Hello again lads,

The 850 has been running good for quite a while now. Recently, however, its stalled a few times while shifting out of reverse, or just as I was accelerating from a full stop. Last night it stalled while coming out of a slow turn.

The engine never sputters and the idle speed is steady. It almost seems like turning the key off - it's that abrupt.

It starts back up and operates normally. Until the next stall out of the blue.

I cleaned the throttle body yesterday and did my best to inspect the vacuum lines.

I'm stumped.

- thumbs

I'm late to this discussion, but want to chime in.
Klaus and HF63 are solid with their posts.

But there's TWO fuel relays to worry about.
One is the Fuel Pump Relay in the main fuse block that supplies
power to the fuel pump.
The other is a relay that enables the fuel injectors, this one is
called the main fuel relay and is located above the radiator in the engine bay.

There's so many problems with these two relays that I recently replaced both of them with new (NOT recycled boneyard relays) to be proactive, and avoid the
hassle when these relays finally fail from old age and kill the fuel flow.
These two fuel relays are like timing belts, when they quit, you're a pedestrian.
Relays will often get funky and flaky before outright failure, a huge heads up.

I found both relays on Ebay for reasonable money, and they are easy to replace.

Bill

Short answer is yes the fuel pump relay can be the suspect. There could be others, but that is a primary for cutting out, hard starting or no start. Many write-ups on the problem. Check the internet also.

http://volvospeed.com/volvo_repairs_how_tos/engine_repairs/fuel_pump_relay_replacement.html

Check the crankcase pressure by putting a latex glove over the oil fill hole. If the pressure is positive, it is time to clean the PCV and check the vacuum lines for it.

Stalling is usually caused by a too rich running condition, easily checked by looking at the spark plugs. Running rich is caused by unmetered air getting into the intake manifold, reduced vacuum tells the engine computer to increase injector flow. To say nothing about the front O2 sensor sensing a lean condition and also increasing injector flow.

Of course, sudden stalls can also be an electrical issue. The engine torques too much, pulling on a ground wire or loose coil wire...
--
Keeping it running is better than buying new

Ah, Klaus,

Again you've given me a lot of points to ponder. I did inspect the plugs yesterday, but no news there, as they all looked to be firing the same. (New plugs, wires, distributor last year.)

I haven't laid a glove on it yet, but it's probably time for a thorough examination of the PCV issues.

One last observation... I believe its running slightly worse after snooping around yesterday. I cleaned the thottle body, sprayed MAF cleaner on the MAF, pulled the plugs... Must have disturbed something important.

Thanks.

- thumbs

You might want to check the fuel pressure regulator for gas in the vacuum line.

Your car been a 93 model it has VVS or adjustable butterfly's inside the intake.

The controller is attach to air filter and under the intake their is a large vacuum servo that controls air into the intake. Check all these hose!

Don't forget to check the codes in A-2 and A-6, there might be a pending code which you can then erase.

If it runs worse now, check the intake hose for leaks/cracks or poor fitment on to the throttle body. (BTDT)

Take a close look at the top engine mount. If it is broken, the engine will shift a lot during torque and shifting.
--
Keeping it running is better than buying new

Can the fuel pump relay produce intermittent, momentary shut downs?

Thanks.

Yes, the relay and the fuel pump can cause this. But take HF63 seriously with the VVS, a malfunction there can cause the same problem.
--
Keeping it running is better than buying new