Re: '86-'87 C900 ig. amp. fix w/photo - Saab 900 Bulletin Board - Saabnet.com
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Re: '86-'87 C900 ig. amp. fix w/photo
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Posted by Cmyles [Email] (#1126) [Profile/Gallery] (more from Cmyles) on Mon, 18 Oct 2021 12:50:37 Share Post by Email
In Reply to: Re: '86-'87 C900 ig. amp. fix w/photo, Phoebe, Mon, 18 Oct 2021 11:28:24
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OK. I re-read your original post and you said that the tach only works if you bang on the dashboard and that makes me think that there may be a loose connection related to the ignition system in there. The jumper in the fusebox that replaces the ignition pulse amplifier connects the ignition module to the tachometer. I'll need to do a deep dive to see what the actual connections are at the tach but if that connection is failing or loose there ya go.


Otherwise, like I said, step 1 is to isolate the issue to fuel or ignition. If there was real pressure in the rail immediately after the car died ("real pressure" being a subjective notion so did a little fuel dribble out or did a bunch spray out forcefully in all directions?) then you can overlook the pump and delivery system and ask whether the injectors are putting fuel into the engine? Since it runs well at times the injectors are capable of good function so the problem would be with either the positive supply to them or that ECU control of them. The ECU units in the 1987 turbos are very reliable, I've only seen one bad one in maybe thirty years so I'd suspect a connection or ground rather than the unit.

Moving to the ignition system, a few very common faults that cause intermittent dying in the LH2.2 turbo cars is a weak connection of the Hall sensor at the distributor (very common cause), a dying ignition module (also very common) and poor connections on the coil terminals. We used to see the coil connections sometimes shorted by contact with the hood (easy fix). One basic test we use when a car dies is to just see if there is actually spark at the plugs. If not then we work back from there. The distributor rotor has a resistor embedded in it which can break and cause ignition failure.

Both the LH system and the ignition system rely heavily on good grounding of their many ground conductors. Any loose ground wire on the forward lifting lug can cause your problem and is something we see a lot. Don't just check the bolts, the terminal ends on those black wires will sometimes break off. Maybe check the battery ground conductor for good contact on the chassis and transmission as well.


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