Reasons for a p0172 on a r53

Things checked or replaced
O2
FPR
Entire Evap system checked and appears to be working. Vacuum at pump in back and stink fuel vapors up front on purge line
New exhaust manifold gasket
New plugs and wires
New Green monster gasket
All lines under hood checked for leaks holes etc
Shrt Trm fuel trims are fine for about 5 mins at idle then they drop to -30. Off idle is fine except for the tip in when -30 as the DME is pulling max fuel.

GO GO GO!

 

This is a tough one, but a thing to check is the fuel regulator on the fuel rail. it may be toast, or not getting full vacuum.

 

Per the first post thats done

 

Smoke test for leaks?

If STFT is going to -30%, likely a significant vacuum leak.

 

Did you understand the fuel regulator on the fuel rail, may be bad. Some testing with a gauge on the fuel rail would be a good step. Good fuel pressure for 5 minutes is not what you need. It is constant fuel regulation. Now, rich/lean condition means the fuel is no longer regulated under idle condition. A test with professional OBDII tester would answer this point. If you don't feel this is an issue, there is also the possibility of the fuel pump going out. (sometimes when they kick in, they over pressure until they stall, before they die.)
Sorry, I don't see in your first post, if any of this was done! If you figure out the pump is dying, make sure to replace the fuel filter too!
Look, I am trying to help from afar. It is not ideal for this problem. It really sounds fuel pressure related to me.
The values on fuel mixture should be around the 14 to 1 area.

 

Sorry I shouldd have clarified. I hooked up gauge and watched it at idle and it never faltered when the trims dipped. Lord knows I was hoping that when the -30 hit the pressure would have gone up. Its odd its going to -30 after about 5-10 minutes of idle. At first I thought it was a evap issue but the evap system has passed its checks via my obd II scanner and even Inpa

I am at 43-45 psi at idle and 50 with the fpr disconnected and 60 off the pump.

This issue only happens in CL at idle. Car drives fine in every other aspect.

Afr are 14.6-15.3 at idle I have a wideband. But the computer has to pull maximum fuel to keep it there and then on tip in it obviously takes the DME a few seconds to stabilize as it was max lean.

 

Ok, the fuel filter is suspect. Have you ever changed it? They say it is lifetime, but that has not proven to be the fact. It is a cheap and easy fix and will not hurt, other than having to remove the rear seat and open the fuel tank, on the top. If you go to this trouble, Make sure to clean the contacts on the fuel sender/pump plug, as they are known to corrode and cause fuel pressure faults. (clean with electric contact cleaner)
It seams to me that the DME is giving the proper signals and something is not responding in a normal fashion.
Keep us posted! I wish I could have been more help. We can only give ideas from here!
I hope you can get this figured out quickly!
Note: At idle, the voltage is at it lowest and if the pump is marginal, this would be when it would not likely build enough pressure to satisfy the fuel needs. (also trying to force enough fuel through a plugged filter)

 

yes filter changed last month. Again only at idle. If the pump couldn't create adequate pressure the car would spit sputter and die. It does not. It idles fine actually.

 

You realize it’s running rich that’s why the ecu is pulling fuel right.....

 

Bump

 

Have you checked the pressure in the fuel rail yet? Too much or too little can cause weird things to happen. The regulators can fail (pin hole in valve, or broken internal spring.
An S should be getting 50 psi, which is fairly low pressure. Get one from a wrecking yard.

 

I give up. You clearly dont read what I post. I think this issue is above your pay grade for real. I am being honest here. You dont read what I say you dont know what trims are and you tell me to replace stuff I have already and say uneducated things like oh your running rich change your filter.

Now unto other things I am starting to think the ldp is loosing pressure after a few minutes. Why? Normally if you pop your cap off while running the afrs will dip down into the 10's until the dme can pull stft to even it back out but even then I suspect the trims will be negatively affected until you put the cap back on. Which leads me to believe the tank is not holding vacuum from the ldp like it should and allowing to much air in. That and well this from inpa I pulled yesterday. This place truly has gone downhill since the FB groups started opening up to more tech oriented people like myself.

 

 

You replaced it, but did you check it. I am sorry, I mean with a gauge? You did not answer that. You want me to answer your questions, Sometimes the digital world is not enough. do you have a fuel rail tester? can you watch the gauge?
Look, I guess my help is not clear enough!
You are too frustrated thinking I am not helping! I don't care that you have a new fuel filter, fuel pump and pressure regulator and a digital view. I must be too old world for you to grasp what I am asking. Fuel delivery can be tricky and I never got to the injectors!
Sorry, I will bow out respectfully.

 

Dont let the door hit yah....bye felicia. And again see above where I give specs at the rail.

 

in case reading was not taught back then. Christ I am 42 and can at least read a forum.

 

That's where my head went on this. If it's not fuel delivery, then why the trim adjustment? And what would change after a few minutes of idling? It'd make sense if the signal reaching the computer was inaccurate. So, O2 sensor made sense to me, and they do go bad over time. But if you're sure you're ok there, then how about a leak in the exhaust prior to the pre-cat sensor? I'm no expert, and I'm just noodling here, because it helps me to learn these systems, but I hate to see anyone get stuck on a diagnosis.

 

Its the ldp pump. It cant hold pressure on the tank. When you open the fuel cap on a running r 53 it goes pig rich till the ecu can pull out a ton of fuel to even it out. Then screw cap back in and watch it go away. On a working system that is.