Engine died after 5 min. 3.2, 1984. Problem solved

[rvidal]

Guys,
I wanted to share a problem solved.
I am in a process of repairing upholstery on my 3.2 1984 (under DIY mode... itīs been more than two years and still not finished). I know...very embarrassing not to be finished..

Anyway, every two or three weeks I run the engine for 10 or 15 mins.
About a month ago, I run the engine and died after 5 min. I did not have time to look into details and assumed had low fuel. The day after, I added fuel and started again. it died again after 5 min.
I checked all fuses, changed the DME relay (I had an extra anyway) and tried again and nothing happened. It did crank but no start.
Checked for spark...nothing. Checked coil (resistance) and looked under parameters.
After many tries, battery went down so had to wait for next day (late at night anyway).
Next day, after reading different threads here and thinking of all kind of failures (I was very worried if my DME was damaged...big money and time), started again. So I gave it a try and the engine started. Life is good again!!!. 5 more minutes the engine died...
I was thinking about temperature sensor. I had bought a sensor months ago as mine had brittle connector (typical problem for old 3.2 as read) even the impedance was under parameters and temp sensor failure does not shut down the engine (right?). So, I started the procedure of changing temp sensor (Nš 1) and noticed that both speed and position sensors (Nš 2 and 3) had aged connectors. I unplugged the sensors, checked resistance and could not believe that one of them had no impedance (Nš 2 which I understand is the speed sensor). Maybe I missed something when reading but speed sensor failure = no spark after 5 min???.
In summary I bought both sensor (while being there) and changed the temperature too.
Problem solved!!!: Now engine runs very stable. Much more stable (I can see the difference now). Life is good again.
I hope it helps to others

If somebody can explain the logic behind this failure, please very welcome.

[DRACO A5OG]

2 years, is nothing, some of us go even longer. it is LIFE. Just get it done as soon as you can but don't rush it because she is much happier if you drive her.

Just a side note, when you start her, idle her at a little high idle 1800-2000 RPMs for 5 minutes to get the oil pump working more efficiently to all the components to limit the wear to them.

Sensors are wear items, some one like Steve W, Ingo, Sal even Lauren aka Dave can explain in more detail I'm sure.

[Discseven]

My connectors are worn so this is the handwriting on the wall for me. Thanks for input Rvidal

[LanceS4803]

As preventive maintenance, should you just go ahead and replace thse sensors?

[theiceman]

I would have thought your problem was your temperature sender but you will never really know as you changed all of them.

the head temp sensors job is to lean out the mixture as it warms up as it needs a richer mixture when cold and to start.

if the temp sensor isn't working it doesn't lean it out as supposed to and when the engine warms up after 5 minutes its far too rich and stalls out and wont restart till it cools down again.


The fact you said no spark would in fact indicate one of the other sensors. All I can think of is heat killing a marginal sensor and no start.

[rvidal]

Thanks theiceman.
I checked resistance of temperature sensor and it was fine as I recall (ordered one time ago due to worn connector), unless I missed something and indeed was bad and killed the engine when warm.
I read several threads about bad temp sensor and called about bad mixture but never about shutting down the engine.
Does anybody have same experience?

[ischmitz]

A bad temperature sensor (failing open) will cause a no-start on engine at operating temperature. If the sensor fails open the DME will assume a mixture for -20 degree C ambient. With the engine cold there will be lots of fuel introduced but most condensates in the intake track of the cold engine and the engine will start just fine. The effective mixture is combustible.

As things warm up the effective mixture will get so rich that it isn't combustible any longer. As a result the engine won't fire even with spark present. To some it feels like a no-spark condition but it really is a super-rich condition.

[rvidal]

Great feedback. i checked the spark by unplugging one spark plug end and ground it by using screw driver. Did not see any spark at all.

[rick-l]

Since it was running and quit with no spark out of the three parts the only one it could be is the speed sensor.

[gomezoneill]

Originally Posted by LanceS4803

As preventive maintenance, should you just go ahead and replace thse sensors?

Yes unless you want to be stranded. I'd say 80 k miles +/- they should be replaced.

[rick-l]

The speed and reference sensor consist of a coil of wire and a magnet. These parts should not age and there are no moving parts.

The plastic covering the cable does seem to degrade however.

[gomezoneill]

Originally Posted by rick-l

The speed and reference sensor consist of a coil of wire and a magnet. These parts should not age and there are no moving parts.

The plastic covering the cable does seem to degrade however.

Snow and salt along with rain can deteriorate them before their time. Not mention heat and age.

[rvidal]

If damaged speed sensor kills the spark, it makes sense to what I saw, thanks.

Speed and position sensors had degrated cable covers (sorry no pictures).
When unplugging both mentioned sensors, end facing towards the engine where very dusty. Mixture of kind of dust and grease (sorry again no pictures). It looks that even working fine, they should require some maintenance by cleaning the end every xx thousand miles (??). Easy to do as no adjustment needed.
Mine has 130k miles but only 20k with me in 8 years. Any rule of thumb for that?
BTW, remove the shock absorber for easy sensors removal.