Ignition Woes

[aRRon]

OMG what it takes to keep an RRC going reliably! (late 89 with 3.9 and duel fuel)
What I've been thru in the past month.... started with having a plate welded into rusted section of front floor before a trip to Moreton Is. Welder couldn't proceed as smelt and heard LPG escaping from tanks. So twin tanks out for retest and new relief valves ($880). Welding done ($500). New tyres were due as was planned - can't complain as previous Michelin Latitudes gave me 78000km and still just legal. Replaced with Michelin Primacy 235/70/16 for another $850.
Then the massive backfiring in exhaust started under load on LPG as was towing trailer to vehicle ferry. Struggled on running fine on petrol worried that my 35 litre tank would not get me there and back- it did (surprising how little difference in fuel consumption dragging a trailer often in low range through deep sand). Tracked backfiring down (I thought) to a punctured vacuum advance diaphragm. Fitted all new dizzy, as for $80 more the 30 year old unit wasn't worth persevering with and got new cap, rotor with it. Also replaced HT leads. Add another $280. No more backfiring. Starts and runs great...except after half an hour or so when is good and warm then starts to miss, stumble and die outright, Wait 30 minutes til cools a bit and away she goes.
So...final problem appears to be suspect coil or ignition module (Did the Bosch 024 ignition module conversion as per Bee Utey's method and a Bosch HEC 715 transformer type coil about three years ago with great improvement in starting, idling etc).
Resistance in primary and secondary windings in coil check out ok. Earth to module is good and no voltage between module and earth.
My only other idea is to check if voltage is there in LT supply to coil when it's hot and has cut out, indicating that the old LT wiring is losing connectivity when hot.
How do you tell whether it's coil or module?

[Meccles]

I hear you re ignition woes been going through similar thing however my Dizzy is different so not comparable good luck!

[bee utey]

I don't like the new Bosch coils as they're all made in China and the internal insulation breaks down too quickly. Do you still have an OEM Bosch oil filled coil? Also check how hot your module is getting, the heat sink might need improving.

[FisherX]

G'day Bee Utey

I've replaced my ignition module with an MSD Street Fire and MSD coil and haven't looked back.

The original ignition module was working but after a trip to the car wash it left me stranded on the side of the road in peak hour traffic. I needed to push it through a set of lights with the help of the guy behind me and the comments of passing drivers yelling out "should have got a Toyota" made me see red. It only took me 10 min or so to get it running again but this situation is very not satisfactory.

I've had a good result in one of my other cars with the MSD so I decided to fit one to the Rangie as well. It's been great and hasn't had a problem since. It starts easier, idles smoother and is a little better on fuel.

Probably not the cheapest solution at about $250 but it works great.

[aRRon]

Thanks to all the above for sharing your valuable experience. I had a spare Bosch 024 module so swapped it in yesterday as process of elimination. Done 60km so far without a hitch so maybe that was it (famous last words). Thought over your advice Bee Utey and when I fitted the Bosch module I went overboard with a very large Aluminium heatsink from Jaycar. Must have half a sq ft of cooling fins. Made sure I had the white goo under the module and bolted it to the back of the radiator mount panel just in front of air filter canister thinking good airflow there. If further problem will try going back to old oil filled coil.

[Traco]

I'm also using an MSD Blaster2 coil (hooked up to a Scorcher dissy) and it's going well. Also swapped the spade connectors on the coil posts for more secure ring terminals.

[aRRon]

Have now replaced HEC715 coil with a new non-resistor Bosch standard oil filled coil.
Have tried a substitute Bosch 024 ignition module in place of existing one.
As outlined previously - dizzy is new, hi tension leads are new Bosch 8mm. Plugs (NGK BP6ES - one range colder for LPG) cleaned and regapped to .032". Also checked gap at magnetic pick up in dizzy and within specs. Timing is 12 degrees BTDC at idle with vac disconnected.
Manifold vacuum is normal and steady on the needle (no sticking valves or leaking valves).

Still getting major stumbling and power loss on LPG once engine has warmed up (30 minute run with some high speed on freeway). This effect is happening very predictably. Almost cuts out under load. Feels like it's firing on half the cylinders.
Switch to petrol and goes smooth with normal power except under wide open throttle/load when feels like it will start to miss. I'm thinking it has to be weak ignition with the petrol being more forgiving.
Both fuels running ok when cold. Starts and idles perfectly.
Seems like classic failing ignition module - but same with both modules???
I'm wanting to test whether it might be loss of connectivity in ignition low tension wiring when it gets heated up (30 years and 300k original ignition harness = cooked wires inside?)
So I'm planning to run a hot wire straight from battery to +ve terminal on the coil once engine has started and see if it still does it s@#t.
Is anything bad going to happen with electricals if I do this?

If no difference I will try fitting the new Chinese ignition module that came with the dizzy to eliminate the rare possibility I have two bad Bosch 024 modules.

[bee utey]

I suggest that you either run a new ignition positive wire direct from the ignition switch to the coil or run a relay off the existing wire. Power for the relay can come from the battery.

Also the "non-resistor Bosch standard oil filled coil" will not work correctly if it is a points coil as it has the wrong impedance. The part number for a Bosch electronic oil filled coil is BIC290.

[aRRon]

Many thanks yet again Bee Utey for your advice.
Will follow up on coil.