Re: FI Computer

["Jim Adney" <jadney@vwtype3.org>]

This bit of fresh wisdom in from Steve Bradly.  I hope he doesn't 
mind my sharing it driectly.

On 10 Jun 98 at 11:48, Steve Bradley wrote:

> Jim,
> 
> I'm pmailing you to so you can "save face" (just kidding).
> 
> > Each wire is numbered. Wire #3 goes to cylinder 1, wire #4 to cylinder  4,
> > wire #5 to cylinder 2 and wire #5 to cylinder 3.
> >>There is a "hot" wire to each injector, but I don't think the number
> >>is the same as the cyl #.
> 
> Wire #4 does go to cylinder 4. See Bentley, page18. This was partially
> incorrect though, wire #6 goes to cylinder 3, not wire #5. This info was
> corrected on a subsequent post.
> 
> > If you have continuity and a good ground, and you are sure that injector
> #3
> > is firing, and you are sure the injector is good, you may indeed have a
> bad
> > brain. If you find that injector #3 is "not" firing however, you probably
> > have a set of dirty or bad trigger points (which was the source of my
> > particular problem).
> 
> >> No, a bad brain would fail to fire both 2 and 3, while a bad set of
> >> trigger points will bring the whole engine to a halt, because one
> >> point not only triggers its injectors, but also resets the circuitry
> >> for the other pair.
> 
> I just fixed a problem on my '71 with a bad set of trigger points that were
> triggering on just one side. Cylinders 1 and 4 were firing, but 2 and 3 were
> not. This was verified by turning on the switch and advancing the throttle
> while checking which injectors were firing.

If you're doing this with the engine off, this is not a good test.  
Even with a perfectly good system, only one pair of injectors is 
triggered if you do this.  Which pair is dependent on the state of 
the distributor contacts.

> I took the distributor out and checked the trigger points and found that the
> contact plate on the 2-3 side had been bent so that when the distributor
> shaft lobe contacted the 2-3 side, the points would stay closed instead of
> opening. All I had to do is bend the contact plate back to its original
> position. This resolved the problem.
> 
> The '71 FI engine will definately run on just 2 cylinders when just one side
> of the trigger points are working. Q.E.D.
> 
> Please correct this info to the list as you have been granted "ghuru" status
> by many listees.
> 
> Steve B.

Thanks Steve.  I have never had a case where a trigger point failed 
closed.  The usual failure mode is a bit of dirt or rust that falls 
into the gap and prevents contact.  This stops the car, all 
cylinders, all years.  Since I have never seen the kind of failure 
you describe, I unfortunately generalized too much.  Thanks for the 
update.

Jim
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Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
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