1998 V70 NA Running Rich

wyethv70 · Post by **wyethv70** » 04 Nov 2014, 11:48

Hello all,

The problem: So for the last two years I have had the code P0172 and with it also the P0103 P0102 have come and gone with repairs but never been able to track down the P0172 culprit. Lately the car has been running roughly in idle. Previously we had a stalling issue (P0103) when coming to stops and drops RPMs when accelerating. The car hasn't done this in a while but the idle is beginning to frighten my wife (she drives the car) because of the possibility of the engine shutting off at a stop. Also interestingly the car would not start in 30 degree weather in Yosemite NP 4 months ago, however it did start when it warmed up a bit. The car is definitely running rich by the smell from the exhaust. I have researched and tracked down various parts to replace or test with no success. I also took the car to one of the better Volvo shops in San Diego three times and they too have been unable to find the problem. I am looking for any ideas or thoughts on further trouble shooting.

What has been done: Replaced MAF checked resistance from ECU to MAF with good results, checked input voltage to MAF with good results, tested pressure at the fuel rail, tested fuel pump relay, bench-flowed/ tested and cleaned fuel injectors, smoke tested vacuum system, replaced o2 sensors less than 10k ago, new coolant temp sensor. All Bocsh/ Volvo/ OE.

Previous maintenance/ upgrades done (all DIY) related to the problem: PCV system overhaul (50k ago), new timing belt and tensioner, new water pump, new radiator, new intake filter, new spark plugs (carbon build up due to running rich), tested plug wires (replaced 50k ago), vac tree replacement.

Also could someone explain why a vac leak would give one a running rich condition (P0172)? Seems that would have the opposite effect, which it did on my BMW (ran lean).

Thank you for your help and time on this one! Wyeth

Post by **jblackburn** » 04 Nov 2014, 12:18

Also could someone explain why a vac leak would give one a running rich condition (P0172)? Seems that would have the opposite effect, which it did on my BMW (ran lean).

It's how the car compensates for it. Forcing itself to run rich when it detects a disparity between MAF and O2 sensors is a better default for the engine than running lean.

Is this a non-turbo V70?

The idle dip and codes do definitely suggest a sizable vacuum leak somewhere. Aside from the obvious vacuum lines to/from the vacuum tree and intake manifold, the fuel pressure regulator dips down and connects to a hidden vacuum line just in front of the right front axle. There are several points in the PCV system that could cause the issue - the PTC rubber seal @ turbo intake hose on a turbo car, or the vacuum elbow behind the power steering pump on either motor. The vacuum tree O-ring where it fits into the intake manifold has been known to go bad. Finally, the intake manifold may have a crimped or bad gasket.

Have any exhaust leaks at the manifold gaskets (there are 5!) or flex pipe been ruled out?

Post by **rmmagow** » 04 Nov 2014, 12:33

Are you 100% positive the small very-hard-to-reach/see elbow on the left side of the motor near the PS pump is OK? That is one of the most common cause points for the 172. It is a tough cookie to replace properly and could have been disturbed during PCV service. Do you have the MAF plug strapped to the MAF itself? The MAF plug can become worn and strapping it in place supposedly helps. Make sure there are no cracks/leaks near the front O2 sensor or in the manifold.
And ALL that jblackburn is talking about too and probably more to the point.

wyethv70 · Post by **wyethv70** » 04 Nov 2014, 12:35

My model is NA (just edited to reflect this)
I have smoke tested the vac system from the intake multiple times and the shop said they smoked it as well. Are there places in the vac system where this test would not be effective? I also have replaced the vac tree (forgot to mention that (edited)). I have also tried the ol' carb cleaner on the manifold gasket trick with not results. Wondering if there is a better way to test the manifold gasket but I would think the smoke test would uncover this. Am I relying on the smoke test too much?
I have not ruled out anything related to exhaust leaks or the flex pipe. (the flex pipe is the one coming from the exhaust to the intake box?) Could I get some education on how this could cause this problem? And thanks for the explanation on the vac leak causing rich condition. ...Wyeth

Post by **jblackburn** » 04 Nov 2014, 12:41

Gotcha. Yes - make sure the mass airflow sensor connector is snugged down (some use zip ties to make sure it is secure). Check for any cracking in the air box to throttle body pipe as well - many are beginning to fall apart at this age.

The flex pipe is where the exhaust manifold connects to the downpipe - visible under the heat shield at the back of the motor. An exhaust leak can fool the front O2 sensor as the readings will not agree with what the MAF sensor is measuring.

wyethv70 · Post by **wyethv70** » 04 Nov 2014, 12:45

My wife's father replaced the vac system about five months before I took over repairs and service of the car. I received the car in good working order with no codes and he said that the codes he had previous to the vac/ PCV system replacement (which included the elbow) went away. I have visually inspected this element and it looked to be in good order (when I was replacing the coolant temp sensor). However i have not given to much time in to visually inspecting all vac lines due to satisfactory smoke tests and the aforementioned. I had also heard of bad connections from the maf jack to the plug but when I inspected it seemed to fit tightly. This is something that I could try though. I will also check for exhaust cracks. ...Wyeth

wyethv70 · Post by **wyethv70** » 04 Nov 2014, 12:53

That flex pipe is definitely something that I have not checked. I will also secure the plug and check for other leaks in the exhaust system. Thanks ...Wyeth

wyethv70 · Post by **wyethv70** » 04 Dec 2014, 20:59

I completed a check on the exhaust system and I found no leaks. I also ensured the MAF plug and jack are fully secure. I did another vac test and the only place I saw smoke come out was the oil dip stick so I replaced the o-ring and that solved that problem so I am pretty sure that the vac system is sealed. However, I am still running rich and a new problem has started. It has been around 60 degrees in the mornings here and this seems to be causing the car not to start. Right around 63-65 degrees seems to be the limit to where the car won't start easily. If the temp is warmer it has no trouble or if the engine is warm it has no problem on the restart. I am hoping that this problem will shed some light on this car's issues. Any suggestions?

Post by **jblackburn** » 04 Dec 2014, 21:12

Weird.

Out of curiosity, do you have a voltmeter? As this seems oddly temp dependent, I would check the resistance values on the @ the coolant temp sensor plug on a stone cold engine, and then again once the car thinks it's fully warmed up.

https://www.matthewsvolvosite.com/forums ... hp?t=52203

wyethv70 · Post by **wyethv70** » 04 Dec 2014, 21:20

I will definitely check the temp sensor. I am sceptical that it is the culprit because I have had issues before and after its replacement.