Bryan Bear

Hello all and thanks for reading what will probably be a long post (in the interest of including all details that may be relevant). Please forgive me if I have posted this in an inappropriate section; I’m new here. I am trying to rule out as many problems as I can, given my limited auto repair experience. Hopefully one of you will be able to give me an idea of what to try before I break down (pardon the pun) and have it towed to a mechanic. I’m sure I will leave out important details, so please feel free to chide me and ask more questions. . .

The car – 2000 Mustang 3.8L 5 speed, 110,000 miles. I am the original owner and until now I have had zero problems with the car. Other than routine maintenance nothing has been replaced. For the last 6 years or so, this has been our back up car, inasmuch as, my wife and I carpool and almost never need a second car. I try to remember to drive it on an errand or two every couple weeks.

The symptoms – A couple of months ago, the car had set for several weeks and refused to start. It had a strong crank, but not the slightest hint of it firing. Over the next week, I tried it a few times with the same result. I did a (very brief) internet search to decide where to start, and saw reference to the PATS not allowing the car to start. I tried it a few times (but don’t remember the order of operations) with the second key and with the key that has been rattling around in my pocket for the last 13 years. After a few tries it started with the new key ran rough for about 30 seconds then all was well. After that it started with either key. I had no further problems each time I used it. Then it set undriven for a few weeks, oops. . . crank, no start. I am not sure if the two events are the same as I believe I remember the theft light flashing when cranking the first time; now the theft light lights for three seconds and goes out (as it should).

What (I think) I know / what I have done – neither key works and as mentioned before the theft light will light, when the key is on, for three seconds then goes out. The car cranks strong but nothing happens, no throttle, half throttle and full throttle, MAF wire disconnected or not – same result. I have charged the battery completely and the terminals look good. The fuel pump fuse in the under the hood fuse box is good. When the ignition is on, I can hear a sound in the engine compartment near the passenger side firewall (unfortunately, I am not sure exactly where it is coming from). This sound lasts a few seconds and at first I thought it was the sound of the fuel pump. When under the car, I hear no sound near the fuel tank when the key is turned on. The inertia switch pops when I tap it and resets okay. Given the age of the car, I went ahead and replaced the fuel filter. I was able to easily blow through it, with the filter off I saw no fuel pumped out when the key was turned on.

Obviously I am not getting any fuel to the engine, what I don’t know (or want to assume) is if the pump has failed (there were never any signs of drivability issues leading up to the problem) or if it is not being told to pump. . . The tank is almost completely full so I am a little reluctant to just change the pump without verifying if it is getting signal. I haven’t checked for spark, frankly I’m not 100% how to do it with this distributorless ignition and don’t want to do anything stupid. I suspect there are several things that could have gone wrong in the chain that would prevent the fuel and ignition from activating. Is there an order of operations I can follow to rule out the simple/obvious things? For example can I grab a meter and check that the pump is getting signal (where, how), are there hidden relays I can check, are there any sensors that are likely to have failed that I can try to check myself. . .? Is there a known issue that is likely to have caused this?

Thanks in advance for your help.

Bryan Bear

I forgot to add that I also tried wrapping on the fuel tank to no avail. . .

Thanks

whudson1980

Hi Bryan,

You said you checked the fuel pump fuse under the hood? I thought your year had the fuel pump relay in the trunk area? I would check this first . . .

If you really want to test the fuel pump before installing a new one, you'll need a multimeter to test voltage. You should see some voltage running through for only about a second or two when you turn the car to the ON position.

Bryan Bear

Thanks for the reply. There is a 20 amp fuse in the fuse panel under the hood marked fuel pump (this checks out okay). There is a unit on the driver's side trunk wall near the inertia switch. I beleive this comp

Bryan Bear

Sorry, accidentally submitted that last post, darn phone. . .

I beleive this component houses a fuel pump relay, but I am unsure if it can be taken apart without ruining it. I have also read things online that hint that there may be another relay somewhere else. I would love to put a meter on and test for voltage (at key on) to the pump. Is there a convenient place to access the leads without dropping the tank? Perhaps out of this component in the trunk (which wires?)? Does anyone know what voltage I should see, or as long as there is a reading, I know the pump is bad?

petrock

I’m pretty sure that your year car doesn’t have a ‘smart’ key, in that it does not have a chip in it that is coded to the vehicle. So your keys are just keys. If it turns the ignition it should start the car.

No, it is not obvious. You haven’t really tested the fuel system. Your guessing. Go to your local auto parts store and rent a fuel pressure gauge (you get your $ back when you bring the tool back) and run a fuel pressure test while cranking. If you have no fuel pressure then you can say that the engine isn’t getting fuel. The pump could be working but not providing enough pressure, or the pump could be just fine but there is a kink in a fuel line somewhere or some other problem.

The basics are: Check fuses & relays. Check spark. Check Fuel. Check Air. Doing those basic checks will narrow down the problem. Once you know what is and what is not working you can narrow down where to test next.

• Pick up a fuse tester from your local auto parts store and test the fuses (or do a continuity test on the metal tabs on each fuse). Replace any fuse that are blown, even those not related to the fuel system. To definitively test a relay requires some electrical knowledge that I don’t know you have. But a quick/dirty way is to swap a known good relay (like the starter relay in this case) with the suspect one and see if the problem follows the relay. Another thing is you should hear an audible click when the relay is energized.
• Test the fuel pump with the fuel pressure gauge I described above and check the inertia safety switch. If the pump and switch checks out, the additional fuel check is to make sure the fuel injectors are being commanded on. You can rent a Noid light kit from your local auto parts store. If the light flashes, then that fuel injector was being commanded on. This tests the fuel injector circuit, but not the fuel injector itself. The injector could be bad, but unlikely in your scenario because it would be highly unlikely they would all fail all at once.
• Test for spark with a spark plug tester. Plug one end of the tester into the spark plug wire boot and clip the other end to the engine block and try to crank the motor. You should see a spark. Be careful because the spark is 100+ volts. So don’t touch it and don’t allow anything else to come into contact with it. 100+ volts won’t kill you, but it will sting/hurt like a b!tch. Read the instructions on the tool to determine where to set the pin screw. The adjustable screw allows you to not only test that you have spark but that you have enough spark to ignite the fuel in the combustion chamber. An spark tester that uses a light to indicate when there is spar only really tells you that you have spark, not that you have enough spark.
• Check for clogs in the air intake (including dirty air filter) and that the throttle plate is moving when you press the gas pedal.

Without those basic tests you’ll just be guessing what is wrong instead of diagnosing it.


Mice. Yes, mice. They love to climb into engine bays and chew on wires & hoses causing all kinds of strange problems. Especially when the vehicle is sitting for a long period of time.


All electrical circuits have a fuse somewhere in it to avoid overloading/burning out the circuit. The fuel pump circuit has a fuse and a relay. The switch in the trunk your thinking of is the inertia safety switch that is usually triggered by a sudden impact/stop. It is just an on/off switch, not a relay. If the red button on it isn’t out then it has not popped. If it has, just press the red button back in and your good to go.

elsmootho

Got the exact same issue as Bryan Bear, same car 2000 3.8 V6 Mustang, i actually did measure zero pressure at the schrader valve on the fuel rail. 20amp fuse good, no fuel pump noise near the tank, but like Bryan i do hear a funny noise under the hood for about 2seconds when i switch on the ignition. Checked the IFS Inertia switch, its good. Not sure if the PATS is the issue, car sat for 6months in storage, now wont start. Like Bryan, is there an easy way to check signal going to fuel pump? What about the Fuel pressure switch/regulator on the fuel rail, could that thing be stuck(maybe dry)? Is there a way to check it? Thanks & Best Regards..

rbowmar

Check your trouble codes. Your local parts store should have one you can use. This can help locate problems.

While it is very unlikely, I found my ECU was dead, which explained why lots of things did not function. The test was that the tester could not find the computer. I can expand on this if the group would like.

musicbox

Please do, because I'm enjoying reading this thread.

PNYXPRESS

You might need to drop the gas tank and clean the pump and fuel lines. after sitting for 6motnh the fuel may have turned to laquer and gummed everything up causing fuel to not being able to be pumped. Or the ethanol may have deteriorated the rubber in the pump and it kicks on but isnt able to prime itself and pump fuel