940 timing anomaly

[billy_bunter]

In attempting to diagnose the rough idling of my '91 940 2lt non-turbo
auto, I came across a worrying anomaly. The timing is around 30 degrees
advanced on idle. The timing increases on revving the engine to around 60
degrees...
The Haynes says it shoud be advanced only 10 to 12 degrees on idle, but I
cannot find a way to adjust this!
The only symptoms are a rough idle - the revcounter dips and returns from
850 to 650 and back, and frequent stalls in traffic queues.

any thoughts ??
I think I have ruled out :
The Idle control valve
The Timing belt
The ignition system as a whole, inc plugs, leads and rotor/distributor
The fuel supply - new filters and both pumps ok
The crank case breather

What is left ?????

 

[Alex Zepeda]

Sounds like the timing belt slipped a tooth.

Pull the timing belt covers off and have a looksee.

- alex

'85 244 Turbo

 

[Stewart Hargrave]

Because there's more to the internet than hits alone, billy_bunter
wrote:

In attempting to diagnose the rough idling of my '91 940 2lt non-turbo
auto, I came across a worrying anomaly. The timing is around 30 degrees
advanced on idle. The timing increases on revving the engine to around 60
degrees...

Something is lying to you. If the ignition was advanced this much at
idle then the engine wouldn't run at all, so the 30 degree BTDC
reading must be wrong. It may also be unrelated to the idle problems
you are having. Electronic timing seldom slips out of adjustment
unless some relevant component has been dismantled and reassembled
inaccurately.

Check that you understand the timing marks properly, and that you are
not mistaking some other mark on the crank pulley for the timing
notch. Also be aware that some timing lights have a calibration
facility, which means that you can adjust where the light flashes
relative to the spark.


--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

 

[billy_bunter]

Stewart Hargrave spluttered almost incoherently...:

Because there's more to the internet than hits alone, billy_bunter
wrote:

Something is lying to you. If the ignition was advanced this much at
idle then the engine wouldn't run at all, so the 30 degree BTDC
reading must be wrong. It may also be unrelated to the idle problems
you are having. Electronic timing seldom slips out of adjustment
unless some relevant component has been dismantled and reassembled
inaccurately.

Check that you understand the timing marks properly, and that you are
not mistaking some other mark on the crank pulley for the timing
notch. Also be aware that some timing lights have a calibration
facility, which means that you can adjust where the light flashes
relative to the spark.

There is just one deep cut on the inner rim of the bottom pulley.
As I understand it, the graded plastic timing marker above the pulley is
marked from -10 to 0 to +10, as in the picture. The idle should be around
12 degress, as in C.
The original mark was shown at A, then after all the cleaning and
replacing/testing the parts, it shows at B...
We are totally confused now !!

http://topqualityfreeware.com/jonico/engine.jpg

 

[billy_bunter]

billy_bunter spluttered almost incoherently...:

Stewart Hargrave spluttered almost incoherently...:

There is just one deep cut on the inner rim of the bottom pulley.
As I understand it, the graded plastic timing marker above the pulley is
marked from -10 to 0 to +10, as in the picture. The idle should be around
12 degress, as in C.
The original mark was shown at A, then after all the cleaning and
replacing/testing the parts, it shows at B...
We are totally confused now !!

http://topqualityfreeware.com/jonico/engine.jpg

Excuse the "Spluttering" header - I gotta change that, but don't know how,
my son put it in there !

 

[Stewart Hargrave]

Because there's more to the internet than hits alone, billy_bunter
wrote:

There is just one deep cut on the inner rim of the bottom pulley.
As I understand it, the graded plastic timing marker above the pulley is
marked from -10 to 0 to +10, as in the picture.

You may be incorrect about this. Certainly on my 2.3 litre engine the
scale is 0 - 20 degrees BTDC. The picture in the Haynes manual shows a
scale of 0 - 30 degrees BTDC, but doesn't say what specific model this
applies to. However, the numbers are embossed on the scale. If all
else fails, remove the top half of the timing belt cover and find the
alignment marks for the top pulley. These should coincide at TDC, and
you can check where the marks are on the crank pulley.

The idle should be around
12 degress, as in C.
The original mark was shown at A, then after all the cleaning and
replacing/testing the parts, it shows at B...
We are totally confused now !!

I suppose you could have found an anomaly in the fabric of the
space/time continuum. It's also possible that your timing light is up
the creek.




--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

 

[Stewart Hargrave]

Because there's more to the internet than hits alone, billy_bunter
wrote:

billy_bunter spluttered almost incoherently...:

Excuse the "Spluttering" header - I gotta change that, but don't know how,
my son put it in there !

It'll be under 'Options' or 'Preferences' or some such. But I thought
it was quite amusing.


--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

 

[Gunnar Eikman]

Our 940 once had mysterious idling problems. Don't know about timing,
cause I did not check it.

The problems started after we had drained the battery and had to cable
start. Apparently the engine control box got into a funny state from the
low voltage and/or the electric transients caused by the cable start.

After a while I related the problem and the cable start, I removed fuse
#1 (supplying battery voltage to engine control box when engine shut
off) for a minute. Then reinstalled fuse, thereby resetting the engine
electronics completely. The car has been idling fine now for the last 9
years.

I have told this story to a lot of people, some think I am crazy. It is
however 100% true. So before trying more complex things, try the "total
electronics reset", by disconnecting the fuse (or battery) for a minute.
It may not solve your problem , but it can't hurt!


--
Gunnar

240 Turbo Wagon '84 200 K Miles
940 Wagon '92 150 K Miles
on Swedish roads

 

[billy_bunter]

Gunnar Eikman said...:

Our 940 once had mysterious idling problems. Don't know about timing,
cause I did not check it.

The problems started after we had drained the battery and had to cable
start. Apparently the engine control box got into a funny state from the
low voltage and/or the electric transients caused by the cable start.

After a while I related the problem and the cable start, I removed fuse
#1 (supplying battery voltage to engine control box when engine shut
off) for a minute. Then reinstalled fuse, thereby resetting the engine
electronics completely. The car has been idling fine now for the last 9
years.

I have told this story to a lot of people, some think I am crazy. It is
however 100% true. So before trying more complex things, try the "total
electronics reset", by disconnecting the fuse (or battery) for a minute.
It may not solve your problem , but it can't hurt!

If it worked for you, you are not crazy -
I will go pull it out in the morning and see...
Watch this space !

 

[billy_bunter]

Stewart Hargrave said...:

Because there's more to the internet than hits alone, billy_bunter
wrote:

You may be incorrect about this. Certainly on my 2.3 litre engine the
scale is 0 - 20 degrees BTDC. The picture in the Haynes manual shows a
scale of 0 - 30 degrees BTDC, but doesn't say what specific model this
applies to. However, the numbers are embossed on the scale. If all
else fails, remove the top half of the timing belt cover and find the
alignment marks for the top pulley. These should coincide at TDC, and
you can check where the marks are on the crank pulley.

I suppose you could have found an anomaly in the fabric of the
space/time continuum. It's also possible that your timing light is up
the creek.

Yes, I'm beginning to suspect the timing light myself....
I'm off to buy another in the morning, spacial distortion allowing.

 

[James Sweet]

Stewart Hargrave said...:




Yes, I'm beginning to suspect the timing light myself....
I'm off to buy another in the morning, spacial distortion allowing.

There's not much I can think of that would cause a timing light to do that,
they really don't have much inside them. Are you sure you have it on the #1
plug wire? This is the one closest to the front of the car.

 

[billy_bunter]

James Sweet said...:

There's not much I can think of that would cause a timing light to do that,
they really don't have much inside them. Are you sure you have it on the #1
plug wire? This is the one closest to the front of the car.

Yes, no.1 (and tested on no.4 to make sure...)

 

[Alex Zepeda]

I have told this story to a lot of people, some think I am crazy. It is
however 100% true. So before trying more complex things, try the "total
electronics reset", by disconnecting the fuse (or battery) for a minute.
It may not solve your problem , but it can't hurt!

This is not entirely unbelievable. The later LH-Jetronic injection stuff
did have adapative controls.

- alex

'85 244 Turbo

 

[billy_bunter]

billy_bunter said...:

Gunnar Eikman said...:

If it worked for you, you are not crazy -
I will go pull it out in the morning and see...
Watch this space !

Ok, after disconnecting the fuse, nothings changed except the lambda light
on the dash is now out - it had been lit for about 4 months since we had a
new tail section put on the exhaust.
The engine is still rough........

 

[billy_bunter]

billy_bunter spluttered almost incoherently...:

James Sweet said...:

Yes, no.1 (and tested on no.4 to make sure...)

Ok, I used another timing light, same results, the timing mark is still at
about 3'o'clock, so about 30 degrees out ??

 

[Dave Shannon]

big snippage

Ok, I used another timing light, same results, the timing mark is still at
about 3'o'clock, so about 30 degrees out ??

Not all that familiar with 900s and haven't read the whole thread but has
anyone mentioned the infamous slipping 2 piece vibration damper/front
pully?? 700s are well known for the 2 piece front pully slipping with the
outer ring getting out of sinc with the inner giving all kinds of headaches
to people trying to smog their perfectly running car which shows a whopping
50 degrees of advance. Needless to say when the smog tech trys to set it
"right" the car goes to crap in a hurry. Come to think of it are 900s even
adjustable? I know the later 700s were not.
Dave Shannon
daveshan_at_spamsoneonelse_cox.net (Spring Valley CA)
1988 240 DL 19X,XXX
1984 245 DL 20X,XXX
1984 245T 19X,XXX
'01 Jeep Wrangler Sahara 14K
http://www.homestead.com/volvo2/

 

[Stewart Hargrave]

Because there's more to the internet than hits alone, billy_bunter
wrote:

Ok, I used another timing light, same results, the timing mark is still at
about 3'o'clock, so about 30 degrees out ??

Surely 3 o'clock would be over 90 degs out? This still doesn't make
any sense.

I wonder if the crank pulley has been reassembled without it's key,
depending entirely upon the bolt being done up tight enough to stop it
slipping - which it has?



--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

 

[billy_bunter]

Stewart Hargrave said...:

Because there's more to the internet than hits alone, billy_bunter
wrote:

Surely 3 o'clock would be over 90 degs out? This still doesn't make
any sense.

I wonder if the crank pulley has been reassembled without it's key,
depending entirely upon the bolt being done up tight enough to stop it
slipping - which it has?

Yes - 90 degrees, geometry never was my strongest subject...
I now have another clue - apparently there are a couple of locating pins on
the rear of the bottom pulley that can shear off, leaving the pulley to
move independantly of the shaft sometimes.

I still fail to understand how it runs under these conditions, but I am
forced into seeking professional help now - It's beyond me. I have a local
man that thinks the bottom pulley is at fault, he is going to test the
ignition electrics and look at the pins.... watch this space !

Why are these volvos so damned complicated??
Bring back the anglia !!
(a 9/16th and a screwdriver was all you needed for a full strip down)

 

[Stewart Hargrave]

Because there's more to the internet than hits alone, billy_bunter
wrote:

Yes - 90 degrees, geometry never was my strongest subject...
I now have another clue - apparently there are a couple of locating pins on
the rear of the bottom pulley that can shear off, leaving the pulley to
move independantly of the shaft sometimes.

I still fail to understand how it runs under these conditions

This sounds a likely bet. The pulley sounds to be a little different
to mine, but if this is the problem then it simply means the timing
notch has moved, not that the ignition timing itself is incorrect.
However it could have contributed to an earlier setup being done
wrongly, which may explain the poor running.

Bring back the anglia !!
(a 9/16th and a screwdriver was all you needed for a full strip down)

Yes, I remember that. I used a pair of mini-mole grips and an old
butter knife for mine.



--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name

 

[Gunnar Eikman]

Ok, so now we know your problem is not the same easy one I once had.

You mention that the lambda lamp came on when replacing the exhaust
system. That sounds a bit strange. Is it possible that the problem
developed at that time? Could the wiring to the lambda sensor have been
damaged while working on the exhaust pipes?

About the timing problem. You can easily check the notch on the belt
pulley. Remove the spark plug for cylinder 1 (at front of engine). Stick
a wire or similar into the hole, so you can touch the top of the
piston. Turn the crankshaft by hand (22 mmm socket wrench) back and
forth until the piston is in top position. You should be able to tell if
the mark on the pulley is in its correct position or not. Piston at top
= zero degrees on the scale.

The pulley (at least on some cars) has a rubber device in it to reduce
crankshaft vibrations. According to old posts in this newsgroup that
rubber can slip, causing the timing mark to be off. I have never seeen
it happen myself, but those posts sounded convincing to me.


--
Gunnar

240 Turbo Wagon '84 200 K Miles
940 Wagon '92 150 K Miles
on Swedish roads