Re: Mystery problems continue - Saab 900 Bulletin Board - Saabnet.com
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Re: Mystery problems continue
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Posted by Cmyles [Email] (#1126) [Profile/Gallery] (more from Cmyles) on Fri, 3 Sep 2021 19:19:15 Share Post by Email
In Reply to: Mystery problems continue, DaleG, Fri, 3 Sep 2021 11:19:28
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I re-read your complaint and had some thoughts. Firstly, did this car run OK recently and then just stop being OK or is this a "new to you" car? Did some repair or maintenance work precede the development of the problem? Trying to imagine why it dies when only one specific injector is disconnected leads to these thoughts:

Are the secondary ignition wires in the correct order? It's easy to mess those up because of the backwards engine arrangement. Of course cylinder #1 is closest to the firewall but more importantly the distributor, when viewed from the front of the car, rotates counter-clockwise. If the wires are attached to the distributor cap as if it rotated clockwise the engine might run but very badly and the reversed timing might result in one cylinder doing most of the work that's making it run.

Otherwise, I think that you might have a fault in the injector circuit. These engines will run quite well on three cylinders (timed properly) but two would be really rough and I can't imagine it running on one cylinder (never tried that?). LH is batch injection so all four injectors open and close in perfect unison. They are wired in parallel so a break in the circuit might create a series circuit where disconnecting one would kill the downstream injectors (like Christmas tree lights). That would also cause them to function sequentially. Your noid light would still indicate that everything is fine and the injectors would spray fuel in a decent looking fashion. So inspect all the injector wires for breaks or damage. It's a very simple circuit, the fuel pump relay provides 12 constant volts to the injectors and the ECU grounds them all 12 times per second at he same time varying the pulse width in accordance with the inputs from all the sensors sensors.

It would probably be worth doing a very thorough examination of all the black ground wires bolted on the front lifting hook too and make sure the hook is bolted down tight. A couple of those wires are the ground connections for the ECU. All of these wires can look OK until you start picking at them. None of my 1987 turbos had the notorious bad wiring but 34 year old wires still have issues especially at their terminals.

->Posting last edited on Fri, 3 Sep 2021 19:24:58.
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