No power after 40 mph

[1991CO]

1991 5.0 auto trans, seems to drive fine up to about 40 mph, then it has almost no power. Very unresponsive to pedal input (can floor it with almost no acceleration increase) until it finally downshifts. I'm wondering if it is shifting to 4th gear at 40 mph? RPMs are at about 1500 at 40 mph.

The only other odd thing going on with this car is that it doesn't warm up. The temp gauge stays at 130 even when driving. After about 15-20 min it may be a line or two above 130 but it never even gets to the 1/4 mark up the gauge. When I turn the car off, the needle climbs to somewhere in between 1/4 and 1/2 and settles there.

And for some reason the mechanical cooling fan is always running. It turns on when the car is started and seems to be running the whole time. I have put in a new ECT sensor but thats it so far.

 

[Legacy5.0]

I have an 88 AOD and yes, the 4th gear shift point is at 40. I would recommend leaving the car in D Rather than opting to overdrive when you're driving in town or in rather dense traffic, as dropping below 40, especially 35, will result in a rather substantial bog in rpms. The OD does jump on at 40 but doesn't really get the chance to shine until about 65mph.

 

[HISSIN50]

The mechanical fan will spin at all times. The ECT has no direct affect on its function, nor that of the gauge.

The gauge's reading is not uncommon. The stockers are not all that accurate and often read low. An aftermarket gauge or interpolating the ECT are better ways of assessing actual temps.

 

[JungleJoe]

My temp gauge did the exact same thing...I change the ECT and BAM, Problem fixed...

 

[HISSIN50]

Again, the gauge does not receive a signal from the ECT.

 

[jrichker]

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
Or for a nicer scanner see http://www.midwayautosupply.com/p-7208-equus-digital-ford-code-reader-3145.aspx– It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

 

[JungleJoe]

Again, the gauge does not receive a signal from the ECT.

I meant the sender for the gauge, NOT the ect....