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  1. #1

    Default '96 Sub Runs rough, again.

    This is driving me crazy. I have a '96 Sub with about 167,000 miles. I have replaced the fuel pump I don't know how many times. After the replacement it runs fine for while then starts to run rough enough that my wife is afraid to take it to the grocery store. Last replacement was with the, "New, Improved Turbine" fuel pump "Guaranteed to eliminate fuel pump problems with GM trucks."
    I have replaced the: cap, rotor, wires (Premium, best, most expensive I could find), plugs, EGR, all O2 sensors, and the fuel filter. The parts guy at Car Quest suggested that I put dialectic grease on the relay terminals and fuse for the fuel pump. He said his brother did some research and found that GM recommends this to prevent moisture related electrical problems specific to the well known fuel pump problems. Did that.
    Yesterday morning I replaced the plugs with Bosch premium platinum plugs (had great luck with them previously) and soaked the throttle body with Deep Creep after injecting half a can into the motor through a vacuum line. Started it up and it ran just fine. Took it for a ten mile test drive (half of it up a 8% grade at full throttle, climbing the hill like a homesick angel) and it ran perfectly.
    This morning the wife took it out and it ran like **** again.
    I have a brother in law who is a SAE certified master mechanic (he knows his stuff in the real world too) and he is out of suggestions.
    Don't tell me about codes.
    Either I am going to fix this thing or I am going to set fire to it.
    And I can't do that because I need it.

  2. #2
    murdog94's Avatar
    Join Date
    Feb 2008
    Cloquet, Minnesota, United States
    Blog Entries


    intake gasket???? Did you clean the IAC when you soaked the Throttle body?? TPS??? PCV Valve plugged?? Fuel pressure regulator on the Spider injector assembly common problem i might add... OH and last but absolutely not least. have you checked the distributor out?? They are plastic and the bushings can go out causing the need to replace the whole unit since the wobble can cause the timing to be off, and it will be very intermitent... My buddies truck had the same problem and it was the dist.. And then three others went out last summer.. MAF sensor been cleaned lately??


    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  3. #3


    Have you monitored fuel pressure? When you replaced the pump, did you put a new pigtail on the wiring?
    When you hear hoofbeats, look for horses not zebras.

  4. #4


    I played around with it again last night. Thought the ground to the fuel pump might be bad since it is an intermittent problem. Did another test drive and it ran perfectly, for about six blocks then the problem started again. Got home to the driveway and goosed the gas pedal a few times and noticed that it was backfiring. That tells me the timing is off, periodically. I hate just replacing parts until the problem goes away but it it sounding more like the distributer mentioned above may be at fault.
    I guess that's next.

  5. #5
    murdog94's Avatar
    Join Date
    Feb 2008
    Cloquet, Minnesota, United States
    Blog Entries


    Well keep us posted.. and i hate "troubleguessing" but sometimes that is what it comes down to, your best guess. which is where ive been at 3 times with my truck now....

  6. #6
    Master Mechanic bigdaddy77084's Avatar
    Join Date
    Jan 2010
    Houston, Texas, United States


    You can get backfire from getting to much gas too,or your cat. is getting plugged..Good luck
    95 tahoe 2dr 4x4 200,000+ miles

  7. #7


    Hey Michaell, I had a Problem with my 99 burb running rough when it wanted to and problems like your having. I then took it down to autozone and they ran a diagnostic code test thingy on it and found out that there was something wrong with the Crankshaft position(CKP) sensor and camshaft potion sensor (CMP), so I cleaned both with electrical connection cleaner. My truck ran beautifully after that and havent had any problems with it running rough or missing since. On my truck, the crankshaft sensor was located on the bottom passenger side of the front engine cover just behind the harmonic balancer. The camshaft one one is actually located inside the distributor(oddly enough) but has a connection to it on the back of the distributor that you can pull off and try cleaning, its tricky to find and get to though. If you have a haynes manual just look up them in the index and it will tell you about them also. I hope this helps. Good luck!
    99 Chevy Suburban 2500 7.4 Liter 4wd
    Currently on: 265/75R16

    Goals: 2" suspension lift
    285/75R16 tires

  8. #8
    Master Mechanic Dr_Zero's Avatar
    Join Date
    Mar 2006
    Sunny Florida


    When I say this Im not trying to be funny but have you considered it might be your wife?

    When I had my mustang my mom always wanted to ride in it but when she would get in the electronic ignition would act up, she would get out and it would go back to normal. Quartz watches will stop a few days after wearing it then when she takes it off will start back up usually.

    So I know crazy things can happen when it comes to elctronics LOL
    My trucks!

    1996 GMC Suburban SLT
    1997 GMC Yukon SLT

  9. #9

    Default Got it fixed

    Took a long time but I finally got the Sub running right. I replaced nearly everything I could think of before I posted here. Someone suggested the crank position sensor or the cam position sensor may be bad or dirty. I cleaned both of them with no change in the problem. Replaced the cam position sensor due to a fault code involving that item but it made no difference. While checking fault codes I also noticed a Mass Air Flow sensor fault so I got one of those too. When I went to replace it I noticed that someone somewhere along the way had installed the existing one backwards! The reason, I beleive from what I could tell was the wiring harness (that includes two plugs) just fit better when the sensor was in backwards. I re-routed the wiring and installed it the right way. TA-DAA! Problem solved.
    I could choke somebody if I could figure out who.

  10. #10


    glad the problem got fixed, sorry it cost so much for a backwards MAF
    2004 Silverado 2500 Crew Cab 4x4, AMSOIL EA air filter, Granatelli MAF sensor, Throttle body spacer, Magnaflow exhaust (true dual to 2 in 1 out muffler), 6" ProComp lift (add a leaf and 5" superlift rear block), Bilstein shocks, 35's (Cooper Disoverer ST) and 4.10 gears, Rhino Liner, EGRUSA fender Flares and widow visors, extended stainless steel brake lines, firestone airbags w/onboard air compressor, Pioneer Avic X940BT navigation, Accel backup camera.
    1960 Land Rover Series II 88
    2001 Pontiac Sunfire
    2013 Toyota Avalon Limited (Wife's Car)
    NRA Life Member

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