Bag of crisps anyone?

[eileandour]

Hi, I’m a long time lurker, first time poster impressed by all the knowledge and expertise I find here. I wonder if I could pick your brains?

I have a Falcon 23 with a Volvo V8 petrol engine. It recently began running like a bag of crisps. I tried all the usual things like replacing the distributor cap and eventually traced it to the electronic ignition module situated in the distributor.

So far I’ve had two new replacement modules, neither of which will work. My old spare module does work when it is cold but breaks down when it heats up. My suppliers took an old module off a running second hand engine but no luck there either. He also told me it is possible to get a faulty batch of new modules and I might just have been unlucky. Basically , old one in runs for a while, new one in complete dead duck.

Has anyone had a similar experience or would you know if there has been an update in the manufacture of the part and might I need another part to make the module work?

Many thanks

 

[No1_Moose]

Thai sweet chilli please

 

[Col]

First thoughts. I would say your looking in the wrong place. If you have tried several new ones and a known good old one, maybe problem lies else where. Can we have some more info? How have you diagnosed. What engine (exact model) and age? Might be able to help with a bit more info?

 

[adrianb]

- as a previous lurker you should know that Col is your man - see above !

Welcome to the forum BTW.


Adrian
www.cleanandshiny.co.uk

 

[eileandour]

Hi Col,

With old module boat only runs well until it heats up then it breaks down. I have diagnosed by using manual and multi meter. Found the module to be faulty. I replaced this module eight years ago using the same diagnostic measures and it cured the problem I was having at that time.

The engine is a Volvo 500A, serial number 4100123766868269 year 1991 based on General Motors short block chevvy.

To recap, I have three modules.

1. Makes it run like a bag of crisps all the time(currently in use)
2. Runs okaywhen cold, bag of crisps when warm (old back up)
3. Doesn't even fart or bang.(brand new)

 

[Lakesailor]

Might be right off track here, but have you tried new HT leads? Particularly the king lead. It may be that it has a high resistance and some modules will overcome it and others not.

Just a thought.

 

[eileandour]

Thanks for your suggestion LakeSailor I will try that next time I am at the boat. I've had the cap off & on so many times that I'm thinking of fitting wing nuts!

 

[Col]

OK 5ltr small block with a carb.
I count 4 modules tried- 2X new ones 1X old spare (yours) & 1X old off running engine from supplier. Is this correct?
While not impossible, I would say rare.
Modules do tend to act up when warm as they start breaking down, but sometimes you get a mindset on a particular component and end up not seeing the wood for the trees.

What do you mean by "running like a packet of crisps"? Misfire? Backfire? Have you also looked at ign coil & HT leads (as Lakey said) Have you checked plug and wiring to module? Or even choke mechanism sticking on (as I don't know what a packet of crisps runs like)

 

[eileandour]

Boat was running perfectly then it started to run rough dropping cylinders the same as if there was moisture in the distributor cap - my first thoughts were a cracked cap so this was replaced with a new one. This did not fix the problem so I reached for my meter to check the ignition system more throughly as I had done several years before.This led me to conclude that the module was faulty.Being a squirrel I looked for my old module & fitted it & engine started & ran well so I ordered a new part being pretty sure this was the problem.I have checked the battery it's ok,new spark plugs were fitted 10 hours ago & appear ok perhaps the leads are shot but I would have thought they would have the same effect on both modules it is most perplexing!

 

[eileandour]

By the way I forgot to say I checked that the auto choke was going off & it appears to be working ok.The coil appears to check out ok as well

 

[alb40]

A friend of mine boat also does this. Last time, it was trapped water in the fuel and filter, but havent diagnosed this time just yet as havent had time to look at it.

 

[Col]

Just a thought. Did you use heatsink grease under module? It can help if you do

 

[eileandour]

Thanks for the tip Col

 

[Will33]

A friend of mine has the V8 in a Falcon, had similar problems driving them nuts!! A new condenser fixed the problem and the engine has run fine ever since.

Will

 

[Shuggy]

Changing the coil is so cheap it's got to be worth doing. It transformed my Land Rover V8 when I was having problems about 3 years ago. I couldn't trace the problem but it was awful when warm. Turns out the internal coil insulation was shot. Took me 2 weeks to work it out though...

 

[davedpc]

Have you got the wrong coil i.e ballast or 12v or is there a track down the rotor arm? Its worth changing the lot is it not? A similar fault beset me once when a so called 'mate' strapped up my secondarys with cable ties in my absince. Dave.

 

[spannerman]

You have to work backwards and having had the engine run OK for a while on other modules that then eliminates everything from the plugs and leads back to the dizzy cap, you next have to consider the components which are in use no matter which cylinder is firing, that is module, rotor, coil, king lead.
You have tried numerous modules and allowing for the variation in these, you then are left with the kinglead which if faulty should break down no matter which module is fitted, same with the rotor. The coil though is susceptible to thermal breakdown and internal shorting which could give you a misleading fault diagnosis about the module, or could have the wrong voltage if the ballast resistor is faulty.
Does the rev counter go beserk when it misfires, try disconnecting the rev counter wire on the neg side of the coil to eliminate that item.
This engine has a ballast coil I think with a thick (green?)resistor wire from the alternator to the ballast resisitor, check you have the correct voltages at the pos side of the coil when cranking and running as I have had these go down on several V8's. The neg side will be in the kv range so set your multimeter correctly.This is where the coil goes to earth through the module so make sure the module has a good earth in the dizzy.
Seeing that you have tried so many modules I feel that the problem lies in the coil, ballast resistor/wiring.

 

[eileandour]

Hi spannerman,the rev counter does not go mad it just drops down as cylinders fail. I don't think there is a ballast resistor but I will check this again as I remember having problems with a mercruiser I had in the past. On Sunday I will have another go starting with battery voltage & working through the system changing coil & leads etc. & metering voltages.Hopefully something will come to light - many thanks for your input & suggestions

 

[Lakesailor]

[ QUOTE ]
having had the engine run OK for a while on other modules that then eliminates everything from the plugs and leads back to the dizzy cap

[/ QUOTE ] That would only be true if the HT leads were not breaking down as they warmed up. He has a situation where the motor runs rougher as it heats up. That could be extra resistance in the HT leads as the current struggles to overcome an initial level of resistance.
I'd go with other people and change the lot. But do it in order and check as you go.
I've had coils that only misbehave at revs. I've had condensers that tick over well but won't allow the motor to pick up.

 

[Col]

Who was that eh?/forums/images/graemlins/laugh.gif