89 760 Turbo engine shutting down!

  • Thread starter Thread starter george
  • Start date Start date
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george

My 760 Turbo will be running along fine, then suddenly the engine just
stops! In a few moments, it will start again and run for weeks
without problems. Could it be the fuel line, or perhaps an electrical
problem?
Many thanks!
Bass Man
 
My 760 Turbo will be running along fine, then suddenly the engine just
stops! In a few moments, it will start again and run for weeks
without problems. Could it be the fuel line, or perhaps an electrical
problem?
Many thanks!
Bass Man
Click to expand...


I think '89 is new enough that the engine wiring harness will be fine, but
it's worth checking for rotting insulation, if you find some, there will be
more in hidden places.

When it shuts down, does the tach drop like a rock or does it drop slowly
with the engine RPM? If you try to start it immediately afterward, does the
tach twitch or just lay there dead? If you get tach activity then the ECU is
getting a signal from the hall sensor, that will help narrow things down.
Ignition power stage and fuel pump relay are both reasonably common
failures.
 
My 760 Turbo will be running along fine, then suddenly the engine just
stops! In a few moments, it will start again and run for weeks
without problems. Could it be the fuel line, or perhaps an electrical
problem?
Many thanks!
Bass Man
Click to expand...
It is vital to determine whether it is the ignition or fuel that is
quitting. Look at the tach the next time it dies; if the pointer has already
dropped like a stone even though the engine hasn't come to a stop the
problem is in the ignition. If you missed the moment, watch the tach while
you crank. If the tach doesn't twitch every second or so, the ignition is
the problem. Also, usually fuel delivery problems have a softer fail, like
the power sags away in a second or so, while ignition failures are typically
abrupt as though you turned the ignition off.

There are a few causes of each problem area - fuel or ignition. Your
description has me thinking it is the notoriously hard to diagnose Crank
Angle Sensor, though. It affects the ignition (and fuel, too, but the
ignition is obvious) and comes and goes as it pleases. Others will weigh in
with more ideas and some troubleshooting will help narrow the search.

One quick item: does your battery have a ring terminal fastened to the bolt
on the positive post as my '85 does? If so, it's worth your while to clean
the battery terminals, including scraping both sides of that terminal to
shiny metal. When it corrodes the ignition cuts out at odd times.

Mike
 
It is vital to determine whether it is the ignition or fuel that is
quitting. Look at the tach the next time it dies; if the pointer has already
dropped like a stone even though the engine hasn't come to a stop the
problem is in the ignition. If you missed the moment, watch the tach while
you crank. If the tach doesn't twitch every second or so, the ignition is
the problem. Also, usually fuel delivery problems have a softer fail, like
the power sags away in a second or so, while ignition failures are typically
abrupt as though you turned the ignition off.

There are a few causes of each problem area - fuel or ignition. Your
description has me thinking it is the notoriously hard to diagnose Crank
Angle Sensor, though. It affects the ignition (and fuel, too, but the
ignition is obvious) and comes and goes as it pleases. Others will weigh in
with more ideas and some troubleshooting will help narrow the search.

One quick item: does your battery have a ring terminal fastened to the bolt
on the positive post as my '85 does? If so, it's worth your while to clean
the battery terminals, including scraping both sides of that terminal to
shiny metal. When it corrodes the ignition cuts out at odd times.

Mike
Click to expand...

Many thanks guys. I'll check out your ideas and will get back to
you. I didn't look at the tach, but the engine cuts out instantly
which leads me to believe it's an ignition problem. The battery
terminals are already super cleaned. You can plow fields with a
Volvo, but their electrical sytems are often a nightmare!
BTW, where is the Crank Angle Sensor located? Is it something I can
locate and replace?
George
 
Many thanks guys. I'll check out your ideas and will get back to
you. I didn't look at the tach, but the engine cuts out instantly
which leads me to believe it's an ignition problem. The battery
terminals are already super cleaned. You can plow fields with a
Volvo, but their electrical sytems are often a nightmare!
BTW, where is the Crank Angle Sensor located? Is it something I can
locate and replace?
George
Click to expand...

It's on the bellhousing, I don't believe it's difficult to replace.
 
James Sweet said:
It's on the bellhousing, I don't believe it's difficult to replace.
Click to expand...
That makes it sound difficult, but it's right at the top where it's only
aggravating rather than maddening. The truly maddening part of crank angle
sensor failures is tracking it down. The failures are often so random and so
short-lived it's hard to get the goods on it. Sometimes they fail suddenly
and completely (like mine did last year), but that is the luck of the draw.

Mike
 
That makes it sound difficult, but it's right at the top where it's only
aggravating rather than maddening. The truly maddening part of crank angle
sensor failures is tracking it down. The failures are often so random and
so short-lived it's hard to get the goods on it. Sometimes they fail
suddenly and completely (like mine did last year), but that is the luck of
the draw.

Mike
Click to expand...

My cars don't have them, but I suspect some freeze spray might make tracking
down the failure easier, or you could just take the gamble and replace it.
If that wasn't the problem, at least you then have a spare which you'll be
glad you have should it ever fail.

I'm curious if it's a hall or VR sensor, the VR type is just a coil of wire
on a magnet and rarely fails, perhaps engine compartment heat is hard on
them though.
 
James Sweet said:
My cars don't have them, but I suspect some freeze spray might make
tracking down the failure easier, or you could just take the gamble and
replace it. If that wasn't the problem, at least you then have a spare
which you'll be glad you have should it ever fail.

I'm curious if it's a hall or VR sensor, the VR type is just a coil of
wire on a magnet and rarely fails, perhaps engine compartment heat is hard
on them though.
Click to expand...
Mine is almost certainly a Hall sensor. It has three leads: power, ground
and output. I can see the output with a voltmeter. In my '85 it is mounted
in the distributor, so I can hold the assembly in my hand to test it. After
replacing the sensor I could also turn the distributor shaft and see the
spark.

When I worked in component level electronics I learned to dread intermittent
coils. They were rare enough, but they failed just like the crank angle
sensors do: open when they want to be, working when they feel like it, and
no temperature sensitivity. It always came down to luck to catch them in the
act.

Mike
 
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