740 running problems

Greetings to all,
My 1991 740GL (Vladina) developed a similar problem about a year ago, at first she keep cutting out when cold and eventually would cut out everytime we became stationary. :-(

I took her to a local Bosch specialist who for the princely sum of £20.00 diagnosed the problem. My Lamba Sond probe and Air Mass meter were both goosed. Since their replacement Vlad has been running like a train. :)

Hope this helps

Volvo Safety Man

Ta for that. Unfortunately, mine is a 1989 and therefore pre-lambda model.

Just to update, in case anyone's wondering, the really rough running turned out to be little more than plug leads, despite their having been changed only a year or so earlier! Apparently, this model is pretty notorious for having them break down.

It was confirmed when, at night, I raised the bonnet and could see a veritable fireworks display going off! There was a mixture of leads where the outer insulation was breaking down, allowing corona discharge paths around the outside, while others clearly had breaks in the conductor, across which sparks would jump, being visible as blue flashes in the centre of the leads.

The current status is that it's generally running reasonably well though starting is still a problem. I've not yet got round to resolving the injector problem (see http://www.volvoforums.org.uk/showthread.php?t=3246) although I did do the injector outer seals to be able to get it to run as they were completely shot.

Strangely, although it's running quite well, I can't get it to idle fast enough. It's currently at about 650rpm with the idle air-bleed screw at the end of its travel. The snag with this is that I couldn't get it started the other day and had to hard-wire the cold-start injector on to keep it running until it had warmed up a bit. It did go through the MOT ok in late November so the mixture and timing can't be too far adrift. My suspicion is that the mixture is currently set to starve the 3 cylinders with working injectors to account for the one that's slightly overfuelling so, if it fails to pick up on that one, it takes ages to get the other 3 to kick in.

The thing that puzzles me is that the cold-start injector is only being fed with 5v (or a touch under). Since that measurement is being made off-load, it implies that there must be a resistive divider chain (otherwise, since no current would be drawn when open circuit on-test, there would be no voltage drop across a single resistor in series, unless something else is also connected that we don't know about). Does anyone know whether this is normal? Has anyone had (or could someone just quickly test for me) their model to see whether the plug supplying the cold start injector should be at 12v during cranking?

As I'm only getting about 4.7v on cold-cranking and the cold start injector only operates from about 4.5v upwards, that's getting a bit close for comfort!

Ta.

[morrow333]

Originally Posted by eeedelli

Hi Folks,

I've had my 740GL 2.0L Estate (B200E, K-Jetronic) for nearly a year. Ever since I've had it, it's always started on 3 cylinders for about 20 seconds before picking up well. Over the last few days, however, it's started to exhibit the really rough running problems mentioned above.

Over the last few months, I've been trying to find the cause of the starting issue and, as a result, have recently discovered that all the seals around the injectors are shot and probably sucking air. I haven't changed them yet as (a) I've only got 2 at present and (b) I need a new injector as, after recent ultrasonic cleaning, I find that one is over-fuelling slightly and (even more significantly) is still leaking petrol after switch-off.

I wonder whether this might be a similar problem for you?

Incidentally, that injector was in No 4, which checked out at 150psi while 1-3 were 195psi. It could be that the excess fuel (especially that which will have been sitting in the bore after switch-off, ready for a nice 'dry-start'!) has washed more oil off that bore, leading to increased wear. However, I've been told that No 4 always wears faster due to poor swirl in the inlet manifold and that this was cured (possibly in facelift models post-89?) by Volvo modifiying it with a baffle in No 4 manifold tube (though since the injector is in the head rather than the manifold, I can't quite see how that would work). I've also been told this week by someone that "all 740s start on 3 - it's a well-known quirk so don't worry about it"!

During the investigations, we've had the head off looking for damaged valves or cracks, injectors cleaned to get a good spray pattern, new leads, dizzy cap and rotor, substituted coil and ignition module, all to no avail. One thing we did find was that the air mass plate was binding slightly in the venturi at rest, which significantly affected the gas reading at idle, as you'd expect. (That's now been re-centred.)

I'm also having trouble getting the right injector. GSF have supplied one that turns out not to couple properly (top cone slightly different) and it transpires it's for a VW. That begs the question of whether it would have delivered the correct volume per minute and work at the same pressure. Anyway, the problem now is knowing whether or not I can get a standard Bosch injector or whether you have to buy one with the correct Volvo plastic carrier and, if so, from where (avoiding Volvo prices if possible!)? I can't see how to get the old one out of the carrier to replace it. Does anyone know if it's possible and, if so, how? Without being able to do so, I don't see how to replace the small seals between the injectors and carriers. (The large ones will be easy!)

Anyone got any suggestions on these various issues? All input gratefully received before I grind to a complete stuttering halt!

My sympathy same problems with my 1987 740, changed same parts as you , also changed temp send, knock send, air valve , fuel dist, and vacume plate , i,m now going to replace main fuel pump and relay and see what happens, i still have a feeling its electrical because of the backfiring in the manifold, its down to a challenge with me now! otherwise i,m going to have a lot of good parts for sale, regards big john.