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

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

Author
Discussion

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 30th March 2021
quotequote all
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 thumbup

cavebloke

599 posts

204 months

Tuesday 30th March 2021
quotequote all
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

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 30th March 2021
quotequote all
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

Trevor555

3,460 posts

61 months

Tuesday 30th March 2021
quotequote all
lazyitus said:
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.
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?

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 30th March 2021
quotequote all
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..

Trevor555

3,460 posts

61 months

Tuesday 30th March 2021
quotequote all
lazyitus said:
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..
Wild armchair guess then, I think I'd replace the complete distributor to start with if any of the TVR specialists didn't know what it might be.

Puzzling that it can instantly fix it's self upon restarting the car though.


rigga

7,551 posts

178 months

Tuesday 30th March 2021
quotequote all
Ignition amp

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

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 30th March 2021
quotequote all
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

Original Poster:

19,917 posts

243 months

Tuesday 30th March 2021
quotequote all
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

rigga

7,551 posts

178 months

Tuesday 30th March 2021
quotequote all
Do you have two or three pin as standard

Found this 3 pin trawling an old thread, supposed to be genuine

https://simonbbc.com/lucas-dab118-ignition-module-...

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 30th March 2021
quotequote all
rigga said:
Do you have two or three pin as standard
Will check - cheers mate

rev-erend

21,161 posts

261 months

Wednesday 31st March 2021
quotequote all
My guess would be ignition amp or coil.

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

lazyitus

Original Poster:

19,917 posts

243 months

Wednesday 31st March 2021
quotequote all
rev-erend said:
My guess would be ignition amp or coil.

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

Englishman

2,133 posts

187 months

Wednesday 31st March 2021
quotequote all
rev-erend said:
My guess would be ignition amp or coil.

Also check the low tension wires to / from the coil.
+1 as the fault seems to affect multiple cylinders. Don't forget to check the wires to the coil themselves and connectors both ends for any signs of a partial break.

rev-erend

21,161 posts

261 months

Wednesday 31st March 2021
quotequote all
Try moving the low tension wires about with the car ticking over.

Its a simple check.

scottliv

96 posts

23 months

Wednesday 31st March 2021
quotequote all
If it four it could be the earth line from 1 of the banks of injectors. The earth for these goes via the ECU and there is a separate line for each bank. I have had this and it was caused by the pin receding slightly in the ecu plug. Pulled it home with long nose pliers and it clicked in place. This was not a misfiring but it was running on only 1 bank, but an intermittent connection could cause a similar misfire.

Penelope Stopit

9,778 posts

86 months

Wednesday 31st March 2021
quotequote all
Injector cable shorting to earth will also give a misfire like the one you're experiencing

Once you've proven that the ignition LT and HT is good

If all is good

Will be worth connecting a noid light into each banks injector cables to see if it is one bank going inoperative or staying switched on

Steve_D

13,549 posts

235 months

Thursday 1st April 2021
quotequote all
Sorry a little late into this one.
As Penny said a short on the earth of the injectors will have the injectors of that bank open all the time which ties in with the OP earlier comment about fuel smells.
In the case of our cars I have twice seen the earth wire from cyl. 2 injector short to the underside of the coil mounting bracket. Temperature, vibration, humidity etc. will all contribute to the random nature of the fault.

Steve

Barreti

6,678 posts

214 months

Friday 2nd April 2021
quotequote all
Ignition amp is a cheap and easy fix. So if tests find nothing this would be the first thing I'd replace.
I had similar symptoms on the way to Le Mans one year. An almost imperceptible stutter not long after we set off. Completely stopped right outside the gates of the circuit. We pushed it to one side, walked to the camp to get some bits and when we came back it started ok. It progressively got worse despite changing things like the king lead (another possible source of your issues and simple to swap out with a known good one)
We made it home I'm happy to say, but it was a PITA.

Here's some details of known good Ignition Amps.
https://tvrgriffithpages.wordpress.com/engine/igni...

spitfire4v8

3,822 posts

158 months

Friday 2nd April 2021
quotequote all
When i do my emerald ecu conversions I do a part exchange where i essentially allow the customer 300 pounds part exchange allowance for all their lucas parts .. ecu, airflow meter, distributor, coils and amps, leads, extenders, cap and rotor arms, stepper motors etc etc
What it means is that I have a stock of items I know have come off fully working cars ..

.. you could have a good known ign amp for say a tenner .. all I do is try and recoup my part exchange allowance on all the parts so in effect is a not for profit sale and I hope the mods don't mind this post in this respect. My preference is always for good known parts rather than the pot luck you often have buying new pattern parts ... if you need any parts let me know.