Misfire then cutting out

[Baxter]

Struggling here with my 63 Vitesse 6. Been running sweetly for the last 2 years since new dizzy, points, condenser, rotor arm, coil and plugs. 11 days ago I was out for the afternoon and after about 1hr driving a small misfire developed. Got a bit more persistent but no problem getting home. It was one of those scorching days and I wondered if it was fuel related or the dreaded vapour lock - though I've not experienced either before.

I cleaned and re-gapped points and plugs, reset valve gaps; checked float levels, fuel pipes and generally anything else as a minor service was due and I wanted to try to make diagnosis simple as possible if the misfire came back. I took the car for a good drive last Sunday - ran better than ever for a good 40/45 mins. Then suddenly a small misfire, this time rapidly developing into very lumpy running then cutting out. Wouldn't restart. Waited 3 hrs for a lift home on a flatbed - by which point it started sweetly and could be driven up my drive.

Recovery chap said coil. Each time it cools down it can then work okay till hot again he said. So I replaced it. Then the condenser and plugs to be on the safe side. Again ran superbly today for 40 mins then sudden misfire and quickly ground to a halt. Any ideas what the problem is?

 

[Baxter]

I just found JohnGT6's cuts out when hot post - so got some good info from there. 

I have a huco electric pump and then a fuel filter between it and the carbs. I think I should try the water-pouring test and maybe remove the filter or put it between the tank and the pump. However, my car will start quite easily each time after it cuts out (so maybe not vapour lock?), but is always then very lumpy and soon dies again. By this point I usually have the bonnet open. There is plenty of heat everywhere, but that's always been a feature of my Triumphs.

[Guppy916]

I had same problem on my GT6 1973, the car had a new coil  (Lucas) from Rimmer's in the rebuild, that lasted 200 miles, then a new coil (Lucas again) which I thought was ok, Put the car in for a rolling road set up Carbs, Timing, to get the webers set up correct, and the guy said I ve fitted a new coil yours was breaking down under load when hot, I said it's only done 75 miles, Now I have a Bosch coil, I told him the coils history, and he said it's the six cylinder engine the way it runs shaking the internals , so the coil is now mounted with a couple of old mini exhaust cotton reels to stop the vibrations, and as the engine is still new 300 miles he only ran it to 3k for the set up, with 150 bhp , he said do another 300 and bring it back for a check up 

he comes very well recommended http://www.aireytuning.com/#home

[Baxter]

Thanks Guppy - hard to believe a new coil could fail so fast, but also reassuring to be returning to my original diagnosis. I'll order some cotton reels then. Still concerned as to why it seems to be about 40 mins till failure each time - makes me think heat level is involved and not just shaking. And why did my first coil last 2 years.

I like the sound of Airey Tuning but as they're a fair way from here I'll probably try a local tuner first. Very impressive set up under your bonnet! I'm hoping for 95 bhp from mine.

 

[Guppy916]

Oliver when the first coil went down, it was very very hot to touch, when I took the car to him for the rolling road set up, he is about a 20 - 30 minute drive from my house, as I approached his place there is a slight incline and I noticed a couple of misses from the engine, which i disregarded as the carbs weren't set up, that could have been the coil starting to go south

[daver clasper]

Not sure if this is of use. Though.

Depending on how much fuel is in the tank, could it be the cap is not breathing, causing fuel starvation. Never happened to me, though others say to remove cap and a whoosh sound can be heard as the vacuem fills with air (not sure if it would do 40 miles like this though?).

Debri in the tank, that blocks the line, though settles after standing.

When it happens, may be worth removing the hose near the front carb and switch ignition on to see if fuel is reaching carbs.

Worth changing rotor arm/points, as repro ones, can often be dodgy?.

Dave 

[Baxter]

Thanks for suggestions Dave.

I have had a few small whooshes in the past when removing the cap for refuelling. But not recently - I've been monitoring it. I do still have concerns it's fuel-related. Tank is only a few years old, filter looks pretty clean. I'll try your carb test if it happens again.

I have a new Bosch coil and two rubber cotton reel (exhaust) mounts arriving tomorrow. I'll then do a test run, taking spare new coil, points, condenser, rotor arm with me. And a red triangle. 

 

[Nick Jones]

Rotor arm (especially if new).  Carry a spare for an instant roadside swap to prove.  Longer term buy a decent (red) one from the Distributor Doctor.

Nick

[nang]

I think that your "Lucas" coils are all chinese these days. I've kept all my old real Lucas coils I've taken off wrecks etc. I have no faith in modern repro parts.

Tony.

[Baxter]

Thanks for continued thoughts and suggestions. I've got news from the latest road test. First I did a couple of things at base:

1. I noticed a small leak from the exhaust manifold gasket, so did a temporary seal on that. (The engine will be coming out in a while as the sump 'seal' leaks badly, so can properly address all gaskets then.)

2. I checked fuel flow. With the car having stood several days, I measured 800ml per minute, from my bulkhead mounted Huco pump, then through disposable paper filter, and out the line just before carb #1. Removed fuel cap: 800ml. Removed filter: 800ml. Did I read somewhere to expect about 1l per min? Does my volume sound sufficient? When it's working, the car certainly seems to go well now.

Road test: Fitted new Bosch coil (made in Brazil) onto two mini exhaust rubber cotton reels. Very springy. Points and rotor arm are from the Distributor Doctor earlier this year and still in great condition. As are the HT leads. Plugs have just done the one previous outing. Took a full set of new spares.

Car ran better than ever. First time I've ever been able to accelerate up a hill near me. Sounded better too - quieter and crisper. All excellent for 17 miles and 35 mins of Cotswold lanes. Then a little misfire. I didn't have the heart for a 3rd breakdown in a couple of weeks so drove straight home. Misfire gradually worsening. Once on my drive the car didn't want to rev. Very lumpy.

I made the cardinal sin of then getting sucked into other jobs at home, so didn't swap out any parts and retest. But it always seems to be at the 20 mile/ 40 minute mark I get this problem - so is it heat-related? 

[Baxter]

Tony, my dad did his automotive apprenticeship at Lucas and I grew up in the shadow of the Dog Kennel Lane site. It pains me to find sub-standard parts being sold under the brand name. Quality of parts in general is a topic that gets me going!

[Baxter]

Here's a link to 10 seconds of hesitant exhaust burble when I got back from my 19 mile, 40 minute test drive.

https://1drv.ms/v/s!AmjW3mQn-IqAjMEFVBfpdop1nrrIGA?e=8vi2zk

It was idling smoothly before I set off on the drive.

 

[Pete Lewis]

do check

the the fuel cap is venting

the coil feed is correct polarity ( this is an old nutshell of it runs stops you get out faf around give it a kick and it restarts till next time  .)

Pete

 

[PeteStupps]

Annoying. The time factor really suggests heat. Does it happen while you're moving, or after stopping at a junction or somewhere? Presume your gauge is telling you water temp is normal?

Your description doesn't quite fit my experience of vapour lock but did you ever move that fuel filter from between pump and carbs? And can you see whether it is full of fuel or not, when the problem occurs? 

Trying to think of some other heat-related problem, apart from coil. Is it on Stromberg carbs? Is your fuel pump in the engine bay?

Pete

[Baxter]

Thanks for the suggestions.

Pete L - I think the cap is venting. No whoosh on opening it. And I specifically did the fuel flow rate test with/without the cap to check for this (and got the same each time).

Went out again last Sat (5th Sep) and it was just the same. Fantastic for 18 miles and 35 mins, then suddenly, on hard acceleration up a hill, started misfiring. Managed to coax it home the last couple of miles, low-speed, and feeling as if 2 or 3 cylinders were switching in and out.

Pete S - it always happens while moving. I think there's a pattern that it begins under heavy engine load. Water temp always normal. Once it's happened it just gets worse till it won't run; though it will always start. Seems to work again once completely cold (following day - leaving it for 5 hours it's still rough).

I only took the fuel filter out to check flow rate (unchanged), then replaced it. I hear that vapour lock can be caused by the larger diameter of the filter, but it always seems full. Fuel pump is now a Huco mounted on bulkhead. I did do one longish day out since fitting this pump, so think it is probably not the cause. Before that I had an extremely noisy facet pump next to the battery, and a flow rate regulator. This was installed by a specialist while tuning the engine using a rolling road, and they set the regulator to 1 out of 5 (approx 1 psi). The car has the full Derrington conversion, so triple SU H2 carbs.

Baxter

 

[PeteStupps]

Have you got any photos of your engine bay showing the fuel line routing? I'm curious.

Any vapour will collect in a high point of the line; when I had my issues the fuel filter was the highest point so you could see it became mostly empty as vapour displaced the petrol.

I wonder if you're getting a bubble somewhere in the line, which the pump can squeeze enough to get some fuel past, but is restricting flow enough that you're getting this starvation at full load. Going uphill, or slowing down because of misfiring, mean reduced cooling from airflow and more heat gets into the fuel line. 

That's my theory anyway! 

[Baxter]

Thanks Pete, I'll paste some photos below. There is a high point between carbs 1 & 2. I tried to replace this fuel pipe per routing when i acquired the car, but can see in the original road test article that they keep this pipe flatter. In first photo the pipe from my tank rises into the filter and then curves up and round/down into the pump. BTW the problem may start under high load, but once it happens i often cant even run slowly on the flat. Your theory could still hold if there's enough of an airlock. Take a look and let me know what you think. Thanks

[Baxter]

 

[RobPearce]

Is that an electric pump mounted lower than the filter? And then the pipe goes round the front fo the engine to the front carb then forward and up before going round to the middle carb? I can see Pete's point about opportunities for heat soak and air locks.

I think I would shorten the hoses on the filter and relocate it so that it's below the pump. Then I would replace that long loop of rubber from the front to middle carb with something that goes down instead of up. I'd even recommend thinking about re-routing the pipe out of the pump across the bulkhead to feed the rear carb first - I'm not convinced that the late 1500 round-the-back-of-the-head route is an improvement for heat but with a bulkhead-mounted pump you can sensibly keep the fuel away from the engine entirely.

[Baxter]

Rob, it is an electric pump and it is a little lower than the filter, and you've correctly identified the route from there onwards.

I'll make the alterations you suggest and check for improvement before thinking about re-routing across the bulkhead. Thanks!

[PeteStupps]

Interesting photos Baxter, thanks. 

Just re-read your comment about it still misbehaving after a 5-hour break, which I'd missed before. That is a long time for fuel to remain hot, I wonder...

But I concur with Rob, if you can re-arrange the pipework from front carb to middle I would definitely try that. I'd also look at lowering the fuel filter to eliminate the upward loop there if possible. 

Keep an open-mind as well, this could be a red-herring. I have a bad habit of developing tunnel vision with problems, only noticing evidence which reinforces my opinion!

[PaulB]

I had a similar problem with my Spitfire.

She would misfire on heavy load and after she was hot wouldn’t restart. 
After checking the various items mentioned above including changing the coil a few times it turned out to be a faulty starter solenoid. 

[Baxter]

Paul, thanks for the starter solenoid suggestion and easing our tunnel vision focusing on just one potential solution. I don't understand how this would cause the problems I have but it does seem you went through a similar scenario. Perhaps one key difference is that my car will always restart - it just doesn't run well once the problem’s happened.

Pete, Rob, I modified the fuel pipe layout as discussed and went for a test drive today. I was so optimistic, yet once again 20 miles and 35 minutes into the drive the misfire appeared. I do think we might have improved things though...if this makes sense, I was able to restart and drive along at about 35MPH, albeit quite roughly. Then with a gentle downhill section the misfire cleared and the car surged up to 60MPH and completed the final mile home well. There is still scope for further shortening of some pipes and lowering of the filter so I think I'll try that.

[RobPearce]

Disappointing that it didn't fix it but interesting that it seems to have made some difference.

When my Vitesse had similar-ish problems (would run fine for twenty minutes or so then misfire if I accelerated hard or exceeded 60mph, occasionally dying completely... although it would usually recover if left to cool for a bit or, mostly, if I just eased off to a steady 40mph cruise for a few miles and kept below 60 after that) the fix was to take the electric fuel pump off and put it back to a proper (home-refurbished) glass bowl AC Delco mechanical pump. But that was a cheap and nasty electric pump - yours looks more proper.

Until very recently my Spitfire has suffered intermittent failure to deliver fuel - carb float chambers will be dry when it splutters to a stop by the road side - but that was caused by POR-15 fuel tank liner being crap and peeling off in sheets so that it blocked the tank outlet. I had to replace the tank to fix that!

[PaulB]

Quoted from Baxter-

Paul, thanks for the starter solenoid suggestion and easing our tunnel vision focusing on just one potential solution. I don't understand how this would cause the problems I have but it does seem you went through a similar scenario. Perhaps one key difference is that my car will always restart - it just doesn't run well once the problem’s happened.

 

On the Spitfire and I think it’s the same for a Vitesse, if you have a ballast ignition system, the ignition feed to the coil goes via the starter solenoid. So if the solenoid is faulty it could interrupt the ignition feed to the coil, hence causing a misfire.

I’m not an expert on ignition systems but I hope this helps. Good luck and let us know how you get on.