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Discussion Starter · #1 ·
The car is my '86 900 8valve sedan. After removing/reinstalling all my turbo piping, changing out the battery cable to the starter (which was cracking and falling apart), and removing/cleaning the grounds on top of the engine, my rpms now do not register at all. The car starts, runs for around 5 seconds and then dies, presumably from the same issue that is causing the AWOL rpms. I've removed the hall sensor connector to verify that it is not in fact the hall sensor, after which the car would not start at all (as predicted). Plugging the hall sensor connector back in, the car starts and dies after 5 seconds again. If you hold the throttle down, it will run at high rpms for a bit longer. What sends the rpm signal?
 

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Discussion Starter · #2 ·
Nevermind. :D

I'm still not certain where the signal originates from, perhaps the ignition module? What I do know now is that the rpm signal does appear to go THROUGH the upshift relay. In my case, removing the relay has allowed the car to run, though I still have no tach signal. When I source a good upshift relay, I'll see if my tach returns. ;)
 

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In 1986 there was, briefly, an Ignition Pulse Amplifier. Its purpose was to amplify the Ignition Pulse to feed increased demands on the bussed Ignition circuit. When it failed, it exhibited those symptoms. You may be confusing Upshift with Ignition Pulse Relay; they were poorly marked.
Try bypassing (jumping) the Relay as though it were a Fuel Pump Relay (12 O'clock to 6 O'clock?).
 

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Discussion Starter · #4 ·
In 1986 there was, briefly, an Ignition Pulse Amplifier. Its purpose was to amplify the Ignition Pulse to feed increased demands on the bussed Ignition circuit. When it failed, it exhibited those symptoms. You may be confusing Upshift with Ignition Pulse Relay; they were poorly marked.
Try bypassing (jumping) the Relay as though it were a Fuel Pump Relay (12 O'clock to 6 O'clock?).
Took another look at my relays and found that I do have an ignition amplifier relay. It's in a different location than my upshift relay and both are pretty clearly labeled in my particular car (it's generally had a very babied life, so all labels are like new). I'm suspecting the upshift relay must have shorted or something to that effect. With an identical relay in place the car runs fine, but still with no rpms on the tach. Removing the relay makes no difference (runs without rpms on tach), but replacing the suspected bad relay is causing a no start. I'm thinking that perhaps a short fried the tach? Removing the ignition amplifier with the good replacement upshift relay in place also causes a no start as you suggested and is almost identical in symptoms to what initially occurred, but replacing the relay allows the engine to run again which seems to point to it working properly.

At this point, the engine is operating normally, I think I just have a bad tach now. I've got spares around, so I'll see if that makes a difference tomorrow.
 

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If you're talking about the signal that drives the tacho, it comes from the negative side of the coil in 8V cars if my memory of the schematics for my 8V ones is correct.

The hall sensor does give a signal too (which is used to keep the fuel pump relay engaged) but I'm not sure if that's what generates the 'engine running' signal of if the neg side of the coil provides that too.

Craig.
 

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I have an 84 8v turbo, and the tach does not work until I rev the motor a couple times, or until I start moving....go figure...

Then again, this car has more electrical ghosts than I can list.....
 
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