1996 Volvo 850 Losing Fuel Pressure Overnight

jonesboy1983 · Post by **jonesboy1983** » 13 May 2015, 10:43

I've been chasing a stalling issue with my 1996 850 and, as part of that, replaced the fuel filter over the weekend. Replacement went fine but I think it was the original as it still had the masking tape on the lines. After replacement I have not had any stalling but I seem to be losing fuel pressure when the car sits overnight or while I am at work. When I get in the car after its been sitting, the pedal is hard and the car seems to have a weak crank before sputtering a bit. It still starts on the first crank and drives great after that. Any ideas? Thanks.

Post by **tryingbe** » 13 May 2015, 15:35

jonesboy1983 wrote:1996 Volvo 850 Losing Fuel Pressure Overnight

jonesboy1983 wrote:It still starts on the first crank

You're not losing fuel pressure overnight.

jonesboy1983 wrote: When I get in the car after its been sitting, the pedal is hard and the car seems to have a weak crank before sputtering a bit

What pedal?

Weak crank? Weak crank is solely cause by the battery/starter/starter cables. Test the voltage on it now

jonesboy1983 · Post by **jonesboy1983** » 13 May 2015, 15:57

It doesn't feel like a weak crank because the car kind of stumbles after it starts but then straightens out after a second. The brake pedal is what is hard.

Post by **misha** » 13 May 2015, 16:13

It's normal that you will loose fuel pressure in the lines after the car sits overnight.That's why the fuel pump prime itself every time the key is turned in position II,work for 2 seconds and then stop.It continues to run when you start the car.
Maybe there is still some air trapped in fuel lines after fuel filter replacement,but it shouldn't be any.Otherwise "check valve" in your fuel pump is bad.

Post by **tryingbe** » 13 May 2015, 16:16

jonesboy1983 wrote:The brake pedal is what is hard.

You have vacuum assist braking system, aka Power Brake, only works when the engine runs. The car might have enough vacuum reserved for a panic stop if the engine stalled. If the engine is running and your brake padal is hard than the brake system isn't working correct, could be vacuum leak, or bad brake booster. Take it in and have it checked out if you can't fix it yourself.

Post by **abscate** » 14 May 2015, 07:03

A good brake vacuum can will hold vacuum overnight. My P2 does, my P80 does not. I'm guessing it's the check valve gone bad

Fuel pressure spec us to drop to no more than half of operating pressure in 20 minutes.

jonesboy1983 · Post by **jonesboy1983** » 14 May 2015, 09:00

Thank you for the replies. If I turn the key to position II to prime the pump and then start it fires right up without the stumble. I am not sure how this is related to the brake pedal harness though. As soon as the care starts the brake is fine and there is no issue.

Abscate, what check valve are you referring to? Thanks.

Post by **misha** » 14 May 2015, 11:14

jonesboy1983 wrote:Thank you for the replies. If I turn the key to position II to prime the pump and then start it fires right up without the stumble....

That's the ONLY proper way to start the car.You ALWAYS need to wait for fuel pump to prime itself before starting the car.The system is designed for use that way.

Sommerfeldt · Post by **Sommerfeldt** » 14 May 2015, 13:20

Sounds to me like everything is working fine - pump primes, you get pressure, car starts and runs fine. The car's not supposed to hold the fuel pressure overnight, or even for an hour. If it did, it certainly wouldn't be a breeze changing the fuel filter like we do. Letting the fuel pump prime the system is our version of waiting for the glow plugs to heat up with diesel engines. Just something you need to do if you want stuff to work right.

Most of my cars have also not held pressure/vacuum in the braking systems overnight. That may or may not be due to some minor malfunction, but as long as the system powers up like it should, i.e. your power brakes function and you're not losing fluid, then you're fine.

Weak cranking, as someone already said, is all down to battery and starter.