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It started with a code P0304 (#4 Cylinder misfire) I found a bad #4 spark plug. I replaced all plugs, wires, cap & rotor (all Bosch & only 11K since last replaced). Easy fix & I cleared code. 40 miles later, I get a P0172. I think I've read all the P0172 posts here & everywhere. I've done all that's suggested & code returns. 13K ago, I had replaced all PCV: 7 hoses, cannister, solinoids, EVAP hoses (at tank), secondary air pump & hoses, SAS valve, etc. I have gone over each vacuum hose since, including tubing from air cleaner to turbo, turbo to intercooler, and intercooler to throttle body. I checked for intake leaks, spraying carb cleaner around intake & throttle body, no change in RPM. I replaced MAF (w/new Bosch unit )& I replaced both O2 sensors (W/Bosch). P0172 code returns after 30-50 miles. It doesn't smoke, fuel milage is ok, runs fine, but will not pass emmision test because of this fault code. Help!
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curious what brand/model of OBD2 scanner you are using?
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My scanner is an SPX/OTC ScanPro #3409. I have access to my buddies Snap On, with all his expensive updates, but this unit fits my needs for as little as I have need for it.
I finally cured the code P0172 problem. It's almost embarassing how simple it was. I found a vacuum cap off. It's hard to believe one small 1/8" leak constantly caused the code, but there are no set, or pending, codes after 1,000 miles. Before, it would go 30 to 50 miles around town and 100 and 200 miles on the highway before setting a code.
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That code will set with a smaller hole than that. Plug up a vacuum gauge to that unused nipple and mount the gauge on your A pillar. Just for fun!
Klaus
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Why are Volvos so endearing? Its just a car.
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A vacuum/boost guage would be nice! The crazy thing about that vacuum cap on the tee, it was the first place I started looking. After hours/days/weeks of removing parts & searching vacuum hoses & lines for leaks and replacing suspect parts, I found the uncapped nipple. A week later the code reset and I found that the new 1/8" rubber cap was gone again. This time I applied a little glue and another new cap. Klaus, if vacuum is negative pressure, could/does the turbo boost cause positive pressure and "blow" the rubber cap off? It still runs great, 26mpg, idles smooth, no problems. Just wondering!
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That's what's nice about a turbo boost/vacuum gauge. Yes, boost causes positive pressure in the manifold. That is how additional air is introduced to the cylinder, rather than relying on vacuum to draw the air in.
The 850 turbos all had a turbo boost gauge in the instrument panel. 'old' cars had vacuum gauges that were calle fuel economy gauges, the higher the vacuum the better the mileage.
Glue? yuck! I would use a small zip tie :)
Klaus
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Why are Volvos so endearing? Its just a car.
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You certainly have gone through the mill on this one!
Have you checked the exhaust for a leak? Either the flex pipe or the rigid portion just before the CAT. Have a helper stuff the exhaust pipe with an old Tshirt, cold engine just started. Then check for leaks at the above mentioned places.
Klaus
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Cynthia Amendt, RIP
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Thanks Klaus, I'll try that tomorrow morning when it's cold. Could a bad catalytic convertor cause code P0172? I was following her the other day and it smelled bad (like rotten eggs) when she accelerated hard.
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Because of the expense of the converter, I always try to rule out everything else first.
If you bump the side of your fist against a cold converter and it rattles inside, I would suspect it is bad.
The sulphur smell is from the 'rich' condition.
Klaus
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Cynthia Amendt, RIP
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Thanks again Klaus. I'll post tomorrow what I find, exhaust-wise. If the cat is deemed bad, what would be the results if I 'emptied' the cat inside, instead of replacing it. Would it set other codes? It sounds (and is) crude, but we did that in the '70's by removing the cat, ramming a rod through it till it is an empty shell and reinstalling it. Or we eliminated the cat and installed a "test pipe". But that was before OBD11.
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That was also before front and rear O2 sensors. Your car would still run rich and fail any testing.
Do a search on cat or converter to find some options on replacements.
Klaus
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Cynthia Amendt, RIP
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I removed exhaust manifold shields, started car cold and had a helper stuff a rag in the tailpipe. I could not feel or see any exhaust escaping around cat, flex pipe, turbo flanges or from or around exhaust manifold. I did not see any tell tale black streaks on the manifold to indicate a crack. I forgot to mention that vacuum at the intake is a steady 17 in hg (which is probably normal for 139K?)& at idle, fuel pressure is a steady 37 psi at fuel rail. If an exhaust leak is not fooling the 02 sensors, what is causing P0172 (system rich)? Klaus, could a fuel pressure regulator and/or damper cause this? Still stumped, Phil
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It used to be easy to check the FPR on the early 850s, a clear vacuum line to the tree. Your car has a hard line that goes to the front of the manifold and then a flexible line to the hole in the manifold.
You could disconnect the vacuum line, cover the hole with some tape or a vacuum nipple, start the car, and if the FPR is leaking it will drip out of the hard pipe.
The fuel pressure regulator is back by the fuel filter.
Klaus
PS, pretty soon it will be time to visit the 'man'.
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Why are Volvos so endearing? Its just a car.
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Thanks for the tip Klaus. My FPR is above the right side of the steering rack. (the damper is on the fuel rail, I'm guessing that's ok). I will do your test, a leaking FPR sounds logical, as fuel could be sucked into the intake manifold post throttle body and causing a rich mixture. I'll let you know, Phil
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Thanks for the tip Klaus. My FPR is above the right side of the steering rack. (the damper is on the fuel rail, I'm guessing that's ok). I will do your test, a leaking FPR sounds logical, as fuel could be sucked into the intake manifold post throttle body and causing a rich mixture. I'll let you know, Phil
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