4.0L P0172 P0174

[19krpm]

2001 4.0 sport Trac 4wd.

So I am the process of getting new wheels to resolve my grinding noise for my auction buy. I thought I would have resolved the very very rough idle by now. I have not put it through a full drive cycle so I know there may be more pending codes that could have aided in diagnosing the issue(s). The idle smooths out when I bring the throttle up.


So far, I have run smoke through the intake, no leak found. I did have quite a bit of smoke in the exhaust even after turning the engine over a couple of times to get valves to where I thought they were closed. Because of that I checked the egr. No vacuum leaks, EGR is good. I tested fuel pressure. It is good. I have only pulled plugs on the drivers side, but the plugs look new, wires look brand new (probably done together recently). Compression is at 165-175 on the three cylinders I have checked thus far. Cylinders and valves look good on the borescope. I haven’t pulled wires off the coil pack yet while running to check spark strength. I did pull the IAC to verify it’s free and able to move. Did a little cleaning to it and put it back.

It is very weird to see a rich code for one bank and lean on the second. I plan on completing the compression test on the other 3 just so I know for future reference. I have searched around here as well as at a couple other Ford forums. I have seen a few other people with the same problem, but none that have said they solved it. Any ideas? I was almost certain it was going to be a vacuum leak, but I don’t see any smoke with the machine on it. Any ideas? When I do get this solved, I will post what I find just to save someone else the hassle.

 

[koda2000]

Does your EGR valve hold vacuum? You might want to check your DPFE too. They tend to melt. There is a way to test a DPFE. Try Googling it.

 

[koda2000]

Does your EGR valve hold vacuum? You might want to check your DPFE too. They tend to melt. There is a way to test a DPFE. Try Googling it.

BTW - Vacuum leaks cause "lean" problems, not "rich" problems. Having both is odd.

 

[19krpm]

Update:

Still runs like crap, was going to order some new wheels and tire so I can test drive it, but TireRack decided to start charging tax in WA so I’m looking elsewhere.

Egr is good, dpfe tests and looks good and I don’t think it would cause this rough of idle even if it were broken. I’m starting to think it’s a bad or dirty injector. I don’t have a tester, and as much as I would love to throw some parts at it, I want to know exactly what is up with it.

I was really starting to think plugged cat(s). Tried to pull them off the manifold and the top bolt on the passengers side collector rounded off. I bore scoped through the O2 bungs and they looked pretty darn good from what I could see. Some subtle sooting but the cells looked well defined. Not as definitive as a flashlight check, but the exhaust seems to flow pretty well anyways. I will have to weld on a crappy socket to the head of the rounded bolt, but it should come off and I will anti seize them.

When the MAF is disconnected it does run better, but I would say it’s still not very good missing on idle.

 

[19krpm]

Well I finally got around to finish compression testing the passenger side. Problem solved!? Or at least found. Broken spring. Looks like the valve still closes partially. Doesn’t appear to have struck the piston. No compression though. Leakdown test blows straight through the exhaust. I was getting ready to take off the heads, but see quite a few people replacing individual springs without removing the cam. Looks doable so I figure I will give that a try just for kicks. All of the other cylinders are 165-170 so I bet this engine has some life left. Bore scope came in handy. It was cylinder #3 exhaust valve that failed just for reference. Lip of the valve is circled in red. That cylinder is at tdc so it obviously not right.