gil57usa

The car is a 2004 mustang with a 3.8 V-6. This has been a very intermittant problem for a long time. Recently it got worse. I replaced the fuel filter and it started and ran for 2 weeks. Then it wouldn't start. The OBD showed a code that was Fuel pump driver module off line. I replaced the driver module with a new oem part. It ran fine until today. Again, cranks fine and no start. My next step will be to check the relay, then the fuel pump. I'm wondering though if the Mass air flow sensor might be the problem. Any thoughts?

petrock

Start with the basics. When you turn the key to the ON position (but not starting the car) do you hear the fuel pump turn on? If you cannot hear it, then the problem is either the fuel pump isn't getting power, or the fuel pump is bad. If you can hear it, try setting it to ON for a few seconds, then OFF a couple of times then try to start it. If it starts, then it is most likely a fuel pressure issue (bad/weak pump, pump not getting enough power, clogged/leaky/kinked fuel line or leaky fuel injector). To verify, rent a fuel pressure gauge from your local autoparts store and do a fuel pressure & leak down test. Just keep in mind that low pressure or it not holding pressure does not mean the pump is bad. Both can be easily caused by issues that are much cheaper & simpler to fix (e.g. bad fuel injector, leaky fuel line etc etc).

Also check the battery terminals for any corrosion/damage and clean/repair as needed. Also check it has proper voltage between 12.4 & 12.8. Anything lower then that and it needs to be charged. If the voltage checks out, check the voltage when you are cranking. If it drops below 10 volts, the battery may be bad. A definitive test is a load test which most autoparts stores will do for free (call ahead of course).

What ever you do, don't guess and start throwing parts at the problem. Alot of guys on forums like this will jump straight to replacing the fuel pump when more often then not the pump is not the problem. Properly diagnose the problem and you'll save yourself alot of time and especially alot of money.

Lwieb

Petrock,

Perhaps you might be able to help me with my issue.
My 2004 3.9 is doing something similar to what gil57usa described above. Last weekend after I changed the oil it didn't want to start. Simply turn over and is seemed to have no fuel or want to start (if you know what I mean). Simply turn and turn.... anyway after we pushed it out of the garage and I did a little searching online, the last two days it will start and run fine if I turn the ignition to on off on off on start. This occurred about 6 months ago in the spring and I had it towed to a local shop. Wouldn't you know it did not act up but started every day for two weeks (without the on off on off I recently discovered) Finally I went and picked it up and it's been fine ever since until this past weekend. Odd it seems but I hope to rule out the difficult task of fuel pump replacement. I recently had a poor ground at the battery negative cable and replaced it. Alternator has recently been replaced. I'm thinking I should check the ground wire from the battery to the engine block and cylinder head to firewall? What are you thinking? I'd like to correct it myself but will need a little time between tests as my work schedule is frantic at this time.
Any help appreciated.