91 N/A 900s 5-speed No Fuel Pump? - The Saab Link Forums

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Old 03-27-2019, 07:00 AM   #1
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Thumbs down 91 N/A 900s 5-speed No Fuel Pump?

Howdy squad...

Long time ghoster, first time poster.

So I've got a classic 900 that died on us last week. The fuel pump isn't running while cranking and thus, I'm getting no fuel. I was able to jumper the pump in the fuse box, and it does run, so I naturally thought relay. If I swap the relay for the ABS main relay it runs with the key on (but then I noticed, this relay isn't setup properly) so I swapped it for another (air conditioning?) relay in the fusebox which is identical (and our AC does work) and it seems as though I'm getting nothing.

While chasing about the various forums there's just so much dis-information and I want to be sure I'm chasing in the right direction.

1. I am getting spark (checked all cylinders at plug<>plug wire via inline spark light.
2. I did not try to crank while the pump was jumpered at the fuse box, and I have not tried starting fluid yet.
3. I did try to crank while I had the ABS main relay in and the pump was running... but I suppose it could've been running backwards? Didn't have time to confirm.

I had read some odd things about ECU's going bad and such which is something I would never normally suspect (coming from Volvo world)...

Where to turn next?

Thanks
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Old 03-27-2019, 09:26 AM   #2
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I have an '88 900S which had a problem that sounds the same. It turned out to be a fault in the ECU. It wasn't closing the circuit to close the fuel pump relay.
I was able to crank it with the fuel pump jumpered in the fusebox and it ran.

Your '91 won't be the exact same setup, but it might be the same issue.

It's been several years so my memory is vague, but there's a thread on here where I was getting troubleshooting help from the group...
https://www.saablink.net/forum/car-p...only/62830.htm
..
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Old 03-27-2019, 10:21 AM   #3
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There is a boost control regulator that shuts off the pump if you get too much boost. Its behind the dash IIRC ( its been about 10 years since I had my 87 900T

If you bypass that and get fuel that's your culprit. You can keep it bypassed there is not worry if you are running stock components.
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Old 03-27-2019, 12:51 PM   #4
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Car is NA. Also, I just jumped the fuel pump at the fuse box. It definitely runs (the pump), but the car won't start with the pump running.

Am I right to look to the ECU?
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Old 03-31-2019, 07:32 AM   #5
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You need to go to that relay and check if the ecu is sending a ground. Pretty sure the wire you're after is purple (it'll be thin, as it doesn't carry much load). With the relay plugged in, and the key on it will show power with a test light. Should switch to ground and trigger the relay when you crank

LH 2.4.2 has a nice built in diagnostic mode to test components, the Bentley manual covers it well, but I can't walk through it from memory
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Old 03-31-2019, 07:36 AM   #6
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So, I chased it down via testing power to relay and everything pointed to the ECU... Which honestly is such a ridiculous thing for me to wrap my head around replacing, but I found one, and replaced it and the car started right up.

So... it was definitely the ECU.

Other than swapping it for another potentially failing ECU, are there other options for ECU? I mean I guess megasquirt but... Is anyone servicing the ECUs?
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