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

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

Author
Discussion

blitzracing

6,297 posts

197 months

Friday 2nd April 2021
quotequote all
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.

blitzracing

6,297 posts

197 months

Friday 2nd April 2021
quotequote all
Another thought, you could invest in two sets of test plug caps and quickly see if the spark has died on any cylinder when it happens. I have no idea how heat proof they are, or if you could fit them in place if the extenders, but the outlay for instant diagnosis is pretty small.

https://www.ebay.co.uk/itm/Sparkrite-Spark-Plug-Ht...

bearman68

3,775 posts

109 months

Friday 2nd April 2021
quotequote all
Ahhhhhhhhhh!!!!!.

God I get so cross with this type of ste.

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

Method1. Change everything until we luck out.

Method 2. Test things until we can find data to support an idea.

I would hazard a guess the primary ignition circuit is going down - how about monitoring (let's say) the primary circuit to see if that is up and good before committing to further expense?

If you think it's something else, let's get a test plan together to check the idea. Just think what a difference this idea would make to society.

lazyitus

Original Poster:

19,917 posts

243 months

Friday 2nd April 2021
quotequote all
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.

Penelope Stopit

9,778 posts

86 months

Friday 2nd April 2021
quotequote all
bearman68 said:
Ahhhhhhhhhh!!!!!.

God I get so cross with this type of ste.

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

Method1. Change everything until we luck out.

Method 2. Test things until we can find data to support an idea.

I would hazard a guess the primary ignition circuit is going down - how about monitoring (let's say) the primary circuit to see if that is up and good before committing to further expense?

If you think it's something else, let's get a test plan together to check the idea. Just think what a difference this idea would make to society.
There is nothing that pisses me off more than someone who to begin with posts much logic and ends the post with a guesssmile

bearman68

3,775 posts

109 months

Saturday 3rd April 2021
quotequote all
Penelope Stopit said:
There is nothing that pisses me off more than someone who to begin with posts much logic and ends the post with a guesssmile
A victim of my own arrogance of course.

But a theory followed by testing is the way to go.

I've got one of these...
https://www.ebay.co.uk/itm/PicoScope-4425A-Automot...

but I suspect there's cheaper Chinese copies that work nearly as well, and there will be other ways of testing

blitzracing

6,297 posts

197 months

Sunday 4th April 2021
quotequote all
Be careful with scopes and ignition primary circuits, although it all appears to be at 12 v the back EMF of the coil primary is between 150 and 300 volts as the coil discharges, that will fry a scope input without attenuation .Bitter experience I'm afraid.

Barreti

6,678 posts

214 months

Sunday 4th April 2021
quotequote all
bearman68 said:
Ahhhhhhhhhh!!!!!.

God I get so cross with this type of ste.

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

Method1. Change everything until we luck out.

Method 2. Test things until we can find data to support an idea.

I would hazard a guess the primary ignition circuit is going down - how about monitoring (let's say) the primary circuit to see if that is up and good before committing to further expense?

If you think it's something else, let's get a test plan together to check the idea. Just think what a difference this idea would make to society.
His issue is very intermittent. How do you propose to test or monitor for something where there is no discernible pattern.
I recommend always carrying spares of certain things. An Ignition Amp being one, a dizzy cap, king lead and longest HT lead being a few more. None are expensive and all would help rule out potential issues in this case.


blitzracing

6,297 posts

197 months

Sunday 4th April 2021
quotequote all
Low tension ? The rev counter is running all the time, so just make note when it happens. Plug caps that show HT? If they can last long enough to show the point that you do or don't have HT, assuming you can open the bonnet in time, job done.

Zener

18,368 posts

198 months

Monday 5th April 2021
quotequote all
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

rev-erend

21,161 posts

261 months

Tuesday 6th April 2021
quotequote all
Any news from your checks over the weekend?

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 6th April 2021
quotequote all
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

Original Poster:

19,917 posts

243 months

Tuesday 6th April 2021
quotequote all
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

Original Poster:

19,917 posts

243 months

Tuesday 6th April 2021
quotequote all
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 laugh

Zener

18,368 posts

198 months

Tuesday 6th April 2021
quotequote all
lazyitus said:
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 laugh
Without going into detail here I'm sure the Picoscope forums can help you (I use a Pico also) or the test function tab within their own software, failing that lots of diagnostic info on Youtube etc , primary coil voltage spikes can be multiplied into the 100's volts briefly yikes so do your homework before going this route Pico Scopes are not cheap as I'm sure your well aware but you can get so much info used correctly

das2000m

222 posts

259 months

Saturday 10th April 2021
quotequote all
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.

lazyitus

Original Poster:

19,917 posts

243 months

Sunday 11th April 2021
quotequote all
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.

Zener

18,368 posts

198 months

Sunday 11th April 2021
quotequote all
If you suspect a wire failure then carry out a wiggle test whilst the vehicle is running , at wiring and termination junctions

gavgavgav

1,530 posts

206 months

Tuesday 13th April 2021
quotequote all
I could suggest having a random peek inside your ECU, its free to do and you never know what you may find ...

lazyitus

Original Poster:

19,917 posts

243 months

Tuesday 13th April 2021
quotequote all
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