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97 Suburban with a 5.7 random low power issues

This is a discussion on 97 Suburban with a 5.7 random low power issues within the Technical / Maintenance forums, part of the General Discussion category; I have a 97 Chev Suburban with the 5.7l Vortec engine. Lately it will loose power while driving down the ...

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    97 Suburban with a 5.7 random low power issues


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    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.

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    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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    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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    Re: 97 Suburban with a 5.7 random low power issues

    What are your codes exactly?

    Joe

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    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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    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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    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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    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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    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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    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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    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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    Re: 97 Suburban with a 5.7 random low power issues

    Well I hope you get this figures out.

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    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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    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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    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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    Re: 97 Suburban with a 5.7 random low power issues

    I have been fearing that one or more of my new parts are faulty, since I just filled up Murphys Law would state the fuel pump is at fault. :) I will keep you posted on what I find out. Thanks.

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    Re: 97 Suburban with a 5.7 random low power issues

    Before changing the pump, you should do the fuel flow test to confirm or just for reference.

    It is actually quite simple, just removed the shredder valve, put a hose on it going to a canister
    and by-pass the relay.......1 pint or 500ml of fuel in 25 seconds...minimum.

    Post result whatever you do,
    good luck

    Joe.

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    Re: 97 Suburban with a 5.7 random low power issues

    Today I finally got a chance to work on it again. The fuel pressure is about 50psi and once the ignition is shut off it drops to 0 in a few seconds. When I pinch off the return line it will climb to 65+ but still bleed off to 0 although it takes about 10-15 seconds. I changed my fuel spider back to the original one (after I cleaned the plugged injector) and it runs again nice and smooth untill about 1/4 throttle and then even in neutral it stumbles and will almost stall. The fuel pressures are similar although it takes 10 - 15 seconds or more to bleed to 0psi without the return clamped. If I try to accelerate it while parked the pressure drops to about 55psi or so (while idling the pressure is about 60-65 psi). I did not check the volume but I am assuming if the pressure drops while it is accellerated then it isn't pumping enough to keep up.

    I think the fuel pump/sending unit might be at fault. Could the electrical connection at the sending unit be partially at fault or do you think it is just the fuel pump or ???

    Thanks again,

    Mark

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    Re: 97 Suburban with a 5.7 random low power issues

    Hi,
    I don't think the electrical connection would be at fault, altough you never know.....
    You should really do the fuel flow test before changing the pump, even if it's just for a reference number.

    I have never replaced the spider, so is a fuel pressure regulator included when you change the hole thing?
    Whatever you do, be sure to write it up.....i'm curious as to what is going on.

    Joe.

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    Re: 97 Suburban with a 5.7 random low power issues

    Ok, I checked the fuel flow and it was really low in the 2-3 minutes range to get a quart of fuel. When I droped the tank I noticed some electrical tape on the harness to the sending unit. Once I had it all apart I pulled the tape off to find someone had cut the wires instead of unplugging them from in front of the frame rail, and when it was put back together they simply twisted and taped the wires together. I am not sure if this was part of the problem or not but I soldered the connections when I reassembled it with a new pump. The pump I had installed a month or two ago was a Delphi pump that I had purchased at O'Reillys and was still under warranty. So far I have driven the Suburban about 600+ miles with no problems and it has more power now than its ever had since I have owned it.

    I wish I had taken the time to clean the dirty injector on the old spider, it would have saved me from buying a new one for $300 that is now sitting on my work bench. All I had to do to clean the injector was unplug it from the bottom of the fuel spider body, soak it in a little carb and injector cleaner and spray it out with compressed air. I did that a few times and you could see the spray pattern getting better, after that I reassembled it and it works fine.

    Thanks for all of your help.

 

 
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