AdderMk2

but pulling the air filter apart and spraying it with cleaner, hoping for a wish in a bottle... is the right answer?

What the OP needs to do is, go buy a fuel pressure gauge that can be installed on the rail. and pick up a spark tester, and leave it in his glovebox...

These are among the few things that 5.0 mustang owners should always have!

MustangBradley

Your assumption that the return line returns all of the fuel is in error. While some fuel is returned, some is used to power the car, so there is a net loss of fuel from the tank. This loss must be accompanied by an introduction of air into the tank, or a vacuum will result. Also, whatever air is mixed into the gas during the return is not air from outside of the tank, therefore the amount of air remains constant, thus that has no effect on pressure. The amount of heat introduced from the pump is not significant compared to the amount of heat the fuel can absorb and maintain its temperature. The largest amount of heat added would be by the fuel rail. Still, in the large picture, this is not enough to overcome the loss of fuel from driving, therefore a vacuum is created.

Have you ever stopped for gas and removed the cap and heard a rush of air? I am pretty sure that is air rushing into the tank, not out. Of course, as with any other post i make, I could be completely off base.

I find it curious that his symptoms were most pronounced right after a fill up.

You may be right about the MAF being bad, but until he pulls codes, it is all a guessing game.

wydopnthrtl

MB, Your assumptions about my understandings are the "error".

Your description and logic of what you imagine I think... is that of a closed system. It's not and I never said it was.
The airating of **fuel** causes evaporation as it spues back into the tank.
Air comes in by the user removable "gas cap". And fuel vapors mixed with that air go out the evap system.
Here is a mental example:
A tank 1/2 filled but sitting still and with a good gas cap will evaporate at a certian rate (slowly out the evap). This is why fuel goes bad over long periods of time. Take that same tank and circulate the fluid such that some degree of the fluid is airated before it comes back to the tank and it'll evaporate much quicker. And because its now in a agitated **and heated** gaseous form.. pressure quickly builds as the bubbles reach the air at the top of the tank.
That pressure significantly out paces the fluids decreasing volume used by the engine.
So much in fact that most cars add engine vacuum to the evap system to help keep the pressure down. Also worth noting.. CAN3 (OBD2) cars measure tank pressure and adjust things accordingly to keep the evap system operating at its best so that the tree huggers don't cry.

There are a few times that a low pressure (suction) might form in a fuel tank. But its very seldom and is usually associated with filling a cold tank with warm fluid. Also a faulty gas cap that doesn't allow enough air/atmosphere pressure into the tank.

The fuel being consumed has to be replaced with something or else the tank would crush from the Delta P of decreasing volume vs 1 bar. It has to be an open system just to keep the tank in its original shape. In a normal pass car there is a combination of the gaseous fumes and atmosphere doing the task. If you ever hear a whooshing sound when taking off a gas cap.. its because the gas cap is bad and not allowing air to enter the tank. (there is a 1 way valve on the evap canist.)

The rate at which a pass car engine uses fuel is not enough to cause a low pressure in the fuel system of a gerotor type in-tank fuel pump. That pump will *easily* suck the tank into itself if it were fully sealed.

The OP said his car was hicupping. When you starve a engine for fuel that is not what it does. Fuel starvation would cause the ECU to add fuel (02s have a hard threshold within the tune). And when it got more than 25% out of the commanded range it would throw a CEL. (Even OBD1 does this) The percentage might not be exactly 25%. The last two fords I tuned were and thats where that number comes from.

Combine his other symptoms with what I've described above.. and there is no possible way its a lack of fuel pressure. The hard starting clue if it were the only one might be.. but not combined with the others. Especially the off/on feeling and slipping tranny. Both of which are hallmark MAF problems.



Adder... "but pulling the air filter apart and spraying it with cleaner, hoping for a wish in a bottle... is the right answer?
"
The solution I gave can easily be done in the dark and get him home. Please re-read my post.


Regards,
Rich
.

MustangBradley

I still don't see how adding fuel can cause his MAF to crap out. Once is a coincidence. Twice is fishy. Three times, go play Powerball. In his post, he mentioned FOUR times he fills it up and shortly afterward, the symptoms return. This seems to cross the barrier of cause and effect.

Since he ran it out of gas, as someone pointed out in this thread, it may have been you, his filter is probably trashed. I believe he has a multitude of problems, one of which may well be the MAF. He still has not reported back on codes. To quote you, "When you starve a engine for fuel that is not what it does. Fuel starvation would cause the ECU to add fuel (02s have a hard threshold within the tune)". I'd argue if the fuel rail is empty, due to the starvation (from a compromised filter or collapsing tank ), having the ECU add fuel is impossible. I have a friend who ran his fuel line too close to his exhaust and in traffic, his car hiccups as he tries to accelerate from a stop due to vapor lock, which is a form of fuel starvation.

If his charcoal canister is plugged up, he could very well be running a "closed" system. As I said, he seems to have many issues with his car.

I do learn a lot on this forum, so I expect this thread to add to my meager knowledge. Thanks for your contribution.