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98 suburban fuel pump replacement woes

Discussion in 'Member Introductions' started by mjh46560, Jan 24, 2014.

  1. mjh46560

    mjh46560 New Member

    Hello,
    I just finished replacing my fuel pump in my 98 GMC suburban. I read several post here and had some great information from many people that had done this before so I felt well prepared.
    Tank was less than 1/4 full so I thought it would be easy to deal with. Tank was dropped fairly easily in about 2 hours. I just had to watch what to disconnect, 2 fill tubes from gas tank filler cap. Put jack under tank with plywood to distribute load, take off two big straps and lower tank slowly. Gas pressure lines are not long enough to lower tank all the way to floor without breaking something. I learned this the hard way. Broke the plastic inlet to the main pressure line to engine, but line itself was fine. I cut off the return line, took off the electrical connection and vent line and pulled tank out from under truck. I pulled out the fuel pump unit, and saw that I had a GFM. There are two styles, GFM and GFN. I took a chance and ordered one from buyautoparts.com. They claim every part is a perfect fit and function for your vehicle and 12 month unlimited mileage warrenty. It was $110, no shipping. GM wanted $420 for a fuel pump. I ordered for buyautoparts.com and they asked all the right questions. While waiting for new part, I bought a fuel line disconnect tool from harbor freight tools. They didn't work as they didn't insert far enough into the fuel line to push back the 4 tabs to disconnect the lines. I went to NAPA and bought another one and it was another scissor style, but had longer 'jaws' that should be enough to push the tabs back. Unfortunately, they completely circle the plastic inlet ports, but that won't let the scissors close and get the jaws into the opening of the fuel line. I had to cut off 1/4 of the way around then so they could completed close. Then it worked perfectly. Ok, one hurdle done. Now I just had to wait for new part. Part was delivered 3 days later. It looked exactly the same and came with a new oring. I installed it and it seemed to fit fine. The electrical connection was different but they included a patch cable and I cut off the old cable and spliced in the new one. Put tank back in and tried to start it. It didn't start. So, I dropped the tank again to check electrical connections and found I didn't have 12Vdc to pump. It took 2 hours, but finally traced it to the fuel pump relay in the engine compartment. I jumpered across the contacts and pump worked and truck fired up. I cleaned the relay contacts and now all is working fine.....or so I thought. I am about 5 hours into the job now over 5 days. I drive to gas station to fill it up and when it is almost full, gas starts coming out of the top of tank and pouring on the concrete. Gas attendant says I have a hole in my tank. I drive home, nervously wondering if the truck will blow up any second. Nerve wracking 2 miles. I get into my driveway, and no gas is dripping. I now have a full 44 gallon fuel tank that I have to drop again. I borrow 2 5 gallon gas cans from my neighbor and buy 5 more plus the one I have at home. I siphon out about 40 gallons and drop the tank. I see dried fuel residue all over the top of the tank, but cannot find the source. I check the fuel lines, vent line, fuel inlet pipe and cannot find any source. I had tank supported up to connect the lines and started truck. No leaks. I spend the next full day trying all sorts of ways to find leak. I finally put all gas back in tank and slosh tank around. Sure enough, some comes out the top of the tank. I didn't get the oring seal in correct. So I pull fuel pump, and spend the next 2 hours trying to get the oring seal correct. I finally put dry oring in tank, sprayed top of fuel pump assembly with WD-40 and slowly put it in place making sure I pushed straight down and when it contacted oring, I didn't still pushed straight down. When I had it seated and the clip in place. I now sloshed tank around, with the 40 gallons or so in it and cannot get it to come out. So to really test it, I tipped the tank on its side so the fuel pump assembly was totally under the gas and waited a full minute and didn't have a leak. Finally I felt like I found the problem and fixed it. With some help from my brother in law and his son, we got the tank back in and it seems to be fine. So learn from my mistakes and check that stupid oring seal before putting tank back in and insure you have 12Vdc to pump.
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Sounds like a frustrating repair, fortunately you were able to figure it all out and complete the job.
    Congrats and thanks for the tips
  3. MrShorty

    MrShorty Epic Member Staff Member 5+ Years 1000 Posts

    That sort of thing can definitely be frustrating (like just about anything we learn from "the school of hard knocks"). As I recall, that o-ring fits pretty snug in its sealing groove, so it will often take a little "persuasion" to get it in place and properly seated. Good advice to make sure this is in place properly before reinstalling the tank and filling.
  4. BRB46

    BRB46 Rockstar Gold Member 100 Posts

    Was the relay the problem to begin with. Sounds like quite the venture. Glad it worked out.
  5. mjh46560

    mjh46560 New Member

    No, the fuel pump was fine before I replaced it. I was trying to fix the fuel level sending unit. But after 15 years, enough corrosion built up that it finely decided to not pass electrons.

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