Im thinking i have a O2 problem. Wanted to know how many to pick up from the parts store tonight on my way home.

Dont feel like crawling under my truck in my good clothes right now.

Thanks for any help.

 

What makes you think you need new O2's?

 

Code 172. Is it just 1 or is there 2?

 

Codes don't mean to change parts. They tell you where to begin the diagnosis. That's a lean code, and changing the sensor that detects it won't make the engine run richer. Step 1 is to determine if the exhaust is actually lean. If it's not, THEN you might suspect the sensor or EEC. But you probably have a vacuum leak.

The number of HO2Ss on that year depends on engine AND trans; i.e., is it MAF? How many large hoses connect to the top of the air filter cover: 1 or 2?

 

Thanks for your advice. I dont have a vacuum leak. Checked everything else. Not sure what else it could be.

The truck is a 94 5.8l 215k miles. Runs real strong. But has extremely rough idle, sometimes it smooths out. Sometimes going down the road when its colder out it will act like its missing part of the time. I get about 10mpg no matter how hard or easy i drive. It has new spark plugs and all the plug wires checked out on resistance. Cleaned the cap and rotor contacts. EGR valve moves freely.

Oh and I get the CEL about 5 minutes after driving it. Usually as the system gets up into the normal on the temp gauge. Then the CEL comes on.

 

SOMETHING is causing it to run lean - which is usually unmetered air - i.e. a vacuum leak. The O2 is simply doing its job and noticing that something is out of whack.

 

Well theres not, i have pulled 20 inches of vacuum. When i pulled a vacuum line off the engine reved up. Causing a lean condition. i replaced several of the vacuum lines this spring. Sprayed carb cleaner all over the engine bay and didnt get any difference in idle.

 

A bad 02 can cause it to run lean. The engine makes adjustments based on what it sees. If its giving bad info the engine, is going to adjust incorrectly? Why is it so hard to believe that an 02 with 215k is bad?

 

If the oxygen sensor gave the EEC bad readings causing the EEC to run lean, then the oxygen sensor COULDN'T also detect that lean condition, because it's bad. Right? So the fact that it sets the code says it's not bad. And if it's good enough to detect the lean condition, then it's good, and doesn't need to be changed. Either way, it's not the CAUSE of the code, so changing it won't fix the code.

Read the books in the owner's manual pack. Oxygen sensors are NOT maintenance items. They don't simply go bad with age or miles. Mine has several hundred thousand miles on it, and it spent a year or 2 in a junkyard. It works fine.

You can't detect a vacuum leak by measuring manifold vacuum, and creating a new leak doesn't eliminate the possibility of another. Use a mechanic's stethoscope without the probe (or ~3' of garden hose) to listen all over the intake while the engine idles.

Why not look at things that can actually cause the lean condition? What's the fuel pressure? How old is the fuel filter? Is the fuel pressure regulator working? Are the injectors clogged? Are the plugs gapped correctly? Are they fouled? Is the coil good? Are the ECT, ACT, TPS, & MAP/MAF good?

You still haven't told us if the engine is MAF or not. What trans (read the caption below), and how many large hoses on the air filter cover?

 

Truck has an E40d. I replaced pretty much every vacuum line already, also replaced the ECT sensor due to gauge issues.

Truck is EEK 4. not MAF. could be one of the TAB sensors, but i dont know how to test them.

 

http://www.ford-trucks.com/forums/92...-poor-mpg.html

heres a thread on FTE.

Fuel pressure is normal. And i doubt that fuel pressure is causing a rough idle, if it has enough to supply the truck at WOT.

 

Im pretty sure i checked the map sensor. Although i dont remember the procedure, but we ruled it out as a possibility.

 

Is there a air temp sensor in the intake, or SD sensor?

 

EEC-IV & MAF aren't mutually exclusive. Some '94 5.8L w/E4OD are MAF. That's why I've asked how many hoses on the filter cover. Look at this:

The ECT has nothing to do with the gauge. The gauge uses the coolant temperature sender, which has a single R/W wire; the ECT is exclusively for the EEC and has 2 wires.The TABs aren't sensors. The TAB solenoid controls vacuum to the actual TAB valve (AirB, often part of a combination valve), which regulates total secondary (thermactor) air. Then the TAD determines if it goes upstream (into the heads) or downstream (to the cat).

.

There is no SD sensor on any vehicle that I'm aware of. There are 3 possible locations for the ACT/IAT sensor: in the filter cover (MAF only), in the #5 or #6 intake runner.

Here's an excerpt from pinpoint test H1:The next few steps test fuel pressure, cylinder balance (injector flow), TAD function, and HO2S condition.

 

32 PSI running, 39 psi not running on the fuel system