2000 Mustang GT CCRM/Fuel Pump issue

Discussion in 'SN95 4.6L Mustang Tech' started by mndtrp, Sep 2, 2010.

  1. The blowing fuse can not be ignored. Confirm if the fuse is in the engine bay (F1=BJB) or the driver's kick panel (F2=CJB). No sense is going any further with any other suggestions. Focus on the blowing fuse. Will need to know which fuse is blowing.

    note, If it turns out to be F2.8, in all likely hood this will be a wiring fault in the O2 heaters.

    Also, since this car has been setting up, any rodent activity?

    Fuse diagram attached.

    BJB=F1=Battery Junction Box diagram-11-1 (attached)
    CJB=F2=Central Junction Box diagram-11-3


    OBTW, I reached out to the admin and requested the thread to be moved where more "eyes" can see it. Thanks admin!

    Attached Files:

  2. I understand now, my fuse diagrams don't have the Fx.xx numbering scheme, just the last two digits. It's F1.14. I'll go through the CJB again, and make sure that nothing in there has re-blown.

    Rodents are unlikely. In the three years I've lived here, I've never seen any, or evidence of one.
  3. Fuse F1.14 is the fuel pump drive module fuse (FPDM). A blown F1.14 means no fuel pump.

    Go to the trunk and remove the trunk liner. The FPDM is on the left hand side of the trunk. Disconnect the wiring connector. Replace fuse F1.14. Try to start. It won't. But what we are trying to do is rule out a short in the wiring harness.

    If fuse F1.14 does NOT blow with the FPDM disconnected, likely a bad FPDM is what the problem was all along.

    The FPDM is easy to replace. May have to go to a salvage yard or Ford for a replacement.
  4. Had this same problem of blowing that fuse and a 02 sensor was shorting out something in the wiring harness could be shorting out.
  5. Search under my name for a thread for no start or blowing fuse.
  6. This must be the thread you were talking about:
    Need technical wiring help! 96 GT

    Unfortunately, the link in the thread doesn't work any more. I'll search here for other O2 Sensor threads. Thank you for the info.

    I disconnected the FPDM (picture linked here, in case someone in the future doesn't know what it is, either), replaced the fuse, and did (3) 3-second cranks. The fuse did not blow. After re-connecting the FPDM, the fuse blew on the first crank.

    I'll start looking tomorrow or Thursday for a FPDM. I'll pull the old one out for the part number, but is that number specific to the one I have to get, or are some interchangeable?
  7. Uh oh. I knew the FPDM sounded familiar, it's already been replaced. I pulled the one out of my car, and it has a sticker stamped with a date of 2009. I checked my receipts, and I did actually buy one, back in May.

    Unless there is a different suggestion, I'll look into FoxRod's O2 sensor idea.
  8. FWIIW, some of the advice given was based upon the information posted. As I recall, the report was "new fuel pump" and "new CCRM".

    IMO, FoxRod's suggestion is of questionalable value as his car was a pre 1999 which has a MUCH different electrical system than a 1999+.

    This is where the details are vital. For example, with symptoms of new CCRM, and new FPDM, and old fuel pump along with blowing fuse, guess what I vote? Replace fuel pump.

    If on the other hand we have blown fuel pump fuse, new CCRM, new FPDM, new fuel pump. What do I vote? Wiring harness problem.

    OBTW, was the picture posted of the FPDM your car? Just wondering because the picture does not look stock to me.

    There is an electrical connector in the center of the gas tank. Access from below by the rear bumper. This connector goes directly to the in tank fuel pump. Disconnect this.

    Reconnect the FPDM. New fuse. Try to start. It won't. Does it blow the fuse?

    Can you confirm if the fuel pump was replaced?

    If this is a wiring harness fault, it will require detailed tests with a volt-ohm meter and the results posted. Do you have a volt-ohm meter? Are you prepared to USE it?

    OBTW, I have ask before about rodent damage. Chasing wiring harness faults can be one of the biggest PIA jobs there is. Especially if looking for a problem that could be ANYWHRE in the car. IMO, wiring problems rarely happen in a vacuum. The vast majority are the result of some EXTERNAL factor or modification. The means that often there is evidence of the fault on the outside of the harness. The challenge is finding it.

    I strongly suggest that a close visual inspection of the wiring harness be done. Look for evidence of cutting, chaffing, burning, rubbing, missing tape, suspension componets out of place, or anywhere modifications were done.

    Hang on because this could get ugly.
  9. I understand. It's also not extremely helpful that I was so hands-off with the original mechanic work, and am having to basically start over. Live and learn...

    I do know that I bought a fuel pump for the mechanic to install, since he said I had burned the original one out. This didn't surprise me, as I thought that the fuel had simply turned on me, and I understand that you can ruin the fuel pump when trying to start with bad fuel. I'm guessing, since the FPDM had been replaced as he stated, then the fuel pump has also been replaced. Obviously, I won't know for sure unless I actually take a look.

    No. I wanted to make sure I was disconnecting the right connector, as there were a few that could be disconnected, so I found a picture online to verify.

    Other than taking the mechanic's word for it? While the decision to replace certain parts may be suspect, so far, he seems to have actually done the replacements. As with most things, though, seeing is believing.

    I do have one, from college, so my current knowledge is relatively limited. I've been familiarizing myself with it again, and I have people close who could give me a quick refresher, so I could certainly test and reply as needed.

    This is also what I don't really understand, how it happened. It shouldn't be applicable, since it was so long ago, but maybe it was the start of some rubbing; about 8 years ago, I had some stereo system work done. I had a box, subs, and amp fit in the trunk, head unit and surround speakers. Around the same time, I had a buddy help me put in a new intake. 4 years ago, I had the subs and amp box changed for better fit, as well as dynamat all over the trunk. The car had no problems running at all, until the last winter when it decided it wasn't going to start.

    If I have had any rodents, they've done an amazing job of cleaning up after themselves, as I haven't seen any evidence of them.

    Which wiring harness, or any/all I can find? The mechanic did say he was hunting an electrical problem, and stated he spent a lot of time looking for it, which is when he believed the issue to be with the CCRM.
  10. What are the results of the fuel pump disconnect test?

    Consider what is on the OUTSIDE of dynamat? Metal foil. What if a stray piece of metal foil is inside one of the wiring connections?

    Consider also that if someone installing the dynamat were cutting/triming it in place, I could see the possibility of cutting through the dynamat and into a wiring harness.

    When you post up the results of the fuel pump disconnect test, I will work up a series of Ohm tests from the CCRM to FPDM to Fuel pump. However, to save both of our time, it would be handy to know if the problem were more likely in the CCRM/FPDM harness or the FPDM/FP harness.

    FWIIW, if my memory serves me, the FPDM to FP harness runs directly on the floor of the trunk. As such, the dynamat would have been installed directly on top of the wiring harness.

    Is there any possibility that the sound system install tapped any power lines in the trunk?
  11. I tried (3) 3 second cranks, the fuse did not blow. Reconnected, fuse blew first crank.

    It's true. I followed the cables as far as I could, and they looked sound. I also checked any other cabling in the trunk I could, short of pulling out the subs/amp and all of the paneling/dynamat, and the cables looked fine.

    I don't think so. I can see the positive cable to the amp at the battery, and I can see the same type of cable connecting to the amp itself. I wasn't able to follow the negative very far, so I'm not sure if it ends up on the grounding somewhere, or if it taps into another cable. The install was done by Quality Auto Sound.
  12. Going to need a battery charger with an amp meter. This will be used to supply power for various tests. The amp meter will give an easy measurement of current draw. In addition, a battery charger is going to have some form of over current protection. Do not get a battery charger with reverse polarity protection.

    When Ohm readings are requested, check the “zero” of the meter before use. Shorting the two leads together must result in a resistance reading of zero. Make special note of the multipler scale used. For a ground measurement, 10K Ohms is very different from 10 Ohms.

    Make sure the Ohm meter’s battery is fresh.

    The next set of tests will be from connector C463 which is located center bumper by the gas tank. This is same one disconnected earlier for the fuel pump test. First tests will be done with the connector disconnected directed TOWARDS the fuel pump.

    Measure the resistance of C463 pins #7(RD/BK) and #6(BN/PK) towards the fuel pump. Record. Measure the resistance of RD/BK to the green ground screw in the trunk. Record. Repeat the ground measurement with the BN/PK wire. All of the ground measurements should be very high or open.

    Use the battery charger to inject +/- 12 volts directly to the fuel pump. The + should go to the RD/BK wire. Other to the BN/PK. Make note of how many amps are shown on the battery charger. You should also hear the fuel pump running. When doing this test, it may help to make a probe out of a stiff piece of wire or a paper clip folded in a crude hook. Clip the battery charger to the probe. May also help to wrap electrical tape around the battery charger clamps.

    The next set of tests will be from C463 as well but directed away from the fuel tank. Make sure the FPDM has been removed. Measure the resistance between RD/BK and BN/PK wires. Record. Should be very high/open. Next measure the resistance between the RD/BK wire and the green grounding screw in the trunk. Record. Should be very high/open. Repeat on the BN/PK wire and ground.

    When reporting the results, it is vital that the correct results are associated with the corresponding test. Confusion here has the very real possibility of causing a wild goose chase.

    What all of these tests are trying to do is narrow down which harness has the problem and what kind of fault the harness has (ground or short).

    Good luck.
  13. .5
    With the 10 Amp setting on the charger, there was 7 Amps showing. The fuel pump did kick on.
  14. Based upon the tests reported, I think you have a short between the fuel pump power supply RD/BK and the outside ground sheild.

    If you ask me to make an educated guess, the harness has been crushed between the gas tank and the car frame. Perhaps when the fuel pump was replaced.

    Next step is to drop the tank to get a better view of the harness.

    Hang in there. I have a feeling you are almost there.
  15. Would you be able to send me instructions for dropping the tank? I'm guessing there is more involved than just unbolting from underneath the car. I've read several other threads, and people are talking about a fuel line disconnect tool, as well as a gasket that I'll end up ripping. Is this valid to the task at hand?

    I did find a couple sets of instructions:


    Gas Tank Leaking?? How to Drop your Fuel Tank / Replace the Filler Neck Gasket
  16. You may need a set of disconnect tools for the high pressure lines. The vapor lines are removed by "hand" pressure. This is a good set. They can be rented.

    Lisle 37000 - Disconnect | O'Reilly Auto Parts

    The Stangnet instructions are spot on. The other instructions are for the pre 1999 MY's.

    Remember to drain the fuel tank. Get as empty as possible. The job will be much easier when man handling the tank much safer/easier. Disconnect the fuel filter and attach a short piece of vacuum line and direct into a suitable container. Use the battery charger to force the fuel pump to run until the tank is empty.

    Consider getting yourself a Chilton's manual so that you have a reference handy. Worth the every $$ paid.

    Advice. Do not cut corners removing the old filler neck grommet. Make sure it is completely removed. Push any piece remaining down into the tank. If this is not done, damage will result to the filler neck check value. This check valve can not be serviced requiring an entire new filler neck. I have personal experience on this. A extra $220 mistake.

    And yes you will need a new grommet. When re-installing, remember to lub with petro jelly.

    Any grommet pushed into the tank can be recovered when the tank is dropped. The tank should be cleaned anyway.

    The Mustang's tank is actually very easy to drop. It took me less than 2 hours from the time the 1st tool came out and having the tank all the way off working completely by myself.

    When you find the problem, request pictures be taken.
  17. I'll round up the tools, grommet and jelly, and my buddy is going to help me out on Saturday.

    I forgot to ask, what did applying the battery charger to the connector towards the fuel pump prove? I understand the resistance testing in each direction, but I'm not sure about the amp testing.
  18. It proved that the fuel pump would run. It also proved it was not drawing excessive current.

    Remember at the time, we were looking for information. There was some doubt that the pump was even changed. If for example, the voltage was applied and the pump didn't run, what would that tell us?

    What if the amp draw were 35+ amps? What would that tell us?

    The test also help to confirm that the correct plug was split and that the tests was performed using the correct pins. ;)

    FWIIW, this problem may not turn out to be a crushed wiring harness. It could be something as silly as an improperly installed ground strap at the fuel pump. This could also be a case of wire chaffing. Recommend taking pictures as you go.

    What were the symptoms of the original problem? What I am wondering is if this was this the problem all along or if a secondary problem resulting from the "repair".

    Time for a disclaimer. I studied the wiring diagrams before making a recommendation. The wiring diagram plainly shows that there is NO connection between the harness shield and either pump power line. Clearly the actual measurements shows there is a connection.

    However, I do not know beyond all doubt that this is THE problem. I have also reached out to another Stangnet member to ask his opinion regarding the diagnosis.

    Shout out to other Stangnet members for confirmation of the diagnosis. Is it normal to have a ground between either one of the fuel pump power supply lines? If present, would it cause the fuel pump fuse to blow?

    Perhaps if I have time, I can repeat the same measurements on my personal car to see if I get the expected opens (where you did not). I can not guarantee that I will have time to do it before the weekend.

    I know it would really stink to go through all of this and not get a successful repair. But I did want to be upfront and honest regarding the risks.

    Good luck.
    Jesse Perez likes this.
  19. The car sat for several months without running, so I assumed the fuel had turned on me, resulting in the car not starting. That was the extent of my investigation, as most people, including me, figured all we would need was to replace the fuel pump and filter, as well as drain the tank. The mechanic did say that the fuel pump was shot, once he pulled the tank and checked. If the current problem was present prior to the mechanic work, he and I were unaware.

    If it was caused by his trying to get my car running, I have no way of proving that. As things went on, I kind of figured that the mechanic's troubleshooting and repairs caused the current problem, since it was running fine prior to parking. With no evidence of rodents, or other influences that would cause a short, it seems to be human error.

    As far as the course of action is concerned, I won't be doing any actual work until Saturday. I'm sure the grommet can be returned unused, should you find some new information causing you to change your mind on what I should do. If the tank is pulled, and no cause can be found, I guess I just learned how to pull a fuel tank for the future. It beats sitting inside scratching myself. No worries on your own personal testing. I'd hate to put you out more than I already am, so if you can't get to it, I won't hold it against you.

    Thanks again.
  20. OK, I performed the same set of tests on my 2003 GT. When testing the resistance between the fuel pump supply and chassis ground, it is OPEN (infinity).

    I get 0.8 Ohm across the fuel pump itself. So that puts it in the same ball park as your 0.5 Ohm resistance.

    So assuming there were no errors in the measurements, IMO the confidence level should be HIGH. I really suspect that the end result will be a poor splice from the fuel pump replacement. Or perhaps wire chaffing right at the pump hat. It goes without saying that harness crushing or chaffing needs to be looked for as well.

    One thing that might be smart is to measure between the RD/BK and gas tank itself. Confirm that you get the previous ground fault reading. Now you can perform various "wiggle" tests when a suspicious area is found.

    Consider it may be possible that the act of removing the tank COULD make the fault go away. If so, this makes finding the problem more difficult as the test conditions have been altered. If so, the visual inspection method is still the best bet. The wiring harness on top of the gas tank is not really that long. With the tank off, access is not an issue. The only exception is to the fuel pump itself. Then it will be necessary to open the pump hat to inspect inside the tank.

    Good luck.