Further To 740GLE Running problems!

You guys have been a great help so far. Thanks.

I have spent a industrious day under my 740's bonnett today.
I checked and cleaned all the breather pipes, vac pipes, filters and fuses.
With bated breath I struck up the beast and......

No change. I have been playing with trying different throttle applying. I
have got this:

Starting is not a problem.
Idling is not a problem
light throttle is not a problem unless engine is cold
mid throttle seems fine although can vary
When I floor it, the revs stick at 3,500 Backing off the throttle lets it
rev through.

Now thanks to your replies I now know how the k jet system works. Now using
that knowledge. Would I be correct in thinking that with the throttle flat
to the floor the throttle flap ((excuse the technical terms) the one in
above the large rubber bellows/pipe that is attached to the fuel control
unit.) Would be fully open, thus creating more vacuum blah, blah, blah! Then
as you back off the flap closes. So as my car will run okay at half throttle
(being able to rev to 5/5,500rpm) could the car be gaining to much air?
I am not dismissing the LACK of fuel completely but because the car will rev
so high I have to wonder how? if fuel is not present.

If I am correct of which I doubt. Would the air control valve be at fault?
If so how could I test it?
I did unplug it whilst the car was running and it made NO difference to the
running at all.

Or could it be the coil breaking down and not giving sufficiant spark under
load?

My list of possible problems grows smaller and your assistance is greatfully
recieved.

For reference I live in the UK in Leicestershire East Midlands I use fake
e-mail address because of the Kindly SPAMMERS But if you wish to e-mail me
just remove the ***nospam***

Thanks again.

Thanks Stewart your input has been invaluable and indeed you are quicker
than the Royal Mail. Unless your newserver is NTL then Royal Mail could be
construed as quicker!

***nospam***Kiefels@***nospam***hotmail.com

 

That sounds remarkably like what my brother's '79 did when the carbon button
in the distributor cap had broken off, however you said you already replaced
that. You have a very elusive problem indeed, please let us know what it was
when you finally figure it out.

 

When you said you checked and cleaned all the vac pipes, did you check the
vac pipe that runs the brake servo? a leak is this or the brake servo itself
could give problems.

just a thought,

Steve

 

From a point at sea, to the circles of your mind, this is Artful
Dodger:

I think I understand you and I think you have the right idea.

But just to establish that we are talking about the same things, below
the throttle valve (operated directly by the accelerator pedal) is the
airflow meter. This responds purely to the flow of air past it; the
more that is being drawn into the engine, the further this flap will
swing open. Close the throttle, and this flap should close also. But
open the throttle, and this flap will only open as the engine's speed
picks up and it demands more air. Fuel metering is directly governed
by the position of this flap.

Two sides of a coin here: too much air; or too little fuel.

If you have carefully eliminated the possibility of an air leak, then
I can't see how it could get too much air. But there is still the
possibility of too little fuel.

Err.. Can I clarify the terminology here. I'm getting a little
confused. We know what the throttle valve is; we've established what
the airflow meter is. When you say 'air control valve' do you mean
'auxiliary air valve?' This is attached to the top of the engine with
a 1" rubber pipe going into the top, another one coming out of the
bottom, and an electrical connector.

In that case, no. This simply controls the idle speed during the
warm-up period and will not affect the fuel metering at all (unless
one of the rubber pipes becomes diconnected. If that happens the
engine won't idle). If this unit malfunctions then you will have
either too low an idle speed when cold, or too high an idle speed when
warmed up. At either instance the fuel metering will be correct for
the engine speed.

Because of the way it works, unplugging it when the engine is warm
will only make a difference after several minutes, when the idle speed
should gradually increase.

It's possible. The spark is certainly given a hard time under load.
But it is relatively rare. As the only real test for this is
substitution, and as a new aftermarket coil for this car costs around
40 quid, it may pay to eliminate other things first.

But whilst we are on the ignition system, did your friendly Volvo
dealer check this system out? It is vary rare for the ignition timing
to slip (unless work has been done and it wasn't reassembled
properly), but it is critical. Ignition advance at idle should be 12
degrees BTDC at 900 rpm and should increase as the engine speed picks
up. A neon timing light will prove this, and also show if you are
getting a good spark.

If the ignition system checks out, the valve timing is OK, the fuel
pumps are OK, there are no induction leaks, then we are left with the
fuel delivery system. K-Jet is normally robust and reliable. One of
the few things that can go wrong is the control pressure regulator
(sometimes called the warm-up regulator, though in fact it regulates
fuel pressure at all temperatures). This will have a significant
effect upon fuel metering. I guess this is best tested by measuring
the flow rate of the injectors, but I don't know the spec. for this
and have never done it myself. A secondhand regulator from a breakers
would probably be about a tenner and it's easy enough to fit.

I'm beginning to run out of ideas, but the answer is in there
somewhere.



--

Stewart Hargrave

A lot faster than Royal Mail


For email, replace 'SpamOnlyToHere' with my name

 

Where would I be without Mr Hargrave.

Okay I have been confusing everybody in cluding myself.
The auxiliary air valve you mentioned is what I meant. Only thing is it is
not what I disconnected.

If you look at the fuel system from the n/side suspension turret (or left
hand side of car when seated) and look at the fuel control unit(the large
thing with the fuel distributor and big rubber hose connected to throttle
housing thingy) to the left and slightly to the rear of the left hand
mounting bracket is another valve (I think)
Is this the control pressure regulator?
That is what I unplugged and it made no difference.

Oh to have a Haynes that showed me a 4 cylinder motor.

Also that air control thing at the bottom of the large rubber hose that is
part of the fuel control system. When I removed the large rubber hose the
plate was almost fully up or I would say closed. Now goin by my limited
experience. Wouldn't the vacuum caused by the throttle actuation further
close this plate?
So does an upwrd movement of this plate open up the flaps on the fuel
distributor allowing more fuel through?
If so I have not got much movement on it!
If pushed slightly, it will go down about 1/4 of an inch.
Could this be a problem?

Ow, Ow, Ow, OW ouch! My head hurts.

I am now beggining to think I am going to be spending Mega Bucks on a fuel
control unit!

 

From a point at sea, to the circles of your mind, this is Artful
Dodger:

Almost certainly. A small metal box that has two pressure pipes (fuel)
connected to it next to the electrical connector.

Unplugging it will affect it in a similar way to the auxiliary air
valve - it takes several minutes to have an effect. In this case, if
it is working properly, on a warm engine the fuel mixture will
gradually enrich, causing the engine to idle unevenly and have flat
spots under acceleration, like you had just pulled the choke out on a
carb. engine.

Disconnecting it from cold shouldn't make any difference to cold
starting, but as the engine warms up it will be like leaving the choke
out.

I suppose it is possible that the overall regulation is no longer
right, so it is regulating the pressure incorrectly throughout its
range. Unfortunately there is no adjustment to be made to these.

Haynes does it's best to confuse you here - the airflow meter flap on
the V6 illustrated goes *down* as air goes in, unlike the in-line
4cylinder, where it goes *up*.

In your case, the fully closed, at-rest position is when the plate is
horizontal, filling the hole at the bottom of the dish-shaped opening.
The 1/4 inch downward movement is normal and is intended to let any
pressure from a backfire escape past it.

If you grip the bolt-head in the middle of the plate you should easily
be able to pull it upwards through an arc, until the arm it is
attached to (underneath) cannot move any further. This is probably
only and inch or two at the bolt head. There may be a little
resistance against residual pressure in the fuel system, but movement
should be smooth and unobstructed throughout the range.

As the flap moves upwards, it moves a small plunger in the fuel
distributor that allows more fuel to the injectors.

If by 'fuel control unit' you mean the fuel distributor, then these
very very rarely go wrong. Even it they become a little worn there is
an adjustment. Total failure is very unlikely (despite my experience
mentioned elsewhere). And a new one would be hilariously expensive.
Eliminate *everything* else and treble check your work before you
replace this. And hunt around for a good secondhand unit.




--

Stewart Hargrave

A lot faster than Royal Mail


For email, replace 'SpamOnlyToHere' with my name

 

The simplest and most effective way to troubleshoot your problem is to
first find a mechanic who can properly test the fuel pressures as I
stated long ago. Failing this you can easily flail around for days and
make no headway. Fuel pressures are critical in this system for proper
operation. Typically the control pressure regulator fails to a high
reading and prevents adequate fuel from reaching the injectors. Low
volume equals lean equals no or low power. Excessive leanness (weak
mixture) leads to backfiring, popping and an artificially low top engine
speed.

If the pressures check out ok then consult the TSB that shows you how to
make a test relay to power the fuel pumps with the key on engine off.
Pull the injectors out of the plastic holders and set them on the valve
cover. Then with the gauges still connected, using a 3mm Allen wrench,
reach into the adjustment hole in the air flow sensor housing just
forward of the fuel distributor, cock the wrench in the socket and lift
the airflow sensor plate. The injectors should flow fuel, and the flow
should increase proportionally to the lift of the airflow sensor plate.
If the fuel flow seems adequate throughout the motion of the plate and
the line pressure stays above 4.7 bar and the control pressure stays
below 3.8 bar then reinstall the injectors (if the fat o-ring seals on
the injectors are hard, replace them, use Vaseline to slide the new seals
in place and to lube the inner surface of the injector stands) and make a
run with a vacuum gauge connected to determine if the exhaust is
restricted.

If the vacuum numbers are steady at idle, drop to zero, and then climb as
engine load decreases then the exhaust is ok. Change the coil and coil
wire. If that fails then check that the cam timing is correct and that
the timing belt has not jumped a tooth or that there isn't a broken tooth
on the belt, although bad cam timing would show as low vacuum at idle.

Perhaps do these last two things first before diving into the rest, but I
suspect that the control pressure regulator will show bad when tested.
The latest iteration of the CPR has a Bosch number that ends in 123 and
may require that you reverse the wires in the plug in order to prevent
blowing a fuse.

Bob

 

Thanks Bob.

Lots to take on board in a oner but I will endeavour.

I will never surrender.

 

A very baxic question, diid you change the fuel filter before this
problem started? I had the same symptoms on my '87 740 and it turned
out I had unknowingly restricted fuel flow by slightly misplacing one
of the "banjo" fittings and slightly crimping the fuel line, thus
resticting the fuel flow.

 

From a point at sea, to the circles of your mind, this is volvowrench

There is a much simpler way of testing the CPR that I've just thought
of:

1) Drive around all the local carparks until you see a car of the same
model and year as yours. Park next to it until the owner returns.

2) Drop into conersation with the owner. Remark upon the wonderful
drive, the luxury, the smoothness, how much better than the previous
year's model, etc.

3) Suggest a drink in a nearby pub. Talk football, darts, women, etc.

4) After a few pints, introduce the subject of the problems you are
having, and add that you have a theory as to what is wrong. Emphasis
what a wonderful guy he is, and then carefully imply that it would be
helpful if you could find someone to swap CPRs with in order to test
your theory. As you do this offer to buy the next round.

It can't fail, can it?


Actually, I think if you are happy you have eliminated the ignition as
the cause, then finding a good secondhand CPR for a tenner would save
a lot of faffing about.


--

Stewart Hargrave

I run on beans - laser beans


For email, replace 'SpamOnlyToHere' with my name