Thread: V8 Ignition queries

When the engine is stationary no current flows through the coil. Therefore the voltage you read at the positive post will be the same as the negative post, i.e. there will be no voltage measureable across the coil. For this reason it is unlikely you have burnt anything out in the distributor.

What is the voltage between the positive coil post and engine earth while the engine is running? Perhaps your alternator isn't charging. Electronic ignitions don't like low voltage. Also check the terminals around the coil, they should be clean and above all, tight. Loose terminals are often the leading cause of poor ignition operation if everything else is working. And when I mean tight, a terminal should resist pulling off with two fingers. Use a pair of pliers to tighten any terminal as required.

Next stop would be to check the ignition switch is working properly. You can hotwire the coil positive direct to the battery, using a toggle switch as a temporary ignition switch. If it goes well then replace the ignition switch as needed.

Failing that if your ignition is actually faulty (very likely, Lucas parts used to die on new Land Rovers all the time) you can replace the Lucas ignition amp with a locally supplied Bosch module. The thread on that is here:

Lucas ignition amplifier replacement by Bosch 024

Not particularly hard to do. I recommend this as a preventative as the Bosch module is considerably more robust than the Lucas one. And cheaper too.

Thanks very much for the response.

Coil +ve gives 13.5v with engine running, same as alternator output, so it all looks OK.

I have now made a new wiring harness from coil to amp, all connections tight and good, but no difference.

Coil +ve direct to battery (and disconnected from ignition) makes no difference, so I am sure the ignition circuitry is OK.

Got a new timing light, the other one must have been faulty, this one is fine.

But the problem is the same, runs fine for a few minutes then misses for a few minutes, then fine again. It is not sparking as the timing light doesn't strobe when it starts to miss. It must be coil/amp/dissy rather than plugs or cables or anything

Tried an other coil and it is exactly the same, so I assume coil is OK.

Gap on the dissy pickup to star wheel is very very small, I guess 0.1mm, I assume it is OK as when it runs it is fine.

I read the other thread regarding the Bosch amp unit. Given that I am back thinking it is the amp breaking down (despite it doing exactly the same thing with two different amps) I read the thread as :

can replace the amp with a bosch BIM024 unit using original DLB198 coil and changing nothing else
OR
can replace with the bosch amp and a MEC717 coil ??? - or is this only for EFI / whatever currently uses the MEC717 coil ?? is it best to replace with a MEC717 as well on a carby and 35D dissy, or to go for one thing at a time and only replce the amp unit first ?

I recently fitted a BIM024 conversion to a stock LR electronic coil, it seems to work just fine. You can use the MEC717 coil if you want, but I suspect the stock coil is more than adequate if you are running petrol only. The ignition system does not care if the vehicle is carby or EFI, the fuel remains the same and there is no influence on timing from a LR ECU in any case.

When you have removed the old amp off the dissy, insert the multimeter probes into the pickup connectors (set m.m to resistance) and manipulate the wires inside. If at any stage the multimeter shows open circuit then you need another dissy/pickup. I have come across a few dead ones recently, but not ones that came good after a while. Dodgy Lucas amps are legion though, about 30% die in various ways in my experience.

Are the leads ok?

Leads are brand new. Doesn't mean they work of course.

I have pushed them all on and wibbled them all about.

Timing light misses on every plug lead in a similar manner, so maybe it is the coil lead ??

I get 2,900 ohm across the distributor pickup wires. I read somewhere it is supposed to be 500 - 1500 ohm ??

At first, if I bent the wires and pulled them about where they enter the pick casing up the resistance flicked randomly from < 500 to > 10K. But now it is a steady and constant 2,870 ohm, bending the wires doesn't change anything. Now I am not sure if maybe there is the problem, or if I had a poor connection on the multimeter or something.

Distributor is fairly new and seems good in all mechanical ways.

I am down to one or more of (or the wiring inbetween) :

coil HT lead
ignition amp (tried two)
coil (tried two)
distributor pick-up

Maybe replace the whole lot at once is the next step.

I am not qualified to comment on the electrics but I can tell you that I spent months trying to get power out of my 3.5 before I finally replaced the fuel pump.

The engine would start and run beautifully, but as soon as I started to go uphill my machine just slowed and slowed until it stopped.

In your case the fuel pump would also have continued to run until the battery was flat so it would have been running without load for quite a while..

I had no way of testing fuel pressure so I assumed what I was getting was good eneough. My pump could put pressure in the line but it could not keep up under load.

BTW the crap in the bottom of the tank may have blocked the filter. A new filter would be a cheap start point.

Having said that, the random electrics you seem to be getting would be the next port of call after the filter, I think.

Good luck.

Jim

The first thing to test here would be the fuel pump.....as stated above....by simply fitting a fuel pressure gauge to the 'T' piece.....and running it up to te windscreen so it's easily visible from the drivers seat.......

Then simply run the car whilst watching the gauge as the problem occurs.....if pressure drop is the cause.....you will be able to see it......

Same can be done by installing an LED to the ignition coil.....if that loses power you can see that as well.......


If it runs for a while then dies......sounds like a fuel starvation problem.....may even be a blocked pickup in the tank.......

Hi have you changed the sparkplug's? my 87 county does not like to sit long and have been using Platinum's and Iridium's, trouble started after going to unleaded, runs rough till I change plugs, I will check whats in at the moment as its been better.
Just one to look at. regards G2