P0171 2003 5VZ FE Driver's Side Crank Case Vent & Intake Manifold Vacuum Leaks

I've been chasing a P0171 code forever.

I think I've finally narrowed it down to a intake manifold and a crank vent vacuum leak. See video below using smoke test (this was late in the day, smoke machine ran out of smoke but you can see escaping bubbling through liquid)

The vacuum hose that runs from the rear part of the intake manifold to the throttle body leaks where the metal part enters into the intake manifold.

The intake manifold gasket looks like a pretty straight forward replacement. Just time consuming.
-Is there anything else recommended to be done while I'm in there?

https://www.youtube.com/watch?v=ILPP5c35Uqg

 

Replace it all down to the intake manifold gaskets. That includes valve cover gaskets & bolt grommets, plenum gaskets, PCV valve, and any hoses you feel like changing. Make sure to check the torque specs for all that - they're all surprisingly low.

 

Got it.

I just realized I made a mistake in my initial post regarding the leak at the crank case vent on the drivers side valve cover gasket.
That leak is at the base of the metal tube that comes out of the intake manifold for a hose that goes to the throttle body, not the crank case vent on the valve cover.
Luckily I won't have to touch the valve covers. I replaced the gaskets and all associated bits about 40,000 miles ago.

Otherwise, replace all gaskets and suspect hoses and use appropriate torque are the plan. I have at least one suspect hose that will be replaced which is a silicon hose I replaced a few years ago, it split already. I'll probably go back to normal vacuum hose material or go overkill and use fuel line.

What I'm wondering is while I have the intake off are there any sensors or anything else that are worth replacing while I have it off?

Edit: Just got this tip from another thread -"Do your knock sensor harness and re-seal the coolant crossover pipe. Good time to replace the 4 heater hoses up there as well (2 for IAC valve, 2 for heater core)" I'm going to add these to the list.

 

Maybe just the coolant temp sensor. Not really anything else that needs touching imo unless you want to send your fuel injectors in for a rebuild

 

Sounds good. I’ll look into the temp sensor as well.
I put put rebuilt injectors in when I did the valve cover gaskets about 40,000 miles ago.

 

I've been chasing P0171 for over a year now.
I did these:
new fuel filter
cleaned MAF
new O2 sensors - fore and aft (there's only 2 O2 sensors). I don't know how the computer knows P0171 (Bank 1). There's only 1 set of O2 sensors for this V6.
new PCV valves

I also tried to put a fuel pressure gauge on it but no easy spot to connect it. I ended up putting a lot of air in the fuel system and the CEL went off immediately. After sputtering for a mile, the CEL came back on.

That told me lower fuel pressure removed the CEL.

My LongTerm (LT) fuel trim is ~30% (very high) and that's probably what is triggering the CEL. Ideally, 0% to 10% is good.

I suppose the vacuum leak is the problem?
My fuel mileage was ~17mpg before and after this P0171 came along. The Taco runs the same as before so I'm struggling to find a reason to spend more time and money fixing this.

Another thread suggested a MAF test/replacement.

Another thread suggested a vacuum leak (of which I can't find any). I would need to learn how/where to use a smoke tester.
https://www.youtube.com/watch?v=8G4iG6JgpUE

 

The test in the video is exactly what I did to determine a vacuum leak.

For the smoke machine I bought something like this but it was like $45 at the time. You might be able to find better options.
https://www.ebay.com/itm/282339070632?epid=689245513

 

So I watched my LongTermFuelTrim %.
When I push the gas, LTFT% goes to 39.8%. The Max.
When I let off the gas, the LTFT% goes to 0%.
I most likely have a fuel starvation issue. Not an air leak.

I tested the kOhms on my MAF. It was within spec.
I tested the voltage as I blew air through the MAF. It shows variation.
I think the MAF is fine.


I just replaced my PCV valve. The old one allows me to blow both ways.
The new one allows me to blow both ways.
A 3rd one at another store allows me to blow both ways.
This Tacoma has an unusual PVC valve function. Am I wrong?
I put the new PCV valve in and left it there.

 

Same problem after new PCV. The LTFT% works it's way to 39.8% after the new PCV valve, albeit a bit slower now.
I still am leaning towards fuel starvation.
I bought the JoyTech fuel pressure gauge system but as many of you know, there's no easy way to connect a guage. No Schrader valve anywhere so I tried the banjo-bolt method by connecting the banjo-bolt to the front end of the driver-side fuel rail.

The banjo-bolt leaked huge amounts of fuel even though the connection appeared snug so needless to say, I didn't get any test results there. Oddly, the P0171 went away after I removed the banjo connector while the pump was trying to fill the fuel rails. Once the engine was running smooth again, the P0171 returned. I still don't know what was going on there because in the case of missing fuel, the CEL went away. That makes my starvation theory wrong.

 

I hooked my fuel pressure gauge inline with the fuel hose. It tests 44psi with the engine running. It held 40psi after 20 minutes. As you can see (if you don't know), this is fuel pressure tested BEFORE the fuel pressure regulator. That fuel hose wraps around to the back side of the engine.

 

Update:
I replaced the Fuel Pressure Regulator. Same Problem. P0171 comes back.
If I pinch the return fuel line, the Fuel Pressure gauge goes from 40psi to 70psi. I highly doubt the fuel pump is bad but I have a new DENSO pump ordered.
Although I've cleaned the MAF twice and tested it electrically to be fine, I ordered a new DENSO MAF. That should be here in a couple days. Easy install!

I also removed my Fuel Injectors and blasted Brake Cleaner through them. They all appeared to spray the same. Tons of spray. I didn't measure flow-rates or anything but they blew fine. I also measured 14ohms across the 2 pins (give or take a bit). They all matched pretty close.
I'm looking for more ideas. Thanks in advance.

Here's the thing: I can throw money at parts for months and still spend less than diagnosis, parts and labor from 4 hours (say $150/hr) at a shop.
Heck, I called the Stealership yesterday. They wanted $250 for a single fuel injector. Imagine how many millions of these 23209-62040 Aisan injectors are out there. I'm betting 10,000,000. They don't fail very often so finding 6 good used ones could cost a few dollars each. I'm hunting for those now.

After all, these parts are all 24 years old with 150,000 miles on them. It's possible they are all about to fail. Oddly, with the P0171, the truck runs and drives as good as ever. That could change and I'm still determined to fix this.

 

I actually have some OEM injectors I bought from another member awhile back if you want them. I got them thinking I'd send them to motorwest for servicing, but then just got new "upgraded" Denso injectors from Motorwest instead.

 

Update:
I bought a new DENSO MAF. Replaced it last night and cleared the codes. Below are before and after ShortTerm and LongTerm Fuel Trims. Both scans/pictures are whilst rolling on I-90 @65mph in similar weather.
I'm not saying those numbers are good. I'm just glad I made a change that shows any difference at all. That's a victory!

Now I just need to drive a little more to see if the P0171 code comes back.




FUELSYS1 flashes from 'CL' to 'OL-Drive' on occasion. Closed Loop vs Open Loop. It looks like a smog-readiness routine is in progress. I've never seen this before on this vehicle. No P0171 code yet!

 

As a reference my LTFT rarely goes above 3% and STFT hovers around there both over and under. Does it get better when under load? I believe the threshold for the check engine light is 25% LTFT.

 

Good info. Thanks for that. My numbers are all sub-10%, plus or minus. It took about 20 miles of driving around town to get the ClosedLoop to stick.
My problem is FIXED!
I just needed a new MAF.

I tested the MAF a month ago and all the numbers were right.

I know it doesn't make sense to throw parts at a car, but this time, troubleshooting did not help. Furthermore, once you open the package on an electronic part, you bought it. The general public is not stocking a known-good MAF waiting for you to test. You can't stop a stranger on the street and ask to borrow their MAF. You have to buy the MAF. That's what I did. $120 for the DENSO OEM MAF.