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350 Vortec needs help

Discussion in 'Truck & Equipment Repair' started by aubbie, Feb 18, 2014.

  1. aubbie

    aubbie Member
    Messages: 60

    I have a 1998 Z71 Silverado, with around 160 miles. I had to take a trip on the highway, [interstate], I found I had to mash the pedal to the floor on the hills to make the speed limit, and fuel mileage is terrible. The oil pressure gague is reading really low, like just up from zero. Truck will always start, no knocks. I have to admit that the oil is dirty, hasn't been changed in quite awhile....just never seem to get around to it. I am going to change it this week but I can't see that being the reason for all the problems. Any body have any ideas? Thanks Guys
     
  2. TJS

    TJS PlowSite.com Addict
    Messages: 1,343

    Begin diagnosing with a mechanical oil pressure check. Use a real gauge. Then check your fuel pressure. Sounds like you need a fuel pump. Very common complaint you have resulting in a fuel pump replacement.
     
  3. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    I briefly drove a GM truck. 2000 4.3. There was a point where it was doing the same as you are describing. No guts at all, had to mash it AND draft a rig to hold highway speed. Started doing this about 1/3 of the way through a 30 hour trip... then suddenly after several hours of this, check engine light came on and power instantly came back. Turned out to be an O2 sensor. When it finally figured out that the sensor was fried, it started ignoring it and ran normal. Thing never got better fuel mileage than when it was ignoring that O2 sensor (about 18 mpg) -- even after the new one was installed (back down to about 16 mpg). Why are GM's so horrible on fuel? My Tacoma got better mileage while hauling that POS on a trailer than it EVER got driving itself.
     
  4. leolkfrm

    leolkfrm PlowSite.com Addict
    Messages: 1,430

    oil change places around here are 24.95, worth it if no time to do it yourself

    I would change the fuel filter, then cut it open and see if dirty inside,
     
  5. aubbie

    aubbie Member
    Messages: 60

    Hey Jason, I really don't know what you mean it ignored the fried 02 sensor...the engine ignored the fried sensor? I'm confused. This is a real hard thing to admit to everyone who reads this but when I dumped the 2.5ltr.s of oil in it that it was down, my oil pressure suddenly came back! Yeah I didn't check the oil for a couple storms and she used quite a bit. I'm gonna book an oil change tomorrow and get a new fuel filter. Without opening the hood and finding it, where is the fuel filter on my truck....1998 350 Vortec
    Thanks Guys
     
  6. jasonv

    jasonv PlowSite.com Addict
    from kannada
    Messages: 1,114

    Yep, usually buried somewhere inside the dashboard is a thing called a "computer". It takes inputs from all the different sensors, and uses it to control things like the ignition timing and fuel injector timing. When the computer determines that one of the sensors is providing an incorrect signal, it will stop using the values from that sensor in calculating engine control values, we call this "ignoring" the sensor. Instead of using values from a sensor, it will use a "best guess" based on a table pre-programmed into the computer from the factory. The computer also alerts you that it is ignoring a sensor by putting on a light on your dashboard... it is called the "check engine light" and tells you that something needs to be addressed.

    As far as oil pressure coming back after adding 2.5 qts of oil... that is very very very VERY bad. If it was running low oil pressure (and power and bad fuel consumption) due to a lack of oil, then you could have and probably did cause *extensive* damage to that engine. Now that you have the oil level back up and have ran it for a bit, the power hasn't returned? I would definitely take a sample of that oil and send it out for analysis, and crack open the oil filter (look for metal debris in it) -- see what kind of damage its taken. My gut feeling is that it may be time for you to look for another engine or truck. Hope I'm wrong.