

    Good luck and keep us updated

    DAREDEVIL Rockstar 4 Years 1000 Posts

    i would do both, not that hard and relative inexpensive !!!
    could aslo be 02 sensors or EGR
  4. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    Subscribing to this thread, my Tahoe has similar symptoms. I've had the knock sensor code and misfire codes. But no Cam/Crank code. Yet. Also have a cutting out problem. Flat out die. Wait a few seconds starts right back up.
  5. lightemup

    lightemup New Member

    I got a pretty good buy on it...The truck is an extended cab w/3rd door, loaded, great shape, 2,500 bucks. The motor is extremely quiet and feels like it has tons of power, but it's just something stupid holding it back (like a bad crank/cam sensor or something)
  6. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner 1000 Posts

    x2 what magna86 said. I would start with the crank and cam sensors. then go from there. those are usually cheap sensors and can definately cause knock sensor to go off.
  7. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    <<<<Update >>>>

    Lucy (the Tahoe) had been getting pretty bad. Ran very poorly Wednesday at lunch. Took three or four minutes to get her started Wednesday night. Absolutely no start Thursday morning. Turns out I had two problems going on. Found one pretty quickly Thurs morning. First, the fuel pump relay and contact were burned. Not an uncommon problem. The contacts get warm from the high current draw of a failing pump. (Lucy has 200K, I put a new pump in last spring). The warming causes them to lose tension. The loose contact now becomes a point of resistance, and sometimes arcing. The problem continues to manifest itself until there is a complete failure, or fire. The problem is more commonly found at the pump pigtail, and is often the actual cause of pump failure. I will be installing a stand alone relay for the pump wire. Eventually I will run a new 12 gauge wire to the pump to ensure optimum voltage at the pump. The poor contact was also likely causing the knocking and knock sensor code last week.

    Back on track here. I bypassed the pump relay, I can hear the pump running. Still no start. Brought home the scan tool. Finally showing a Crank Sensor Code. After consulting with the Haynes manual and a mechanic friend, I investigated. Apparently is much more common for the CKP pigtail to fail as opposed to the CKP itself. Took my connector off. Tested the CKP, dead. Popped in the new CKP, runs fine. Just need to get a CKP relearn done this week.

    Ran around town this morning, ran great. Taking it for a 150 mile trip later, I will report how she runs.

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