I am having trouble figuring out the cause of these two codes. P0171,Po174 Right and left bank "lean". Last winter they appeared, after many searchs for the cause I discovered I had a partially plugged fuel filter. I replaced it and had no further trouble until now.
I live in California, the weather here isn't extreme, I doubt it's weather related.
I have: Replaced air and fuel filters again, they were clean.
Swapped o2 sensors with a friend's Ranger
Swapped temperature sensor in snorkel.
Cleaned mass air sensor with alcohol, it wasn't fouled.
Swapped Idle air motor assembly.
Replaced PCV, and tested for engine for vacuum leaks.
Cleaned trottle body, the inside of the intake manifold appears black and slightly oily.

I have an "Autotap" that I read the codes with. It's sensor scan reports all sensor running within normal range except B1S2 o2 sensor "fuel trim". It reports a 99.99 reading that doesn't fluctuate. I have no idea what this means, or if it is actually used by my Ranger. Since my Ranger has only 3 o2 sensors, I don't think Bank 1 sensor 2 is used, however my "autotap" still reports it.

The CEL after reset will not come on for a few days of driving, but it will come on again. The engine appears to run normally, fuel economy isn't affected. If I lived somewhere without a smog check, I would simply ignor it, but I have to find the fix.
Can anyone suggest something, other than trading it in?

 

Welcome to FTE!

You've come to the right place. These lean codes seem pretty typical on the '98 era 4.0L Rangers. Many times they are caused by either a vacuum leak or a fuel pressure issue. I see a lot more posts about them when the weather gets cold, I think due to gaskets and seals shrinking and making vacuum leaks bigger. You said you live in Cali, but cold weather isn't absolutely necessary for a vacuum leak to be present. Also, perhaps the clogged fuel filter left the fule pump damaged and now it is really dying?

The code is tripped by the fuel trim being set to the full rich during two consecuitive trips. So you are probably looking at the fuel trim numbers and they are crowbarred to the rich side as the computer tries to compensate for a perceived lean condition due to a vacuum leak or low fuel pressure.

Here's a thread in which I described the problem, common solutions and linked some other good threads about it.
Cold Weather Related Issues Informational Thread

-Jim

 

Thanks for the quick reply, and the tutorials.
I checked my fuel pressure, 65 psig, and it seems steady through higher revs.
I also removed the egr and checked it, no problems there either.
I ran it after checking the fuel pressure, it ran like crap, missed, also stalled several times. Went to Auto Zone to check on fuel rail, manifold gaskets, which they don't carry. Got in the truck again and it ran great. Revs at idle were at 600, it usually revs at 900, and uneven, surged up and down. No more missing, stalling. ?????????
No codes set yet.
I'll put the gasket job on hold until I can put a few more miles on it. I'll also put the auto tap back on and look at the sensor putputs.
More to follow............

Thanks again.

 

I think the upper intake gaskets will be a Ford-only product. They are like rubber o-rings. Watch out on other gaskets though, as the aftermarket replacements are sometimes cork where the motorcraft are usual gasket material and rubber. The '97 was the year with the fuel rail gasket issue, so you might want to hold off on that one unless you suspect it.

Our forum sponsor (link near the top of the page) is a motorcraft dealer too, if you want to wait for mail order.

Keep us posted on your progress!

-Jim

 

Welcome to FTE pill90

In that both banks are indicating lean & with the past reported clogged fuel filter, I'd maybe suspect a fuel trim or intake manafold vacuum leak, downstream from the MAF sensor.

You may need to do a fuel delivery rate check, seeing as how the psi seems ok, maybe the pump is weak or the filter is clogging up again & flow is unable to keep up with demand.

Did you find out what clogged the fuel filter the first time????

If you suspect a manafold vacuum leak, you could do a intake manafold "sniffer" leak test, by rigging a propane bottle, with a hose, fitted with a sports needle, as the probe, then with the engine running, listen for idle rpm increases at a leak point.

Will be interesting to hear what the scantool has to say about sensor PID's.

 

I went yard sailing with the truck today. Numerous starts and stops. Still running ok, no codes.

The filter was plugged with fine, brown silty looking dirt. Maybe just dirt. I changed it again 2 weeks ago. There was nothing in it this time. Put a new one in anyway.

I tried starting fliud around the manifold. i couldn't detect any change. I will hook my laptop up and watch the rpm on the screen while I do the propane test. I will report back after, probably this afternoon.

Should I be getting the 99.99% on the B1S2 o2 sensor "fuel trim"? maybe it's gone now also. I will soon know.

 

Update:
No further codes set. Did the propane check around the intake manifold, and numerous vacuum items. No increase in rpm noted.
O2 sensors checked again, all nearly at perfect readings.

Did a vapor system test, on the auto tap. Don't know what this is all about. It failed 2 elements:
Vapor generation max pressure rise-> results -63.896 (min listed at 1.987 max is zero)
Bank2 switch ratio and max limit test-> results rise 1022, (min listed at 0.749 max is 0)

I have no idea what these are.

If this is a cold weather problem I may have to wait, it's about 70 outside today.

 

There is no B1S2 on these, hence your goofy scanner reading. Basically the computer is reporting an "open circuit" due to lack of sensor.. but also your computer is programmed to ignore this, for obvious reasons.

Also sensor #2 ford does not call an oxygen sensor.. they call it a "catalyst monitor"... the rear sensors are not used to determine fuel trim, but rather to measure the efficiency of the catalytic converters.

I'm not familiar with the AutoTap system so your diagnostic results look like "greek" to me... but I think PSKSAM is on to something... these intake seals are VERY prone to leaking... and alot of time the only leak when cold, which makes diagnostics very difficult, as the vehicle is usually running and warming up while you're doing your testing.

If you notice when you get new intake seals, they'll be about twice as thick as the original. They have been redesigned for exactly this reason.

Good luck

 

Thanks for confirming my suspicion about the secondary o2 sensors MRg in STL .

I'm going to ignor the goofy Auto tap results and stop by my local Ford dealer for a gasket set, ( Or by them from FTE sponsor) and just do it. I've spent more time troubleshooting this then it will take to replace the gasket set.
Once completed I will report my results. Thanks again.

 

Update- cold weather came back, so did my CEL- >
I got ambitious and removed the upper manifold. The gaskets, there are 3, were flat but showed no evidence of leaking. It looked as though if they leaked, they probably leaked a tiny bit, not in any 1 area , but all around.
I replaced the 3, (15.$) at my local Ford dealer. Cheep, but there isn't much to them. After the replacement I restested my vacuum and to my surprise it read in the normal range. An improvement. It read slightly low before the work.

I recommend that if you undertake this job, get a replacement green "o" ring for the top of the EGR tube, it looks like a possible leak spot also. Replace the throttle body O ring also.

The job took a little more than an hour.

So far no codes and the engine is running well.

Thanks everyone for your help.

 

Good find, fix & feedback pill90.

Sounds like you may have found the culprit.

The intake side gaskets on a 4.0L of our vintage belong high on a lean code, or low vacuum, suspect llst.

Will be interesting to see if it'll now pass continuing cold temps/soaks without problems.

The brown "silty looking dirt" you found in the old clogged fuel filter, sorta fits the description of rust.

Maybe from fill ups at a not so clean fuel station, or one with storage tanks or pipes in bad shape, or maybe a fill up during a fuel delivery, or shortly there after, if the attendant didn't take that tank off line for the specified time, for sediment to settle out.

I'll bypass any station thats taking a fuel delivery, for those reasons, because nowdays you never know if the attendant knows what they're doing, or is on their toes!!!!

 

Nice work. Glad you have your truck running right again. I don't think it takes that much of a vacuum leak to cause issues. When I had it, I didn't find one with a smoke machine test or the carb cleaner method. I also didn't notice any evidence of leaks, on the mating surfaces of the intake plenum.

-Jim

 

pill90, I have the same problem, live in Calif too. I'm going to try the same fix and hope it gets rid of those pesky P0171 & P0174 codes.

You did alot of trouble shooting, Good job.

 

I forgot to mention that there is a vacuum hose running from the bottom of the throttle body to I don't know what over the left wheel well. It was in poor condition, while trying to remove it I broke a 90 degree plastic coupler that was in the hose. The plastic was very brittle. I recommend you pick up a replacement hose and completely replace it, and don't put the 90 degree connector in it. I don't see any value in it anyway. It might save you a trip to Auto Zone half way through the job.


Good luck.

 

Good job!

I have a similar problem (although mine is a '94) so I just want to make sure I understod you correctly: Did you only change the gasket between the two halves of the intake manifold or did you also change the fuel rail gaskets?

Thanks.