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Discussion Starter #1
Hi, I ama bit of a Saab newbie so would appreciate any thoughts you guys might have on this.
I recently bought a 1998 900 2000cc non-turbo. Since I have had it there has been an intermittent failure to start problem where the car cranks but doesnt fire. I tested the fuel pump relay when this happened and there was no power to it, tried replacing the relay and this made no difference. When the relay is bypassed by taking a spare 15A feed from the redundant rear wiper the engine starts fine.
The garage have tested the CPS and said there is no problem with it, the only thing they can think of is that it may be the immobiliser. Sometimes when this happens resetting the immobiliser cures the problem, sometimes it doesnt so I'm not sure if thats the issue.

At the moment I carry around an inline 15a fuse holder and when it happens just take an ignition live feed to the fuel pump and it cures the problem.
Since the local Saab garage cant find or fix the problem, I was wondering if
a) there is some other cause I havent thought of
b) Could I just leave the bypass in the fuse box so the fuel pump is just live when the ignition is on?

Many thanks for your help,
Dan
 

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The problem with having the fuel pump running whenever the ignition is on is a potential safety risk. The design is to have the pump operate only when the crankshaft is rotating.
 

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Many cars have their fuel pumps on without the engine on , My 90' Volvo 240 does, so did my 61 ford falcon, which I converted from a manual to an electronic fuel pump. I believe my old VW scirocco had it as well. Maybe Saab does have a safety issue with having it on , but I know many other makes don't.
 

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NCviggen said:
i had a very similar problem with my trailblazer a few months ago and it turned out to be the ignition switch...
Now, would that not be something if the TrailBlazer and Saab were supplied with the same switch.....globalization and all.....

A '61 Ford Falcon, Eleven22 ?
Quite a good car, IMO, so easy to work on.... the basis of the Mustang.
Today, there is so much more stress on safety and pollution - maybe a good thing, maybe
 

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Discussion Starter #7
hkayssi said:
Test the CPS (Crank Position Sensor)
http://www.geocities.com/[email protected]/NG900SET/CPS/CPS.html

The CPS needs to be tested both hot and cold.

Do you see the Tachometer move at all when attempting to start the car?Another possible cause could be the ignition switch (electrical part) going bad.


- I have tested the CPS on three separate occasions now, both with a cold and hot engine, and it never opened the circuit at any point, so it could perhaps be that it is just beginning to fail and this is manifesting as a very intermittent failure.

Regarding having the fuel pump live with the ignition, the main issue seems to be that if the car were to crash then I would have to be able to take the key out of the ignition to cut the fuel feed to the engine which wouldnt otherwise happen automatically
 

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Yeah but those worries can be eliminated if ther wire feed is from wires that are live when the car is running like the coil feed for example.

I think there are multiple reasons behind that design for the fuel delivery system; it also reduces stress on the pump and on the fuel rail thus making them last longer. The immobilizer also prevents the car from being stolen by stopping the fuel from being delivered.

Was the ignition part checked? Those fail quite miserably for a good quality car :nono; We see soooooo many with bad ignitions electricals causing many such wierd problems.
 
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