P0300 P0303 P0171 - diagnosing

Great advice! I will

 

I decided to buy these upgraded set of fuel injectors from Motor West Performance instead of rebuilding mine.

Will snag a pressure regulator too.

 

I did the same and I think I got my fpr from napa. Works great now.

 

That's what I got. If you have any questions, I should be able to answer as I just did my injectors about a month ago.

 

Just a note on the injector install- The FSM (and Timmy) use gas as a "lube" of sorts on the installation of the injectors. I had horrible results with the gas- despite being extremely careful, I ended up with several pinched o-rings, resulting in fuel leaks. The MotorWest injector kit includes a small tube of super lube. Use the super lube- just a small dab and spread it around the o ring, and then send it. From what I found, the gas causes the rubber o-ring to expand and that causes the pinch. The super lube does not cause the ring the to expand. Several month later no leaks or adverse side effects of using the silicone rather than gas.

 

My new injectors arrived yesterday. Still waiting on the FPR.

And the misfire codes and coolant leak still have not returned. Have run this thing hard recently, and temps have fluctuated from hot days to snowing this morning... so I think we can safely say that the K Seal Ultimate actually did what it said it would do. I'm impressed and glad!

I'm going to tackle the suspension as well. It's riding like a rocking chair.

 

All the parts arrived… upgraded injectors and FPR. As soon as the engine cools down I’m diving in.

I will report back whether this clears the lean code.

 

Welp. After work today I dove right in and replaced the injectors and the fuel pressure regulator. Cleared the P0171 engine code, and left for a test drive.

Truck definitely accelerates much, much better. Glad I did the injectors. But, after 5 minutes, the CEL came back on. P0171 code is back "System too lean".

So back to square one on this damn code.

In addition to the fuel injectors and the fuel pressure regulator, I have also done the fuel filter, and I have done the mass air flow sensor twice. The last time I did the MAF sensor was 12 months ago, and so it could be dirty. I'm going to pull it and clean it off right now, and leave the K&N filter off for another test drive.

I've searched for vacuum leaks and found none.

Other possible culprits - upstream O2 sensor... maybe the fuel pump?

Any other ideas? I'm really struggling with this one.

Edit: oh yeah, I did coils, new wires and spark plugs 6 or so months ago.

 

Have you checked fuel pressure? If not I would start there.
What do fuel trims look like idling and driving?

 

no I need to learn how to check the fuel pressure.

STFT idle fluctuates between 0 and 10%
LTFT idle is around 39%

STFT driving fluctuates usually below 5%
LTFT driving is around 28%

im not positive these numbers are accurate. Still learning how to use this OBD scanner I have.

I’m in salt lake area around 5,000 feet elevation.

 

You have to tee into the line, there is no fuel pressure tap.
I can't remember for sure but I believe later model 1st gens have a quick connect fitting similar to 2nd gens where the fuel line from the engine hooks up to the fuel line on the frame, if it does that's probably where you will want to tee in.
If it does you will need something like this.

$33 BETOOLL Fuel Pressure Test Kit 0-100PSI with 9.497.896.30 Fuel Line Fittings

https://www.amazon.com/BETOOLL-Fuel-Pressure-0-100PSI-Fittings/dp/B07LF26ZTJ?th=1

Fuel pressure should be 33-38 psi idling and should not decrease under load.

 

I don't have a schraeder valve on the fuel line so I'll have to T in somewhere. I'll test the pressure.

 

Hmmm. system too lean. too much air not enough fuel. dumping fuel. hugely high fuel trims. needs to add a shitload of fuel because (insert reason here).

You sure you don't just have a huge intake leak?

 

a huge intake leak would cause a lot more air to come in than is measured. This would mean that more fuel has to be dumped in to the cylinders to compensate for the unmeasured air coming in. Yes, low fuel pressure could cause this, but it would be much cheaper to triple check and make sure you have no intake leaks. what's your measured airflow at idle?

 

Very, very good points @CodeSeven - No, I'm not positive I don't have a massive intake leak. I tried testing for vacuum leaks. I had a small one right at the MAF sensor on the K&N intake pipe. Sealed that with silicone, no more leak there. What more could I do to really test the intake for leaks?

I picked up a fuel pressure test kit tonight at O'reilly, but it doesn't have any usable adapters for the supply fuel hose connection. So I need to get another fuel line from a junker .

 

gonna try something like this:

 

None of the junk yards in Salt Lake have any 1st gen Tacomas... Just realized I could pull that fuel piece from any Toyota with a 5VZ. Found a 97 4Runner at the junk yard so I'll head over there this morning.

 

Fuel pressure testing doohickey complete. Got the hose bit from a 2000 4Runner at the junkyard for $1.39.

Fuel pressure is testing at a constant 44 PSI at idle and at RPM in the driveway.

That seems good to me.

I'm going to try to rig up a smoke tester now and test for vacuum leaks. :/

 

I did a smoke test into the intake boot. Propped the throttle body open. Waited as I pressurized the system with smoke. No smoke visible anywhere that I could see. I'm searching online to see if there are other places on the system where I should apply smoke to determine air leaks.

Kinda bummed - was really hoping the smoke test would show a big ass air leak and solve my problem.

Right now it would seem there is no air leak and the fuel pressure is good. I'm stumped.

 

I'd start looking for potential secondary things... Exhaust leak, O2 sensors, EVAP system. Something is feeding your ECU bad data.