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Cam timing and MAF/02 Scan readings

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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Posts: 25
Joined: Thu Sep 26, 2019 7:01 pm
Year and Model: 97 850 turbo
Location: Us
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Cam timing and MAF/02 Scan readings

Post by Lolvolol »

So I’ve got a camshaft position sensor A performance code, and not knowing what to check first I checked the timing. Now I don’t know much about cam/crank timing and all of that, but I believe the tooth is supposed to be aligned with the little notch in the cover. The second to last picture I circled where the cam tooth mark is, and I believe that to be correct, but the very last picture I circled where the tooth notch is and it appears to be way off track. Am I stupid and they made their own marks? Or is it retarded? On another note, I’m getting a p0440 and p0172, and I’ve heard the causes can range from vacuum leaks, to the 02 sensors. So I decided to read the data while the car was idling, (see pictures) and I’m honestly not sure how to interpret the results. I want to make sure the MAF and 02 sensors are operating correctly. Any help is much appreciated since I’m still quite the noob!
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Joined: Sat Jan 11, 2020 12:09 pm
Year and Model: 1999 V70XC
Location: Minneapolis
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Re: Cam timing and MAF/02 Scan readings

Post by melmwood »

Not sure if you need the help anymore, but it looks like the PO (or PM - previous mechanic) either goofed something up when doing the timing, or was really lazy. If your car is running rough, then maybe they goofed. If it's running fine, then they were likely just lazy but didn't mess it up.

That yellow-ish mark is likely the original timing mark, and it's supposed to line up on that hole in the cover when the crankshaft is also at TDC (to see the crankshaft on a '99 you have to remove the crank pulley via the 30mm nut, and a few 10mm bolts, to see the marks, unsure if the same on a '97). If all three marks (one on crankshaft, one on each cam, if the '97s have two cams) don't align at TDC after you've manually rotated the crankshaft, then your timing is off and the belt has to be removed and timing reset. You can't "check timing" just by looking at the cams with the timing cover off. Those gears just stop randomly when you stop the engine, so they never just end up on TDC perfectly (like a one in a million scenario). You have to manually turn the crankshaft to get everything in place to verify. If you turn over the crankshaft to TDC, and the cams don't align with their TDC marks, then you have to keep turning the crankshaft until the cams align with their marks, then remove the timing belt (so the cams don't move during the next step), then turn the crankshaft so it aligns with its TDC mark, and then you can put the timing belt back on (careful not to move the cam gears while putting belt back on).

There isn't really a reason (that I know of) to mark the cam gears the way someone appears to have done, unless they were really lazy and didn't want to set everything properly to TDC when doing the timing belt removal (you could just mark all three - two cams, one crank - in random spots with their "current position" when replacing the belt, and just make sure those new marks all align when done...but it's a sloppy way to avoid 2 minutes of turning the crank to ensure TDC is properly set).

While not for a '97, I imagine most of the timing marks/alignment steps are the same as outlined in this article:
https://www.pelicanparts.com/techarticl ... cement.htm
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