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Last year I replaced the contacts in the rpm sensor connector (to the wiring
harness). It seemed to cure a rare, intermittent no-start condition.
But my car's intermittent no-start condition is becoming less intermittent and
more regular now. The hotter it is underhood, the more likely to not start
(just cranks normally...). Happened twice today (a new record, but with the
oil change it got an extra opportunity...). Each time the engine fails to
start, a gentle tug on the rpm sensor wiring near the connector will clear
the problem.
Often accompanied by the check-engine light, and a code 2-1-4. (Today a tech
at the dealer also pulled a 3-something Α-1-2?] that was also about rpm sensor.
The two codes were apparently set at 45 dC and 80 dC coolant temp, fwtw.)
I'm not going to replace the contacts again, though I am considering soldering
the wires together and elminating the connector as a potential trouble source.
(The new contacts are better spring-loaded than the originals, suggesting that
perhaps Volvo recognized the original design as a weak point?, and also that
maybe no amount of spring loading is sufficient to reliably conduct such a
low-voltage signal.)
Here's the rub: the engine cannot run without a signal from the rpm sensor.
(This is so that, in the event of an accident in which the engine is no longer
running, the fuel pump will stop...) And my engine has never stalled.
OTOH, the engine only needs the cam position sensor to start the engine; once
running, the cam position sensor isn't used/needed.
And when I did the rpm sensor connector, I removed the rpm sensor and tested
it (it's just a coil, so passing a magnet by it will either generate an electric
pulse across the 2 leads or not, and it did, though the sensor was cool at the
time).
So before I decide to go after the rpm sensor, connector, cam position sensor,
I'd like to hear what others have to say about these components.
I suppose that a very tiny physical gap (something's acting like a thermostat)
in the circuit might continually make/break contact once the engine is running
due to vibrations, sufficiently often to let the ECU know the engine's still
turning and thus keep the fuel pump running. But the connector contacts or the
sensor itself? Anyone with experience out there...? Do either of these 2
sensors have a significant failure rate?
I'm starting to think I need to at least carry, if not install, one or both of
them. If it were easier to get to, I'd have already eliminated the connector.
But since it's not particularly easy to get to, I'm looking for some feedback
before I take anything apart again.
TIA,
- Dave; '95 854T, 127K mi
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