lightscythe

Greetings all,

I have an issue with my '04 4.6L. When I go to start my car, I listen for the fuel pump to kick on and then start cranking. This morning, and a few times recently, I have not heard the fuel pump start, and coincidentally, the car does not start, even after multiple attempts. I then give the car some time to sit, and then try again about 10 minutes later with no luck. When this happened again recently (about 2 weeks ago), I replaced the battery and there were no more issues. Then, about 4 days ago, the issue started again. I asked a friend if he would help me jump it again just to try ruling out the battery being the issue. As soon as we connected the batteries and I turned the key to the ON position, I heard the fuel pump start, and the car immediately started when I cranked the engine.

The only modification that I have done my Mustang is a Cold Air Intake. All connections are stable that I can tell. The only factor that is similar from what I have noticed when this happens is the temperature of the weather outside. The car is not garaged and is exposed to the elements. This seems to only happen when it sits in sub-40 degree weather.

I have talked to a friend of mine and my supervisor about this situation. My supervisor thinks that the fuel pump's grease or ball bearings may be getting too cold and freezing, or making it difficult to activate or spin the motor. He also thinks that when the second battery is connected from another vehicle that it provides enough juice to cause the motor in the fuel pump to activate. My friend thinks it may be a sensor going out such as the crank sensor.

My question is this: has anyone else had this happen to them, or heard of this happening, or worked on a situation like this? If anyone has any kind of feed back or knowledge regarding this situation, it would be greatly appreciated.

Thank you!

Stevo86

Fuel pumps get fickle when they are on the way out the door. Sometimes they will work and sometimes they won't. If I were you I would just buy one and put it in. It is a super easy job if you do it when the gas tank is empty as opposed to when you just fill her up and then your pump dies for good. Because for whatever reason they always seem to die when the car has a full tank of gas.

petrock

I doubt this is the problem. It has to be really really frickin' cold for gas to freeze (like lower then -150* F). So unless there is a lot of water/condensation in your gas tank, there isn’t really anything that can freeze.


If by “juice” he means Amps, then yes that is a possibility. If the batteries amp output is low then you’ll get strange electrical behavior. When you jump a battery you are putting the two batteries in parallel, which adds the amp output from both batteries together and averages the voltage output from both batteries. E.g. one battery is 30A/12.8V. The other battery is 15A/12.0V. Putting them in parallel should produce 45A/12.4V.

So if jumping the battery makes the fuel pump start working then that would suggest your cars battery is weak. Weak batteries tend to start acting up when it gets cold (physics). I’d charge the battery up over night and see if the problem reproduces in the morning. If it does then I’d take the battery to a local auto parts store and have them load-test it for you. It might not have enough CCA (cold cranking amps). Also get your alternator tested while your at the auto parts store since weak batteries can put excessive stress on an alternator, lowering their life expectancy.


Doubtful. The crank sensor has nothing to do with the fuel pump circuit.


Yes, its easy if you know what your doing. :-) My first pump replacement was a PITA trying to balance the tank and lower it at the same time with just a floor jack, all while making sure the floor jack didn’t cave the tank in. However, fuel pumps aren’t cheap so I would exhaust all other options before throwing a new pump in the car. Better to diagnose the problem then throw parts at the problem. Its like throwing darts in the dark and hoping to hit a bullseye. Just sayin’...

lightscythe

Thank you both for your replies.

I do not want to have to replace the fuel pump, but if I have to, then it must be done. I definitely want to check all the potential points of failure before ruling that as the cause.

I don't think that the battery is weak since it is a brand new battery that I bought from Autozone less than a month ago. The CCA on the battery is 660, where the old battery had 540 and I believe came with the car. I can also tell a difference in the strength of starting the vehicle. The new battery sounds much stronger at cranking the engine.

After doing a bit of research, I've heard of a couple different things that it "could" be. The first being to test to see if the fuel pump is bad or not by using a multimeter to test for voltage by the connection to the pump by the fuel tank. If that is getting voltage, bad fuel pump. If not, then check the inertia switch. If no voltage is getting there, then it could be the fuel pump relay that is tied in with a module of some sort by underneath the passenger side fender.

Unfortunately for me, I do not have the means to be able to repair the car. I want to be able to figure out what the issue definitely is and have a repair center fix it without having to charge me for an issue they think it is, have it be incorrect, and I pay for something that wasn't the true source of the problem.

Either way it goes, it's cold outside now and I don't want to have to lay under the car in the snow to figure this out, but if I must, then I shall.

Stevo86

Here is why I say just throw the pump at it.
#1 if the battery can turn the starter motor it can turn the fuel pump.
#2 Yeah the fuel isn't frozen.
#3 There is no sense in checking the pump by jumping the battery because you already said sometimes it works so your problem is intermittent.
#4 The FPDM could be going bad but it is much less likely and usually has other symptoms.
#5 The inertia switch doesn't really go bad (It's just a ball and angled metal) so that is almost 100% out.
#6 Like I said fuel pumps get fickle right before they break and they are under $200.

Otherwise man I couldn't agree more about shotgunning parts. That is what gives mechanics a bad name. It's guys guessing at stuff that makes us all look bad. But sometimes when you have an off and on issue you just have to add it all up and take an educated guess. Also next time put a piece of plywood on the jack, it helps to keep it steady. Or do it when you are out of fuel then you just do it by hand.

AZ01GT

I'd say its a fuel pump to. might want to confirm power is leaving the FPDM though, you can easily do that with a $3 12v light tester.

As to the Mechanic thing, a lot of Mechanics are capable of properly diagnosing issues, the problem is customers not wanting to pay for their time to do that diagnosis so they do what their experience shows them has been the issue.

Stevo86

OP I never fully read your reply to petrock. Never go into a mechanic and tell him what to fix. Let him do his job and diagnose the issue himself. Don't take this the wrong way but if you're asking us what is wrong, you obviously don't know better than the guy who will be doing the repair.

lightscythe

I would never go into a mechanic and tell him how he/she should do his/her job. I wouldn't expect anyone to do that to me, why would I do that to them? I have respect for mechanics and thier knowledge of vehicles. I work in an IT position so I understand how much information is required to even be able to work on anything. And on top of that, I never claimed to know what exactly what the issue is either. Simply trying my own troubleshooting and explaining my findings is all I have done.

That being said, the more heads that can be wrapped around a situation to understand the problem in order to make sure that the correct job is being done the first time is my goal. That is not to say in any way that anyone is less knowledgeable than anyone else, for if that were true, I would be the less informed.

I would gladly spend an extra hour of time and money on correct and complete diagnostics from a mechanic to be sure that the correct problem is being fixed instead of fixing what one of the other issues could be just because it popped up as a potential problem and they stopped their diagnostics there. Unfortunately, in my area, there are loads of "backyard" garages that I personally don't feel safe even taking a walk around in broad daylight. I am only being careful with my one and only form of important transportation.

Besides, I enjoy troubleshooting and doing as much as can for my vehicle, which I'm sure is the reason why most mechanics become, well, mechanics?

Either way, this has digressed from its original topic. This is about asking the community what they think could be wrong with my Mustang, not giving tips and tricks on how one should handle themselves.

Back on topic, I added HEET and seafoam cleaner to the tank and I was able to jump the car yesterday and let it run. After about 5 minutes of running at idle, however, the car died and would not turn over again. It would still crank, but never stayed running. I then gave it about an hour, went back out and tried to start it again with the same results.

My friend still believes that the crank sensor could be the cause of all my issues and suggests that I try to bypass everything. He states he believes that because the sensor starts the ecu, and the ecu controls the fuel pump. I could understand how/why the crank sensor may keep the fuel pump going during the engine running, but what I question is does the sensor tell the fuel pump to intiate before the first crank of the engine to prime the fuel? If it does, then perhaps the crank sensor could be the cause of this issue?

WJL

If you are going to pay someone to fix it diagnosis is part of the cost, don't take Stevo the wrong way i think what he's saying is if you go in and say my battery is bad you automatically bought a battery with no argument "you told me the battery was bad i was just following direction" All you should really tell them is the car wont start, if the mechanic knows what hes doing he will figure it out on his own. BTW it is not the crank shaft position sensor the fuel pump is activated once the key is in the on position. From all that you explained it sounds like the fuel pump to me.

Good luck

Stevo86

^Yeah that, I didn't mean to offend. I

Your crank sensor just tells the engine where it is so that is can fire the correct spark plug or fuel injector at the right time. Also of course for RPM signal, it has nothing to do with fuel pump operation. Good money is still on the fuel pump