occasional gutlessness 99 GT

[Dbdbb]

Hello all, I have a problem with my 99 Mustang GT. I've had this car for a couple of years and it's done this since I've had it but it is now getting worse. the car has over 230K miles on it and it is no race car, it's just a nice convertible I use on nice days. Most of the time the car runs fine but it has been after being stopped at a light and going on green the car will have little to no power and I can't get up to highway speeds. I've been pulling over and shutting the key off and restarting and it would run fine again. There is no CEL on and no codes present. Up until a couple of weeks ago this was usually one time a day if at all, now it is happening several times a day and I was wondering if anyone else has encountered and fixed this problem? I plan to add a few engine to body grounds and then start digging deeper into checking individual sensors and connections but any help would be appreciated, thanks.

 

[wmburns]

It would help to know things such as:

• MAF flow
• EGR flow (DPFE)
• System voltage
• Fuel pressure
• long term fuel trims (LTFT) on bank 1 and bank 2.
• Input air temperature (IAT)
• Engine coolant temperature (ECT).
• ODB2 Mode6 misfire detail by cylinder.

Do you have an ODB2 scanner? An ODB2 scanner might make short work of this issue.

ForScan ODB2 scanner w ELM327 USB

ForScan ODB2 scanner w ELM327 USB

While working on your car have you ever wanted: to find an ODB2 operational PID value (say fuel pressure or MAF)? How about graph a PID value over time? Or compare multiple PID's over time? Access a bi-directional PCM control such as test a...

www.stangnet.com

I always recommend starting EVERY trouble shooting session with a review of the battery and charging system. This goes DOUBLE when the suspected problem is electrical in nature.

Howto perform charging system voltage drop test

ForScan ODB2 scanner w ELM327 USB

While working on your car have you ever wanted: to find an ODB2 operational PID value (say fuel pressure or MAF)? How about graph a PID value over time? Or compare multiple PID's over time? Access a bi-directional PCM control such as test a...

www.stangnet.com

In the absence of an ODB2 scanner, one of the first things I would do is to rule out excessive EGR flow. Start by disconnecting and plugging the vacuum line to the EGR valve. Does the problem get better? Note, this trick won't work if the EGR valve is leaking.

 

[Dbdbb]

I do have Forscan and the torque app, when I've ran a scan no codes have came up and I mentioned to a buddy that I might have to have him drive while I watch what is happening on the real time data, not that I know what the values should be but see if anything is looks wrong from when it's running good as to when its running bad. Thanks for the input.

 

[wmburns]

I can't tell you the number of cars that I have fixed by just "looking" at a few PID's. Sometimes it does help to "know" what normal is. Other times it's just a matter of picking a PID and monitoring it.

For example the ECT. What should the ECT read when the motor is stone cold? Did you say "close to outside air temperature"? Same for the IAT sensor. Fuel pressure should be about 40 PSI.

You have a very capable ODB2 scanner. This offers the possibility to data log several PID's during a drive cycle. Even better is to compare the PID's to each other over time (graph). Sometimes the problem will just "LEAP" off the page.

The other advantage of graphing several PID's at once is the ability to analyze the data offline.

 

[Dbdbb]

Well I took the car out for a drive today with my laptop running Forscan and while it was running good everything was looking to be normal, after a while it started running rough and I was able to notice the fuel pressure drops down when it is running bad. At the lowest pressure and running the worst with my foot to the floor it was reading 3.5 PSI. I would have to think this is the problem, most times the pressure has been hovering around 40 PSI, now I just have to figure out why the pressure drops so low at times.