940T Stalling

Hi All,

Got a 1994 940 Turbo Estate. More and more regularly now it's cutting
out. Tacho drops to zero (even if the wheels are still turning the
engine) and Lambda light comes on. Leave it a minute or so and it will
restart and drive normally - until it happens again.

Seems mostly to happen after a hot restart - not so often when cold.

Now the fault code that is set (although it doesn't set a code every
time) is 1-4-4 - no fuel load signal.

My first thought was the ever troublesome fuel pump relay - but with
the tacho dropping too it could be the ignition amplifier on the front
inner wing... Or am I wrong?

Checked all the connections to the AMM and to the ignition module on
the wing and to the sensor just downstream of the AMM - all look good -
clean and tidy with a smear of grease on them.

Any thoughts would be jolly helpful!

 

You're right - the tach dropping while the engine is still rotating is a
convincing indication of the ignition dying.

Three common trouble sources come to mind:
1) The crank angle sensor. In the 940T I think it is in the top of the bell
housing, but it could be in the distributor. I'll leave it to the experts to
clarify that. The crank angle sensor has caused more frustration than any
other intermittent failure because it fails when it wants to and comes back
when it wants to... no rhyme or reason.
2) The ignition module. Since ignition module problems are almost always
heat related and you have done a basic check I don't think it's your
problem.
3) In some models of Volvo in this era there is a "radio suppression" relay
somewhere near the A/C drier. My 765T doesn't have one so I don't know what
it looks like. User or Mike F would be the top sources of that sort of
detail.

A less common source but too easy to overlook is a bad connection at the
battery. If that maintenance is overdue now is a good time... but I don't
think that is the problem.

Mike

 

With me was same car same problem. Turned out to be the Crank position
(angle?) sensor.

When it hard failed it left me stranded with a $100+ towing bill.

Howard

 

I think you're right - crank position sensor for hall effect pickups, crank
angle sensor when it is the optical type like my old Nissan had.

Mike

 

Michael said:

Well - I've replaced the CAS and the ignition module - still exactly
the bloody same!

Any more thoughts?

 

Look for a black relay with 4 round pins, it's usually clipped somewhere
near the shock towers under the hood. It's the next most common cause
of these random stallings.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Mike said:

Cheers Mike - seems that the fuel pump relay was the culprit. A bit of
resoldering and all appears well.