1996 Volvo 850R Random no start but runs perfectly

Volvovlo · Post by **Volvovlo** » 18 Sep 2020, 06:38

Title says it all, I have a stubborn 1996 850R that wont start 20% of the time. Its completely random, when the engines cold, when the engines hot, after running all day or first thing in the morning, pretty much whenever it feels like. But when it does start
80% of the time, it runs perfectly, doesnt miss a beat, doesnt stall, runs like a dream. Then if I turn the car off, theres a 20% chance it wont start again. In this case I have to try cranking the car over several times over a period of 5 minutes to an hour, and 90% of the time the car will then start before completely draining the battery. I cant understand why it may have issues starting, but when it fires up runs so well. There is a spark at the HT leads, fuel pressure at the rail and no CEL. Ive tried letting the fuel pump run for a few seconds before starting, sprayed easy start down the intake, (engine tries to run on this so i have spark?) cleaned the distributor, changed the plugs and none of this has worked, im thinking my next step is the cam sensor or fuel relay? Ive read a lot of threads online about intermittant starting and running bad but if my car starts it runs and drives perfectly until i shut it off. What should i look into next?

Post by **slickdizzy** » 18 Sep 2020, 06:52

Sounds like a classic fuel pump relay failure to me. The part is quite cheap so I’d start there.

Post by **abscate** » 18 Sep 2020, 07:30

This

, fuel pressure at the rail

Has to be measured in psi or hPa

To troubleshoot fuel delivery. Just looking at a spritz from the valve is not sufficient.

I took a second in applied math so I cringe at random , when pseudo-random Is correct. Sorry about my issue.

Klausc · Post by **Klausc** » 18 Sep 2020, 09:39

Remove the fuel pump relay when the engine refuses to start. Insert a large paper clip into 15 and 87 slots. The fuel pump will run continuously with the key in the on position. Be careful, the paper clip will get HOT in a few minutes of engine on.

If the car still won't start, it may then point you to a fuel pump problem. Most of us 850 owners carry a spare fuel pump relay in the glove box.

Volvovlo · Post by **Volvovlo** » 18 Sep 2020, 14:51

Lucky I have a donor car, I will try replacing the relay and pump today in that order if it doesnt start. I must ask though, what 850 owner has a working glove box

Volvovlo · Post by **Volvovlo** » 18 Sep 2020, 16:06

Just tried jumping the slots 15 and 87. Fuel pump runs constantly when I do that but still no start. I have no way of accurately checking fuel pressure unless i buy a tool for doing it. Should I try changing the fuel pump or look at the cam sensor? I heard some people have trouble with the coolant sensor too