car stumbles when cold

[icemetalstang]

When I start car after it has been sitting overnight and at work it idles fine. When I give it gas it stumbles and hesitates. If I back off the throttle and ease into to it the car smothes out. After a tenth of a mile no problems and car is smooth. I have cleaned MAF and barely made a difference.

When car is hot it turns over a couple of rotations more and starts slowly. Sometimes I dont think its going to start but it always will.

Feb. new- old- iat sensor, ignition module
Distributer
fuel filter
temperature sensor
tps
injectors
02 sensors
cap, rotor, plugs, wires
iac
ccrm
fuel pump

 

[HISSIN50]

Have you checked the ECT calibration?

 

[icemetalstang]

Im not sure what the ECT calibration is. It only started doing it about a month ago.

 

[HISSIN50]

ECT = Coolant temp sensor. It's the sensor that tells the EEC how cold the engine is. If it's out of calibration (but not absolute spec), it can cause drivability issues, esp when the car is cold and needs enrichment.

If you feel like it, with a cold engine, just turn the key on and take a voltage reading from the sensor.

 

[toyman]

ECT = Coolant temp sensor. It's the sensor that tells the EEC how cold the engine is. If it's out of calibration (but not absolute spec), it can cause drivability issues, esp when the car is cold and needs enrichment.

If you feel like it, with a cold engine, just turn the key on and take a voltage reading from the sensor.

Do you happen to have the voltage vs. temp table? I was wondering if it's different from the transmission fluid temp sensor table.

 

[HISSIN50]

Richard, it's the same as the IAT chart if you have that. I don't think I have ECT stuff saved.


IMS, at 50*F (around what a cold engine might see), the ECT should show ~3.7V. When you test it, if it's not between 3 and 4 Volts, something is probably amiss (unless your temps are below freezing or you live in the tropics). If that's so, give us a guess on what the coolant temps were during the test.

 

[toyman]

Richard, it's the same as the IAT chart if you have that. I don't think I have ECT stuff saved.


IMS, at 50*F (around what a cold engine might see), the ECT should show ~3.7V. When you test it, if it's not between 3 and 4 Volts, something is probably amiss (unless your temps are below freezing or you live in the tropics). If that's so, give us a guess on what the coolant temps were during the test.

I had forgotten that my AEM software has these tables. The ECT and IAT sensors do indeed have the same voltage vs. temps values. FWIW 50*F = 4.84v in my calibration table.

 

[HISSIN50]

I had forgotten that my AEM software has these tables. The ECT and IAT sensors do indeed have the same voltage vs. temps values. FWIW 50*F = 4.84v in my calibration table.

Richard, ss that an AEM table (Is it supposed to be for Ford values)?

4.84 is at the extreme of the VREF limit (5.0V +/- 10%). In other words, the ECT would be useless at that temperature or below. The useful range for the sensor voltage is ~ 3.5V to ~ 0.3V.

 

[icemetalstang]

My low speed fan was not kicking on. My car had a 117 code. So i replaced the coolant tempature sensor. It was still under warranty. Now it works. The problem is alot less than before. In the morning it will still hesitate. I will check the voltage. I also live in Florida. I cleaned my Iat sensor. It also helped. Problem is still there.

 

[toyman]

Richard, ss that an AEM table (Is it supposed to be for Ford values)?

4.84 is at the extreme of the VREF limit (5.0V +/- 10%). In other words, the ECT would be useless at that temperature or below. The useful range for the sensor voltage is ~ 3.5V to ~ 0.3V.

That is the Ford calibration table in the AEM software and is the one that I'm using. 3.5v = 150*F and 1.56v is the minimum voltage for 261*F (fail safe limit). It's just the reverse of the scale you are suggesting ie. useful range is 1.4v ~ 4.99 (261*F ~ 41*F). ECT's below 41* are referenced in the warm up enrichment and the extra start vs. ECT tables but it is not clear how those lower temps are being read. I'll see if I can get clarification on the AEM forum. As I don't use the car in the winter I've never noticed the discrepancy before.

 

[sln583]

Are these the correct values?
Ford Fuel Injection Engine Coolant Temperature Sensor (ECT)

Im having a similar problem.
My 88 cranks and starts, and then after runiing for about 5 seconds, it stalls.

 

[HISSIN50]

Are these the correct values?
Ford Fuel Injection Engine Coolant Temperature Sensor (ECT)

Im having a similar problem.
My 88 cranks and starts, and then after runiing for about 5 seconds, it stalls.

Those are correct for a Fox III (I've also checked them against a SN95 IAT, which might or might not have been in calibration. The read values were congruent with what was in the table however).

 

[toyman]

Those are correct for a Fox III (I've also checked them against a SN95 IAT, which might or might not have been in calibration. The read values were congruent with what was in the table however).

WOW. The response back from a AEM moderator was that the temp range provided was correct and is a Ford sensor range limitation. I've sent the link provided to see if there is an calibration table error in the AEMPro software. Seems to me that after this many years any error would have been picked up and corrected but I'm sure stranger things have happened.

 

[toyman]

It just occurred to me that we are probably talking about two different things. The ECT values in the link are the output voltage readings from the sensor whereas the calibration table I was referring to is different because the EMS uses a pull-up resistor for that circuit. That will alter the voltage vs. temp values and would explain the difference.

 

[HISSIN50]

That makes sense I think. I poked around on the AEM forum a couple of nights ago, and in a very cursory search I didn't find any raw Ford resistance specs for the Ford ECT (using resistance removes the variable of voltage-push through the thermistor).

I have another source which almost parallels the FFI info above.