Over the past 9 months or so, my car would occasionally refuse to start

when cold after having sat for more than 24 hours. Sometimes I'd check a

bunch of underhood connectors, other times I'd just retry it later and it

would start (though twice it chugged to life and once it made a sound that

was like a muffled backfire).

Last Thursday p.m. it happened again. After numerous retries, still no

life. I pulled the plugs. No smell of gas; plugs were clean and dry,

though there was more of a layer of black carbon than I'm accustomed to

seeing at the bottom of the threaded part (ie, the combustion chambers have

more of a coating of carbon than I'm used to seeing in my engines, incl

this one). Also, perhaps 30 minutes after cranking I momentarily opened

the Shrader valve on the fuel rail, and the fuel was apparently under low

pressure at that time (some came out, driven by more than gravity but not

under high pressure). By the time I put everything back together I'd

missed my appointment, so I connected a small battery charger and let the

battery charge overnight. The next day the car started more promptly than

it has in a long time, with no anomalous behavior.

Over the past week I'd kept an eye on the battery condition. I found the

fluid level slightly low in 4 of the 6 cells, and added a little distilled

water. It kept falling slowly to below 12.5V follwing normal use, so I

kept the charger handy, and made sure the battery was "topped off" before

starting if the car hadn't been used for more than a day. All seemed fine.

Then, again yesterday, after not having been used in the a.m., the car

refused to start in the p.m., despite a topped off battery and good

cranking. I put it back on the charger and waited for today.

But this week there was no overnight/magic cure. My car won't start!

Some of you may recall that last year I posted a bit about this then-minor

inconvenience, and noted that the ECU had recorded an "rpm sensor signal

intermittently missing" code. I noted this after the ECU light had come

on following a successful start within an hour of unsuccessful starts.

That was with an old/worn distributor cap/rotor, which I subsequently

replaced.

Since then the engine has run great (when it starts). The ECU light has

not come on again. Last week when it wouldn't start, I checked and found

an overboost code, which I cleared. In the past week I ran the car hard

but not too hard. No codes this week.

Based upon what I've read, I'm aware of 4 main suspects:

1. Battery (mine's 3 yrs old so it's probably due, but I don't think that's the prime culprit. I was thinking of going to go replace it, but my car

won't go...)

2. RPM sensor - without the signal from this, there won't be any spark or

fuel delivery.

3. Ignition Coil - I've heard they fail, and without any ECU code being

set.

4. Fuel Pump Relay - I've heard they also fail. But I don't even know

where to look for mine!

I have questions related to these 4 culprits, and would appreciate any

feedback:

1. Can I assume I have enough voltage for the Bosch ECU to compute if the

3-yr-old Volvo battery can vigorously crank the engine?

2. Any test for rpm sensor besides repl? I believe it's just a Hall-effect

(no moving parts) sensor, similar to ABS wheel motion sensors. Connector

problems? Do they commonly fail? If this part had been failing for 8

months, wouldn't there be a(nother) code? Wouldn't the engine's

performance have been faltering?

3. But if it's a bad ign coil, wouldn't I have noticed fuel-fouled plugs?

4. Since the fuel was still under some pressure many minutes after a

failed starting attempt, can I presume the relay's OK and look elsewhere?

5. Any other suspects?

What is the recommended procedure to verify the presence of spark without

any special tools or risk of ignition system damage on these cars? (Just

pull one plug wire and look for an arc between it and the engine block

while cranking?)

Even though this is a cold-starting problem, it seems to be more likely

to appear when the ambient temperatures are not very cold. Also, I have

never noticed an increase in cranking speed, as others have reported (which

has been attributed to sticking valves and/or excess fuel washing oil from

the piston rings, thus reducing compression).

TIA,

- Dave; '95 854T, 111K mi