[T3] 69 fi troubleshooting update

[steve crispino]

Steve here,

Thanks for the advice.  See my comments in {}.


> [[[Was there a gauge on the fuel pressure while the engine was dying? If
so,
> was the pressure holding at 29 right up to the end?]]]
>
> Steve said the gauge was on it when it died the previous night, but not
> installed last night. We didn't want to install the gauge on a hot engine
> last night, but we will now as this check is worth repeating.

I only asked because dropping fuel pressure is exactly what this
sounds like, and an inadequate fuel supply will also not respond
properly to increased load.

{It's never dropped below it's setting while running.  I did down-adjust it
to ~29 as it was originally at ~32 (assuming the gauge is accurate).  I
will install it again for Friday night's test.}

> I like the suggestion to re-check the valves, as these could have a
reaction
> to a warming engine. That's the thing here; it takes this motor getting to
> running temp. before it starts it's death spiral.

If the valve adjustment had only been done before the engine was
first started, it could have been swayed by rust or crud that built
up since the engine was last run. This stuff would have worn away
quickly when the engine ran, resulting in improper valve clearances.

{It was spotless when rebuilt.  I oiled components to prevent rust between
reassembly and first run.  I will check them before restarting again.}

> I thought about the trigger points, but I couldn't see how they would
> work when cold but not work when hot.......

If the trigger points are maginal, they can work at one temp and skip
as they warm up. This is a long shot because that generally results
in a complete miss or the engine dying, not slowly weakening.

{They look clean and, as Dave said, I cleaned them with an alcohol soaked
card.  The ohm-out nicely and the cam and lobes are visually in good shape.
 Is there a spec for the opening?}

> and then the motor would fire with spraying a flammable into the IAD,
> so I kinda ruled out the trigger points to myself....but I could be
> wrong.

That tells you that the ignition system is working but the FI is not.

{we did have a no / low fuel issue - :-(}

> I forgot to say we did check voltage at the battery, and we could get it
to
> over 14V with about a mid-range rpm setting. We will check AT the
generator
> though, thank you. We also swapped out the coil with a known good one and
> that didn't matter. His Bosch points and condenser are new (although that
> doesn't guarantee anything).

{Points are good.  Not sure how to check the condenser - easiest test is to
swap it with a known working one from the fleet}

If you checked voltage at the battery, that's enough. I just
suggested checking at the generator because that's an easy place to
make a quick test. The battery test is the real test.

{I tested it at the generator as well and saw 14.2 - 14.4 volts.}


If the dwell and timing are okay then the points are good. If the
condensor or coil were going bad that would show up as misses, not
weakening.

{it doesn't do what I would call "miss"}

> When I saw it was a heat induced death, we immediately checked the
> resistance of both temp. sensors, but they were in spec.....so I thought
> maybe the brain reacted wrongly (is that a word) to the lowered ohm
> readings???

The temp sensors are a good suspect. If this '69 still has it's head
sensor below the #4 exhaust valve that can cause a problem as the
wire gets bent sharply and tends to short to ground. That, however,
also stops the FI completely and instantly, not slowly weakening.

{I re-insulated the entire length of the wire with heat-shrink tubing when
I replaced the spade connector end - soldered of course.}

I don't expect the brain to react oddly to slowly changing
resistance. These brains have been REALLY reliable, but I have good
tested B brains here if you run out of options.

One more thing to check might be that the distributor is really
pushed ALL the way down and fully engaged in the drive gear. That can
stick and slip as the case warms up.

{I checked that too - no movement.}

I'll report back Friday or Saturday.  Again, thanks for all your help.
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