A problem I've had for years - misfire help!

[lazyitus]

I've had this issue for years, intermittently. Once went a year without issue but invariably, it's always been there.

Driving along, the car starts to seriously misfire resulting in a massive lack of power and a stench of unburnt fuel. Normally cured by pulling over, turning the engine off and then restarting..

I can drive for 2 hours with no issue.
I can then drive for 1 hour with one issue.
I could then drive for 1 hour with 5 issues.
I could then drive for 3 hours with no issue.

Best shots guys, please !!

I need to sort this. I've put up with it as I love the car. But it's not ideal. Apart from this, it's been mega reliable. But with these smart motorways everywhere, I can't afford to be pulling over on the inside lane to stop and start etc.

TIA

[lazyitus]

cavebloke said:

Is it just one cylinder that drops out and is it always the same one? My first guess would be heat affecting the spark leads.
Cheers,
Simon

Couldn't say, Simon. It's more like 4 or 6 are dropping out. It's certainly not just 1. Thanks

[lazyitus]

Trevor555 said:

I had a similar issue once to what you describe, restarted the car as was instantly fine , but it wasn't a Griff.

It turned out to be a sticky valve.

But I guess one sticky valve on a V8 wouldn't cause a huge missfire?

No, I doubt it. This seems more electrical related to me. Not that I know. Hence it's never been found yet..

[lazyitus]

Trevor555 said:

Wild armchair guess then, I think I'd replace the complete distributor to start with.

Had many new ones over the years. Ain't that !

[lazyitus]

rigga said:

Ignition amp

Used to get similar, random incidents, replaced the amp with a genuine lucas item, not happened since.

Any idea of the proper Lucas part number for a 95 onwards 500 ?

Edited by lazyitus on Tuesday 30th March 22:35

[lazyitus]

rigga said:

Do you have two or three pin as standard

Will check - cheers mate

[lazyitus]

rev-erend said:

My guess would be ignition amp or coil.

Also check the low tension wires to / from the coil.

[lazyitus]

bearman68 said:

Ahhhhhhhhhh!!!!!.

God I get so cross with this type of ste.

How do we all solve a problem.....?

st! A perfect genius to whom I’m sorry that I disturbed your evening with my question.

Thanks to the other posts folks, I’ll systematically try things which have been suggested.

[lazyitus]

blitzracing said:

What does the tacho do as it dies? A failing amp will give you an erratic or no RPM signal, even if you are rolling to a stop with a smooth decrease of actual engine RPM.

Often erratic

[lazyitus]

rev-erend said:

Any news from your checks over the weekend?

Waiting for my ignition amp, this is the next thing to try by the looks of things

[lazyitus]

Zener said:

If you are connecting your Pico Scope to the ign low tension side make sure you use an attenuator otherwise you can damage the scope with a transient voltage spike , you have been warned

Thanks - I'm not technically gifted with these matters but I'll take note even if I'm not sure what you're on about

[lazyitus]

das2000m said:

I had a very similar problem with my last Griff....it would sometimes run for long enough then start misfiring and loosing power ..... it always came ok again until once it died completely and had to be recovered by the RAC. Once home and off the back of the transporter and pushed into the garage the car started and ran perfectly!! I eventually found the issue by chance whilst troubleshooting with the ignition on .....every time I touched the multi plug that goes to the immobiliser patch lead (loom side) the ignition would flash on and off. It ended up being a bad joint where one of the wires were crimped to a pin.
Hope you find the cause of your problem soon.....intermittent faults are hard to trace.

I always thought it may be to do with a wire somewhere. Thanks for your input, das.

[lazyitus]

Zener said:

If you suspect a wire failure then carry out a wiggle test whilst the vehicle is running , at wiring and termination junctions

Thanks Zener

[lazyitus]

gavgavgav said:

I could suggest having a random peek inside your ECU, its free to do and you never know what you may find ...

[lazyitus]

tofts said:

Off top of my head without reading through the whole post and replying to OP:

primary cause I see for running issues:

Leads and extenders. if you have original leads or you have extenders. Bin them now before you check ANYTHING ELSE and buy the accel ceramic leads on the Racing green site. Money well spent. Also, never buy magnacore, they are rubbish even brand new and as a garage I would never fit them. Ever. Likewise, if they are fitted, bin them, they are crap.
Make sure center spring in distributor cap is OK, clean terminals and rotor arm whilst there.
ONLY once this is done should you go through the following list.

So, after replacing leads, dizzy, rotor and plugs, I found that 2 shrouds / extenders looked to be cracked and not entirely in good shape. I sourced 2 good used ones from top man Spitfire4v8.

Touch wood, I think the problem has been resolved! Been on 20 trips without issue since replacing them.

Actually so chuffed as it really was a bloody headache which I’d come to accept. Fantastic. Thanks to everyone for their input

[lazyitus]

Paulprior said:

What happens if you just keep driving rather than stop and restart, on mine it would start to work ok again after 1 or 2 minutes

I didn’t ever keep going as it became slow and rough. Hopefully my answer above this could be the solution for you.