Dreaded P0172 ‘99 1st Gen Supercharged

Hello all. Been working on the rig a lot lately. Started out as a leaking injector shooting fuel all over. Got that resealed and now stuck with a P0172 and I have reset the ECM numerous times. Replaced MAF and Upstream 02 sensor with genuine Denso parts, injectors from LCE Engineering that are sonic cleaned, flow tested Aisin injectors. Verified crank and camshafts timing, compression is 165-180 cold. Leak down test showed very minor loss through piston rings. Plugs look good, Denso plugs and are gapped within specs. They ohm out good, wires ohm out good and coil packs. Fuel pressure holds rock solid after prime and engine shutdown. Running idle fuel pressure is around 48 PSI. Does seem a little high maybe. I disconnect the vacuum line to pressure regulator and no change, stays at 48 PSI which seems odd. No fuel out of regulator though. Possibly a failed spring inside the regulator? This pressure regulator has no name or part number. Does it look familiar to anybody? No change with hoses from charcoal canister removed. I’ve completely verified no vacuum leaks. Upstream 02 switches rich/lean once in closed loop and downstream stays lean like it should. I create a vacuum leak and they both show go lean on the voltages. My short term fuel trim will hang around -2 to -6 at idle and my long term fuel trim will stay pretty much at -40 Mh long term will barely get better with some load or RPM, but at idle it’s stuck at -40. Thank you anyone with some input!! Feels like a slight hesitation at idle, but off the line runs perfect. Truck has 312K Pulls like a mofo through the gears still even running like it does now.

 

If you’re running iridium plugs keep the gap that they come with. Don’t gap to stock spec.

also, get rid of that fuel pressure booster. Run methanol for extra fuel up high and make sure you’re referencing boost 1:1 by having the FPR plugged into the manifold boost port on the s/c.

 

I will double check the plugs again to verify! This fuel pressure regulator setup has been on this truck for at least the last 150K running fine with no check engine light.The other vacuum hose runs to the PCV valve on the passenger valve cover? Is this correct?

 

@Wulf you fought a p0172 code for awhile, what did it end up being I forget?

 

The plugs really have nothing to do with it. Just a suggestion though.

48psi seems too high. I’m pretty sure it needs to be around 43. but I don’t think that would explain throwing a code for running rich.

 

Welcome to TW Toby
This is by far the most comprehensive and accurate diagnostic description ever posted to Tacoma World.
Such a far cry from the average of
HELP my truck goes pop cuts off and won't start.

 

Thank you all for the quick replies. I seriously have been butting my head with this issue. I’m at such a loss and I need some help with this girl! I would also like to mention I replaced the head gaskets around July 2019. When I took the heads to the machine shop they had no leaking valves so I opted out of a valve job. Wow no leaking valves at 285K! TOYOTA FOR THE WIN! The recent cylinder leak down test would’ve exposed an issue there anyway... The Spark plugs I wouldn’t think to be an issue either. I don’t think there is insufficient combustion and too much fuel leaving the cylinder. Exhaust exhibits no smoke and doesn’t smell rich with fuel. The live data concludes to me that the cat is cleaning up the exhaust as well. If it’s out of spec let’s say 5 psi of fuel pressure. I also agree that 5 psi wouldn’t cause an over fueling rich condition! Just doesn’t seem excessive! The IAC is functioning correctly, verified with power probe and cleaned it anyway. TPS is within voltage spec and no hiccups seen in my voltmeter or live data on scan tool.

 

Here is some good diagnostic info. There is more in the rest of thread. I ended up replacing the injectors with a second hand set that I cleaned and it cleaned up my fuel trims, rough idle, and code

 

He's getting a 'system too rich' code (P0172), wouldn't a bad or inconsistent fuel pump be more likely to cause a too lean condition?

 

That’s what I would think. Fuel pump is dumb, It just flows fuel. It’s the FPR that regulates that flow.

 

I would think if the pressure regulator has failed and is keeping the fuel pressure too high at idle. Maybe this would cause a rich condition due to over fueling injectors?

 

Is that Cobalt Blue Pearl that I spy?

 

Maybe the fuel pressure is taking a dump on throttle. Think of it like your finger on the end of a hose. You get more flow at lower pressures and instead of atomizing fuel it’s just for of dumping though the injectors.

 

Yup i read it too fast

 

Someone shoot me. I’m hung up on the fuel pressure still. Sits at 48 psi at idle. Unplug vacuum line and still sits at 48 psi with no change.

 

Has anyone experienced a fuel pressure regulator like this. I’ve ran into the usual fuel squirting out because of a rupture diaphragm. Not the opposite.

 

If I understand your post... the LTFT reading of -40 is telling you that the front O2 sensor is maxed out tyring to take fuel out of the system in an off idle situation. If possible I would locate a fuel pressure regulator that can be used in both a normally aspirated and boosted applications that is adjustable. Aeromotive makes a good line of regulators. I would drop the pressure to 44 and see what happens. I think shortman5 is correct... you regulator might have an enrichment factor greater than 1:1 and with the flowed injectors it could just be too much. The problem is is driveway engineering rarley works and you get stuck with fixing and patching a system that doesnt have matched components that are know to work together. Electronics can only do so much.

 

Not saying that any of this is a bad idea, just unnecessary. OP should replace the FPR and make sure the vacuum line is hooked up to the lower manifold port on the S/C.

You don’t need an adjustable reg, those are largely for motors that are converted over to a fuel tank return system.

40-43psi is what you want. And that’s it. If it’s not running properly with a new reg and that pressure you’re problem is somewhere else.

EDIT: OEM reg.

 

Here’s the spec. Mine runs at 40psi at idle. With new FPR, Pump, filter, and “rebuilt” OEM injectors.

https://workshop-manuals.com/toyota.../system_information/specifications/page_1384/

 

Would it be ok to go back to the factory FPR even with the supercharger? This truck is bone stock.