3500S keeps cutting out... - Why does my V8 run then die?

A

Anonymous

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Having previously been an avid viewer of the comments and advice on the forum, I've been driven (or not) to seek some solace from fellow P6ers - my '76 3500S has developed the selfish habit of cutting out on me, seemingly whenever it takes her fancy. She'll start ok in a morning and warm up, then at some point into the journey (usually between 10 - 20 minutes in), will cut out - in the middle of rush hour traffic, Sunday traffic, either whilst stationary or under acceleration or ambling along, she cares not. And then she won't restart. I can turn it over 10, 20 times, she won't fire. As you might imagine, this can be very awkward, esp. if at a junction or in a queue etc. If I can pull over, it's not too bad. Then after 5 minutes or sometimes longer, she'll fire up again. Then she'll either be ok for the rest of the journey, or if she's particularly fitful, she'll do it again a couple of times (though the second and third time, I can usually turn it over again whilst still moving and she'll be off again.) It has been happening for a couple of months, during which time I have changed plugs, leads, coil, dizzy cap, cleaned out carbs, and last weekend, replaced the existing lumenition with a new one. She was good on the day I did that before reverting back to her bad behaviour this week. When it happens and I try to start her up again, I notice that there is a different smell of fuel burning coming through the vents. She runs on Optimax and has up to now been a joy. I have also noticed that fuel consumption has started to become excessive and undpredictable. Has anybody else experienced this? My plan was to go through and change various bits as and when I can, to try and eliminate possibilities. All helpful tips and suggestions would be gratefully received! ???
 
Caszh,
Sounds like an annoying little problem, most likely with the fuel supply from the description of your symptoms (well, the car's anyway!). After 10/15 minutes from startup the engine should be warm enough not to need any choke - so is the choke sticking, slightly closed? If not, it could still be choke - there are "O" rings on the cold start valve on the HIF6 carbs which perish in time and give these sort of symptoms.
This is where I'd put my money with known symptoms so far.
Rare, but also a possibility, is fuel starvation (but this wouldn't give you excessive fuel consumption) caused by blockage in the fuel tank breather which creates a vacuum in the fuel tank which, when equal to the fuel pump pressure causes fuel flow and engine to stop - After 10 mins or so the air is drawn back into the fuel tank allowing you to start again - This can easily be checked by starting and driving with the fuel filler open to see if symptoms are still there.
Hope this helps, (go for the "O" rings!) advise future symptoms, Regards, John.
 
Another possibility, although not too likely, is pieces of crud in the fuel tank being periodically sucked up and blocking the pipe. When the car stops this will eventually fall off when the vacuum in the fuel line disappears and off you go again. Also try checking all the rubber pipes for perishing etc which could intermittently let air in.
Yet another possibility is the inside of the rubber lines collapsing under suction and releasing when the suction ceases, much like worn brake lines can do, causing brakes to sieze on. This could be caused by the use of modern fuels over time which are known to attack older rubber components.
Does the car literally cut out, nice and clean, or does it splutter a bit first? A clean cut out usually indicates an electrical problem. Check every bit of cable on the ignition system and replace any that look old and dodgy. Also check the earth strap between the engine and the body, is it loose or corroded? And just because you've replaced a component, don't assume it is ok. I've known several cases of new but u/s dizzy caps and capacitors.
Good luck, let us know how you get on.
 
Yes, I had the old dirt-in-the-tank symptoms on a previous V8 model that we owned but spluttering and no-power symptoms disappeared once reserve tank had been pulled so this could be worth a try also.
Regards, John.
 
I have suffered from a failed dizzy low voltage lead failure, (on a chevette) it wasn't obvious at all, and adjusting the points gaps helped but was only masking the problem. I only spotted it when I had the bonnet open in the dark and saw the wire glowing where it was broken inside the sheaving.

I would also have suggested condensor, but you say you have luminition which should remove that problem.

Intermittent rich mixtures and excess fuel useage would suggest the choke problem John describes.

Richard
 
i had exactly this problem and sorted it today - it was (as suggested by rovermorris999) the engine earth strap - verified by running a jump lead from the engine block to a good earth on the body...obviously i'll replace the offending part before attempting to use the car again!!

it had me puzzled for a while too!

anyway, it's the least of my problems.. i've just examined the sills, and... oh dear. so you guys might be seeing a 3500 with SD1 5 speed conversion in the 'free to a good home' section soon - i think the body repairs needed may be beyond my welding capabilities!
 
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