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Re: [T3] Dead Injectors Puzzler

On Sat, 13 January 2001, "Jim Adney" wrote:

> We've now got one pair of injectors, normally triggered by the same 
> trigger point, which run normally until something happens and they 
> both cut out at the same time.
> It has to be either the brain, the trigger points, or the wiring 
> between the two. Mark's almost home.

OK, with my spare trigger points in the dist. and spare B ECU in the car and with everything cold, I measured essentially zero ohms between trigger point pins (outside to inside, both sides).  Same zero ohms for the three wires at the connector to the corresponding slots at the ECU connector.  I started the car, let it idle and begin to warm up.  While the car was running normally I carefully jammed the VOM probes into the top of the connector for the trigger points (at the dist.) to make electrical contact.  Measured a pulse between 2.5 to 3 volts for both sides, so I guess the "dwell" of the trigger points is the same for both sides.  When the car was at or near temp, injectors 1&4 went out again.  With the car running on just 2&3 I measured the voltage coming out of the trigger points again and got the same 2.5 to 3 V pulse, both sides.  Shut the car off and checked resistances at the trigger points again and again got as close as my VOM could measure to zero.  So I am pretty certain the trigger points ar

Now, when I changed the trigger points and ECU out early last week, I changed them together (I know, very bad...).  Feeling sure that the trigger points that are in there now are good, I reckoned that the old ones may have been bad (tho' I never tested them as extensively as the current set).  So I figured with good replacement points and probably good wiring, the replacement ECU was my new culprit.  Started the car again, and the car stayed on just 2&3.  Shut the car off.  With the motor still hot, I put the original ECU back in.  Turned the key and it started right up on all 4.  With that old replacement ECU it would never restart on all 4 when still warm after an episode of "failure mode"-- it restarted on all 4 only when cold.  

So with the original ECU back in and with the replacement trigger points, the car idled just fine for about 90 minutes.  I drove into town to run errands, and it ran like a top.  I kept the car running for a long time.  I felt sure everything was in good shape.  Later in the evening I went out again to the store.  But when i was ready to go back home, I found myself back in the old "Won't Start" mode.  Remember that??  The intermittent stalling/no-start condition that I had before swapping in that spare ECU I have.  Remember I'm back with the old ECU now.  

In the parking lot, I jammed my VOM probes into the top of the connector for the trigger points on the dist.  I suspected maybe poor electrical contact there.  Then it started up and took me home OK.  In the "Won't Start" mode, sometimes that has worked and sometimes not.  Maybe I was just lucky this time.  

So I have come full circle on this.  I need to eliminate completely the possibility of bad wiring at the FI trigger points, so I plan to splice (solder) in a good harness piece for the trigger points.  I'll cover the joint with shrink tubing.  The harness piece that is on there now is not very pretty, it looks like somebody once took the connector apart.  Makes me worry about the possibility of intermittent contact in there.  If new wiring does not make the "Won't Start" condition go away, I will swap in a third ECU.  Or maybe first re-try my old spare ECU first to see if I lose injectors 1&4 again.  Stay tuned.   

I have already ruled out bad temp sensors, bad pressure sensor, bad grounds, bad fuel pump, bad timing/points, bad FI trigger points, bad coil, bad dist. grounding, bad spark (all 4), bad fuel pressure, dirty fuel lines, bad fuel, bad battery, bad starter, bad ignition switch .......

-Mark Fuhriman
 '69 Fastback

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