Further To 740GLE Running problems!

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.

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.

[snip]

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, c*ck 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. "volvowrench ioip.com>" > > Where would I be without Mr Hargrave.

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.