Severe misfire - Engine dies

[stuartgb100]

Thinking my electrical problems were solved, I set off for the MOT yesterday (now expired).

After about 4 or 5 miles a misfire began to develop.
I noticed it first in higher gears at lower revs.
I found that if I dropped to a lower gear and used higher revs that it seemed better.

After another mile or two it was significantly worse and I was kangerooing, finally coughing and spluttering, and it died.
It started straight away but would not rev, and died again.

I changed the plugs, started and made 200 yards before the same again.
Plenty of fuel in the bowl.
I changed a third set of plugs - made about 50 yards.

Arranged a tow home (which wasted a couple of hours), and pushed it up most of the driveway. Decided to try it again and managed to drop the clutch at high revs and get it in the garage.

Left it for another two hours. It was now quite cool with the temp guage only just off its' stop.
Tried it first time and it fired.
After 10 seconds or so it cleared and revved away freely.

This engine has only just come off the dyno, so its' got to be something in my car that was not connected to the engine during the dyno session. The Aldon distributor, leads, plugs and fuel pump were there on the dyno.

The coil was not. I'm wondering if it's getting too hot.

Any thoughts please?

Regards,
Stuart.

[alaric]

Hi. Sounds like a short in the coil. This can show up as the coil gets hot. Symptoms all fit. I'd try another one if I were you - i.e. it's not necessarily getting too hot, it's just faulty.

All the best.

Sean.

[neilsjuke]

Sounds to me that you have a Aldon igniter they use to be very reliable but have had seen a few of them faulty lately don?t seem to like heat of twincams if not a condenser fault if you?re on points then maybe the coil.
Neil

[stuartgb100]

Thanks both for the help.
We'll see how it goes.

Have a very pesky neighbour, so engine revving is a problem !!

I fear an inninent ASBO !!!

Regards,
Stuart.

[terryp]

Stuart
Surely your neighbour must be OK with the sounds of the iconic Lotus twin-cam!
You tell them one night of revving otherwise we all go round and rev every night!
I agree with Sean with the coil theory sounds perfect for the symptoms

All the best
Terry

[worzel]

Hi

Had something similar years ago- turned out to be the amplifier pack of the Lumenition system- it worked for a while then died. Wait an hour or so and it was ok then it repeated itself.

Bought a new amplifier and it's been fine for the past 20 odd years.

John

[bast0n]

Stuart

I posted this elsewhwere as I have had several coils fail, especially in hot climates.

"I have had a similar problem and it was the coil overheating. (Aldon distributor etc). I was advised by someone hugely more knowing than me to reposition the coil in the cockpit as racers do. I have moved mine to above my feet and to the right, (right hand drive). Since doing this no problems even when going a bit mental in plus 35c!"

Hope this helps. David.

Don't grow old too quickly!

[martinbrowning]

Currently have/had the exact same problem with my S130.Changed everything including new carbs but forgot about the coil. In desperation took the head off and,well,one thing led to another.Currently got engine and gear box on the bench for overhaul/rebuild and engine bay stripped for a respray(it was tatty).trouble is,can't remember what I set out to do that sunday afternoon all those weeks ago...

Martin B

[Galwaylotus]

I had the same problem on my Mini (Kettering ignition per the factory in 1990). I could keep it running if I kept the revs up but when I had to stop (28 mniles from home!) and park it at work, there was no restarting even when it was cold. I eventually traced it to a faulty coil. Replaced it and all was sweet again!!

[spanner]

An old time mechanic I used to work with, would quickly diagnose (heat failure) vintage aircraft magneto coils, by giving them a quick blast with a spare CO 2 extinguisher.

If stuck on the side of the road, a blast might get you home!

Spanner

[stuartgb100]

Managed to get the car back out for a run, aiming to replicate the previous problems (and then to swop out the coil).
The problems duly manifested, but for some reason (I was never positive this was an electrical problem)
I decided to remove the cover from the front carb - not a lot of petrol there !
The rear carb was marginally better.

So, we definitely have a fuel issue, and maybe an electrical problem.

Now, this engine has just come from a dyno session, so how can this be?
Well, a quick call to the dyno guys confirms they use their own fuel rig ( and, incidentally, their own ignition source)
so they had effectively bypassed my coil and fuel pump.

So a replacement fuel pump (which was new anyway) and maybe a new coil (which was running fine on the Sprint before)
should soon sort the problem !

Not so easy.

The new engine is based around a tall block, rather than the twin cam pre-crossflow block. This block is wider than the
twin cam. It gives no more than 7mm clearance between the flange of the fuel pump and the inner bulkhead. There is
no way that pump is coming out.

The only way to remove it is to disconnect everything and move the engine/gearbox forward best part of 12 inches.
And there's no way I'm going through that again !

Plans are therefore to go for an electric pump, and a hidden switch for some security.
Will probably fit an in-line on/off switch whilst I'm at it.

Regards,
Stuart.

with new engine/gearbox - score so far:
miles driven (20) v miles towed (25) !!!

[Elanintheforest]

Stuart
I had this problem on an E Type....turned out to be rust scale in the petrol tank. The smaller stuff would get thorugh OK and get caught in the filters, but there were a few large lumps that would occasionally get sucked up into the fuel line, bung it all up, and with lots of banging and popping, bring me to a halt. Sometimes it would clear straight away, sometimes it needed the jolting on the back of the tow truck! Maybe worth checking out the tank (and blow out the fuel lines) before replacing the pump.



Mark

[gjz30075]

Block is wider??? I thought the only difference, besides the height, are the bosses for the mount on the exhaust side which are longer than the TC, which necessitates either machining down or shorter spacers. Maybe neither was done and the block is pushed over to the intake side, hence, so little clearance by the fuel pump. Just askin'.....

But the electric fuel pump should eliminate the fuel variable here and if your mechanical pump is wonkered, it could have a perferated diaphram, allowing fuel in the sump so be sure to check your oil. Level could be higher than normal and have the smell of gas.

Greg Z
'72 Sprint

[types26/36]

[quote="sgbooth"]The new engine is based around a tall block, rather than the twin cam pre-crossflow block. This block is wider than the
twin cam. It gives no more than 7mm clearance between the flange of the fuel pump and the inner bulkhead. There is
no way that pump is coming out.
The only way to remove it is to disconnect everything and move the engine/gearbox forward best part of 12 inches.
And there's no way I'm going through that again !
quote]

Hi Stuart, I like Greg was not aware that a 711 is wider (except for the mounting lugs) I will go and measure one later today.
I was helping a friend the other day fit his engine and due to brain fade fitted the engine mounts on the wrong side! (Weber engine)
Before we got any further I noticed the mechanical fuel pump was almost touching the fibreglass body and there would be no way to remove the pump should need arise and I have had them off many times with the normal set-up.......I suggest you double check you have the correct mounts on the appropriate side.

[stuartgb100]

Greg, Brian and all,

Thanks for the replies.
Yes, the block is wider over the mounting holes. Sorry not clear.

I've a weber engine in an early Spyder chassis with a big-bore exhaust manifold.
The chassis has had to be "adjusted" to accommodate the manifold, and the engine
mounts slotted and spacers altered.

The gaps between the manifold/body and fuel pump/body are nearly equal (ie 6-8mm).

I don't see how there's enough room.

Regards,
Stuart.