For the past month or so, my 850 will randomly stall out on me when driving. It's happened maybe a dozen times and I have yet to be able to find a common thread between these occurrences. Often it will stall within the first few miles, other times it'll run for hours before crapping out. Sometimes it will start right up, or within a matter of minutes, after stalling; more often than not, it takes several hours before starting again (usually after a tow). Sometimes there's a strong smell of gas associated with it, sometimes not.

I've now taken it to several mechanics, none of which have been able to reproduce the problem. However, the suggestions that I've gotten have indicated that it's either fuel related (which I initially suspected) or a faulty sensor. The Fuel Relay Switch and Fuel Pressure Regulator were recently replaced (apparently they were pretty rigged up by whoever owned the car before me). After realizing that this didn't solve the problem, this led the mechanic to then suspect that the fuel pump may be going out, since the way they were rigged would have put an unnecessary strain on the pump. Aside from that, his best guess was possibly a faulty coolant sensor that might be triggering excess fuel to get pumped to the engine, causing it to flood - which would explain why I typically smell gas when this happens.

I've also spent some time reading through the forums and some of the info I found led me to think maybe it's a faulty MAF sensor. After checking the codes, I did get a response of 1-2-1 (MAF); but have also read that that's not always indicative of a problem. I was also informed that my air filter needs replaced soon, but was told that's likely not related.

I don't have the money to just start replacing parts on a whim, not knowing whether or not it even fixed the problem until next time I'm stranded on the side of the road. I'm hoping someone may have experienced a similar issue, or have further insight into what could be going on here.

 

If you want to fix this on the cheap, then you will need to diagnose it when it won't start. You can do it. You need some diagnostic tools and a procedure. The diagnostic no start procedure in the shop manual is very good in my opinion.

I am a strong proponent of owning a fuel pressure gauge, but a tire gauge might work for fuel pressure on the 850. I am not totally sure it'll fit, but it looks about right. It's hard to get my gauge on there anyway. You'll need a volt meter. They give them away free at Harbor freight, or $5 if you don't have a coupon.

 

If you have a MAF code then you should clean or replace it.

Also, if you try to start it you should hear the fuel pump activate if the fuel pump and the relay works.

Stalling with NO CODES is usually fuel related. If you have a code, follow that route. What year is the car?

 

It might me your MAF, especially if you have the code.

My MAF is good, but when I was changing the air filter a couple of weeks ago, I forgot to plug it back in after the filter change. I got a CEL and the MAF code 1-2-1, but didn't notice much difference in the driving characteristics of my 850 with the MAF unplugged EXCEPT at idle. If I turned the steering wheel to full lock or turned on my AC, loading the engine at idle, it would drop to like 400RPM, almost stalling. I'm sure if I did both at the same time, it would stall.

Basically, it couldn't compensate for an increased load at idle. I suspect this is because the car has a default map it uses when the MAF fails, and this idle works ok with little to no load from the accessories, but when given a load like the PS pump at full lock or the AC compressor, the engine couldn't compensate for the increased load on its default map. After I plugged my MAF back in and cleared the codes, the car ran and idled normally again.

Long story short, check your MAF.

It also wouldn't hurt to recheck your fuel pump and relay, just to make double sure.

https://volvoforums.com/forum/volvo-...p-relay-64044/

Good Luck!

1995Volvo850

 

My bet is the fuel pump. I just went through this with my son's 1997 GLT and tried several things, including replacing the fuel pump relay and cam position sensor. It ended up being the fuel pump.

Go to your local Pull-A-Part, Pick-A-Part, etc and grab a fuel pump. They're easy to get out through the access cover in the trunk and should cost you maybe $20-$30.