problems with etype v12 roadster misfire / ignition

[stmh]

Hi

I have a 1972 series 3 roadster. I have had an ongoing issue with an intermittent misfire - the car is fine when cold, after about 15 miles the misfire starts.

It has been to 2 specialists, neither of which have been able to sort the problem, despite it being tuned on a rolling road and being thoroughly roadtested under a variety of conditions - typical issue with intermittent snag, never happens when car goes to garage....

today took car for a run of about 100 miles. As usual, misfire started, but seemed minor. Did short period on motorway - at about 75 mph, car suddenly backfired and lost all power,rev counter at zero despite still in gear and moving - obviously had lost all power. Coasted onto hard shoulder, pulled various connections, eventually got restarted, went a mile, same thing happened again. After calling rescue services ,waiting half an hour & pulling all connections off ballast resistor, coil etc again, got car started and drove 20 miles home with no problems whatsover - not a hint of a misfire and running really strongly

It must be something really simple. Suggestions extremely welcome!

Thanks
Steve

[raysearles]

Sounds frustrating.

My V12 E Coupe had what sounds like a very similar problem about 8-9 years ago. Would start fine and then within half a mile of leaving home would start to splutter lose power and on extreme occasions end up dead. I remember once having to turn back on way to show only 5 minutes from leaving home.

The RAC man who picked me up the second time it failed fully was quite diligent unlike many these days and he diagnosed a intermittent short circuit somewhere around the ignition coil though I cannot remember whether it was HT or LT.

Another thing to check is the location of the ballast resistor - I recall reading that it can get very hot in its factory position in the V and many people - including me have moved it on to the frame.

Other thing to check is whether your fuel pump is up to snuff. Mine started playing up and had to be replaced. Again similar symptoms sometimes it was fine others - not so. Though the latter should be easier for a specialist to diagnose.

Anyone else with a suggestion?

Regards

[J44EAG]

Wasn`t there a problem with the original Opus ignition amplifier on V12 units?

Later sorted with the ReOpus which I believe Derek Watson markets.

Mike K

[oldtimer]

Yes Mike, allegedly so, but my old XJ soldiers on untouched for 40 years. These problems are long tedious jobs to sort out. There is no magic bullet. Yes mine has a frequent misfire when it has not been in use for a while which is caused by corrosion on the alloy segments in the distributor cap. It looks white lime scale which cleans off quite easily The blue Intermotor cap with aluminium segments seems to be the problem. An OE cap with brass segments is a much better deal for little used vehicles.

As for the electrics where does one start. These cars are very mature so anything in the system can produce a tedious minor fault with pretty disastrous results. One can easily be drawn down the wrong line of thinking so it is important to decide if it is a misfire or cutting in and out.
A genuine misfire can normally be identified which points to HT. Intermittent operation on the other hand may be LT. which will need investigation from the ignition switch onwards.

To late to write a book but do let us all know how you get on. Perhaps we can help in some way

Oldtimer

[stmh]

After much consideration, entire ignition system replaced with sng Barrett kit including distributor, amplifier, ballast resistor and coil. 200 miles done this weekend, didn't miss a beat, thank goodness...

Love/hate relationship with car - now swung back firmly to love end of the scale!

[J44EAG]

I work on the basis that everything in life has a finite life. When it occurs can be a very variable factor. Particularly so with aged machinery and even more so with electrical or electronic equipment. I`ve worn out seven laptops in nine years!

When one considers the harsh environment which this kit lives and operates, it suprises me not at that equipment can and does fail. In a marine environment deterioration speed can be truly staggering. I`ve lost count of the times customers have said "But it shouldn`t have done that". All I can do is raise an eyebrow.

Glad you got fixed up. I think you did the right thing by zero timing these important items. It will no doubt make for a more reliable and enjoyable driving experience knowing you are running new prime parts.

Mike K

[stmh]

After another 100 mile trip today on a glorious summer day in Devon, cant recommend the SNG barrett ignition kit enough - in all conditions from motorway to stationary stuck in heavy traffic in Exeter, the car never missed a beat. Fully confident now that the problem has been resolved. Best money spent on the car so far without a doubt.