Stall, crank + no-start, no CEL

[malty]

My 2002 V70 has intermittent "stall, crank + no-start, no cel" issues.
Arm chair diagnostics and fix recommendations welcomed.

V70, 2.4T, FWD, 125K miles, owned 3months.
Bought at local independent dealer ; no history of previous ownership and maintenance.
General use of the car is daily 20min commute and other mixed hiway and around town travel.

Recalling the genesis of symptoms :

1. 1) Car ran fine for first ~1month.
   2) Hail storm ; brake lights inopp but no breakage of lense ; how / why BL inopp due to hail ?
   3) Suspension parts replacement at independent shop #1
   4) Oil leaks repaired at independent shop #2. CEL next day

_ Succeeding points over the space of ~2weeks

• 5) Very infrequent momentary engine stumble at driving speeds (above 30mph)
  6) Brake lights inopp repaired at independent shop #3. Codes scanned = Oxygen sensors.
  7) More frequent engine stumble - maybe twice during the 20min commute.

_ Succeeding points over the space of ~4days

• 8) Momentary stumble then ~2min later stall during in town driving (stop and go, 20-45mph) ; restart Ok, drive home.
  9) Start, drive 1/8mile, stall, crank + no-start ; let it sit overnight ; starts fine and drives with infrequent engine stumble.
  10) Start, idle 1min, stall, start, drive 5miles, stall, crank + no-start, sit overnight, start ...

_ Car is sitting in driveway undergoing inspection, testing, parts replacement, etc.

• 11) Codes scanned = Oxygen sensors. Oxygen sensors replaced, codes cleared. No CEL henceforth.
  12) Starts on some attempts, may idle for 2min then stall when hood is closed, has idled for 10-15min with no issue, then crank + no-start on next attempt.
  13) Persistent crank + no-start ; tap on MAF while cranking, starts. MAF sensor replaced.
  14) After MAF replacement ; start, idle ~15min, key off, restart, all seems good.
  15) Next day ; persistent crank + no-start.

Tentative conclusions :

• The behaviour is random ; coincidental with passing clouds, chirping birds, position of second hand on watch.

Work done to car since owned (all within past ~45days) ; approximate order of work :

1. Suspension -
   1. CV Axle Shaft Assemblies Left & Right
      Lower Left & Right Control Arm, Bushings, Ball Joints
      Front Wheel Left & Right Hubs+Bearings
      Front Left & Right Strut+Spring+Bearing Assemblies
      Rear Shocks
   Rear view mirrors - left & right (due to hail damage)
   Visual check of timing belt ; no cracking or fraying.
   Oil leak fixes - rear cam seal, turbo drain seal
   Brake light fix ; not sure what the shop did - mentioned wiring repair in the right BL wire harness.
   Headlight bulbs - Wagner H7 NightDefense, Nokya NOK7611 9005. (left low beam was failed , but replaced / upgraded all for good measure)
   Oxygen sensors - upstream (Bosch 17137) & downstream (Bosch 16446)
   MAF sensor

[MadeInJapan]

Which MAF sensor did you buy? A lot of MAFs that are suppose to be for our cars don't work well at all...just saying. Also check for vacuum leaks and open or split intercooler hoses. These can give you false MAF/O2 codes. I suspect temp has something to do with this- the crack is not large depending on the temps but as they increase (summer is coming on), then they are larger and have more impact. You might have replaced 02's and MAF unnecessarily. I'm thinking you'll get this sorted. However, your biggest problem is the timing belt. You just said you inspected it with no frays. This car is over 10 years old and at 125+K miles, it is way overdue. It typically isn't the belt that goes, but the tensioner that does and takes the belt with it. Get that changed out along with tensioner, roller and water pump! You're driving (or will be driving) on borrowed time and all of these repairs will be for naught if your TB goes and pistons get bent!

[MadeInJapan]

Oh, and have you read your codes? The stumbling can also be typical of bad ignition pack. You need to know if a cylinder is mis-firing and which one if that's it...change the location of that (those) to a different cylinder and see if the issue follows the bad one(s)... Hopefully others will add to this. Also, can't verify the 02 sensors you used (sorry- no time to look them up- maybe someone else will)- yes, Bosch is good but they have to be very specific to your car to work properly.

[stinger04038]

The throttle bodies on these are very poorly built. The first thing I would do is go get a can of good carb cleaner and clean the throttle body. While you're there take a look with a mirror to see the color of the label, white original, yellow newer. These were built so badly Volvo extended the warranty for ten year or 200k, which ever came first.

[malty]

The problem is resolved ... but the manner of resolution and the explanation is not completely satisfying.
Just thankful to have a working car again.

The story :
Towed the car to a local shop that claimed some Volvo experience.
Explained the randomness of the symptoms, mentioned the troubleshooting chronology and parts replaced, wished Larry luck tracking down the cause, and hoped for the best.
Next day Larry called and said he had the car running.
He had run the car in the shop and driven it around the neighborhood for the better part of an hour.
No more random stall and crank + nostart.

Larry's explanation of what he found ... as best I can remember and understand from his tutorial using a Volvo 5cyl engine in the shop :
1) Checked obvious things like injector fuel rail pressure and coil spark.
2) Checked codes - found O2 sensor codes and speed (crank) sensor code.
3) Dug into crank sensor area and found an o-ring sitting on the flywheel sensor trigger ring (the thing with square holes attached to the flywheel and which triggers the Hall-Effect sensor). O-ring was just sitting on the trigger wheel next to the sensor.
4) Seeing no problems with the crank sensor itself, removed the o-ring and put everything back together.
5) Cleared codes and tested the car, start run etc.
6) Concluded that the o-ring might have been bouncing against the crank sensor causing bad sensor reading to the ECM.

I attached some pictures of the crank sensor area and the suspicious o-ring which seemed to be the only anomaly circumstantially related to the problem.
Pics are just ones found in forums and websites but are representative of the actual situation with the 2002 V70.
Also found this thread that discusses a no-start problem related to faulty crank sensor : http://volvoforums.com/forum/volvo-240- ... elp-60939/

In summary, glad to have a working car but intellectually unsatisfied how an errant o-ring causes crank position sensor problems.

Pic collage of crank position sensor and the suspect o-ring riding on the sensor trigger wheel.

[abscate]

I'm not too happy with the oring theory either. More likely bad wiring or connectors that have been ameliorated by the disconnecting and reconnecting during servicing. Time will tell

[01_Nautic_V70]

As an electrical engineer, I'm not on board with the diagnosis. The electromagnetic permeability of rubber is approximately the same as air. Placing an o-ring between the sensor and the toothed or similar ring won't do anything. While messing around in that area, he may have bumped a loose connection.

Hall effect sensors are very very simple devices and pretty robust in that they are hard to break and the mechanism that makes them work (magnetic flux) never stops existing or working.

I'm not trying to be difficult or worry you, but I'm not confident he fixed it permanently. In you hypothesize what could cause your symptom, check that and reformulate as necessary. Until you find a deficiency that could actually cause the symptom, you haven't fully troubleshot and repaired the issue.

[malty]

Abscate's theory sounds plausible.
I'm going to get a code scanner to be able to keep tabs on any CEL occurrences.

I'm not too happy with the oring theory either. More likely bad wiring or connectors that have been ameliorated by the disconnecting and reconnecting during servicing. Time will tell