1984 340GL 1.4 - Fuel Pump playing up?

[retrodave]

Hey there,

Just wondered if you guys could offer me some advice on a possible fuel pump problem I'm having with my 1984 1.4 340? The car's been great until now (it runs hot on tickover, but the mixture is fine), but with a little weirdness on ignition - the engine's been taking five seconds or so to reach the right revs sometimes, other times it's come right up to speed straight away.

The last few days, I've stopped the car for ten minutes or so (when it's been running flawlessly), and when I've got back in to start her up she won't fire! The engine feels nice and free under the starter, it just seems like there's no combustion going on in the chambers. Sparkplugs seem fine, distributor seems fine, and my local expert mechanic has told me it's probably either a dirty / sticking carburettor part or perhaps the fuel pump is jamming (he says this was sometimes a problem with these pumps).

I'm going with the fuel pump for now, as as soon as the engine fires it runs beautifully, it just seems to falter a *little* every ten seconds or so on slow tickover, and sometimes has trouble getting started - it feels very much like a flow problem, once the flow's there it's okay etc. And if the diaphragm is sticking in a certain position this would explain why the car won't start only on certain occasions, especially in hot weather, right? When this happens, the only way to start her seems to be to pull the choke out fully, put the gas pedal to the floor and run the starter for a good five seconds until she fires. And the gas pedal has to stay there for another seven seconds or so afterwards, otherwise the engine dies! It feels just like the choke's in, the tickover speed's low, and I'm hardly touching the accelerator - like there's just insufficient fuel flow.

So I'm thinking about checking the fuel filter, changing the fuel pump, and if that doesn't work, stripping the carburettor and cleaning it (which I'd like to save as a last option if possible!). I've never done this before (this is my first engine, I only did my first brake caliper change a few months back), so I don't know what to expect. What I was wondering is:


1) Can I take the cap off the fuel pump (like the Haynes manual says) and have a look at the fuel filter and valves to see if anything's stuck / gummed up?

2) If I can, is it sufficient to use two hose clamps on the inlet and return pipes to stem the flow of fuel after the top is open?

3) Will I need any replacement gasket etc. for the top if I do this?

4) I think the fuel pipes are attached using those damn one-time crimped clips - is there a good way of getting them off (without slicing through a fuel line!) and what should I use to replace them?

5) I'm considering just changing the pump completely (was planning to look at the existing one first in case I could get the car running quickly as I use it daily) - if I buy a pump, will it come with replacement gaskets or do I need to buy them separately?

6) The Haynes manual talks about oil escaping when the pump is taken off - is this just a bit of oil, or a huge great flood of the stuff? I mean, I won't have to drain all the oil from the car or anything to do this job will I?

7) And finally, has anyone come across this problem before? My local mechanic really does seem to know his stuff, just wondered if anyone here can back this up or add a second opinion?


Cheers for any help anyone can offer me, including any warnings a novice like myself needs to hear - I really don't want to break my car!! Any advice is much appreciated. Thanks guys!

All the best!


Dave

[petefarrell360]

Hi Dave,

At a first glance of your problem, I'd suggest checking this item first, being a 340 and having a carb, Volvo fitted cloth covered sections of fuel pipe from the pump and to the pump in the engine bay from the main plastic fuel lines running to the back of the car where the tanks is, then from the pickup in the tank and the return to the main lines under the boot floor. These perish and then all that is drawn through them is air and sometimes a drop of fuel! A bit like trying to suck a drink up through a straw with a hole in it, not easy, if not pretty impossible. I'd say that may explain the problem in restarting as the fuel isn't in an air tight fuel line to the pump, so when sat air creeps in and the fuel returns to the tank, or leaks out!

I've had it where the car would run, but on any kind of heavy acceleration the pump couldn't get enough fuel to the carb, as is was more air than fuel! I've also had it where restarting after stopping for a while is a big issue, and also the complete non starting as the lines are far too perished.

If you lift the boot carpet, there is a round plate with three screws in it, fairly central, off to the o/s a bit. Remove the screws and lift the plate, it may be sealed down with some sticky gunk! Here is where the short length of possibly offending cloith covered fuel hose meets the tank. If they are wet after using the car, your problem seems obvious, the same goes for those in the engine bay.

If these pipes are still the cloth covered ones, and if you are in any doubt about them, change them! I now do it as a first job on any carbed 300 I buy. Even if they appear to visibly be ok, they perish under the cloth, where it is not easily seen.

The best thing to do is buy a length of the correct internal diameter 'FUEL INJECTION' hose from a motor factor/Halfords etc etc. not the cloth covered fuel hose. Fuel injection hose is far superior, as it is designed to cope with pressurised fuel flow, as opposed to the low suction of the pump on the engine of the carbed 300! I'm afraid I can't remember the internal size of the hose required, but if you remove one of the pieces on the car for reference and take it with you, that would be best.

As to the metal one piece clips you describe, before removing anything, especially if you need the car all the time, get some hose clamps of the correct size, at least four, not jubilee clips, but hose clamps, they provide better constant all round clamping pressure and don't pinch the pipe like a jubilee clip will. The metal one piece clips will not be reusable, and I remove them with cutters in the crimped piece that sticks up, taking care not to damage the internal pipes.

The most difficult part of the operation is the rear pipes above the tank, as you will probably not have enough slack on the main fuel lines to get to the connection where the new hose clip will go on the join! This requires from memory the job to be done underneath the car at the back, take care if you raise the car, axle stands etc. and once disconnected from the tank, trace under the car to the n/s where the pipes should run and gently pull it off of the top of the tank to get to the end, possibly if you don't feel brave or stupid, tie a lenth of cord to it first, threaded down through the hole in the boot floor, so once repaired you can easily guide it back to the tank connections without getting hands stuck or not being able to find where it goes! Remove the old one piece clip and hose, making sure there is a small metal insert in the end of themain plastic fuel line that stops it getting crushed by the clamping force of the hose clamp. This is where you need to aim for with the clamp and overlap of the new fuel injection hosing.

Take care in not mixing up the pipes, so one at a time maybe, same in the engine bay pretty much and take care altogether, as this is fuel! If in any doubt get a pro in, but that would be my first route of approaching this problem, if only to prevent any problems further down the line and to rule out any other factors. It seems likely as you say when it is cranking it shows no sign of firing, then stutters, as if the fuel has drained back, it would need a few seconds to suck enough back up to the pump, then to the carb to fire.

Keep us informed as to progress, good luck!

Pete

[grass hopper]

the fuel pumps are very reliable,i would check the plugs and especially the distributor cap and rotor arm.

there was a mod to the carb top gasket for poor hot start were the section above the float bowl was modified with vent holes,but if the car has been ok for a while i guess this has been done,also the carb top can come loose and cause start/running problems

[retrodave]

Hey guys,

Thanks for the responses - it was a while back I posted this message, but I'm still having that trouble with the car so it's still very relevant and your help's much appreciated!

Thanks *very* much for that info Pete!! What you say fits the bill exactly and it does sound like a very possible cause of the trouble. There *is* still a fabric pipe in the engine compartment (I *did* change the fuel pump and noticed that at the time), so the ones at the tank end are sure to still be there too. I haven't noticed any dampness on the pipes after running offhand (although I will check properly now you've mentioned it!), but I do notice a definite petrol smell when slowing down and stopping at lights, almost like vapour's leaking out of the carb somehow - but vapour off a leaky pipe sounds *very* likely from what you've told me! Also it feels exactly like an air leak or something, and when I first try any serious acceleration the engine often falters like it's being starved of fuel, in a way similar to that you described.

I was afraid to take off that circular panel in the boot that you mentioned before as I had a feeling I might be breaking the seal on the tank or something daft like that by doing it - now I know it's okay I'll carefully have a look inside. I *did* use jubilee clips on the hoses by the way Oops! And they do squash the pipe like you said - next time I work on them I'll get some proper hose clips instead!

Cheers to grass hopper too, those are good suggestions - I have changed the plugs and the distributor looks good (my mechanic informs me all cylinders were firing perfectly, even when the fault was happening), I don't know if the carb's been modified, but I believe the engine had been running well since '84. I've only had the car for a year, and it *did* have a slightly dodgy start now and again at first, now though the fault happens almost every time. I don't *think* the carb top's loose, I actually stripped the whole carb down to look for problems and didn't find any (except an aging choke diaphragm which really needs replacing! Sealing it didn't help though), and it all looked beautifully clean with needle valves etc. working perfectly, float not leaking etc., and it got securely bolted back together!

I've been advised to change the whole carb - but at £150 a time I'm definitely more than happy to change the fuel pipe ends first!! I think I'll do that anyway, just in case. Thanks *so* much for your help, I'll definitely keep you posted and have a look at the lines next time I take her for a spin.

Cheers guys!

[petefarrell360]

Hi Dave,

You're very welcome, I hope it helps you sort out the problem, it sounds like one of those problems you could replace lots of parts and still not cure the problem, spending lots of money in the process, when it could be something simple! I always now replace these bits of pipe on carbed 300's to save any hassle.

Let us know how you get on.

Pete

[retrodave]

Hi Pete,

Thanks very much for your reply! Well, a couple of months passed where I wasn't able to do any work on the car, but I did buy some rubber fuel hose and finally got around to changing those nasty fabric-outer pipes (just before a long journey as it happened!). The first time I turned the ignition... she started straight away! And continued to start quite cleanly for about a week or two, so unless it was just a co-incidence (weather temperature or something), which seems unlikely, what I did must have had some effect. Unfortunately I didn't realise the return fitting on the tank is *smaller* than the main fitting, and my hose clips (and hose!) were a little too big to fit comfortably... but fitting them tightly did seem to do the trick at first.

Then I left the car standing for a week... and progressively the problem returned, over a period of about a fortnight! Now the *reverse* is happening - the engine is *very* hard to start after standing for a few days (a good 10 - 20 seconds on the starter motor), but once it's been running it starts first time again! I'm *hoping* the wrong-sized hose was fitted tight enough at first but has now worked loose - some smaller hose is on the way, I'll fit that next weekend probably, and see if it helps. Does seem like maybe pressure or air getting into the system and causing the fuel to return back down the pipe, or evaporate or something...

I have another issue perhaps someone can throw some light on (I'm thinking about starting a new thread on this one!) - the car is great until I hit about 60mph on the motorway, then I start to feel a steady, but quite strong vibration through the pedals and steering column (possibly the gearstick too). The vibration goes away after 65, and returns when the speed drops back down. It goes away again when the speedo falls below 60. Dropping the clutch and letting the revs die away REMOVES the vibration quickly with the revs (even though the wheels are still running at 60!!) So it's not a bearing or wheel-balancing problem I don't *think*. Read somewhere I should check my engine mounts... oo-er... anyone got any ideas? Can a clutch start to vibrate like that or something? I don't like the idea of a bolt coming off or shearing somewhere when I'm on the M4!!

Any light anyone can throw on this for me would be much appreciated. Thanks for your help guys!