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97 Suburban with a 5.7 random low power issues

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  • 97 Suburban with a 5.7 random low power issues

    I have a 97 Chev Suburban with the 5.7l Vortec engine. Lately it will loose power while driving down the road at highway speeds. So if I am doing 75 or so and it starts acting up I will be lucky to maintain 60-65. If I push the throttle in more it will get worse and usually wont go beyond 2500-3000 RPM even when in neutral.

    I pluged in my scanner and found that when it acts up the shrtft1 and shrtft2 go to 0 and fuelsys1 and fuelsys2 read OL. Longft1 and longft2 read simmilar around 7 with some variation depending on RPM and throttle setting. I do have a few codes; a random misfire, and both O2 pre-cat sensors(which I had before the current problem). I have recently replaced the fuel pump(delphi), fuel filter, and spider. I think this problem was present before but not as bad. Before as you drove down the road you would occasionally feel the power increase without changing the throttle or anything. Any help would shure be appreciated.

  • #2
    Re: 97 Suburban with a 5.7 random low power issues

    Did you replace the fuel pressure regulator when you replaced the spider?

    Joe.

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    • #3
      Re: 97 Suburban with a 5.7 random low power issues

      It does have a new regulator that came with the spider. My cats were gutted by a previous owner and the cap, rotor, plug wires and plugs have all been recently changed as well.

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      • #4
        Re: 97 Suburban with a 5.7 random low power issues

        What are your codes exactly?

        Joe

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        • #5
          Re: 97 Suburban with a 5.7 random low power issues

          I'm thinking it *may be the distributor drive gear, cap & rotor or the coil.
          I had the multiple cylinder misfire (P0300) and it was a combination of all those parts I listed.

          Now from dumping all the extra fuel into my exhaust I now have bad Cat's (P0420).

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          • #6
            Re: 97 Suburban with a 5.7 random low power issues

            I am going to check the timing this morning, the drive gear was just replaced. I will also check which codes I have exactly. If I remember right the timing should be set to 0 deg BTD +/- 2 while reading the scanner at about 1000 rpm?

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            • #7
              Re: 97 Suburban with a 5.7 random low power issues

              Yes, anything below 1,000 RPM's is inaccurate.
              I have an abundance of info on this topic, if need be, I can either post my findings in text (here) or email you PDF's.

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              • #8
                Re: 97 Suburban with a 5.7 random low power issues

                I'll PM you a link to YouTube (can't post links yet, new to site).

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                • #9
                  Re: 97 Suburban with a 5.7 random low power issues

                  Timing checks out, but I notice an occasional "pop" in the exaust and I still have the P0300 random misfire code and of course the two O2 codes (P0151 and P0161). when I drive my 98 Suburban and watch the data I notice the fuel trim numnbers are all close and rarely exceed 10 or -5 or-6 and in the 97 I sometimes get as high as 50, not sure if this helps. Also in the 98 when at wot the fuel systems (fuelsys1 & 2) change from CL to OL-drive and on the 97 it usually reads just OL and this usually happens somewhere between 50-75% throttle. When I really start to loose power fuelsys1&2 read OL even at idle and the shorth fuel trim(shrtft1&2) read 0 and do not change with throttle settings.

                  I am thinking with the P0300 code and the ocassional "pop" in the exaust the new cap and rotor may be at fault. But I also think I have another issue with the fuel system.

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                  • #10
                    Re: 97 Suburban with a 5.7 random low power issues

                    Ok, so another issue I had was similar to what you said about loss of power.
                    In my 1997 Silverado It'd take just a little longer than usual to fire up (+2 seconds) and at about 60 MPH it was a dog. I thought my transmission was slipping because it'd rev and rev up to 70 mph but it took forever.

                    So I replaced my fuel filter and it was better.
                    Then I went to fire it up one day and it wouldn't start.
                    Pulled the bed off (you'll have to drop the tank) and tested the fuel pump. I just unhooked the sending line and turned the key on and it was working but went ahead and replaced it.

                    Turns out it just didn't have enough pressure.

                    After that, it was like a night & day difference!

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                    • #11
                      Re: 97 Suburban with a 5.7 random low power issues

                      I have thought of that. I did just replace the fuel pump a few weeks ago when I did the spider and filter everything checked out then. Unfortunately this problem was present before then, although not as bad.

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                      • #12
                        Re: 97 Suburban with a 5.7 random low power issues

                        Well :damnit: I hope you get this figures out.

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                        • #13
                          Re: 97 Suburban with a 5.7 random low power issues

                          I have also noticed that it seems to be better when its cold. Is there some other sensor that controls the injection system that I should be looking at?

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                          • #14
                            Re: 97 Suburban with a 5.7 random low power issues

                            Today I swapped out the coil and it runs smoother now but it still looses power above 1/3 to 1/2 throttle. The only codes I am getting are the P0131 and P0151 for the two oxygen sensors. Has anyone had problems like this caused by the oxygen sensors?

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                            • #15
                              Re: 97 Suburban with a 5.7 random low power issues

                              Hi, your P0131 and P0151 are lean condition for more than a predetermined time.
                              That means there is no fuel getting to your engine......Iknow you have replaced many parts but that means the possible faults are
                              -pump...low pressure or low flow
                              -filter blockage
                              -bad fuel pressure regulator.

                              So the test you can do;
                              -fuel pressure test with a guage.....between 60 and 66 psi.
                              -fuel flow test...you should get a pint in around 25 seconds.

                              I Know cause I got the same thing

                              Good luck,
                              Joe.

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