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Discussion Starter · #1 ·
P0172, System too rich, bank 1, reported by the upstream O2 sensor. I recently got a bluetooth OBD2 unit and downloaded the 850 OBD-II app onto my phone to get more detailed data to fix this issue, it gave me an EFI-231 DTC code, long-term fuel trim, part load.

Symptoms: fuel in the oil (a lot of it), and very slight stuttering when starting from a stop. Otherwise the car drives fantastically.

What I've done so far: the car had red injectors, I replaced them with the correct orange Bosch injectors. Replaced the vacuum line that runs to the passenger side of the intake manifold (found a cracked elbow). As preventative measures, replaced plugs, wires, entire PCV, MAF sensor, most of the vacuum lines, coolant temp sensor, thermostat. I've done a compression test, it was good.

Next steps: investigate fuel pressure. The regulator, I have discovered after much false information from various sources, is not on the fuel rail, nor is it on the top of the fuel tank, or under the passenger floor. Instead, it is dangling above the steering rack on the passenger side of the car, suspended like a trapeze performer by rubber fuel and vacuum hoses.

Seems safe.

Anyway, here's a question: if the regulator isn't getting vacuum from one of the vacuum lines attached to it, will that cause it to fail open and keep the pressure too high, or the opposite?

I'd like to test the fuel pressure at the valve on the fuel rail while the car is idling, but I'm not sure what it's supposed to be normally. 40 psi? 50?
 

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Discussion Starter · #2 ·
Update: Yesterday I got a fuel pressure gauge and tested it. With the key in position 2 (priming the pump) I got 40 psi of fuel pressure. With the engine on and idling it waffles between 48 and 52, and rises to about 56 when revving. So, all normal from what I've researched on the subject. Looks like the fuel system is behaving normally. For good measure I leak-tested the vacuum lines that run to the FPR and they're good, as well.

So, the last thing to look at that could cause this problem is the O2 sensor. If I end up needing to replace it, should I replace the upstream and the downstream sensors at the same time?
 

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This popped up recently on the wife's '97 GLT. Turned out to be a split vacuum cap (At the vac tree on the intake). You may still have a small vac leak someplace.

If your car is a '98 XC70, that should be an LPT motor and should have the red injectors(-759). At least the ones I've seen in the yards have. Did you use "orange-top" injectors, or full orange ones?
 

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Discussion Starter · #4 ·
This popped up recently on the wife's '97 GLT. Turned out to be a split vacuum cap (At the vac tree on the intake). You may still have a small vac leak someplace.
I've looked at every vacuum line in the engine bay and replaced most of them already. It's possible that there's still a leak somewhere, but if there is it's the grand master of hide-and-seek. I'll take your advice, though, and replace all the caps on the tree for good measure. Those are cheap.

If your car is a '98 XC70, that should be an LPT motor and should have the red injectors(-759). At least the ones I've seen in the yards have. Did you use "orange-top" injectors, or full orange ones?
Nope, red injectors are not the correct ones for the B5254T engine, it should have fully orange Bosch 62682 injectors (Volvo part number 9454555 / 1275194). Bosch, unfortunately, incorrectly lists the red ones as applicable to the LPT on their parts website.

Regardless, the car had red injectors previously and had the same issue (it's one of the reasons I researched the injectors and installed the correct orange ones).
 

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Perhaps only the '97 GLT's (With the -936 ECU) got the reds, but it's the same engine. The old engine is long gone (B2544T3 is in its place now), so I can't verify the sticker, but it was the 2.4L LPT B2545T.

It could be the O2 sensor, which is where I was leaning towards when ours came up. After I found and replaced the split vac cap, it hasn't been back since.
 

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Discussion Starter · #6 ·
Update: replaced upstream O2 sensor and ensured that the vacuum line running to the port on the left side of the intake manifold is good. Still have the persistent p0172 but now I also have a p0455 (evap system leak, large).

What are the first five things you would check for that? Maybe there are vacuum lines running to the back of the car I haven't looked at...
 

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You need to know the components in the evap system and how it works but basically it’s made up of a charcoal canister either in the LF fender or the rear (I’m not sure of the vin break). The evap control purge valve is near the canister. Associated rubber nipples, hoses, check valves, and a filter are involved. Lots of places to leak. Start at the canister and replace every piece of rubber while there or go cheap and fix the problem area(s) only. The components are pretty sound so it’s usually a rotted rubber problem.
 

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Discussion Starter · #8 ·
Update: While looking at the evap purge valve I found rotted hoses running to it. They crumbled away as soon as I moved the valve. I replaced them with fuel safe hose and replaced the purge valve for good measure. After a short drive, I still have the P0172 code, but the P0455 hasn't resurfaced yet. I'll be looking at the canister and its hoses next, if I can find it. The purge valve was in a bracket attached to the fan shroud, but the Volvo service center told me to look at the fuel tank area to find the canister. Fun.

The hunt continues.
 

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Discussion Starter · #9 ·
Update: replaced two more older vacuum lines that were starting to crack and while I was doing that I pulled on another one and it broke apart. Unfortunately it was the worst vacuum line in the engine bay: the red line running from the TCV to the bottom nipple on the compressor, which is nearly impossible to get to. After four hours of profanity and pain, I got it replaced. I don't know if these vacuum lines will fix the issue but tomorrow I plan on taking it for tires and oil so I guess I'll find out when the CEL's sinister orange glare returns. I'm sure it will.

Abandon all hope, ye who enter the realm of the P0172.
 
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