c900 1984 - One or TWO Fuel Pumps?

Pretty sure it does.

That sounds like the filter?

I think that's called the "pre-pump". You need voltage there or you'll get...

...yeah, that.

Have you checked fuses and/or relays marked fuel pump?

OK, we're going with Main Pump/ Prepump setup.

No, I know CIS systems in general pretty good. I don't have much Saab time though, I'm a mainly VW wrench.

Under the car, right by the tank, right near the wheel is a fuel accumulator. It has a diaphragm and a spring inside it's job is to provide _some_ pressure to avoid the equivalent of vapor lock.

Yep, I get 12v at the relay in the engine bay but no 12v back at the prepump.

Now, one thing to add; I didn't jumper around the relay and I did find and replace a 25 or 30 amp fuse for the pump. It has a known good fuse right now.

What I might do next is jumper the Hot 12v to the fuel pump feed to see what happens. (At one point I put a battery charger's 2A/12V feed to that pump and it didn't seem to do anything so maybe I have multiple problems.)

TBerk

That's what I'm thinking, but '84 is a gap in my ownership history. I'm driving an '86 right now though which is pretty close.

Almost completely surely, your experience will carry you then.

Ah, there. Yeah, the filter is probably closer to the front of the car, and looks, well, filter-like. Beer can type thing with the usual banjo fittings & a hex on one end, held to the body with the clamp that you'd expect.

Do you have a wiring diagram for the '84? If not, let me know and I can take a look for you. The Bentley manual should have what you need, if not I have the full set of c900 shop manuals.

Was the old one known bad, or was this just a "let's eliminate that from the equation" step?

Well, you could have no voltage there because it's shorted, but then you'd have a fuse blown somewhere. Something isn't adding up here just yet.

Dave Hinz

900 w. injection yes? You are not looking at the fuel level sender on top of the tank?

I doubt that. Probably to a coal cannister, e.g. the one behind the left front fender, near the APC unit.

Fig. 3.15 in the Haynes 1979-1988 900 manual only shows one pump in the fuel system, in the tank.

Should the pump not only be running for about 30 sec. after the ignition switch is turned 'on', and then stop running if the engine is not started within that short time? - to prevent pumping the tank empty when the engine is stalled, e.g. in an accident while the fuel lines may be ruptured.

-- MH '72 97 '77 96 '78 95 '79 96 '87 900T8

Yeah. Fuel Filter is in the motor bay. Big ol honking Bosch filter. Mounted on the inside of the fender, it's right next to the Fuel Distributor.

It's really my roommate's car, he has a Haynes around somewhere (lost) that I bought for him, no Bentley at the moment.

The latter, it's a common trick to get you back home if you have a fuel problem is to pull the relay and jumper the hot to the pump leads.

The relay has one always hot 12v and it's corresponding ground. It also has a 'latch' side with switched 12v (from the Ign switch) and it's 'ground- in this case by way f running through the fuel pump.

The idea is to hard wire the 12v directly to the pump, the draw back is it's keep running with the key off, until you pull the wire.

TBerk

IN the trunk there are TWO items, one is the level sender, under a flat lid is a fuel pump, it really is a pump. It has two electrical connections and a banjo type fuel line coming out of it.

UNDER the car is an accumulator as described.

The accumulator needs a vent on the backside because it's internals expand, blah, blah, blah...

This is wonderful news as I only ever found ONE pump in the car.

No Love, No Joy- pump won't get 12v, pump doesn't seem to turn when licked with 12v from another source. (This part needs more study though.) Replaced blown fuel pump fuse- didn't help, change anything.

I am wondering if there is something else besides the FP relay that can inhibit the 12 volts going to it?

My ext plan is to hot wire around the FP relay and verify I can get 12v to the pump at all.

Thx folks, TBerk

Have a look at

where a short history of Saab fuel injection systems is given. From 1988 and onwards the fuse is the last component before the pump (the relay sits between the battery and the fuse) but IIRC the relay was the last part before the pump before that time (at least on the 99 model). I think I could use the same cable with a 99 and a 900 to start the pump manually but for the 99 you plugged the cable in place of the relay while for the '88 900 you plugged the cable into the fuse box (between a hot line and one side of the fuse). Thus if you have voltage at the fuse/relay but not at the pump the most likely cause is a bad contact inside the fuse/relay box followed by a bad contact at the pump. A broken cable is very unlikely.

You can run the pump with the ignition off as the fuel flows back through a return line. The relay is mainly there for safety, in case of an acccident where the engine stops the relay prevents fuel from being pumped out of the relatively safe location of the tank.

Sure, but it will/should not vent any petrol fumes into the atmosphere. It is a closed system, with a coal cannister to absorb/desorb any fumes.

-- MH '72 97 '77 96 '78 95 '79 96 '87 900T8

If it's the same as '86-'88 it does, the main pump sticks down into the tank, and on the end of it is a resivoir with a pre-pump stuck to it which keeps the resivoir topped off. The car will run on only the main pump but the pump will be noisy and wear out quicker when the tank is low.

connections.

Resolder the circuit board inside the relay, that will likely fix your problem.

Well, yeah. I only described the small hose on the back end for the visual.

TBerk

Sounds like it changed right about then, and he's only got one pump.

The 1985 model has two pumps. Mine has failed twice in

80K miles. The good news is that it's the same pump as used on some Chevrolets so the replacement cost isn't extravagant.

What chevrolets? I replaced the pre-pump in the 900 with one I got from a surplus place for 5 bucks, recognized it as a pre pump and wish I'd bought more. I had to shorten the feed pipe slightly but that was easy enough to save $300.

Not as such. The 83-1/2 and up C900's have fuel pumps that are configured differently and have a 'supply pump' which primes the main pump via an encapsulating fuel reservoir which keeps the main pump primed more efficiently. The whole thing operates as a sealed unit and it's the only part of the fuel tank assembly which is pressurised.

The fuel tank is fully-pressurised on earlier models (such as my 1982/83

900S) which has the older style of pump.

Is the car fitted with a turbo? I've heard of extra fuel pumps being added (not in Saab's) where turbo's are fitted as a way to run with higher fuel pressures.

Can you trace the wiring back to the fuse/relay block and run a continuity test on the power supply to the fuel pump from the fuel pump relay? Can you get the fuel pump to run with the fuel pump relay removed and a jumper wire installed between terminals 30 and 87 of the fuel pump relay socket (page

234-4 in the Bentley 8V manual).

It could be a dud fuel pump relay, even though you say you're getting +12V in places which appear to be coming from the the fuel pump relay, or it could be terminals might have come loose under the fuse/relay panel.

It could also be that the supply pump has failed. The main fuel pump can still be fine, but if the supply pump doesn't work the main pump won't be primed. Page 234-5 in the Bentley 8V manual details how to test the supply pump.

Regards,

Craig.