2016 Honda Accord 2.4 GDI P0172

Need suggestions! Yes this is being recorded.
Symptoms: check engine light, car runs good on my test drive but my brother said the customer complain of some driveability issue too.

Total fuel trim is -35 (0.83 on LT and 0.82 on ST) at idle. At 3000 rpm ST improves to near 0% (1.00) and LT stayed the same.

After clearing code LT reset and when I redo that test, at 3000 RPM trims are normal. So rich running at idle only (it seems)

PCV and Purge systems blocked off, no change

Upstream wideband sensor and downstream O2 react to full lean and full rich conditions. Wideband range is -1.4ma full lean and .56 to .60 ma full rich (would love someone to confirm these numbers)

Downstream O2 is pretty steady at .6 to .7 volts (pretty certain this proves that we are not taking fuel away needlessly from a faulty upstream wideband sensor, though I am still questioning it)
We confirmed with a 5 gas, no excessive O2 levels coming out of the tailpipe (false rich from a bad upstream wideband would cause elevated O2 levels and a lean downstream O2 IMO)

HIGH PSI fuel pump (GDI) bleeds down on shut down. Stuck a camera in each cylinder to look at injector tips and none of them show signs of fuel seepage.

Fuel trims will normalize with MAF unplugged. Swapped MAF sensor with another car in the shop to no avail (yep, I'm a parts changer lol)

Calculated load near 100% at wide open throttle (confirming good VE and MAF calculations)

Worried about valve lash (Honda crap) with 144k on the engine but MAP is 28.3 KOEO and 7.9 at idle (over 20 inches of vacuum) so leaning away from this.

Worried about alcohol in the fuel or type of fuel but this usually leads to lean conditions, not rich.

Headgasket (HC test) confirmed to have no leak

I really need a lifeline here. I'm not sure where to go and heading back to my brother's shop in a few hours.

Thanks everyone!

I don't know about suggestions, but I got some WAGs! :silly:

I wouldn't sweat the valve lash for now. Most newer Honda engines don't suffer from valve seat recession the same way that older ones did, in my experience.

Anything upstream of the MAF that would cause an issue with laminar airflow? What's the g/s reading at hot idle with no loads?

While you have the scan tool connected, you might try running the Cylinder A/F Test just for giggles. It's usually pretty decent at finding rich or lean injectors.

HIGH PSI fuel pump (GDI) bleeds down on shut down. Stuck a camera in each cylinder to look at injector tips and none of them show signs of fuel seepage.

I know it's tough to quantify, but how quickly does it leak down? If you pull the dipstick and take a whiff of the oil, does it smell fuel fouled?

Anything upstream of the MAF that would cause an issue with laminar airflow? What's the g/s reading at hot idle with no loads?

Nothing noticed, air filter is good and mounted correctly. Around 2.5g/sec and 1.14v at idle (same as the donor MAF)

While you have the scan tool connected, you might try running the Cylinder A/F Test just for giggles. It's usually pretty decent at finding rich or lean injectors

Did that test and they all failed equally for rich condition is what the result said.
I also did the automated GDI fuel pressure test and it passed. (No data, just pass or fail)

I know it's tough to quantify, but how quickly does it leak down? If you pull the dipstick and take a whiff of the oil, does it smell fuel fouled?

Pretty quick. I can watch it drop from 500 psi to 300 psi in 15-30 seconds?
Also cranked it over with coils removed to gain psi and had it at like 1100 psi and that also dropped pretty fast.
As for the oil smelling like fuel. I need to check that but thought with the PCV hose pinched off that I'm eliminating that variable

My best guess is a leaking High Pressure pump. If you stick the 5-gas into the oil cap, do you get a HC reading of hundreds? Or, thousands?

First test I'm going to do today, thank you! (But I did have the PCV blocked to no change)

Maybe the oil level would show high if the pump was bleeding down into the case. I'm not sure if pinching the PCV is conclusive, but you'd know better than me!

ScannerDanner wrote:

Fuel trims will normalize with MAF unplugged. Swapped MAF sensor with another car in the shop to no avail (yep, I'm a parts changer lol)

Could try hooking up a scan tool to the other car to get some "known good" data. Mostly for MAF and wideband O2 but wouldn't hurt to take a quick look at all the engine data.

Different engine, (V6 on an Acura) same MAF (unfortunately)

Quick follow up question.
Have you ever seen a GDI system bleed down like mine is, where it was NOT a problem? Important question!
Thanks guys! On my way there now

ScannerDanner wrote:

Quick follow up question.
Have you ever seen a GDI system bleed down like mine is, where it was NOT a problem? Important question!
Thanks guys! On my way there now

I have seen some BMW high pressure pumps that bleed down almost instantly after engine shutoff, and it's completely normal. I'm not sure what about their design makes them that way...

Most other pumps I've seen do not bleed down normally. If anything, the rail pressure is supposed to increase during a hot soak.

Could just be bad injectors flowing to much.

Update:
350 ppm HC in the crankcase. Oil was not overfill, nor did it smell like fuel.

Fuel psi climbed on shut down after running for less than 5 minutes

Fuel psi only started bleeding down again with engine hot.

Manifold vacuum was 20.7 at idle.

After clearing memory, the negative trims are intermittent. With it having only a -6 ot 7 total fuel trim at idle. Then other times -17

Pinching off pcv and breather (inlet) results is more negative trim!??? Why? I don't know. But legit -15 or -20 more negative with PCV pinched off. Weird.

It's getting a valve cover gasket (leaking) and valve clearance checked and a waiver for PA state emissions for now.

I legit walked away from this. I'm not confident in a $200 AF sensor. I'm not confident is selling injectors or a high psi pump. I'm not confident in anything and I'm NOT going to start throwing parts at this.

Appreciate all the help and any additional feedback. Just know that I'm not going back to this car. I feel defeated. And with 4 hours of footage, it will take Caleb a week to put this together to get something watchable. But we will do it anyway and your feedback here may help give us some closure?

Is this a turbocharged engine? If so I'd be surprised by the intake vacuum at idle.

Non turbo

I would say to do a in cylinder to see if cam lobes are worn or cam shaft journals in head are worn out. Though with the latter would make a heck of a racket. What other stuff is on the maf circuit?

ScannerDanner wrote:

Pinching off pcv and breather (inlet) results is more negative trim!??? Why? I don't know. But legit -15 or -20 more negative with PCV pinched off. Weird.

WAG but maybe TPS is one of the inputs used to determine base fuel map? So the throttle opening to compensate for loss of PCV air increases base fuel? And if TPS does affect fuelling that could be the problem with vehicle..........

Does SI have any info on what a bad MAF failsafe would cause, for some clues on why unplugging it would correct trims? Like a P0101 description. May show a connection to another sensor, like evap pressure, or something not obvious.

First time answering a question on here so be easy on me lol. I work at a honda dealership, have been a Honda/Acura dealer tech for 20 years and these fuel injectors are not very reliable. We have fixed many of misfires replacing high pressure fuel injectors. They chalk it up to debris from the machining process causing the tips to become clogged and or leak. I would recommend replacing the fuel injectors and high pressure fuel pipe.

Thank you so much! That was one of our main suspicions but we couldn't prove it. Even used a bore scope (video coming up) and we were just never the thousand to fifteen hundred confident in making that call. This really helps and will get a mention at the end of the video!

Least I could do for all the content you have provided so thank you sir and keep up the great work