Volvo 740 running problems...

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

This isn't answering your specific question, but I am thinking:

Fuel pump Fuel pump relay Fuel pump fuse Carb. icing Vapour lock Blocked fuel tank vent

I suggest these without any confidence whatsoever, since I've only ever owned injected Volvos.

carburettor

Well for an engine to run you need fuel, air, and spark, so if the spark is always there that eliminates that, the air is probably not the problem because an issue with that is rarely intermittant, so it's very likely a fuel problem. I've never seen a carbureted Volvo up close but from experience with lawnmowers it sounds like the carb has a fuel bowl that's occasionally not being replentished, these usually have a float that operates a needle valve to regulate fuel in the bowl and it sounds like that may be sticking or getting clogged, but you say the carburetor has been changed, hmm is there a fuel pump? Perhaps air is getting into the system somewhere, or maybe the return vent to the tank is clogged, does it still have this problem if you remove the fuel filler cap?

A few of these can be eliminated because IIRC the carbureted Volvos lack an electric fuel pump. Seems silly that a company like Volvo used carbs on such recently produced cars.

hello Jack

i suspect your EGR valve is stuck open the easiest way to deal with this is to simply close the tube from the valve to the inlet manifold permanently with some exhaustsealer or silicone(let it dry out long enough so it will not be sucked into the cylinders) this metal tube is visible under the carb,it is fastened to the manifold with 2 bolts also eliminate all the vacuum tubing related to the EGR and Pulsair systems,a colourfull bunch of tubes only there to anoy people an older volvomechanic who knows carburetted volvo's shoud be able to disconnect EGR AND pulsair and leave the necessary vacuumlines in place

i hope this will cure your problem

Marc Brack

4x 960 1x 740 16v 1x tatra 613-4

JackH wrote:

Hi James... yes, fuel cap was one of the first things I thought to try, and it made no difference whatsoever!

Fuel pump wise, I've been led to believe it has a mechanical one under the bonnet, *and* an electronic one in the tank... I've looked at the fuel filter at times, just after it's stopped running yet again, and this always seems quite well stocked with fuel.

It's just so bloody frustrating - the car is in too good a nick to scrap, yet it's too old to justify spending a stack of cash on in order to *maybe* find out what is up with it!

ARGH!!!!

-- JackH

Hi Mark.

The above sounds like a fairly easy and, if necessary, reversible suggestion.

I'll give that a try next... paging any Volvo mechanic who knows his onions and knows which pipe to unhook from what etc.

-- JackH

Fuel filter seems well stocked, even when the car has died.

That was one of my initial thoughts actually, but it doesn't seem to be that; I do know from past experience with other makes that Pierburgs tend to suffer with this, mind.

Hmm...

Don't think so, as no rush of air if you undo the filler cap after its stalled.

Cheers

-- JackH

I know you said earlier in the thread that you had replaced the carb, but have you checked the diaphragm for a split? They are well known for splitting, and the symptoms you have are the same on one of my mates Volvos, a 745 2.3 with carb. Was the replacement carb second hand? I fixed his problem with a small dab of bicycle tube puncture repair kit glue on the split on the diaphagm.

Stuart.

Afterthough..... have you filled the damper on top of the carb with oil? Engine oil will do. A dry damper doesn't usually have the great effects you are having, but it is necessary for the carb to function properly.

Stuart.

Stuart

I don't think it has that sort of carb - this one looks like a conventional weber'esque twin choke special.

-- JackH

conventional

I thought you had the Pierburg carb? Solex(Zenith) and Pierburg used on Volvos have a diaphragm and oil damper, SU carbs have only the damper. The Solex Cisac is a twin choke type. As far as I know the carbed engines only have a mechanical fuel pump on the engine, no electrical pump in the tank. Have you tried a new mechanical fuel pump?

Stuart

Hi Jack. ; )

I too have a 740 with running problems and really do not wish to part with it. I am not as clued up with the Volvo as most people in this group but I have had a similar problem as you are experiencing with an Audi 100

You say if you floor it you can clear it's throat? I don't wish to deter from the trend others have followed and I don't wish to undermine your mechanic BUT.

Try the distributor. Remove the cap and see if there is oil present. The oil seal on the rear of the distributor had perished slightly on my old car causing the odd drip of oil to creep through and foul on the contacts of the cap. "Flooring" used to clear it and then it would be okay. If I stopped the car for an hour or so then went back 7 out 10 times the problem had returned. A new seal cured it.

I know your mechanic said there is a spark at all times, he however did not say if it was erratic or weak.

Just another simple thing for you to check.

Carbs:

Pre 1987 models were fitted with the Pierburg 2b5

1987 on Were fitted with Pierburg 2B7

Both are twin BARREL, fixed jet, downdraught. Auto choke.

Twin Barrel but not twin choke.

Two fuel pumps are fitted electric fuel tank pump and mechanical main pump. Apparently.

The Pierburg 2B7 does not have a fuel return connection.

You could always try a company called "Braydon Motor Company" - they have been good to me in the past.

They're in East London, and they specialise in Volvos though as they aren't Volvo dealers they can replace with secondhand parts if you want. They're usually cheaper than the others - you could give them a call and see if they have an idea. They can't be bad - I've got a 1990 740GLE Estate 2.3 with over 230,000 miles on the clock and it's still going strong!

Mark

Hello all: I suspect the problem is with the "hall sensor" inside the distributor that seems to act up when the Volvo motor is about 12 years old. This happened to me with a 1985 B230F when the car was 12 years old. Worth a try... Cam

-- Cameron Price Newington, Ontario, Canada

snipped-for-privacy@cvolvo.com

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F2000SL 3,862.2 km Cannondale Volvo Team Replica R600 2,708.5 km Cannondale road bike Jekyll 3000 3,629.0 km Cannondale Volvo Team Replica

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carburettor

I have... a 2B of some description, which has no diaphragms as such, other that ones on the vacuum side of things (and which have tested as being ok), and which is of a conventional Weber style twin choke design.

-- JackH

'ow do.

Same here, but I'm not re taxing this one unless I can get it to run properly, and I absolutely *loathe* these problems that no-one seems to be able to just say 'ah yes, it's that'!!!

Basically, if I floor it whilst I'm driving, it will make it cut out that little bit quicker from cold, than if I keep it on low throttle settings.

Once it has cut out, you have to leave it alone for a couple of minutes, and then it will eventually fire... once it starts to splutter, you have to floor it to get it to catch properly, and once you've done this, it will idle fine.

It will then drive a little further before doing it all again... heavier application of the throttle will accelerate it towards cutting out that much quicker.

The more I think about it, the more it seems to be something electrical messing about when under duress or once it has got to a certain temperature.

Many thanks, I will check that out later this week.

Indeed... and tbh, I'm beginning to think that this was one of his 'don't know, can't be arsed', specials.

Yup, that's the kiddy.

Ah, ok... I'm not exactly a carb expert, but that sounds about right.

Ok... well I'm getting to the point where I can't be arsed with it any more... I'd like to think that somewhere based in Kent or SE London knows their onions on these, so if anyone can recommend me a place that won't piss me around or savage my wallet without good justified reason, and who will know what they are looking at, rather than changing parts willy nilly in the hope of hitting the jackpot, I'd be grateful; I've already spent around £100 on parts etc., on the recommendation of others, and to no avail.

-- JackH

It sounds very much like the fuel filter is becoming blocked. Some of these filters are very small and IIRC you have an in-tank pump unit which can get pick-up blockage.

Cheers, Peter.

Have you checked the fuel lines and filters for blockages (all fuel filters that is).

Cheers, Peter.

You could try attaching a hose to the fuel pump input and sticking it in a small cup of fuel, saw that trick once when we were trying to get an old truck with contaminated gas tanks half full of 7 year old gasoline running. If the rest of the car is in decent shape how hard could it be to get going? Worst case you could drop in a whole new motor from a junkyard.