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Signs of a weak fuel pump??

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by wayne, Apr 5, 2002.

  1. wayne

    wayne 3/4 ton status

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    Ok, I think I might have a pump going out. What happens is the truck sometimes noses over when I hit the gas from a stop. It idles and drives fine except under real light throttle like in a parking lot, it seems to surge a little. It does this with a full tank or with a 1/4 tank so I don't think it is being caused by the baffle in the tank. Timing is good, everything else seems ok. I am going to change the fuel filter and plug the egr valve. This is an 89 350 tbi. Any other ideas. BTW the pump is most likely origional.
     
  2. xnoahx

    xnoahx 1/2 ton status

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    I had my fuel pump start to go out on me once, the truck would idle fine and got good slowly but oce i started getting going it would shudder because it wasnt getting enough gas. this was on a 85 silverado with the pump on the block. Real pain to replace.
     
  3. gokartergo

    gokartergo 3/4 ton status Staff Member Moderator

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    I'd be willing to bet it is dirty fuel injectors..Try running some cleaner threw it...Dan
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Can you check fuel pressure easily on TBI? I wouldn't replace anything until I knew what the cause wa, especially something as painful as an in-tank pump. Scantools are a little pricey ($150) but invaluable on a vehicle you can use them on.
     
  5. joker89blazer

    joker89blazer 1/2 ton status

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    On the work trucks (all GM) I have used I have had 3 fuel pumps go bad.All had high mileage(one of our trucks has over 400k on factory motor!).all three would idle fine but when you touched the throttle motor would die from lack of fuel,none give any warning symptons.you said your truck has problem under light load and light throttle, If fuel pump was "weak" I would think it would give trouble under higher loads and work fine at lower loads. Has the check engine light been on when you had problems? if so finding problem may be as easy as checking codes.
     
  6. wayne

    wayne 3/4 ton status

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    No check engine light comes on. Wide open throttle is ok too. Like I said though it does not do it all the time. I am going to change the filter and run some fuel injection cleaner through it and see if that helps. When I drop the tank in a couple weeks to do the flip I am just going to put a new pump in. This is probably origional and the truck has over 150k on it so a new one won't hurt.
     
  7. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I just had the same problem as you. I changed my fuel filter and did a tune up and it is all fixed now. My cap and rotor were real bad so i think that contributed to most of my trouble but also the fuel filter looked pretty dirty on the inside.
     
  8. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Another suggestion for you. When you drop your tank you should measure where the sending unit is located and cut the rear floor and make an access panel so in the future if you have troubles with the pump you can change it without dropping the tank. This can be a life saver if you ever have to change the damn thing on the trail sometime.
     
  9. KMH87K5

    KMH87K5 Registered Member

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    My 87 had the same problem. I plugged the egr valve during lunch at work, and when I drove home, it ran like a champ. Haven't had those symptons since.
     
  10. TJS

    TJS 1/2 ton status

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    Hi,
    I have not posted in a while so bear with me. Let me give you some history of me first. I was a service Mgr at a large
    Chevy dealership for 4 years. I also helped Techs diagnose
    driveability probs. I also reprorammed PCM's and the Tech II
    hand held. I am not a mechanic by all means, but through experience maybe I can help. Yes you may have a fuel pump problem, but I had rarely in my days working there cannot think of a TBI pump failing, maybe once in my 4 years there.
    Before that I worked for a Buick and Ford Dealership as well for 10 years. Ok, nuff said. What you should check is inside the distributor cap. Remove the cap and rotor and look inside the cap at the towers. Also look where at the module and where it is mounted. If you see kinda green/whiteish fine
    fuzzy stuff then you have what we called "fumunda".
    This means that the brass windings in the pickup coil are deteriorating causing a reaction with the alum. and the little
    particles are flying around and the pick-up coil is going bad.
    Also your advance is part of the input from the module and the pickup. If you have "fumunda", then remove the dist and
    pop the gear off and get the shaft out then the pick-up coil
    is held on the dist. body by a clip. You need replace the pick-up with a new GM one and also the module. Also when you have the shaft out inspect the magnets at the top of it cause they are prone to cracking as well. Shafts are relatively cheap too. What is not cheap are the modules GM (90.00).
    At the same time replace the cap and rotor, try to get brass ones and not alum. ones. Also replacing the wires maybe a good idea as well. These dist. are cake to rebuild, even easier than the older HEI's. Sorry so long. If you need details on how to take it apart and what tools you need then email me off line. I just did this to my 95 Tahoe and it had "fumunda"
    at 85k miles. Thanks for your time. Hope this helps.
     
  11. ftn96

    ftn96 1/2 ton status

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    Wayne, if you'll visit my post on Engine diagnosis help in the garage section I believe, it will show all the stuff, parts and money I've thrown at mine for doing the exact same thing. At least from the way you describe anyway.
    Mine runs fine, when the engine is cold, or open loop... Then once it warms up, goes into closed loop, it hesitates and studders and stumbles under "any" form off acceleration, "EXCEPT" for full throttle, (which is still weak) and just giving enough gas to maintain speed.
    Now if I go to give it some gas while driving down a highway say at 50 MPH in 3rd or 4th (with TC locked) it will shudder like crazy till the TC unlocks and then its "OK", but still not up to par.
    I have replaced the fuel pump, pre-pump filter (aka sock), frame rail mounted filter, PCV, O2, EGR, Cap, rotor, plugs, wires, timing chain, checked timing, cleaned the IAC (idle air control), Air filter, fuel injection cleaner, 2 cans of spray cleaner and still --------- NO RESULTS..../forums/images/icons/mad.gif
    I hope you dont go through all this. Im replacing the TPS (throttle position sensor) tonight. This, according to a couple of outside sources and the Haynes Emissions Guide, is the most common symptom of a bad TPS. This is due to the TPS giving out erratic voltage levels to the ECM, compared to smooth levels, like it should. If this fixes it I'll be the happiest MOFO you ever met.

    Why this could be it and not give a Check Engine Code? I dont know. If the shoe fits Im gonna where it.

    I actually took mine to a shop that had the OBD1 system analyser adn it said that my O2 adn my EGR where not funtioning. I replaced both of them adn it didn't hcange anything. And yes, I reset the computer after installing them.

    I also un-hooked the O2 and drove it around with no result. I drove around with the ECM/ignition bypass un-hooked.....with no results.

    Just more detail on symptoms, like going up hills (driveway for example) giving it gas enough to pull yourself up the hill it starts cutting up, stumbling/hesitating, then all of a sudden for a flash second it runs ok, then back to crap.

    Then after or beyond say 2000 RPM's it seems smooth but not as much power as normal.

    Im thinking it sounds like a fuel problem as well. But I just put in a new fuel pump following the recommended steps and additional proceedures adn no change. My new pump is still a little noisy. So maybe my bad luck kicked in and delivered me a bad fuel pump right outta the box. ....... Who knows.......

    Keep me posted on your end, I'll put this in my favorites list and let you know how the TPS works! Good luck!!!!

    LAter, Brandon
     
  12. ftn96

    ftn96 1/2 ton status

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    TJS!!!! Thanks for that info. I dont re-call seeing the "fumunda" while I was in there. That does make a great deal of scense though. I will check that out while Im at it again tonight. /forums/images/icons/wink.gif/forums/images/icons/cool.gif
     
  13. ftn96

    ftn96 1/2 ton status

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    Well, I haven't had a chance to check for "fumunda" but I did replace the TPS, with non other than....No Change! /forums/images/icons/mad.gif[cussing]/forums/images/icons/mad.gif[contemplating postal behavioral tendancies]
     

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