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850 97 Volvo 850 no start. Spark, no fuel.

D-Man9000

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Joined
May 10, 2004
So my dad just picked up an 850 NA wagon. Got it dirt cheap because of a 'bad' fuel pump. It'll start to turn, or even start briefly then die. It's as if it gets enough fuel to start, then stops.

Fuel pump is fine, injectors seem to be fine, spark is fine.

We replaced the injector relay that sits next to the radiator, still it'll start, then die.

We jumped the old relay and it fired up and ran fine. So we had assumed the relay was bad and replaced it. But it still does the same thing.

Does anyone have a wiring diagram of the fuel system for an 850?

Or just some suggestions on where to go back from the relay.
 
Cam sensor.

Crank sensor controls spark, cam sensor is used for the fuel system. If it dies while the vehicle is running the engine will continue to run but starting will be difficult if not impossible, though you MAY get a few bumps.

Grab one from the local yard. See if you can find one with the all alum. housing as that's an updated one to the plastic backed one.

BTDT.
 
Sweet, I'll try to score one at a yard.

He's already ordered a crankshaft sensor though...apparently the Haynes manual he is using states that the crankshaft sensor has to do with fuel, while cam has to do with spark.

Poking around the tubes backs up your side that cam is fuel, crank is spark. Oh well, a new sensor won't hurt.

Thanks again!
 
Cam and crank are both fuel and spark... A problem with either one means no RPM signal which means no spark or fuel.

Your problem sure sounds like fuel pump relay oddity. Are you measuring voltage at the pump as it's dying? Can you hook up a fuel pressure gauge to the schraeder valve at the end of the rail as it dies? Either one of these may illuminate a problem with the pump or relay. The relay on the radiator is the Motronic relay, that is for the whole shebang. Injectors are tied into it as well I believe. If the relay is dropping voltage you will be dropping spark as well. I'd count that out. I'd count the crank/cam sensors out, the motronic relay, and focus on: pump relay (under fuse box), pump (sounds like you've already addressed it), and fuel pressure regulator.

Check voltage at pump, check fuel pressure at rail, observe results and enjoy the solution :)
 
I just fixed an 850 that had a loose fuel hose in the tank.

+3 on checking the fuel pressure at the rail
 
Fuel pressure at the rail is good as is voltage at the fuel pump.

I'll make sure to check the pump relay then.


Gaaaah!

It starts with ether sprayed into the intake as well. I definitely have spark. But looks like no fuel, unless the fuel injector relay is jumped.
 
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Was it running normally til you turned it off last time?

A dead crank sensor will kill the engine, a dead cam sensor will allow it to keep running normally but it won't restart, as it is only used during startup(Per the greenbook).
 
no clue. Bought it this way for cheeeeaaap figuring it'd be an easy fix.
 
It was a wire from the ecu to relay. The relay had some scorch marks on the board and the wire appears to have burned up about halfway from the ecu.

Remember the OSI model guys.
 
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