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 13th April 2021
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gavgavgav said:
I could suggest having a random peek inside your ECU, its free to do and you never know what you may find ...
thumbup

saxon

394 posts

227 months

Monday 19th April 2021
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I suffered this exact fault on my pre-cat for over 10 years only mine suffered the misfire so often that it was pretty much unusable i.e. it would happen within 5-10 miles 50% of the time and sometimes wouldn't even restart and neither of two well known TVR dealers/repairers could ever find the fault.

Turned out to be a poor MAF connection on that scart plug type thing that plugs in there. Some scraping and contact cleaning of the terminals on the plug cured it and I haven't had a hiccup out of it in over 2000 miles!!

Found by running the car on the drive and then wobbling/pushing around all the cables/plugs hoses by my engineer. Sometimes the simplest investigative techniques are the best. No barrage of fault code readers or code scanners ever found it - wobbling wires and cables did!

Saxon



Edited by saxon on Monday 19th April 09:29

tofts

409 posts

133 months

Monday 19th April 2021
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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.



Check connection in the vee for ECU water temp signal, will run very rich if it goes High Resistance. (there are two, one for gauge, one for ECU)
Likewise, check in software water temp is largely correct to outline possible failure.
Make sure JPT connector is OK on MAF (as above) often fouls the bonnet which causes broken wires.
Lambda sensors could be shot, check in software for Long and short term fuel map. If either are at 100% then lambda is dodgy BUT this might only be a symptom and not the cause (see below)
IGN amp is worth changing, they are circa £20 and easy peasy, dont fail too often mind you and usually a simptom of a totally loss of IGN rather than a loss of power or poor running.


Slightly less likely but still common:
Camshaft - if your millage is around 70k then likelihood is camshaft is a problem. Lambdas can compensate for a time, but then give up completely when they get clogged
MAF - Can be faulty, only way to know for sure is swap for known good
Stepper/Air leaks - Stepper may not by itself be at fault, but combined with an air leak can send it crashing in to itself trying to compensate and die internally. Once solved, check base idle sans stepper motor, should be circa 500rpm


Unlikely but possible:
ECUS are bullet proof and I see one 14CUX ecu cross my bench for every 100 MBE ecus so pretty much ignore it.
never seen a dodgy injector on any of the V8s I see
Clogged Cats - it does happen, especially if its been running rich. Particularly, the pre-cats break up and clog the post cat.




Edited by tofts on Monday 19th April 12:58

Hoover.

5,965 posts

219 months

Wednesday 21st April 2021
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My car was plagued with an intermittent running issue for a few years, and after having swapped/replaced nearly every sensor and replaceable component known to man and not fixing it...... I was pondering throwing the towel in and getting shot.

BUT having owned my car for so long, and it being "family" I couldn't bring my self to do it.... so a phone call to Dom @ Power and a few weeks later back with a modern ignition system and ECU and have not looked back since.

The 14CUX / wiring loom etc whilst is the control system of the car it is now approaching approx 30 yrs old in some cars, I found cables brittle after they have been cooked by the V8 and way past it's best.

I know there are some champions of the 14CUX, and I commend them for what they have/are achieving....... but sometimes you have to realise when to take an nag out and shot it, and get a nice new filly wink

rev-erend

21,162 posts

261 months

Wednesday 21st April 2021
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Any news of the fix.

Hope you are not living up to your username biggrin

Paulprior

802 posts

82 months

Wednesday 5th May 2021
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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

Paulprior

802 posts

82 months

Friday 11th June 2021
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Hi, any progress on this, I have a similar issue which is rather frustrating

lazyitus

Original Poster:

19,917 posts

243 months

Friday 13th May
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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 thumbup

lazyitus

Original Poster:

19,917 posts

243 months

Friday 13th May
quotequote all
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.

Polly Grigora

9,778 posts

86 months

Saturday 14th May
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spitfire4v8 said:
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.
Was it this very generous offer that sorted it?