1996 850 Turbo sedan engine cuts out intermittently Topic is solved

[Dave in Maine]

I have a 96 850 Turbo sedan. Approx 180k miles (odometer broke at 163k), replaced fuel tank and pump about 20k miles ago (1/2015, before the odo broke), replaced water pump (anticipating trouble rather than reacting to it) at the last timing belt change (11/2015). Until recently, smooth sailing.

At odd, random intervals the motor will cut out, as if there is no fuel or electricity going to it. Just dies. Sometimes, when the vehicle is moving, it tries to restart itself (the old compression start). Sometimes it succeeds, sometimes not. I pop it into neutral - guide it to a safe spot on the side of the road if needed - and restart. No funny noises from the starter (no grinding or anything one might associate with a funky starter). It will start right up again. Sometimes it sputters but most frequently it just starts cleanly. If I rev it a bit on the restart, it won't gag or cut out. If I don't, sometimes it will gag. I took it to an AutoZone and they put the meter on it - the battery is fine and the alternator is fine.

The only "consistent" things which seem to "relate" to it dumping out are these: (1) it seems to happen more when the car is cold (even in warm weather) than when the car is hot, but it will happen when the car is warmed up. (2) it seems to happen more in city driving than in highway, particularly when pulling out from a stop sign or light (initial acceleration at/from low RPM). (3) it may happen more on rough pavements (cobbles, potholes, etc.) than on really smooth, but there's a small sample size on that.

It was very occasional until this week. The only times it would stagger or droop would be first thing in the morning on a cold morning, pulling out from the first stop sign of the day. And not every day at that. This week, it really started happening frequently. I think it cut out 5 or 6 times (didn't count exactly) in about 130 miles of driving today. If it cut out on the highway today i didn't notice it; all the times it cut out were on local streets, in parking lots, and pulling out from lights/signs.

My gut tells me it is something electrical, but what, where should I look, and most importantly can I fix it with duct tape, electrical tape or something similar. I am 450 miles from home on an extended project and can't get back to my regular mechanic until, probably, the end of June. The Yelp for the only mechanic close enough to where I'm staying to make dropping it off worthwhile includes the word "gouge" a couple times too often for my taste.

[cn90]

I suspect you have a bad fuel relay.
Your best bet is to buy a jumper wire with a built-in fuse (20A).

I wrote a DIY Fuel System trouble-shooting below, just scroll down the page to see how to jump #15 and #87 (you need Torx keys to open the fuse box).
Jumper wire is cheap at local auto parts store, buy some spade connectors and crimp them on as shown.
A paper clip may work in a pinch but it can burn your fingers if you touch it (search forum and you will see).
In fact, any owners of 850, S70 should carry this jumper wire in the glovebox.

viewtopic.php?t=52252

[JDS60R]

This is a common symptom of a bad relay . There are 2 that cause this often. The first is the fuel pump relay which was noted previously. There are tons of them in junkyards or just get a new one. It beats having to disconnect the fuel pump jumper wire each time you stop so you don't drain the battery or burn up the pump. But you should keep an extra or the jumper wire in the glove compartment.

The other relay is the main relay located above the radiator (powers injectors etc). You could wait to see which one it is ( fuel pump one goes bad more often) but when folks stop in with this issue (on original relays) and there is nothing acting up at the time I replace both relays. I have buckets of them from different junkyard cars. There are at least 2 different fuel pump relays so make sure you are putting the correct replacement in.

I'm sure an 850 expert will chime in on the red and yellow fuel pump relays and what years take which.

If the relays don't fix it we can look at the fuel pump, cam sensor or ignition coil itself.

[erikv11]

What JDS60R said about spare relays - in every 850 at the junkyard, virtually every relay works just fine. Grab a few, especially the two fuel relays, test them out when you get home, and your relay troubles are over forever.

[cn90]

...It beats having to disconnect the fuel pump jumper wire each time you stop so you don't drain the battery or burn up the pump...

FYI,

If the jumper wire is installed, once you stop the car and remove the key, the ignition is turned off and the power supply to the MAIN RELAY (upstream of the fuel pump relay) is cut off ---> fuel pump will be OFF with key out of the car. Been there done that.

So, in theory one can leave the jumper wire in there permanently, although I don't advise it. The proper way is:
1- Brand-new Volvo Fuel relay.
2- Fix it with new capacitors (search for Ozark Lee's post).
3- Used relays at junkyard should be fine, but no warranty how long it lasts.

[Dave in Maine]

So, if I go and get a jumper wire to use as a temporary fix until I can get a relay do I have to disconnect the jumper wire when I park the car or not? Running the battery down or frying the new fuel pump I had installed in 1/2015 are two downsides I am not interested in. (Damn fuel pump, tank and labor cost over $750.)

[cn90]

Get a voltmeter and do this:
- Black probe to ground and RED probe to terminal #15 in the Socket (fuel relay socket).
- Key out of the car: should be zero Volts.
- Key in position II: 12 V.

You can verify it yourself.

[cn90]

Another ghetto check with the jumper wire in place:

- Turn key to position II, fuel pump will run: get a screwdriver as a stethoscope and place it against the fuel pipe feeding the fuel rail (near the timing belt area) and your ear, you will hear fuel running through the pipe.

- Remove key (jumper still in place), you will not hear anything, i.e., fuel pump is OFF.

[Dave in Maine]

Fuel pump relay 9434225 ordered, shipped & in transit. I'll swap out the old and see what happens, then let you know.

Thanks in advance, folks!

[rspi]