Misfiring. Suggestions please.....

[Splat]

Much as the title, I have a misfire and wonder if anyone here has a suggestion as to either the cause and/or cure.

It first manifest itself at a track day last year. For the first session the car pulled like a train. It was then parked up for half an hour. During the second session the car developed a severe misfire. Smooth running under a trailing throttle, but under load a very bad misfire and no pull whatsoever, the engine bogging-down, with plenty of unburned fuel exploding in the exhaust manifold.

I noticed that the good quality, 3 ohm Lucas coil was very warm to the touch. Not unbearably hot, but hot nonetheless. Being at Thruxton, I nipped the four miles home and returned with the Lambo (#firstworldproblems!).

I swapped to my spare coil, but test-driving produced the same results; strong performance from cold, but once rested for a few minutes, a very noticeable misfire.

My car runs an Aldon dizzy with Igniter (contactless ignition by Hall effect) and no vacuum-advance. If it makes any material difference, I think that it's the 100ARS-I found here:

http://www.aldonauto.co.uk/ignition/dis ... s-a-series

My next step was to replace the coil with one of Aldon's 3 ohm Flamethrower coils, the 40501 model here:

http://www.aldonauto.co.uk/ignition/coi ... ower-coils

My last drive of last year (and the only one since a quick test drive after installing the Aldon coil) was to work for a day trip to Kos. So 55 swift A-road and motorway miles to Heathrow, a ten-hour-or-so rest (the car, not me!) and then 55 miles back home. All on a nice, sunny Saturda, with no sign of the misfire whatsoever.

But this afternoon I went out to bed-in new pads (Mintex 1144; and with the 9" cross-drilled discs, MGB callipers and the larger-bore APRacing master cylinder it now STOPS!!!). Pulled like the proverbial train for about ten miles until I parked up at a lovely boozer about four miles from home. Twenty minutes to sup a half of bitter, straight from the cask behind the bar with Ed the landlord, out in the sunshine, then back in the car. Started straight up, but then on pulling away an appalling misfire under any load. It eventually conked-out entirely about a quarter of a mile down the road and wouldn't restart.

I lifted the bonnet to find the new coil again quite hot to the touch. After five minutes of cooling and quite a long starting crank, the engine finally caught and idled smoothly, but the rest of the journey home was terrible; an awful misfire under any accelerative load, explosions from the exhaust manifold and a constant threat to bog-down and cut. Back in the garage, the coil was again very hot. Holdable, but you wouldn't want to grip it hard for an extended period.

So: any suggestions?

[Westfield 129]

I run the same system without problems.

I would take a look at your alternator output. It may be way too high (or too low, or fluctuating...) , perhaps around 15~16.5 volts. This can cause the problem you are experiencing. This is also hard on the battery, and you might also be replacing electrolyte frequently. I have seen this problem primarily on Lucas alternators, but a defective regulator might cause this problem on any alternator or generator. Unstable voltage can cause problems with both points systems and Pertronix Ignitors (the OEM for your ignition components). I have seen high alernator output cause all sorts of strange ignition problems, as well as over heating due to burning the points, advancing the timing and causing over heating, after burning up a battery...

I had a similar problem with one of the "Ignitor" units. It was promptly replaced by the manufacturer and the ignition has been perfectly reliable. Since your problem is related to a warm engine, you might have a hot short or heat related problem with the igintion component. You can try some freeze spray on the Ignitor unit when the problem manifests itself. If it goes away, you found your problem component. Then check the alternator output voltage...

Also, check your wiring connections, especially the grounds, and make sure that the Ignitor unit is properly installed and tight, with proper clearance between the pickup and the reluctor installed under the rotor. The distributor cap and rotor might be worth an inspection. If you have a ballast resistor, you might check that as well, or take it out of the circuit and see if that helps.

The "Ignitor II" has a protection circuit that protects the unit from over voltage or continuous voltage with the engine off.

And, as your car is likely RHD, you might check to see if the distributor cap has been knocked askew or is rubbing the foot box. This may be related to an engine mount problem.

If your ignition harness is old, that might be a problem as well.

I have been running the same system for, well, decades, without problems. Only one Ignitor has failed and was promptly replaced under warranty. The only problmes I have run into with this ignition system are the ones that I have stated.

Now, having said that, you might take a look at your fuel pump, with the understanding that most fuel system problems start with the distributor...

[Splat]

Thanks for the reply, Jan. Lots to look into. The harness is a good-quality, silicone set and the cap is a NOS Lucas, with a red (riveted) Bosch rotor. All looks good, with no burns. The fuel pump (brass-bodied, electronic SU) was next on my hit list and the rebuild kit was already waiting. Stripped and rebuilt it yesterday, with new diaphragm, spring and outlet valve/discs, although all looked good. However, the mounting screws that support the electric PCB weren't loose, but nor were they tight. They also hold the Hall shield in place, and just the tiniest movement of the shield has a huge effect on pump speed. So that's now properly adjusted and the screws tightened. Next will be a check of the alternator output.

Unfortunately, after a blazing weekend (25°C, although I spent most of it in Istanbul, where it was only 18°), Spring is back with a vengeance! My test drive was after I got home from work on Sunday afternoon. On Monday I took a mate of mine out on a fifties-immersive experience (James and I used to instruct together and nowadays he's a fellow Airbus skipper with BA). It became a little damp, as can be seen in the video:

https://goo.gl/photos/wSn78TzJS2Z9PJmK7

(and yes, the second is a barrel roll, not a loop!)

[Splat]

OK! So what's the major difference between the before and after shots of my fuel pump?

[Splat]

Yup! It's the +ive terminal.

Notice the chewed screw-heads? Notice the missing SU seal, which serves to waterproof the end cap? Someone's been in here before me.

Notice how, post-rebuild, the terminal is now 180° around? It's attached to the PCB, onto which is also mounted the small coil which, together with the offset magnet on the end of the diaphragm input shaft, forms the electronic "points". Mis-mounted, it would never have worked properly, if at all!

With the PCB correctly mounted, and the Hall shield adjusted, the pump now buzzes like an enraged hornet. I wonder if that's "problem solved" ?

[Westfield 129]

Yes. obviously a barrel roll. Nicely executed. Good to keep those skills sharp!

Put a volt meter on the alternator or the battery with the engine running. It might be more than 15V.

This may have caused problems with your fuel pump as well.

[Splat]

(Damnation! He's going to be proven correct. Again.)

The fuel pump is much better. Recently, it's been all-but silent with the ignition on but the engine off. Now it's making a healthy click every ten seconds or so. But I was less than convinced that this was the cause of my problem. However, with the engine warm after its run on Monday, I'd drained the oil and was waiting for a replacement filter before I could refill it and investigate further.

I finished work early today (a day in the classroom, but I'd been a girlie swat and done most of the online learning in various hotels over the last week, which negated about two hours of tedium today) and arrived home to find the filter waiting.

Engine refilled, oil pressure built up and then started, I was able to put a multimeter to the alternator. Guess what? 17.5V at idle, rising to 19V at 3000rpm! New (genuine Lucas) alternator ordered.......

Thanks, Jan. I wouldn't have got there without your advice. Fingers crossed that that's the end of the misfire.

[biggles]

Do you mean swotting or swatting? Your poor girlie....Still, whatever you get up to on the weekend

Lovely video btw, loving the old school crackly effect, very atmospheric!


(Edited due to posting under the influence of jet lag and a 2008 Rioja )

[Westfield 129]

ND 18504 Alternator (or a Chinese copy) will fix your problem much better than trying to fix a Lucas (if that is what you have) unit with the failure prone rectifier and voltage regulator. You will need to do a simple modification to the mount tab, and make a lower bracket from a couple of rod ends (LH and RH thread, with a RH/LH threaded tube) for a turnbuckle.

I had the same problme on another car, but with overheating (the points burned, advanced the timing, causing over heating, along with the miss. The builder and the next owner were never able to figure out what was going on... The car had only a couple of hundred miles on it when it was presented to me. Eventually, the alternator killed the battery through over charging, and we checked the voltage...

The electronic ignigion systems are voltage sensitive, which was another car, another time. It's always good to watch the system voltage. You can put a voltmeter in the panel. Very useful. My own car with the Ignitor II quit one day due to a voltage spike. The Ignitor shut down to keep from burning up. It came back later... Replacing the alternator fixed the problem permenantly.

I am pretty sure that you have found the problem. If you have further problems, it may be due to damage from the over voltage. The coil and Ignitor might have been cooked. We shall see.

However, since it starts and runs, the components are likely OK, and getting them the right voltage will return the performance and reilability.

Have Fun!

[Westfield 129]

I have had lots of genuine Lucas alternators fail (new, overhauled, used... Doesn't seem to matter), and repaired each of them several times... I bought new ones, then started repairing them. They kept failing, always at the rectifier (it came apart and shorted, or the insulators melted)) or the voltage regulator (often going to 16~17 volts and frying the battery, or cooking off the electrical system components. All of the over voltage problems I have seen on Spridgets, or Westfields can be traced back to a new or rebuilt Lucas alternator.

Of course, the Lucas is easy to fix, but it doesn't stay fixed long if you drive the car...

The Chinese ND copy has never failed... Outlasted the Lucas units by about 6:1 so far. I have also used the actual ND part, but the cost is about 4X the cost of the Chinese copy.

Oh and the ND type weighs about half that of the Lucas unit.