Where would you start? Runs rough when cold/great when warm - no codes KOEO

5spd GT

"the 5.0 owns all"
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Aug 7, 2002
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Just like the title says, my car runs rough (stutters when under load, pops, etc.), but when it warms up all that disappears. I assume this is related as well, but it will not idle without feathering the gas for a minute or so. After that, it idles like a champ.

Timing is 16-17* at idle (spout out). I used a Equus 3145 OBDI code reader and found no codes with KOEO and the Check Engine Light is not on.

Where would you start?

306 - AFR 185 Comp's, FTI Billet Cam, FTI Ported SMII
 
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No code 11 (two flashes when the computer dumps the codes)? The 11 code is computer passed its internal self test.
If you don't get an 11, you have computer or wiring problems.
Please check and repost.
 
I have had it running for several weeks now, but got the timing much better recently. The car acts like it is timed incorrectly (popping, giving it gas with no response, etc.) when it is cold, but not when warm.

75mm Pro-M Bullet (7 years old; never been cleaned), 30 lb injectors, 65mm TB, 1 5/8" Longtubes into a 2.5" ORH, with dual 40 series flows. There is no tune on it, stock AOD chip (5spd swap). Basically, it sat for two years and I just changed the H/C/I on it.

From doing a search, I was kind of thinking it could be the IAC valve, but not sure how that relates to when I give it throttle with no response. When it warms up, the car runs great. It spins the drag radials over in 2nd gear a bit like it should.

Could the timing be advance to far possibly? Would that cause these symptoms?

On a side note: Is there anyway to know where the rev limiter is on this car? I technically should be revving it past 6300 RPM (6600-6700), but I'm nervous to test it with the stock gauges.

Jrichker - Yeah, sorry, I did get the 11 code, but nothing outside of that. I do have an old Motorcraft 02 sensor and a new parts store brand 02 sensor, if that matters.

The coolant temp sensor is a brand new Motorcraft one.
 
The factory limter cuts fuel off at 6250rpm unless you do something through a chip to extend it. Id check the 02 and I assume you have nice new plugs?

Stock PCV with closed cap on valve cover?
 
The factory limter cuts fuel off at 6250rpm unless you do something through a chip to extend it. Id check the 02 and I assume you have nice new plugs?

Stock PCV with closed cap on valve cover?

New plugs, wires, cap, and rotor.

Hmm...now I do just have the "hose" that went from the TB to oil fill tube open to the ambient air. I guess I could plug it real quick, then start it and see if that fixes it. I have had that "hose" uncapped for 7 years or so, since I bought it. That would be nice if that fixed it.
 
Do a voltage or resistance test on the ECT sensor. It may be off enough to cause problem on a cold engine but not far enough off to set a code.

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. Warm the engine up until you get good hot air from the heater and then dump the codes again.

The ECT sensor has absolutely nothing to do with the temperature gauge. They are different animals. The ECT sensor is normally located it the passenger side 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 :

50 degrees F = 3.52 v
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
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor harness 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
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms

Diagram courtesy of Tmoss & Stang&2birds

88-91_5.0_EEC_Wiring_Diagram.gif


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