cold starting issues!

Helmsdini

New Member
Nov 15, 2001
39
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Connersville, IN
I have been running into some pretty big problems with my stang here lately.

The worst issue so far is a hard cold start. When my car sits and cools down and I go to start it it wants to idle down to 500 RPM and eventually die. It acts this way for at least 3 minutes until it gets warmed up, then it will start up without a hitch and idle right down to 650 RPM. I can also repeatably start it once it is warm, its only on cold starts that it acts like a fool.

basicly i have tried replacing my Pro M meter with the stock one, switched to a different throttle body, replaced the EGR and both O2's because that turned up on a code scan, messed with the TPS to no end, turned the idle up and down, replaced every gasket in my intake tract from the lower on up, cleaned and greased my 10 pin harnesses, replaced the IAB, and turned my mass air sample tube every way possible and still no beans. I even did a leakdown and the engine passed with flying colors on all cylinders.

This problem just popped up about 2 weeks ago and has gotten progressively worse since then. When i first installed this cam it would start right up no problem! the car throws no codes or anything like that and it seems that if i try to drive it off when its in this state it will sometimes backfire and pop a little. it also seems that the throttle has no real bearing on it, if i give it gas it revs right up but sometimes will hesitate a little if i hold it at a set RPM below 3000 when it is having its fit. I have pulled the plugs and it fires so well that you cant even tell the plugs are getting used. All headers are hot so it is firing on all cylinders. the cam is a lunati grind.. .500/.510 lift. I also have a 75mm bullet calibrated for my cai and 19# injectors.

I just cant figure it out. Its either some sort of electronic issue, a fuel problem, or a spark problem. I have done everything i can think of to make sure its not an air problem. The fuel pressure stays set at a constant pressure durring all of this, it doesnt fluctuate or drop or anything like that. After 3 minutes or so the car smooths out and wil hold an idle just fine and runs great. as long as the temp in the block is still warm it will start right up every time.

I need some suggestions or im either going to swap back to the stock cam or rip the fuel injection clear off the car and go carb if i dont sell it first.. its driving me nuts.
 
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first place i might start is the ECT (and ACT). one or both might be out of calibration but reading within spec (tossing no code). i.e. the ECT is telling the puter the motor is warm, when it is really cold. so the trim is lean, for a warm motor.
that kind of thing. JR has been kind enough to post values of both sensors at various temps - if he does not post them and you are interested, i have a link saved somewhere.

my two cents. good luck.
 
hllon4whls said:
Does the 5.0 have an IAC? That is exactly what happened to my taurus and it was the Idle air Control valve.
yeah, Hllon, good point. i knew i was forgetting something (still feels like there is another likely culprit - im too tired).

on the IAC line: does the motor compensate when the a/c is turned on, or does it bog? if bogging, id hit that first and foremost. nice catch, Hllon. :)
 
IAC and IAB are the same thing. I have messed with the IAC to no end and switched it out three times.. no luck with that.

I am going to look into the ECT and ACT sensors now.. i need to find those values so i can make sure they are correct. all signs are pointing to one of those on the fritz.
 
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 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. 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

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