[Cobraman1024]

This code is stuck in the memory of my 93 2.3L with 5-speed. I've tried a bran new junkyard O2 sensor, replacing all vacuum lines at the PCV, throttle body, vac tree, fuel pressure regulator and brake booster. tightened the EGR sensor to the upper intake (bolts slightly loose), tightened the cap over the EGR pirt on the header (filled with a penny) and filled the port on the EGR itself with a dime. No leaks that I can see. I also Seafoamed the engine with half a can and the other half went in the gas tank.
Any other ideas?

[zonker]

some thoughts:

1. iat sensor resistance too low
2. ect sensor resistance too low
3. lack of egr is filling the cylinder with more O2 but the same amount of fuel compared with a working egr.
4. tps is out of adjustment
5. "junkyard" o2 sensor belongs back in junkyard
6. clogged fuel filter
7. low fuel pressure

[Cobraman1024]

Originally Posted by zonker some thoughts: 1. iat sensor resistance too low 2. ect sensor resistance too low 3. lack of egr is filling the cylinder with more O2 but the same amount of fuel compared with a working egr. 4. tps is out of adjustment 5. "junkyard" o2 sensor belongs back in junkyard 6. clogged fuel filter 7. low fuel pressure

1. IAT sensor; I have though about this and I'm going to pull a couple of them from a junkyard that has a bunch of these 4cyl Mustangs.
2. ECT; Not sure where this one is located, I know where it is on a 5.0 engine but shouldn't be too difficult to find it.
3. wouldn't the computer compensate for this?
4. might be out of adjustment but at least I know it isn't bad lol.....I'll check the idle voltage though.
5. junkyard O2 sensor; the sensor I pulled looked like it had been in the exhaust pipe for literally less than 100 miles, not one trace of carbon or residue on the metal tip at all and it was perfectly clean, no dirt on the wiring harness or anything.
6. brand new fuel filter installed back in October, only 4000 miles on the car since it was installed.
7. low fuel pressure would be one of three things; clogged filter, clogged regulator or weak fuel pump. add to it a clogged or weak fuel injector(s). I could probably throw a mechanical fuel pressure gauge on the fuel rail and check the pressure to rule out the pump and regulator but its difficult to check pressure while the engine is under load. The CEL won't come on if the engine is just idling. only after about 5 minutes of driving will it light up.

[Cobraman1024]

Ok so I replaced the IAT and then I found a vac line disconnected from the top cover of the air filter box so I reconnected that. There are two nipples on that cover next to each other. The loose vac line connects to one of them, where does the connection for the other one come from? Possibly the charcoal cannister?
I also found a broken green plastic line but where it was broken was covered up with the black corrugated tubing that is used as a harness I guess for several of these tubes together. I reconnected the ends with a piece of rubber hose and the car still runs the same; CEL is still turning on after about 5 miles of driving. Gas mileage is still 28-30mpg. I just have this annoying CEL with code 172 and still haven't found the cause of it yet.

1. Haven't checked fuel pressure yet; need to find a guage for that.

2. Didn't change out the ECT yet> this sensor is connected in line with a heater core hose right? threaded into a metal t-tube that goes between two rubber hoses?

3. have not checked TPS voltage yet, completely forgot to verify that.

[zonker]

Originally Posted by Cobraman1024 Ok so I replaced the IAT and then I found a vac line disconnected from the top cover of the air filter box so I reconnected that. There are two nipples on that cover next to each other. The loose vac line connects to one of them, where does the connection for the other one come from? Possibly the charcoal cannister? I also found a broken green plastic line but where it was broken was covered up with the black corrugated tubing that is used as a harness I guess for several of these tubes together. I reconnected the ends with a piece of rubber hose and the car still runs the same; CEL is still turning on after about 5 miles of driving.

The vacuum nipples on top of the airbox is a thermostatic valve for the hot air flap diaphragm, located in the bottom of the airbox.

one nipple goes to a manifold vacuum source via a plastic line that is black and joined with the green vacuum line behind the corrugation on the firewall.

the other nipple is connected to the hose that goes to the hot air diaphragm itself.

[Cobraman1024]

Must have disconnect that one for the flap when I yanked out the airbox. I'll take care of that when I get home tonight, thanks!

[Cobraman1024]

Zonker, this quote is from your post about the guy with the "no e-fan, no temp gauge" thread:

Originally Posted by zonker 172 could be telling you there a fuel system problem. Pull the vacuum line from the pressure regulator and see if is any fuel in it. If there is, then the pressure regulator needs replacement. Then run a pressure test on the fuel line to see if you're getting good fuel pressure. Fuel filter replacement is not a bad idea either if it's been on there for a number of years. If fuel pressure is down, and the regulator is not leaking fuel, then u might need to replace the fuel pump.

I've been messing with a 172 code now for a few months on my Mustang. This thing is a little bastard to say the least lol........A tuneup and new fuel filter were installed right after I bought the car and then the 172 came after I installed the Ranger header. I swapped out all of the vacuum hoses and all of the engine gaskets with new ones (obviously the ranger header got a brand new exhuast gasket). After verifying that I wasn't getting any fuel in the vac line on the fuel pressure regulator, I hooked up a fuel pressure gauge and found that I was getting normal readings; 32psi at idle and 42psi with the vac line removed from the regulator. The only other thing I could figure is maybe my injectors were dirty. I installed the 19lb injectors and then the 17lb injectors-------still got the 172 code. I then reinstalled the factory 14lb injectors...........code 172 is still there.

Also, the TPS voltage is normal; .95 or .97 or something at idle, forget which but I remember when I checked that it wasn't out of the normal range for idle.
Only thing I haven't checked yet is the ECT. I tried just removing it from the metal piping section that its screwed into near the heater core at the firewall but that damn thing is going to be a bitch to remove if it turns out bad. I'll check the resistance of it tomorrow when the engine is cold and when its warmed up after driving to pick up my new clutch cable from Advance. I was shocked at how many broken strands there were on the factory cable when I got under the car yesterday lol........

[Cobraman1024]

I checked the ECT with the engine cold; 58.85 kohms I think.
With the engine warmed to the needle just on the bottom hash mark for 'normal' I got 3.75 kohms so I think the ECT is working perfectly fine.
The IAT reads 14.15kohms and rising with the running.

[Cobraman1024]

Add "new oxygen sensor" to the list of shit changed. I couldn't get a switching reading off the old one and I can't get a switching reading from the new one either.
Only thing left is the fuckin' computer. I'm sick of chasing this shit.

[zonker]

could the new one be bad?? you should be able to get a reading from it.

[Mikel89us]

what are you trying to see an o2 switching pattern with???

[Mikel89us]

and what is the code description for a 172??

[Cobraman1024]

Originally Posted by zonker could the new one be bad?? you should be able to get a reading from it.

Very unlikely but as with any electronics, it's always possible. I'm pretty sure I'm reading off the right pins; the top two nearest to the press to release tab on the connector of the sensor.

[Cobraman1024]

Originally Posted by Mikel89us what are you trying to see an o2 switching pattern with???

Fluke DMM, not sure of the model because it's not right in front of me but I think it's a 188.

[Cobraman1024]

Originally Posted by Mikel89us and what is the code description for a 172??

Oxygen sensor not switching/indicates lean condition.

Looking around, a failing fuel pump would make sense. I'm going to recheck the fuel pressure tomorrow to see how quickly it builds and how well it maintains pressure at 2000+rpm. I was only checking pressure at idle before and the code does not light the CEL at idle.

[Cobraman1024]

The meter is actually a Fluke 87 series V DMM.

I thought i was reading from the correct oxygen sensor pins on the plug; the two top ones nearest to the push tab but that was giving me 0mV every time. I then checked the bottom two pins (which I thought were supposed to be the sensor heater) and got a varying voltage of 192 - 232mVdc. ------definitely a lean reading.

I ordered a brand new 255LPH fuel pump today, hopefully this upgrade helps things.

[Mikel89us]

Originally Posted by Cobraman1024 The meter is actually a Fluke 87 series V DMM. I thought i was reading from the correct oxygen sensor pins on the plug; the two top ones nearest to the push tab but that was giving me 0mV every time. I then checked the bottom two pins (which I thought were supposed to be the sensor heater) and got a varying voltage of 192 - 232mVdc. ------definitely a lean reading. I ordered a brand new 255LPH fuel pump today, hopefully this upgrade helps things.

You cannot read an O2 sensor with a DMM, it will only show you an average of the voltage, and will never show you switching. You must use a lab scope. Thats the only true test of an o2 switching pattern. That will help you a lot if you find the right tool for the job.

[Mikel89us]

Have you checked the intake for leaks?

[Cobraman1024]

Originally Posted by Mikel89us You cannot read an O2 sensor with a DMM, it will only show you an average of the voltage, and will never show you switching. You must use a lab scope. Thats the only true test of an o2 switching pattern. That will help you a lot if you find the right tool for the job.

The reason a shop uses an oscilloscope is because of its high input impedance, usually 1 or 10 Mohms. Also, not too many shops have oscilloscopes anymore, their scan tools usually have a scope on them in some form.
My Fluke meter has an input impedance of 10 Mohms and will show a varying voltage by activating the "max - min" mode.

[Cobraman1024]

Originally Posted by Mikel89us Have you checked the intake for leaks?

I don't have any high idle issues so I'm pretty sure I don't have an intake leak. The IAC was thoroughly cleaned and all intake-related gaskets were replaced.