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When it gets hot the idle starts cycling up and down between normal idle speed and very low RPM. The hotter it gets the more likely it is to stall.
A generic code reader reports P0300 misfire multiple cylinders.
VIDA shows code ECM-3502 and when watching misfire live data cylinders 3 and 4 are showing the most misfires when the problem is happening, but not at other times. The other cylinders show zero or noticeably less misfires.
I swapped some coils around to the cylinders that didn't have any/many misfires but the misfires did not move.
Pull off your oil fill cap - you should have only very light positive pressure coming out. If you've got lots of air whooshing out, you've got a bad PCV system. Fuel pressure would be a good check, too (think you can get that with VIDA).
What's the car's mileage, and when's the last time it got new plugs?
Pull off your oil fill cap - you should have only very light positive pressure coming out. If you've got lots of air whooshing out, you've got a bad PCV system. Fuel pressure would be a good check, too (think you can get that with VIDA).
What's the car's mileage, and when's the last time it got new plugs?
About 120,000 miles. Fuel pressure is correct and consistent (checked in VIDA). Just put in new plugs and made no change to the problem. Will do the oil fill cap check you suggested and report back.
Pull off your oil fill cap - you should have only very light positive pressure coming out. If you've got lots of air whooshing out, you've got a bad PCV system.
I tried this PCV test and I have vacuum - I put a rubber glove on the oil filler and it was sucked in lightly. Does that mean anything?
Also, with the oil filter cap off or the dipstick out, the car ran the same - no change.
notice anything different about your temp gauge that may point to an issue with the ECT sensor? And yes, if the glove sucks in slightly or puffs in and out then your PCV / oil separator is working as normal. Can you measure fuel trim? misfires can be caused by running lean or too hot a spark (say due to an intake air leak). What's the color and condition of the plugs? They should be swapped out every60K miles or so
notice anything different about your temp gauge that may point to an issue with the ECT sensor? And yes, if the glove sucks in slightly or puffs in and out then your PCV / oil separator is working as normal. Can you measure fuel trim? misfires can be caused by running lean or too hot a spark (say due to an intake air leak). What's the color and condition of the plugs? They should be swapped out every60K miles or so
Temp gauge shows normal and watching the temp in VIDA it shows as normal.
Fuel trims seem pretty normal but now that I have read a bit more about them I will go on another test drive and watch them again.
Old spark plugs were black with some browinsh/greyish deposits building up. I have since replaced them with new Bosch ones a few days ago.
Stop press. While diagnosing by cooling components with a garden hose I found that I could repeatedly stop the problem by cooling the crank sensor. I need to replace the part now but I'm pretty confident the problem may be resolved.
That does make perfect sense - a crank sensor can cause all sorts of odd, intermittent (or not) problems, and your symptoms fall squarely into that range! I'll bet dollars to donuts that you'll fix it with a new CPS.
New crank sensor fitted and problem is now resolved. Thanks for the answers and advice! My advice is don't expect the ECU to give you any useful fault codes and use a garden hose to diagnose heat related faults
The problem is still present, even after I replaced the crank sensor and later I changed the plug too. I think it didn't get hot enough on the first few drives after I replaced the crank sensor.
Weirdly I can get the car up to a temperature where the problem happens and then spray the crank sensor area with water and the problem usually goes away for a short time until the water dries up. Not sure if I am cooling it down or affecting an electrical connection. This test is a little inconsistent, most of the time the water will stop the problem but not always, so I am second guessing my diagnosis now.
One thing I noticed during this testing was that I could influence the problem by removing and then reinserting the dipstick or oil cap, so I am now suspecting PCV/oil trap (again). Even if I run the water over the crank sensor and the problem goes temporarily, if I then remove and then reinsert the dipstick the problem usually happens again straight away.
Is it likely that the PCV would only affect the engine when hot?
I have vacuum at all times (problem happening/not happening) idle according to the rubber glove test so I thought my PCV was ok. The idle/stalling problem still happens with the dipstick in or out, I just seem to be able to induce the problem by doing this.
The fact that anything odd is happening by removing / inserting the dipstick (opening the crank to the atmosphere) would seem to point at a PCV system problem, though your rubber glove test does seem to be indicating that the system is probably working... the fact the problem seems to be intermittent and seemingly thermal could mean you're just not seeing the "bad mode" with your rubber glove test...
Anyway, I have a rule of thumb about problems like this. If a problem could possibly be caused by a "maintenance part" (something that is commonly replaced regularly as preventive maintenance), I'll just shotgun it. Worst case, it doesn't fix the problem, but I'm now caught up / ahead on maintaining that part (meaning I won't have to worry about it again ever, since I won't be keeping the car for another quarter million miles). I guess if it was my car, I'd just swap out the PCV valve and see what happens.
Oh, and I meant to mention that the photo of that plug was a little scary... that's some fairly serious deposits, and it seems to me that the gap is past spec (just eyeballing the non-gappable triple-tab plugs looks like the prongs should be closer to the center electrode than in your photo).
As I was consistently able to make the problem go away by spraying water on the crank sensor I have tried something today that might have worked - at least it has for one test drive so far.
Looking at the old sensor, it has a small hole or crack. Maybe there is some contact between sensor and flywheel. The clutch was replaced by the previous owner so maybe that had something to do with it. Anyway, I added a thin washer under the crank sensor and so far it has idled fine and not stalled. I hope this could be it, but at least I seem to be on the right track.
Seems like if there was physical contact, there would be evidence on the sensor's "nose"... but you might well be onto something even if the sensor wasn't touching the flywheel. Knowing that the PO did a clutch job does open up some variables. Maybe he did replace the flywheel (or did something that somehow changed its position slightly). Seems like there would be an optimal distance from the sensor to the flywheel, and I suppose that there's such a thing as "too close"... if so, your "cooling the sensor" would effectively increase that gap (by "shrinking" the sensor, if only very slightly).
Keep us posted, if only to let us know that it's been perfect for a few months (might help future searchers).
Now that I am suspicious that my problem might be something to do with the recent clutch replacement I started searching online for crankshaft sensor faults after clutch replacement and found that this is quite common.
I found lots of posts about Nissans, and then this forum thread about Volvos.
Interesting - I scanned over the thread - ugly, ugly story for the OP. ;-) I'm betting you don't have the "dirty mating surface problem" though, or putting a spacer under the CPS would make it worse, not better. My bet is on one of two things:
1) The new clutch plate is a little thicker or has a different metallurgy that causes it to put too much metal too close to the CPS. Hence, your washer seems to "fix the problem".
2) The new clutch plate isn't perfectly flat and the variation from "low to high" points is a little too much for your CPS to work with. By moving the CPS out a little, the percentage difference in the low and high spots drops enough to make your CPS happy.
Yeah I'm thinking some variation with the new clutch or flywheel if that was replaced too. But for now the car is working great still a week later so I am happy. Even though it's taken me over three months to solve this.
09-22-2020, 04:19 PM
S40/V50 2.4i with P0300 misfire at hot idle only
