850 turbo intermittent no start

69silver2k · Post by **69silver2k** » 27 Jan 2009, 23:32

Hi All, I'm a noob to volvo's and this site, but not new to cars. I have a 96 850T wagon, with 110k, that has an intermittent no start. Here is what I have checked so far:

fuel pressure - 39# at fuel rail
fuel pump - runs in key pos 1
sparks while cranking (held the coil wire to ground, spark is strong and white)
cam pos/hall effect sensor - circuit checks out, although resistance to ground is 30 ohms (still 30 ohms after it restarts)
crank pos sensor is within tolerance as well.
last tune up was less than 5000 miles ago, (cap, plugs, wires)

Wife says it tends to happen when the fuel goes below the 6 mark on the guage. the first few times it happened, it was after 10- 15 mins of running, then was shut off for a few minutes (more than once when getting fuel)... then the crank no start issue. after letting things sit for a while, it will restart as normal.... What am I missing? car runs good, so it's not a timing or turbo issue, I have a new hall effect sensor, but don't think thats the issue either... help?

Thanks!

Post by **rgrady** » 28 Jan 2009, 04:18

Does your fuel pressure hold at 39 PSI (should be 43 to 44 PSI) with key on, motor off or does it bleed down? Could be the hose has come loose inside the fuel pump assembly that connects the pump to the discharge nipple.
There are some good pictures of the problem in the "How to remove fuel pump" thread in the repair section. The pics are in a post at the end of the thread.
My 95 turbo would idle great but didnt have any power under load. Would almost die but never did and was a little hard to start.

69silver2k · Post by **69silver2k** » 28 Jan 2009, 13:01

fuel pressure bleed's a bit from the 39 psi (not running) but only a psi or two when left for 15 mins. Do you think the 4-5psi mentioned would be a pump or fuel pressure regulator? would this cause the intermittent start? power is good when it runs.... I'm sourcing a fuel filter right now, as it can't hurt to change that... and it eleminates one of more possibility. Do you think the discrepancy between my fuel pressure and recommended would be enough to cause the problem?

I'll check the replacement instructions

Thanks
69silver2k

Post by **rgrady** » 28 Jan 2009, 17:02

Mine would jump to 43 when key was turned on and bleed down to almost 0 within 10 seconds.
I think you can check the FPR by pinching the return hose with a pair of pliers and see if pressure rises quickly. If it rises it is good. Do not hold it shut for very long at all.
Have you noticed a loss of power?
My 95 turbo would do this when I filled up and get better when it was closer to empty. Being a plastic fuel tank I think the sides flex a little from full to empty changing the way the pump hangs just enough to make a difference. Only took a half hour to pull the pump and check it. That is where I would start.
Hopefully Im not leading you down the wrong path but it sure sounds like fuel delivery problem.

69silver2k · Post by **69silver2k** » 29 Jan 2009, 10:41

so I put the fuel pressure guage on last night prior to changing out the fuel filter.... no pressure "0" checked the relay, and checked for voltage at the fuel pump connection all checked out ok. I ordered a fuel pump this morning, we'll see if the old pump was weak, causing the 39psi. I agree, there were only two possibilities, fuel or sensor, the faulty fuel pump threw me off since there was pressure, and it ran the first time I gauged up. Engine power was fine, idle or load, so I'm guessing that there was a dead spot in the pump that would just randomly surface... or I have multiple issues that are compounding the problem. Nice choice of trucks by the way. I too have a ram/cummins. Mine's a 93 and gets better gas mileage than the volvo