Tough to start when hot.

If you shut off the injectors, does it fire right up?

The ECT is a definite possiblity. Here arethe ECT tables so you can check yours...

Code 21 – ECT sensor out of range. Broken or damaged wiring, bad ECT sensor.
Note that that if the outside air temp is below 50 degrees F that the test for the
ECT can be in error.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are
different animals. The ECT sensor is normally located it the RH front of the engine in
the water feed tubes for the heater.

The ACT & ECT have the same thermistor, so the table values are the same

ACT & ECT test data:

Use Pin 46 on the computer for ground for both ECT & ACT to get most accurate
readings.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is
a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower
intake manifold, the voltage readings will be lower because of the heat transfer.

Voltages may be measured across the ECT/ACT by probing the connector from
the rear. A pair of safety pins may be helpful in doing this. Use care in doing it
so that you don't damage the wiring or connector.

Here's the table :

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61

Note that all resistance tests must be done with power off. Measuring resistance
with a circuit powered on will give false readings and possibly damage the meter.

Ohms measures at the computer with the computer disconnected, or at the sensor
with the sensor disconnected.
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

Diagram courtesy of Tmoss & Stang&2birds



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

daddystang said:

I'm not sure what you mean to shut off the injectors.

Click to expand...

If you achieve ~3.71 TPS volts (what the computer considers to be WOT) during cranking, the injectors shut off. This helps clear a flood condition.

On cars with larger than stock injectors and no tune (or a tune which didnt address cranking fuel), the plugs can foul while trying to start the car. This is more common with 30's than 24's but it can happen with the latter.

If it cranks for a bit and won't catch, I'd simply hold the gas pedal down to the floor while cranking (obviously only during cranking. I had to say it for future searchers) and leave it for a couple seconds. The car should start by then, and if it doesnt, I stop trying to crank.

When you have the issue, do you cycle the key off and then back on, or do you just let the key relax from 'start' to 'run'? This is actually something I might note because if turning it completely off and back on makes it start, that even further suggests a sensory input issue (and not really a flooding or cranking fuel issue).

Good luck.

had the same problem durring warm and hot starts. had to hold the gas pedal down just for the car to start. also had a really bad fuel smell when the car finally started. replaced the ect and problem solved

Save some $$$ and get out your DVM. Check the resistance or voltage against the table I posted.
If it is too far out of range (more than 15%), replace the ECT. If it is in spec range, you have other
problems. The PIP sensor and TFI module are also hot start culprits.

This problem sounds like a dirty Mass Air Sensor. The ECT being the culprit is way down on my list but a possibility. I tune my own cars with a Tweecer and have owned over 31 Fox Mustangs. This is a common problem area with K&N filters oiling up the MAF (mass air meter).

Possible solution. Clean your MAF after it has cooled with NON-Chlorinated brake parts cleaner. Specifically NON-Chlorinated. Spray it right on the wires and let it air dry. Do not touch them. The cleaner should evaporate pretty quick.

ECT: When they fail it puts the car in RICH mode. The car would always burn your eyes at idle usually. The voltage for a hot engine (overheated) is the same for a failure. OR simply UNHOOK it and you should get the same RICH results and hard starting after it is warm.

ACT: Same as ECT in failure mode.

Remember your O2's aren't online until the car is warm and in closed loop. So not a cause for hard starts, no need to look there.

If the TFI unit was failing it would NORMALLY NOT start right up until it has substantially cooled. I've never seen one fail and start right up after the second try until a cooling period.

I hope this helps, Patrick.

Patrick, the point is not that the ECT or ACT are completely toast (and running off a FMEM-like default setting).

Unless he noted an actual ECT code that I missed, the point was that if the sensors are in absolute spec (no codes) but out of calibration (hence JRichker's 15% tolerance), it can cause issues. Imagine that his ECT is telling the computer that the coolant is 50*F when it's actually 200*F. It's not out of absolute spec but certainly not calibrated.