Tough to start when hot.

[daddystang]

I've been searching the threads about this to solve my issue, but thought I'd throw it out there again. Sorry for the repetition.
The car starts up quick first try when it's all cooled down (first start of the day), but if I shut it off after it's up to temperature 180* it will crank for 10-15 seconds before it starts. If I crank it and it doesn't start after just a couple seconds, I can stop and then turn the key again, and it starts up immediately.

It's just a pain more so than anything. In searching other threads I'm wondering if it's my ECT which I replaced with the new motor a year ago along with most of the other sensors on the motor, TFI too. One thing I've learned over the years is just because it's new doesn't mean it's good. Anyone have any thoughts on this. I'm leaning toward a new ECT since it is only when warm.

Other than this, it runs real good, I'm very happy with it.

Thanks in advance for any input and thoughts.

Joe

 

[HISSIN50]

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

 

[jrichker]

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]

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

I'll check the voltage readings later tonight or tomorrow.

Thanks guys.....

 

[HISSIN50]

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

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.

 

[daddystang]

Gotcha Hissin.... I have been trying to build some data on when it doesn't start right up as far as should I hold the gas pedal to the floor as if it's flooding out, or do I need to pump the gas as if maybe it's not getting enough fuel. It's a bit tough to do that though, because when it does this, I stop cranking after a few seconds, then try again at which point it starts right up.

It has been dyno tuned, and I've been trying to build data on each of the tunes that I have to choose from with the SCT chip. I talked to the guy that tuned it who said the more data I can form about each program and situation will help him better tune it next time. So, I'm trying to do my homework before I go back to avoid a lot of time/money on the dyno.

Thanks for your knowledge. I've got to check the voltage on the ECT also to rule that out.

Thanks again....

 

[HISSIN50]

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.

 

[Haus]

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

 

[daddystang]

I dont turn the key completley off, just relax it to the run position. When i do hold the pedal to the floor, it starts right up, but it also starts right up when I just relax the key to run and then turn it to start right again. I haven't checked the voltage on the ect yet, I have to run to Auto Zone tomorrow so i may just grab one while im there.

Now that the weather is warm here in Maryland, im seeing the problem on warm starts more frequently now. It's just been tough to narrow down if it seems like a fuel problem (Or flooding problem) due to the fact if i just let off the key, and then crank it again it 99% of the time will start right up. Mabye ECT????

Thanks again guys for the input i really appreciate it.
Joe

 

[jrichker]

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.

 

[daddystang]

Your absolutley right Jrichker i might as well put my Fluke to some good use. The TFI is a year old so im hoping it's not that. This is probably a silly question, but could you please tell me exactly what the PIP sensor is, and where its located on the distriubutor and how i would go about replacing it. Also, is the PIP something I can get at Auto Zone?
Thanks,
Joe

 

[patrickmx2]

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.

 

[HISSIN50]

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.

 

[daddystang]

ECT Voltage was a bit off, so I replaced the sensor, and cleaned out the MAF. Started up really good, when it stops raining will get it up to temp. and see how it does. I'll update later.

Joe