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Discussion Starter · #1 ·
Hello

Sometimes after een few min of driving my tachometer shows the wrong RPM, its like its 400rpm off. Sometimes 100 rpm sometimes even 800 rpm off. Very anoying because i dont know where my redline is when the needle is off that much


When i shut the engine down the RPM needle stays at the RPM its off, say 800rpm. Next day everything is normal again. Dont know after what time its back to 0


Does anybody have any experience with that? V50 T5 AWD 2005


Sorry for the english, i had hard time explaining
 

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So when the car is off it still shows 800rpm? Has someone tampered with the odometer/speedometer? You can take it apart and pull the needle off, the car isles around 800 rpm and just press the needle back into place. But it sounds like a software issue if that doesn't work.
 

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Almost definitely a problem with the gauge itself. You can verify by using Torque or other OBD-II type reader to display the engine RPM value, but the ECM would be throwing codes like there's no tomorrow if it thought the engine was running that far off the actual rpm.
 

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Hrm. That's odd - I wonder if post start you can disconnect the Crank Position sensor and leave it there, drive it around and see if it's got a short by errantly reporting values when it's not even plugged in. I don't know, just a thought.
 

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Discussion Starter · #5 ·
The needle show sometimes 800 rpm off, sometimes 200 rpm, sometimes 0 rpm off. Or any other rpm

When the engine is cold, i dont know after what time everything is normal again. I can check with the obd if that also reads the same rpm as the needle.


If i disconnect the cranks sensor wont that trigger any codes. the ecm reads some important stuff of the crank sensor.
 

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The needle show sometimes 800 rpm off, sometimes 200 rpm, sometimes 0 rpm off. Or any other rpm

When the engine is cold, i dont know after what time everything is normal again. I can check with the obd if that also reads the same rpm as the needle.


If i disconnect the cranks sensor wont that trigger any codes. the ecm reads some important stuff of the crank sensor.
For starting up sure - I don't think anyone has tested with the engine already running whether it causes you issuesby disconnecting - I'm sure it'd give you a CEL but we gotta pay to play in this case - if you're getting odd readings from the Cluster AND the ODB2 port - it means the readings are coming straight from the ECM which is reading it from the sensor..
 

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The car isn't going to run without the crank sensor. It magnetically picks up the signal from multiple lobes on the flywheel, which are spaced at specific intervals, with a gap as a reference point. The ECM does some rather interesting pulsetrain analysis to determine the rpm of the engine as well as the position of the crank, and even the relative acceleration of each piston as they fire. If the signal is flaky enough to affect the rpm reading by double-digit percentages, that ECM isn't going to be commanding spark and fuel very well at all - you'd certainly see other effects.

That said, with marginal or intermittent signals, lots of unpredictable things can happen.
 

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Discussion Starter · #8 ·
Ive tested with an OBD2 unit, and when the RPM needle started to drift of the idle RPM is spot on 750rpm. And my tacho could be even 1800rpm.

Next day everything is good again. then after some time the needle start to drift of again
 

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Ok, it's the DIM, then. It's a challenge to swap this part. It requires software programming, and a copy of the car's mileage is stored as well. If this mileage differs from the CEM's value, the "tamper" indicator is set, which can have consequences.
 

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Ok, it's the DIM, then. It's a challenge to swap this part. It requires software programming, and a copy of the car's mileage is stored as well. If this mileage differs from the CEM's value, the "tamper" indicator is set, which can have consequences.
I've swapped dims. The mileage is stored on the dim though. It's plug and play no codes. I think you can tell though vida that I swapped them. The dealer here refused to do anything with the dim. But if you don't care about mileage and aren't tying to commit fraud when you sell the car, just swap out a cluster from eBay and make a note the mileage. Just disclose it when you sell the car what the actual mileage is and you're good to go.
 

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Ok, it's the DIM, then. It's a challenge to swap this part. It requires software programming, and a copy of the car's mileage is stored as well. If this mileage differs from the CEM's value, the "tamper" indicator is set, which can have consequences.
I seem to recall reading something about if the replacement DIM mileage is lower by some amount than the original then it flags the Tamper indication. But if the replacement DIM mileage is higher than it does not. I could be wrong though.
 

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Discussion Starter · #12 ·
Now i have drove it again, the problem of course came back. After a few km of driving the tacho is off again. It starts slowly and after a while its of by almost 1000rpm. Really annoying

DIM is original i think because VIDA km is exactly the same as the gauge says. And now tamper indication of whatsover.y
 
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