Ok, I have a constant P0171 code (Bank 1 Lean) that comes back within a few miles. Also sometimes hard starts or no start (particularly when cold). When really cold outside it will refuse to start sometimes until it warms up outside for a few days. I'm trying to​ rule out any issues. This is not the only thing I'm doing to check over it. Please tell me if you know of a common problem that causes this!

The Bank 1 STFT is reading between +11 to +25% all the time. Bank 2 seems to be moving some but stays between +10 and -10%, so within spec.

The MAF is clean and original. 203,000 miles.

Does anyone have a pin diagram of MAF, of what is what on Gen 3 monteros?

Does anyone know what the code reader app live data should show at idle as well as what it should do as RPM is raised? I've heard at idle it should show roughly what the liter is, so my 3.8 should show about 3.8 at idle? This is a general rule of thumb and I'm not sure if it's relevant for Montero.

Does anyone know what the Hz and/or Voltage should do if I back-probe the MAF and read it's output that way?

Maybe I can find someone who is really bored and will test their known good MAF and Fuel Trims and post results here? Please tell me if results were from a hot vehicle, or cold, or both. Thank you!

 

It sounds like you have a vacuum leak on bank 1. Possibly a bad gasket or wvwn a cracked o-ring on fuel injector. Try to rule out that first before diving into MAF. An issue with MAF would have affected boyn banks at the same time

 

That's right I forgot about reading that. MAF usually effects both banks. Thanks for reminder. Makes sense also.

MAF reading seems to be moving up and down accordingly today as I drive around town. MAF bottoms out at 3.5 at lowest idle and perks upward to 70+ when revved, so it should be good.

I'm gonna make a smoke canister and smoke it good this week for vacuum leaks. No visual leaks and no response to carb cleaner and no hissing I can make out. Ya know my traction control (showing it's off) light comes on everytime engine code comes up...from what I recall that is also vacuum controlled. And my 4x4 sometimes won't come out or go into 4x4 mode which is also vacuum controlled right (I have to cycle ignition to get it to work)? Maybe all related to same vacuum leak if those systems aren't isolated somehow.

What's weird is my other 2003 and this one both have P017x codes but for opposite banks. They both have similar poor fuel trims but on opposite banks. And both Montero post-CAT oxygen sensors (all 4) constantly move up and down rather than being steady high as I understand they should do. I guess that could be them responding to the constant air flow, or worse case, excess fuel being jacked up by faulty injectors operations.

Ahhhh I hope I don't have to remove that damn intake for the 6th time! Lol

Have you had to do injection orings or injector themselves? If so, any special tools needed or fuel rail gauges? Maybe a fuel pressure test could tell me if it's leaking to begin with? I HATE doing unnecessary labor and parts! I'd have to go borrow a fuel pressure gauge....

 

I suppose it is possible that a vacuum leak in 4wd control system might be sufficient to throw the code, but I'd venture to guess that it is more likely to affect both banks, since the "feed" for it is right off or around the throttle body

There is an o-ring on the bottom if the injectors. I don't know if you can source it easily. I had my injectors cleaned recently (mail out service) and they came back with all new rings top and bottom.

Are you able to view live fuel trim readings? If so, there is a way to tell if the Lean condition is coming from the vacuum leak or from poor fuel delivery.

 

What company did ya use for that injector service? I suppose they clean them ultrasonically? What's cost per injector? Sooner or later I'll need this service on one of my aging vehicles, I'm sure...

You mean the orings are hard to find also, by themselves? That's so lame, if so! I found a set on Amazon but they appear to be the top orings that go into fuel rail.

I can read the fuel trim live on my device. What method tells me if it's fuel feed or vacuum causing lean? Right now the STFT pings all over the place, no matter what driving conditions, steady RPM or whatever. Sometimes the LTFT moves around also.

Thanks!

 

I send my injectors to "Mr. Injector". It is a small outfit not far from where I am. He does ship them anywhere. The website is https://www.mrinjector.us/ All the details are posted on there.
The cost was $17 per injector and includes flow testing before and after, cleaning and new o-rings/seals. I was very pleased with the price, work quality and how fast the turn around was.

The way you tell if your lean condition is related to vacuum leak or to poor fuel delivery is as follows:
1. Pair your reader with PCM and run engine at idle. Note Short Term fuel trims (at least the range, say - +15- +18%
2. Increase RPM by opening the throttle (2-2.5k RPM).
3. Note STFT again, if they drop as RPM is increased.
4. Drop RPM. Did STFT go up again?
5. Repeat few times to confirm.
If this is behavior you are experiencing - you got a vacuum leak. This is because engine vacuum is maximum at idle (throttle closed). When you open throttle, more air can get into the engine and vacuum is reduced. If you had vacuum leak, less un-metered air is entering intake and fuel trims go closer to "normal" or zero.

If on the other hand you have opposite response - STFT is increasing with increased RPM and staying up there when you run high idle, you have a fuel delivery issue.
I hope this is clear enough to be helpful.

 

Cool I saw that company on a web search. You're from Idaho? I want to move to northern Idaho. A friend moved near Sandpoint 2 years ago and we visited this past summer and liked it a bunch. I gotta launch two kids from high school and then we will likely do that in 2 years. I'm in Western CO now near Glenwood Springs. I love the big sky, Rocky peaks, and sunny environment but the ski bum and out of control cannabis culture has really become a PITA! And I'm not against cannabis, but it's become so irresponsibly sold and marketed it's stupid. And I'm tired of all the transient culture that swallows up ski-vacation areas...we have Vail, Aspen, Beaver Creek, Snowmass, and 4 other small ones all within 1.25 hours from us (we're in the middle). I didn't foresee that problem when picking this area 7 years ago. It really is a negative thing for the steady locals...too many transients that mess up the dynamic for good community. All the town's people are like slaves to the vacationing folks that don't give a damn because they come and go.

Thanks for test procedure! I'll try that test today or tomorrow on it and post results. I was gonna run my smoke gadget on it also...if I can use coconut oil instead of mineral oil, which I don't have laying around presently.

 

I live about 2.5 hours south of Sandpoint in Washington. But I treat the entire North West my home , especially Idaho panhandle.
Standpoint area is gorgeous. There is a lot of tourism there, but not anything like the ski resort towns in Colorado.
If you do move this way, we'll have to have a beer and look at each other's Monteros 😁

 

​​​​​​Ok got to do these tests just before dark...what do ya think? Is this what you're talking about?

Vacuum testing on Bank 1 (the one with lean code P0171):
At hot idle STFT +2 to +4.
At 2500 RPM STFT -7 to +2.
When I go from idle to 2500 RPM the scanner shows STFT dip to -17 to -20 for about a second then it comes up to the -7 to +2 range as it settles into the 2500 RPM load. When I release fuel pedal it returns to a steady +2 to +4 after about 10 seconds of rolling around in the -5 to +10 range.

So when I rev it to 2500 it sharply spikes downward to -20ish but then adjusts after a second and rolls around in the -7 to +2 range thereafter.

Bank 2 STFT does same pattern but it's about -2 to +2 when idle and -10 to 0 when 2500 RPM.

 

I think it is a vacuum leak. Any luck with smoking it?