Hey guys,

I have long known about FTE, and came around to get some advice on a problem I have been having, because I know there is a plethora of knowledge on there.
For starters, I have a 1998 Ford Ranger, 4.0L 4x4 4-door extended cab with everything. It has nearly 180,000 well maintained, miles on it. She is in GREAT shape for the mileage. :-)
I have had this problem since last winter as I can remember. When it gets cold outside, the regular check engine light that comes with the cold is quite annoying. That is, when the temperature starts to go down outside, my check engine light comes on every so often until I clear it, and then after a little while again, it comes on again. Specifically I get trouble codes p171 and p174 which I'm sure you guys know means that banks 1 and 2 are running too lean, so the computer has trimmed the fuel rich to compensate for this lean condition.
Upon first glance, you might tell me to cleam my MAF sensor, but I'll just save you the trouble and tell you that I have already done this. I've changed spark plugs (not specifically due to the check engine light, just routine maintence, but just wanted to tell you everything), checked the air filter, and all the really obvious vacuum hoses, like the PCV, etc. I have gone as far as to purchase myself a vacuum gauge, and if I take off any of the main connections to the intake, I am pulling about 21.5" Hg, though I am not sure what I am supposed to read at the main vacuum connections. Let's see what else have I done...oh, I have noticed that the vacuum line that closes the valve to the heater core is quite sluggish in gaining vacuum, it takes quite some time to build the 21.5" I read at the intake, but it does get pretty close to this number.
Other things I've noticed, maybe, maybe not related to this problem have been that when I first start my truck when it is cold, my brakes seem to be a little bit spongy, and they seem to get better as the truck gets warmer, or it runs longer, I am not quite sure which. Also, it seems to me that the vent selectors take a little bit longer to move than usual, ie from defrost to vent, etc which would suggest a vacuum leak.

My thoughts are this. I know most of the things that cause this problem. So I will go through and try to remember every angle that I have checked. I have not yet checked the fuel pressure, I know sometimes this can cause a problem. I have checked for air leaks after the MAF, and can find none. I have checked the vacuum, again I get 21.5" Hg at an idle. The PCV system seems to be ok. My O2 sensors were replaced a little while ago, but I really dont feel that they are the culprit (no reason for this, other than that I would think if they were bad, I would get an O2 code, what are the odds that all the O2 sensors fail in the same lean condition). The thing that really gets me is the cold. That leads me to like 2 or 3 basic conclusions. The first is that the Air Intake Temperature sensor is not functioning correctly. The second is that since it is cold, I am using my heater controls more often, and if indeed the leak is coming from the HVAC section of the vacuum system, than that would make sense. I am a windows down guy in the summer, and I can only think of one instance over the summer where the light came on, and I think I might have been using MAX a/c. Maybe that is the explantion? At any rate, I know that ford has TSB's out for at least two instances that seem to describe my problem, however I cant seem to find the full text versions, and I am too cheap to pay 30 bucks to get them. I have not exhausted my free resourses as of yet :-). At any rate, my gas mileage has declined, after being up over the summer, go figure, and I need to get this fixed. I HATE when the check engine light comes on, even know I can clear it.

I greatly appreciate all insight.

Greg

 

Several '98 owners on this board (including me) have had luck changing the Upper Intake Plenum Gaskets. The cold weather seems to shrink those gaskets and cause a vacuum leak. These codes only appear (and cause the CEL to light) after two consecutive drives where the lean condition is hit. So in the summer, these gaskets are warm and sealing, but in the winter they shrink. The low gas mileage is a common symptom, mine improved once I changed the gaskets.

I tried starting this thread earlier this fall, guess I was a month early. It still has some links to other threads about these codes.
Cold Weather Related Issues Informational Thread

-Jim

 

Jim,

What brand of gaskets did you put on, OEM, or aftermarket? I assume you had the type with the "plastic" intake, you are talking about the gaskets underneath the big black plastic portion of the intake, that sits on top of the fuel rail? I checked out your links, and I might just replace the gasket between the lower intake and the fuel rail as well. Hopefully the problem does not lie in the low intake gasket...All said, I think I am putting off the inevitable, and I should probably just change the gaskets since such a common problem is known. I am going to check the fuel pressure first, just in case. :-)

Does anyone have any idea how much vacuum a 98 4.0L with no problems is supposed to pull at idle? This could be helpful in determining a leak.

I appreciate all the links, they were very helpful. Know any place I can find full text TSB's for free?

Greg

 

I have the same issue, but it's not caused by cold. My check engine light came on and the codes are P0171 and P0174. My ranger is a 1997 V6 4.0 with 101K miles due for servicing. O2 sensor was changed a year ago. Anyone have an idea whats causing the code failures?

 

It appears that the 97's have a problem with the gasket located between the fuel rail, and the lower intake manifold. Changing that gasket seemed to helped others out. There were several suggestions posted, however you have to take the link that is in the first reply in this thread left my Jim to see them. They had pretty good advice.

-Greg

 

Welcome to FTE, opalminer! Greg was correct that on the 97 there was an issue with the fuel rail gasket. Perhaps this could be your problem, but you should check the other obvious culprits as well (other vacuum leaks, fuel pressure).


Greg,

Yes, the gaskets lay into the upper plastic intake plenum and seat against the metal lower intake/fuel rail assembly. I used OEM gaskets, they aren't very expensive for the set of three, and just doing the uppers worked for me. Unless I was suspicious of the lower gasket (coolant leak, etc), I would just do the uppers as a start. If you still have the issue, you'll know exactly how to do the lowers (It also shouldn't hurt the new uppers to have the plenum off again). The lower is a more expensive gasket, and you'll definitely want to spring for the OEM since the aftermarket ones are made of cork.

If you haven't seen it, there is a really good step-by-step technical writeup with pictures by Rockledge that describes how to do both of those jobs. Should be in one of those threads that I linked.

-Jim

 

Gents,
I too have a 1997 Ford Ranger, V6, 4.0L XLT with extended cab, 4X2. I also have the check engine light on and get the same PO171 and PO174, "system running to lean" codes when checked. I have had this problems since 2002. I have tried EVERYTHING with no permanent success. Everytime someone (a garage), or me, tried a solution, they all worked for a short time. Sometimes a week, sometimes a couple months. But none solved whatever the prevailing problem is. I too have changed the O2 sensors, the MAF, the upper intake gasket, the lower intake gasket, you name it. I have resolved to just "accept" the check engine light being on. The only time I have issues with my vehicle is when it comes time for inspections, but luckily, I have always been able to get it "approved". BTW, my truck has been almost exclusively in warm weather, CA to NC with short intermittent trips up north or in generally cold weather. I never noticed any difference due to the cold or warm weather. My truck has 230,000 miles on it and except for some dings, stratches, wear and tear and a recent fender bender slightly bent front bumper, it still runs fine. Oh, wait, my windows suck. The driver side window works 97% of the time, but every now and then it decides it doesn't want to work. Also, the weather stripping on the windows don't seal properly so I have a high wind sound at high speed. I just suck it up. The truck is paid for and there is something to be said for not having a truck payment.
If anyone can tell me anything else about the O2 sensors, hell, I will try it. If it doesn't work, I will just add it to the long list of things that didn't.
Thanks
Clark

 

Clark,

The first thing that I would do is to be SURE that the intake gaskets are not leaking, as this is probably the largest source of "error" for the trouble codes you mentioned. Just because you (I assume it was you) replaced them previously does not mean that you (or the garage if that was the case) did not make a mistake in their installation. My truck has the same motor as yours and I know the lower intake gasket surfaces were a b*tch to get clean. The upper gasket is pretty straight forward, however they aren't what I would call a very large gasket, meaning they dont really provide that much "squish" room in order to ensure their sealing. Also, how long has it been since you changed them? I would be willing to bet that the upper (or possibly the lower) gasket is still giving you problems. I used Permatex Copper Spray a gasket when I replaced my lower gasket to ensure the gasket sealed properly. Again, the upper ones are easy to replace.

At any rate, if you are convinced that is not the problem, I'll delve into other sources of error. I would look for any gasket leak that would allow air into the cylinder in an unmetered state. In other words, anything past the MAF sensor. That means throttle body gasket, etc. Some other things to consider would be with 240,000 miles on it, do your valve covers leak, and also...the inevitable head gasket. I've seen head gaskets leak, without losing coolant, and without SERIOUSLY effecting performance, especially if it was over time. One way to perhaps narrow down the problem would be to simply pull the spark plugs. They will tell you a lot. If you find one or two that are completely different than the rest, then you have a place to start looking for a more centralized leak. Also, you said you changed your O2 sensors, but did you change all of them? If not, it's important to do so. This may be a stretch, but if your truck has been burning oil, coolant, or the likes, it likely ruined the o2 sensors, and could have clogged the catalytic converter. You may not notice the difference in performance because it would have taken a while to clog the converter. This would result in the computer trying to over compensate, and could possibly peg the system rich.

Lastly, the other end of a lean condition is lack of fuel in the mixture. Things to check would be fuel pressure, injector nozzles, FUEL FILTER, etc. Changing the fuel filter in my 98 ranger at nearly 150,000 miles made a WORLD of difference. Again, looking at the spark plugs may help you in that area.

I hope that helps get you started. If you start checking into things, feel free to post your findings and I will guide you the best I can.

-Greg

 

Greg,
Thanks for your response, I really appreciate it. Like I said, I have been dealing with this since 2002 to no avail and have resolved to just accept it. At this time, I can't address it again, but I will need to soon as my inspection will expire in a few months.
I am limited in my automotive skills so I only do the basics. I leave the more complex stuff to the pro's. The upper intake gasket was a local repair station here in NC. The lower intake gasket was another possibility by the Ford dealership back home in New England. I don't think I have changed the O2 sensors in a few years. I figured/assumed they were not the source of the problem, but doing what they are supposed to do and identify the error/problem. I have not thought of the catalytic converter, oil burn rate is not noticable, i.e. seems normal, and the coolant has a small leak but that is external to the engine (I haven't pinpointed the leak, but know the general area and it is on the radiator). The fuel filter has been changed a couple times, but good idea on the spark plugs.
Basically, if I want the truck to last longer, I will need to address some issues soon to keep it up and running. I really like telling people how many miles it has, paid for etc, kind of a pride thing.
Thanks
Clark

 

Have you ever replaced the fuel supply manifold gasket? Keep in mind that the fuel supply manifold gasket is not the same thing as the upper or lower intake gasket. See: 1997 Ranger 4.0L Fuel Supply Manifold TSB

 

Would these same leaking gasket problems apply to an 01 Ranger with the 4L-6?
I have the same two codes 0171 & 0174.

 

Your '01 Ranger 4.0L (SOHC) is a different design than the 4.0L (OHV) that is discussed in this thread. But the answer to your question is still yes, because the SOHC can also develop leaky intake gaskets causing both banks to run lean.

Another possible culprit could be a vacuum leak in the PCV hose assembly (not all that uncommon on the SOHC).

Check out this relevent thread: https://www.ford-trucks.com/forums/6...171-codes.html