[850] Misfire on all cylinders (What is a crank sensor?)

ToriWhite · Post by **ToriWhite** » 14 Jul 2018, 12:40

Where should I start to diagnose misfiring on all cylinders? What could cause that?

Took the 850 base manual 97' into oreillys for an OBDII read, spat up a bunch of P30(X) codes, (P300, P305, P302) and said I was basically having misfires along all my cylinders.

Performance wise, I don't notice anything unusual- it's not my daily driver, so i wouldn't necessarily have a good reference, but it feels like it idles fine, and I'm still getting nominal speed / RPM output (40 MPH @ 2k RPM in 4th gear, and 5th gear gets me 50 MPH at 2k RPM) - however, occasionally when turning the engine off, it feels like it keeps 'turning over' for a split second after I've cut the juice.

Fuel pump / relay are both new(ish), put in a new distributor cap at the same time a while back.

In my amateur opinion I don't think it's the spark plugs, it doesn't make sense that they would all start fail at the same time.

Recently I pulled the engine to swap the clutch out / replace the main seal. so I fear I may have bumped or plugged something in wrong in the reassembly, Could it be related to the speed sensor? I know I had to play with it to get my speedometer to read (it was initially plugged in backwards, or too loose, so I flipped it around and plugged it in snug, and the speedometer works again)

Any ideas?

Post by **bmdubya1198** » 14 Jul 2018, 15:39

Definitely possible the crank sensor/engine speed sensor is a problem, that will definitely cause a multi cylinder misfire. Check the connector for that. They are known to disintegrate over time. I wouldn't quite completely rule out plugs, how do they look?

Those codes are for cylinder 2 and 5 misfires, as well as multiple cylinder misfire. Same set of codes I had when my crank sensor was bad, except I also had a code that specifically said crank sensor.

ToriWhite · Post by **ToriWhite** » 14 Jul 2018, 16:31

bmdubya1198 wrote: 14 Jul 2018, 15:39 crank sensor/engine speed sensor

I've been reading around looking for a visual of "Crank sensor / engine speed sensor" and am getting a lot of results that look like something else entirely, the plug I played with plugged right into the engine block, on top of the transmission housing. Two prongs, reversible..

now that I'm reading that the speedometer is connected to ABS (which was also left unplugged, and I also plugged back in at the same time- for sake of keeping gunk from flying into it) .. I realize I don't know what that blue plug is, and I just took it and flipped it around for no reason? (What was I thinking?!)

I'll post up a picture later tonight of the plug, its really easily visible / accessible, I hope it has something to do with timing and is the culprit of all this nonsense.. if only all repairs were as easy as unplugging and replugging it back in..

Post by **bmdubya1198** » 14 Jul 2018, 19:08

The crank sensor is mounted right on top of the transmission bell housing, with a white connector that is usually mounted to bracket just above.

ToriWhite · Post by **ToriWhite** » 14 Jul 2018, 20:50

Here's three pictures of increasing zoom (To show some landmarks for reference) onto the plug in question..

: Overview

: Zoomed in between airbox, near ABS computer

: same position, color corrected - plug is on top of the transmission

.. is that the crank sensor?

Post by **bmdubya1198** » 14 Jul 2018, 21:18

That’s not for the crank sensor. The crank sensor has a smaller, more narrow two-terminal connector, nearby the distributor cap.
Hmm... can you see where the wires go?

Edit- It’s kind of hard to see... is it damaged? It could possibly be the crank sensor connector, but it’s usually situated on the front side of the engine.

ToriWhite · Post by **ToriWhite** » 14 Jul 2018, 21:35

it doesn't feel damaged, and it is a 'two-terminal connector' if by that you mean it has two live prongs that corrospond to a socket of two holes
(It may be damaged now that I've reversed it, although, the fact that it's so easily reversible makes me think it's arbitrary which way its connected.. or maybe its that some part securing its entry one-way has broken off.. it does come off and on suspiciously easy compared to the rest of the plastic socket plugs I've found on my volvo)

(Current plan of attack is to buy a code reader/clearer from oreillies or napa, clear the codes and re-reverse the plug, and see if any codes come back on)

However, I'm worried that this may have something to do with the timing belt..
I haven't replaced the timing belt since I bought the car.. and I'm sure it was already overdue then.. I know what kind of damage can come from a broken timing belt, while I've got a replacement planned in the near future.. I'd like to know if this is related to it already failing (If its already failing, that means I cant make the 3 hour drive to where my tools are to repair it, and I'll have to take it into a mechanic, goodbye $900..

)

Post by **abscate** » 15 Jul 2018, 05:31

Current plan of attack is to buy a code reader/clearer from oreillies or napa, clear the codes and re-reverse the plug, and see if any codes come back on)

A very good plan. Which code comes first is often valuable information, and multiple misfires will generate spurious codes, too.

How old are cap rotor plugs and plug wires? These are the consumable parts on Volvo’s. Figureabout $150 to get all those parts ...but check the Fora to get good quality, no skimping here.

Post by **bmdubya1198** » 15 Jul 2018, 07:23

Definitely a good idea to get your own code reader. I recommend checking out Harbor Freight, that will probably yield the best price if you're just looking for a budget reader (or a better one, too).
https://www.harborfreight.com/zr4-obd2- ... 63808.html
and a coupon... just open this on your phone and they can scan it in-store http://www.hfqpdb.com/best_coupon/ZURIC ... READER+ZR4

This most likely isn't related to your timing belt. You would know for sure if it was, and the car likely wouldn't run at all. If you're worried about the condition of the belt, you can pop off the timing cover and take a look. Just one 12mm screw and it pulls up.

ToriWhite · Post by **ToriWhite** » 15 Jul 2018, 11:40

bmdubya1198 wrote: 15 Jul 2018, 07:23 Definitely a good idea to get your own code reader. I recommend checking out Harbor Freight, that will probably yield the best price if you're just looking for a budget reader (or a better one, too).

Thanks for the heads up! I'm a little hesitant to buy anything aside from sockets and fluids from Napa / O'reillies, everything else is marked 150% up and for only 50% quality in my humble opinion, lucky thing too I've got a harbor freight nearby!