04 Gt Falls Flat On Its Face After About 20 Minutes Of Driving

[BlakeusMaximus]

So, I’m a fox guy, my son owns a 04 GT. I drove the car this evening and he has been telling me about this and I finally had time to drive it. It ran perfect and then It started acting up after about 20 minutes. Falls flat on its face! I’ve read through similar posts and no one really said what fixed their problem. I know about the voltage drop test, and checking for vacuum leaks, alternator is new. Battery is newer. Cops are new, spark plugs look ok, installed them 20k or so ago. Seems like this can be an issue with these cars. Just wondering if anyone solved this issue and can tell me what they did to fix it. Appreciate any responses.

 

[wmburns]

Likely you don't find posts about what the fix is because there are soooooooooo many causes.

Do you have an ODB2 reader capable of monitoring operational data? With data logging? An ODB2 scanner may prove to be vital to solving a problem such as this.

Very near the top of the list has to be to rule out misfires. The easiest place to get this is in the ODB2 type 6 data.

I'm assuming the car runs great for 19 minutes. If looking for an educated guess I would rule out excessive EGR flow. One method is to pull and plug the vacuum line to the EGR valve. If the issue improves this means you are on the right track.

Note regarding EGR problems. In my experience the DPFE sensor is at fault about as often as the EGR value is.

Other "Possible" causes may include:

• weak fuel pump.
• excessive EGR flow
• Incorrect FRPS.
• incorrect ECT or CHT sensor value
• incorrect MAF sensor value
• incorrect O2 senor values
• PCM pulling timing due to "other" sensor problem.
• Base motor problem. Need compression and leak down test.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

 

[BlakeusMaximus]

Thanks for the reponse wmburns. This is a annoying issue. I do have a OBD2 reader, but not one that can data log. There isn't a check engine light on either. I was just hoping someone may chime in with what may have fixed their similar issues. This is an extra car and we are considering selling. Like it stated before, it feels like you slammed on the brakes, then released them a few seconds later. Im going to start with the obvious the go from there.

 

[wmburns]

Are you hopping to solve your problem as a "pattern failure"? IE someone else had the same symptom and did "x" to fix it. I will try it.

FWIIW, almost every ODB2 scanner can access ODB2 mode 6 data. On some cheaper scanners the data maybe presented in "raw" form but it's there.

Regarding that it feels like someone put on the brakes, what have you done to rule out a traction control problem? IE the PCM "thinks" there's a wheel slip and actually does apply the brakes.

Are there any other "issues" with this car or work done that may provide clues?

The data logging capable ODB2 ELM327 USB dongle is only $35. Yes I know that learning the use an ODB2 scanner can have a steep learning curve. But trust me. Once you actually use it to solve a problem you will wonder what took so long. But if only used to give direction where not to look for the problem IMO makes it worth the $35.

 

[BlakeusMaximus]

Yeah, I was hopping for a "Oh, yeah its this, that happened to me too!" kind of thing. 5.0s are a lot more simple and easier to me to diag. I don't think its a traction control problem, wouldn't the traction light come on if there was? I meant that is suddenly loses all power, (like you slammed on the brakes, but it feels more mechanical) for a second then goes back to normal. I have a cheap OBd2 reader, but I think I can borrow one here at the shop from one of the body techs that can log data.

 

[BlakeusMaximus]

Just an update. I ran a datastream test after I checked for dtcs. No dtcs came up. I failed to mention that when my car ran like , that I had about 1/8 tank. Haven’t driven it since Tuesday or Wednesday or whenever it was. Hopped in the car today, (with the same amount of gas in it), and it did the same thing. I went and put 10 bucks of gas in it and it ran fine, and I drove it like hell for half an hour trying to duplicate the problem. It didn’t. When I ran the datastream test it said my fuel pump was at 37%. Does that mean it’s on its way out? New fuel pump time? Here’s a pic of the scanner screen. What do you guys think?

 

[wmburns]

A 1999-2004 Mustang uses a return-LESS fuel system. The PCM varies the duty cycle to the fuel pump to vary the fuel pump output to meet demand. It would not be normal for the fuel pump to run flat out except at WOT.

The method you are using to determine the health of the fuel pump is not going to tell IF the fuel pump is bad. The only exception is IF the fuel pump duty cycle is chronically high virtually all the time.

The better method is to monitor the actual fuel pressure. IF the fuel pump is toast it will show up as lower than normal fuel pressure.

 

[BlakeusMaximus]

A 1999-2004 Mustang uses a return-LESS fuel system. The PCM varies the duty cycle to the fuel pump to vary the fuel pump output to meet demand. It would not be normal for the fuel pump to run flat out except at WOT.

The method you are using to determine the health of the fuel pump is not going to tell IF the fuel pump is bad. The only exception is IF the fuel pump duty cycle is chronically high virtually all the time.

The better method is to monitor the actual fuel pressure. IF the fuel pump is toast it will show up as lower than normal fuel pressure.

Should I check the fuel pressure at the rails And monitor the pump while I have someone drive it at wot? The scanner has the ability to check fuel rail pressure.

 

[BlakeusMaximus]

So here’s a couple videos of the fuel pressure and pump, at WOT. The fuel pump percentage at its highest got to 50%. The fuel rail pressure was reading around 263.09kpa, at WOT, 2nd 3rd gear. It’s kinda hard to see, but let me know what you think of the numbers, or if they mean anything to you. Nevermind, the videos won’t load, here’s screen shots of the video.

 

[BlakeusMaximus]

 

[BlakeusMaximus]

Sorry I had issues posting these pics for some freakin reason.

 

[wmburns]

Should I check the fuel pressure at the rails And monitor the pump while I have someone drive it at wot? The scanner has the ability to check fuel rail pressure.

When is the problem happening? Does it only happen at WOT? Or is it happen during normal driving?

Does the problem happen suddenly like someone flipped a switch? Does it get better just as quickly? Or is the onset slightly slower?

IMO you are trying to force the fix to fit a pre-conceived idea. Don't over think this. Remember the KISS theory. Go where the evidence takes you for the best most accurate, no "parts changer" result.

Simply monitor the fuel pressure while driving normally. When the motor power drops off simply note the fuel pressure (help up by noting in PSI). IF the problem is being caused by a lack of fuel pressure, this will be apparent in the scan data.

If the fuel pressure remains constant during the problem THEN you will know that a weak fuel pump is not the cause of the symptom.

Next repeat the exercise for the MAF. Look for a CHANGE in the reported MAF numbers when the problem happens.

Followed by:

• EGR flow
• Front O2 sensors (bank 1 & 2). Don't look at the rears.
• PCM voltage
• Misfire
• Long term fuel trims (LTFT)
• Timing advance

I'm sure that you can see this where a data logging ODB2 scanner makes things easier.

There is SOMETHING changing right at the moment the problem occurs. More than half of this battle is to find out what that something is.

Note if looking for a WAG educated guess focus on the MAF sensor.

 

[mogs01gt]

Honestly it sounds like a fuel issue but if the pressure isnt dropping at the rail, thats an odd issue you are having.

 

[BlakeusMaximus]

I haven't been able to duplicate the problem. They only time it happened to me was when it had 1/8 of a tank in it. We drove it for 30 miles yesterday with no issues. Maybe, I was just low on gas? Maybe my fuel gauge isn't accurate? But, I don't think that's the issue. We'll continue to monitor it while driving.

 

[BlakeusMaximus]

Honestly it sounds like a fuel issue but if the pressure isnt dropping at the rail, thats an odd issue you are having.

I haven't seen the fuel pressure drop. It hasn't given me trouble for two days. We were going to sell it, but I have to take care of this issue first. It seems like it only happens when its low on gas, below 1/4 tank. I'm going to drive it a few more times this week and see if I can duplicate the problem. I cleaned the MAF, I had some Mass airflow sensor cleaner on my shelf. We'll see.

 

[BlakeusMaximus]

When is the problem happening? Does it only happen at WOT? Or is it happen during normal driving?

Does the problem happen suddenly like someone flipped a switch? Does it get better just as quickly? Or is the onset slightly slower?

IMO you are trying to force the fix to fit a pre-conceived idea. Don't over think this. Remember the KISS theory. Go where the evidence takes you for the best most accurate, no "parts changer" result.

Simply monitor the fuel pressure while driving normally. When the motor power drops off simply note the fuel pressure (help up by noting in PSI). IF the problem is being caused by a lack of fuel pressure, this will be apparent in the scan data.

If the fuel pressure remains constant during the problem THEN you will know that a weak fuel pump is not the cause of the symptom.

Next repeat the exercise for the MAF. Look for a CHANGE in the reported MAF numbers when the problem happens.

Followed by:

• EGR flow
• Front O2 sensors (bank 1 & 2). Don't look at the rears.
• PCM voltage
• Misfire
• Long term fuel trims (LTFT)
• Timing advance

I'm sure that you can see this where a data logging ODB2 scanner makes things easier.

There is SOMETHING changing right at the moment the problem occurs. More than half of this battle is to find out what that something is.

Note if looking for a WAG educated guess focus on the MAF sensor.

Yeah its like a switch is being flipped on and off. HAppens out of the blue. No warning.

 

[Rusty67]

Like wmburns said, a small amount of data logging will go a long way. If you are having the fuel pump cut out when the tank is low on gas that could be the fuel pump on its way out but it is best to log the info and see what is happening when the issue actually occurs.

 

[BlakeusMaximus]

Like wmburns said, a small amount of data logging will go a long way. If you are having the fuel pump cut out when the tank is low on gas that could be the fuel pump on its way out but it is best to log the info and see what is happening when the issue actually occurs.

Yeah, I’m borrowing the scanner when I can. It’s belongs to one of the techs at work, so it’s kind of hard to borrow. I had one just like it and sold it when I needed the cash to rebuild the trans on my notch i sold last year. I totally get what you guys are saying. It’s also hard to monitor that scanner by myself, especially when the cars not acting up. It takes two to play that game.

 

[wmburns]

Regarding the possibility that the fuel gauge isn't accurate. Think about it. IF the problem is it's low on gas, THEN when the problem happens it's almost out of gas. In such a case it wouldn't improve. It would just run out of gas.

As an option, perhaps water in the gas tank. But the problem with this theory is how does it ever improve without the tank being filled up? It seems that actually quitting and never being able to restart should be the expected result.

If you still feel it's fuel related, one way to deal with water in the gas tank is to disconnect the fuel filter and force the fuel pump to run until the gas tank is totally empty. Drain into a clean container so that the contents can be inspected. It is possible to force the fuel pump to run by powering the RD/BK and BN/PK wires to the fuel pump. There is a round connector near the center of the rear bumper visible from below.

Another method is to use an ODB2 scanner with bi-directional controls.

Or they make kits to test for water in gas.

FWIIW, I have worked on MAF problems where the motor power drops to nothing like someone flipped a switch. And just as suddenly it comes back. Data logging showed the MAF return signal dropping out exactly the same time.

 

[BlakeusMaximus]

Thanks for all your insight, Im not certain its fuel related. The only reason its a possibility to me is it did happen when it was close to empty, then I put some gas in it to trouble shoot and hasn't happened since.