My P0172 has been resolved

My P0172 has been resolved. It was a combination of the charcoal can being faulty, and me having it connected to the wrong port on the throttle body that sees vacuum 100% of the time.

The charcoal tested bad. The fresh air hose was plugged up with dirt as well which contributed.

 

Any idea how many miles this 2RZ currently has? That might help with folks offering troubleshooting advice.

 

you have covered all of the normal tests. I have a couple of suggestions. Monitor the ECT (engine coolant temp) via the scan tool to see if she is running too cold while you are driving and look at the g/ps of air that the MAF is reporting at idle. A good base line at idle is 1 g/ps of air per liter of engine size.

What toyota uses as the testing parameters to actually trip a P0172 I do not know.

 

Check all grounds making absolutely sure that they are connected. There is one particular ground that cause a start but not run issue with my engine. This ground is located next to the front ignition coil. Check the battery to body ground, Engine to body ground as well. If you want a peace of mind and literally know if those grounds are in fact working you can set up a multimeter on Ohms and check them. Anything above .03 Ohms is too high of resistance so remove, clean and reinstall the ground. This procedure goes with all terminals whether ground or hot. .

 

I wish I knew, the engine came from a Tacoma that had burned up. I'm going to be checking the valve clearance here soon

Coolant is spot on so that's not it. The front AF sensor detects a rich condition

Thanks, I'll doublecheck them

 

Mechanic friend of mine thinks I have a leaking injector. Wants me to idle it for 10-20min and then pull the plugs to see if one smells of fuel etc. If anything this is really easy to try. I'm just skeptical that an entirely different set of OEM injectors that have been cleaned have the exact same issue as the old set. It could happen, but I'm leaning towards the AF sensor right now.

 

Have you checked for cracks/leaks in the exhaust header.....is it cast iron one??

Fuel trim off like that usually means an airflow problem somewhere.....
between the MAF and the O2.......

 

Have you verified that all grounds to the ECM are good (incandescent test light - 2 amp min), and that the ground for the MAF is good as well? That definitely looks like a good candidate, but since you say it almost seems to run better with the old one, I'd want to verify the connections first. Pin fitment good, no corrosion, and good power, ground & signal at the connector.

 

I have heard of instances where a particular vehicle just wont "fix" no matter how many times the codes are cleared. What the tech ended up doing is disconnecting the battery and unpluging and repluging the PCM after a 15 minute wait. Does this bleed the capacitors off fully and/or does the repluging clean the contacts after 20+ years? This is a cheap and easy test.

 

Its a stock manifold. I haven't but I'll do a thorough check of the manifold and exhaust leading to the 02. I guess it could be the gasket where the header meets the downpipe where the AF sensor is.

I have 1 wire that is suspect and that is the blue wire connection at the maf connector. I have a new pin and am going to re-pin it here soon

I'll do this when I pull the ECM to check for cap or trace damage

 

I don't think it's the MAF. The calc load and volts have been correct for both MAF's I've tried.

VG 'maf signal line' in spec when blowing through MAF and probing VG and E2
THA 'iat power' idling 2.63V
EVG 'ground for VG' continuity to ecu is ok
B+ 'power to maf' is 11.3 key on, and 13V idling
E2 'ground' continuity to ecu is ok

 

How did you determine that?

 

Continuity from ecu pin E-17 to the maf pin is ok.

I installed the new AF sensor and LTFT was within spec well into closed loop, and then started hitting -17% @idle. Anything off idle under any load and fuel trims are ok. I think I'm going to crack the ecu open and look at it. Then check exhaust for cracks and check valve clearance.

 

Again, how did you determine that? If all you did is a continuity check with DVOM, it's meaningless. You can easily have a circuit which has continuity but is incapable of flowing current. You need to verify with a load ideally >2 amps or more. If it can light an incandescent bulb of a decent size, you're okay, but if not... Bad grounds have been the root of at least 75% of the electrical gremlins I've chased, and a good many of those have shown continuity, but couldn't flow current to save your life. This may well not be the issue, but you need to positively eliminate it before moving on.

 

I'll circle back around and check VG. FSM says to measure voltage between terminal VG of the ecm connector and body ground while engine is idling 1.2-1.5V with ac off -done no issue there

The ECU is clean inside. No obvious damage to the board.

I checked the valve adjustment and found 1 of the Exhaust valves definitely needing an adjustment. It is .007 while the rest were .010

I'm going to remove the ECU coolant sensor and check it out as well

 

It wasn't the ECM coolant sensor.

Hot compression test.
175ish 175ish 175ish 190ish

I had one exhaust valve at .007 and I adjusted that out with a yota 2.850 shim to get .011

Unfortunately for me adjusting that one tight exhaust valve didn't fix this issue.