Sensors Used in Warm-Up

My 03 Mustang GT is stuttering every now and then (about once a month) when the engine is cold and being driven so I'm trying to narrow the possibilities down of what it can be. So far, the MAF has been cleaned, the IAC has been checked and looks clean and the EGR is fine as well. The PCV valve has also been replaced and there are no vacuum leaks. I'm thinking now it's either plugs/boots or a sensor gone bad. So, what sensors does the engine used while the engine is still cold (I believe it's in open loop when cold, correct)?

The Coolant Tremp Sensor is your richening sensor for cool running...

It's the likely Culprit...


FE

My vote is for the plugs/boots. How many miles you got on it? Those things go into closed loop quicker than you think, but it is harder to fire the rich mixture and more likely to misfire at this time.

I got 44k on it but was planning to replace it at 50k. What makes me think it's not the plugs/boots is the fact that it only happens when the engine cold only. I don't know if this makes a difference but this started about a month after I got my headers on. Would that screw anything up?

I'm with FE on this...replace your ECT sensor.
-J

At the very least...

Pull the diagnostic codes before replacing any sensors.

Sometimes the codes don't help,
but why wouldn't you ask the computer what the problem might be?




Several issues could be doing this...
Since it is more intermittent, I would guess a ground or other wiring short type issue.
Just a guess though.

Good Luck,
jason

The reason why I haven't checked the computer since the Check Engine Light only turns on once in a while but then turns off fairly quickly. Not only that, the only place that does offer free code reading by me is Autozone and I hate driving there (about 1/2 hour or more away w/ terrible traffic). I've just replaced the plugs though w/ Autolite 103's (1 step colder) to see if this solves the problem. If not, I'll replace the ECT sensor. As far as grounds, the ones that I did spot all seem to be in good condition.

Originally Posted by bassman97

The reason why I haven't checked the computer since the Check Engine Light only turns on once in a while but then turns off fairly quickly. Not only that, the only place that does offer free code reading by me is Autozone and I hate driving there (about 1/2 hour or more away w/ terrible traffic). I've just replaced the plugs though w/ Autolite 103's (1 step colder) to see if this solves the problem. If not, I'll replace the ECT sensor. As far as grounds, the ones that I did spot all seem to be in good condition.

The CEL does not tell you about ALL codes. You can have codes stored, and never see the CEL come on.
There are code pulling routines that don't require a reader. You can use the CEL or an indicator light bulb, depending on year.
If you don't want to mess with that, then look for a $35 reader at the local parts stores.
I believe Schucks/Kragen carries them, and others should as well.

My point is...
If you are going to work on an EFI car, then you should take the effort to learn at least a little of the diagnostic stuff.
I'm not trying to be rude, even though I probably am coming off that way.

The ecu is a tool and will help you, if you use the tool properly.

If not, then forget the codes, and just start swapping sensors.
But what happens if you actually have a problem with the Vref? Swapping sensors won't fix that...

Again, I'm not trying to be rude, just trying to make a point...

good luck,
jason

Ford ects rarely fail. If you have a good digital volt meter you can check the operation of the ECT with out replacing it. You would need to back probe the connector terminals and watch the readings. Trying to find a problem that happens once a month is almost impossible. Codes are nice and will help you find problems but having a 5 dollar an hour noob scan your car and tell you what is wrong is a waste of time. If you plan on working on your car much then break down and buy your self and scanner, used if you have to. There are many of them out there. I have 4 different ones and a cheap code reader. I use the cheap one to tun off engine lights when people fill their tanks with engine running. I have a Ford New generation star test which I use on all the Fords. I use my Snap On Modis for most other cars. I use my Snap On 2600 to work on the older (pre OBD2) cars and my Mentor when others are hooked up and I dont want to disconnect them. Some times I have to hook my Vantage lab scope to check got dirty patterns. If it was as easy ans having Autozone read it and replace the part I could sell about 20k+ worth of tools.

I understand, my plan was to get one once I have cash for a programmer since most programers can check and clear codes.