'93 Eldorado, 4.9L - Bad Fuel Pump?
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HT4100 4.1, 4.5, 4.9 Discussion, '93 Eldorado, 4.9L - Bad Fuel Pump? in Cadillac Engine Technical Discussion; 1993 Eldorado, 4.9L, 199k miles. Went to start my car this morning, engine started, then died after 1 or 2 ...
  1. #1
    kdcing is offline Cadillac Owners Fanatic
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    '93 Eldorado, 4.9L - Bad Fuel Pump?

    1993 Eldorado, 4.9L, 199k miles. Went to start my car this morning, engine started, then died after 1 or 2 seconds of run time. Now, starter engages, engine turns (i.e. battery is strong), however, the engine will not fire up. No codes.

    I haven't done much troubleshooting yet, however, I do not hear the faint high pitched whine of the fuel pump anymore and suspect that it is likely bad. It has never been replaced in the 135k miles that I've owned the car. I do not have accommadations (i.e. no garage) to do a drop the tank, so I was wondering if anyone has attempted to cut a hole in the floor of the trunk or back seat to gain access to the pump? Also, does anyone know approximately where the fuel pump access hole would need to be (i.e. in trunk or underneath the back seat?). I know this access hole is probably a crazy idea, but not as crazy as dunking the new pump into a gas can on the passenger seat and running a fuel line to the FPR...just so I can drive this thing to a friend's garage.....hhmmm, hold on a minute.....

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    HUF's Avatar
    HUF
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    First make sure it IS the fuel pump. Check the related relay. Dropping the tank is not a big deal if someone assists you.

  4. #3
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Thanks Huf....I had the fuse on my checklist, but totally forgot about the relay. I found an article online which indicated that the Fuel Pump Relay can be triggered On/Off via PS05 in the PCM Overide in the Diagnotics. Per the quick audible check that I just performed I did not hear the pump turn on, nor the relay click, when toggled via PS05. I plan on getting a voltmeter/ohmeter on the relay block in the morning when the sun hopefully returns. My hopes are that I will be able to:
    • Get my ear closer to the relay to hear it click when toggled via PS05.
    • Remove relay from the relay block. Apply battery voltage to the relay's trigger terminals via temporary wiring. Measure resistance on the relay's terminals to the fuel pump.
    • Check continuity (or lack thereof) of the fuel pump via the termnals in the relay block.

    If these troubleshooting steps do not seem correct, or if there other steps that should be taken, please let me know. My hopes are that the relay is bad as my apartment/condo association does not look kindly at auto repairs in the parking lot. Thanks for the tip.

  5. #4
    HUF's Avatar
    HUF
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Very good plan. Good luck.

  6. #5
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    ...looking more and more like the fuel pump is gone. Here are the troubleshooting results from this morning:

    1. The relays for the Fuel Pump and Headlights are identical Omron relays (i.e. same PN and wiring printed on the sides). I swapped relays...the headlights worked w/ the "fuel pump" relay and the engine did not start w/ the "headlight" relay in the FP spot.

    2. At the 2 terminals for the FP on the relay block, 1 terminal read 12V w/ the key on. The other terminal likely goes back to the pump, thru the pump, then to ground. A resistance check of that terminal showed a high value (i.e. 75k-700k ohms). As a comparison, the new FP that I purchased last night has 4 ohms across the terminals.

    3. I jumpered the 2 terminals in the relay block (forcing the 12V to the wire going to the FP) w/ a paper clip. No noise was heard from the fuel tank. Also, the engine did not fire when I attempted to start it.

    4. To confirm that I did not overlook the ignition system, a timing light was hooked up to 1 of the spark plugs...simply to confirm that the ignition was firing. When the engine was cranked, the timing light strobed normally.

    At this point, it is probably not needed, but for final confirmation, I may pick up a fuel pressure guage this evening from AutoZone and have a look at the Fuel Pressure at the fuel rail.

  7. #6
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Duplicate post - please delete.

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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    The last hope would be the fuel pump connector, but to get there you probably need to drop the tank anyway.

  9. #8
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Well, I'm down to replacing the Fuel Pump from above (my condo association rules prohibit the use of car jacks in the parking lot) or selling the car. Not a huge loss as I have definitely gotten more then my use out of it....it is worn. The car's value is only $500-$750 in running condition, so it is hard to justify the $270 labor at Goodyear (+ my $110 in parts from AutoZone).

    I'm looking at the possibility of replacing the fuel pump from above by cutting a hole in the floor of the trunk or back seat. I have the back seat fully removed (i.e. seat and backrest) and have pulled the carpeting back in the trunk.

    I've attached a picture of a fuel tank that I found on the web. It is a used tank that someone is selling and has indicated that it is for a '93 Eldorado.

    My questions for the group:
    • Can anyone confirm that the tank in the picture is actually the tank used on a '93 Eldorado?
    • There is a round hole in the tank shown in the picture....this is where the fuel pump would be installed, correct?
    • I placed a red dot on the picture...this is the approximate location where an access hole (approximately 1.5"x2.5") is located in the trunk floor for wiring that supplies power for some systems that are underneath the trunk (likely wiring for the Fuel Pump, ELC, etc.). I removed the cover plate and thick rubber seal to have a look around. I can see only about 3-5" into the access hole, but do not see the large hole in the tank as shown in the picture.....this is why I am asking if anyone has seen the top of a '93 Eldo tank...am I looking in the correct location for the fuel pump. My jig-saw is idling.....

  10. #9
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    It's the only place whee the fuel pump can be located. Cannot comment on Eldo part.

  11. #10
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    ...got her going again. It was the fuel pump and replaced it thru the top (i.e. thru the floorboard w/o dropping the tank). Only about an hour to do the actual hole cutting and replacement, but a bunch of research and planning. Some button up work still to do (i.e. patching the hole). More details to follow later.

  12. #11
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Quote Originally Posted by kdcing View Post
    ...got her going again. It was the fuel pump and replaced it thru the top (i.e. thru the floorboard w/o dropping the tank). Only about an hour to do the actual hole cutting and replacement, but a bunch of research and planning. Some button up work still to do (i.e. patching the hole). More details to follow later.
    Wow! Looking forward to seeing the details and pictures, if possible. What did you use for cutting?

  13. #12
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    ....used a 5/16" diameter drill bit and drilled a series of holes in the area that I wanted to open up in the floor board. The holes were spaced with 3/8" - 1/2" of metal left between them. Tin snips were used to cut the metal between the holes. The holes were drilled to make a 3-sided opening in the floorboard...then the metal was peeled back like a sardine can. The metal is relatively thin in the floorboard and my manual tin snips easily cut thru. I had considered cutting w/ a grinding wheel or hack saw but did not want sparks so close to the tank. When drilling the holes, it was imperative to not allow the drill to go thru too far (to avoid drilling thru the fuel lines, fuel tank or wiring).

    The local pick-your-own-stuff-junkyard was invaluable for planning this project. I found a Seville w/ the tank already dropped...so that I could see how the pump/sending unit attached. I found a Deville w/ the tank not dropped and was able to open up the floor board from above to determine exactly where I needed to put the hole.

    Btw, the picture of the fuel tank that I attached in a previous post was not the correct tank for my car....nor was it the tank used on the '92 Seville or '95 Deville @ the junkyard. While all of the tanks are plastic, the position of the fuel pump was not as shown by the red dot in the previous picture. The correct position is shown by the black dot in the picture attached to this post and is positioned in the hump of the back seats.

    An important part of the project is closing the hole back up. Since it is effectively in the passenger compartment, the hole can let in rain, snow, hot air, cold air.....and worse....like exhaust fumes, gas fumes....and fire in the case of a collision or rollover. My plan is roll the "sardine lid" back down, then epoxy the seam w/ a JB Weld type material to make it air tight.

    In the next few days, I'll take some snapshots and post them.

  14. #13
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Good job! I like radical solutions. Sure, dropping the tank seems easier, but your experience is very valuable for those who for some reason cannot drop the tank. My tank is all metall, BTW.

  15. #14
    kdcing is offline Cadillac Owners Fanatic
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Pictures attached
    Attached Images

  16. #15
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    Re: '93 Eldorado, 4.9L - Bad Fuel Pump?

    Wow! Thanks for the pictures of the surgery! lol How long did it take to remove the seats?

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