Well, it is time to try and fix this... On my way home tonight I got a code 173 - HEGO indicates always RICH. This is the second time I have gotten this code in the last two years. The first time I put a new Motorcraft HEGO on. It has been fine ever since. I did get a code 172 - HEGO indicates always LEAN a few months ago, but I cleared the code and it never came back.

Now on to the 173. As some of you know my mileage is terrible right now, about 10 mpg mixed. Due to this I am positive this code is not a random error, but rather a real issue. Pair that with an exhaust that smells rich and I know there is a problem. I want to go through everything sensor wise that has an effect on gas mileage and the engine running rich. I want to narrow this down and fix the problem. So, to all you guru's of the EFI systems in this truck, what all do I need to test? ACT? ECT? MAP? FPR? Injectors? TPS? IAC?

 

I'd start by checking fuel pressure at the rail to see if the FPR has failed closed.

 

That is one of the first things I am gonna check. Just have to go rent a fuel pressure gauge.

 

Checked the pressure. Engine off but primed it sits as ~42 psi. Engine running is ~37-38 psi with the vacuum line on the regulator and ~48 with the line pulled. Seem like it is working properly to me. Nobody else has any input?

 

How about static pressure?

Put the gauge on it turn the key on allow it to build pressure, cycle key off on off on couple times if you wish then turn the key off let it sit there.

Watch the gauge, does it hold or does the pressure bleed off. If it bleeds off how much and how fast, time it.

Manual states something like must hold within 5psi of spec for 1 minute yea fine but my trucks will hold at 40psi for couple hours or better easy, based on comments made I believe that holds true for many here as well.

Point is a good sold working fuel system the pressure does not begin to drop off the second power is taken away. If drops 5psi in the first minute how long suppose takes to get to zero? LOL

Didn't see where you mentioned when it had its last full tune up, plugs wires cap rotor etc?
While that condition alone, worn ignition components, wouldn't necessarily create a rich condition it certainly could add to an another underlying issue that be enough put it over the edge.
Then ignition coil, is it original? if so and "works" its what 22 years old now. I've replaced all the coils on my trucks, marginally "newer" than yours and all had original coils. They worked but I replaced them anyway due to age and its function, fire in the hole.

Anyway check the static pressure, let us know what you find.

 

Static pressure was 38 psi and didn't bleed off at all during the 40 minutes I let it sit for. As for the ignition components, plugs have less than 2k on them, cap, rotor wires and coil all have about 8k on them.

 

So you pretty much covered FPR, no reason to doubt IAC as stated nothing about crazy idle speeds/nothing do with fuel trim. TPS yea and no but easily tested, it either passes testing or it doesn't and easily tested a minute.

How about ACT and ECT sensors, did you test those at all? myself I wouldn't bother in the time it would take to do that you could simply replace them, they are cheap. Testing be worth it if for no other reason find fault, always nice to find a clear cause of the problem. Say for example test the ECT with engine up to full running temp, you know the coolant is 195deg, test sensor returns value for 110deg. Not usually that cut and dried though!


Better off at this point with fresh sensors regardless especially if in doubt.

I've replace those on my trucks as well, again had original equipment yet and the PCM relies on them for vital information as to conditions the truck operates in.

Wouldn't be a terrible idea pulling the PCM out removing its cover checking it for obvious signs of problems, the computers in these trucks are aging at this point, unless of course you already had.

 

I tested the EVP, TPS and MAP just now. Also checked the wiring to the HEGO which came back fine. All checked out just fine. TPS was sorta on the edge of being out of spec on the idle side of things, but was great from there to WOT. I think I will check the wiring for the ECT and ACT and if the wiring seems good I might just throw some new sensors on. I will pull the ECM as well, but I don't think I will find anything there...

 

Well, you can test the HEGO... I get it, it's new(ish) and it's Motorcraft, but guess what? Even the good names in aftermarket parts can make a bad part every now and again, including Motorcraft.

Then move on to the sensors and controls that most directly affect fuel/air mixture, and work your way "outward" from there. It could be as simple as an injector that isn't closing all the way due to gum/varnish build up.

Don't waste your money and just start throwing sensors on it - you could end up replacing them all and still have the same issue. Then you're out a few hundred dollars and have gained nothing. Take time to diagnose why it's running rich - you'll save money and time.

 

I would replace the coolant temperature sensor as a matter of course. Those things are thermocouples with finite lifespans (most believe that replacing it once a decade is good) and they're cheap enough. You can test them, but for the amount of time you'd spend testing an old sensor you might as well just replace it.

 

I'll pull the HEGO out and test it to make sure it is still good. As for the other sensors, I was only going to replace the ACT and the ECT. I will go ahead and take a ohms reading in them in the mornig before work to see if they are in spec cold, then when I get to work to see if they are in spec warm.

As for the injectors, the ones I am running right now were removed, cleaned and rebuilt about 5k miles ago. However they were junkyard injectors so there is a decent chance one might be leaking. Is there anything else I am missing here that plays a significant part in fuel economy?

I also went ahead and drained my rear tank to see if the gas looked new as a possible indicator of a cross flow issue. I haven't used the tank in a few years and the gas that was in it looked old. But now that I know it is empty I can drive it for a week or so then check the level again to see if it has gone up at all. If it hasn't I'm gonna run some cleaner through the tank and start using it again.

 

So you're saying that it's never worth the time to test a sensor to find out if it's actually bad, and that you should just replace them any time they're suspect?

Not trying to "attack" you but that's just bad advice. I agree that sensors have finite lifespans, but so does everything else on a truck, and age isn't always the only consideration. That's why testing and diagnosis is so important - so you don't replace parts unnecessarily. And yes, there's always the possibility that a bad sensor can test good, but if you're not going to bother testing it at all, why bother working on your own truck? Plenty of shops are willing to take your money and put all the parts on it they can find without actually fixing anything or diagnosing the issue.

 

The KOER w/vacuum hose attached pressure is too high. Subford posted this in another thread: https://www.ford-trucks.com/forums/1...l#post14490932

I have never seen a V8 truck with more than 45 PSI with the vacuum hose removed.

 

Well in that thread he says that low vacuum causes that condition. My truck makes 21 inches of vacuum at idle. Could this mean the FPR is bad after all?

 

Yes....

Or the fuel pressure tester you used is out of calibration.