Damage due to plug leads fitted in the wrong order
Discussion
Help! Foolishly I put plug leads 5 and 6 round the wrong way when fitting new leads and tried starting it before I realised the problem. It backfired through the inlet but didn't sound serious. Trouble is now the leads are in the right order it runs like a pig. Won't idle and misses very badly (too bad to actually drive it anywhere). Put the old leads back - same problem. Could the inlet manifold gasket have blown when it backfired? Any other suggestions on what may have gone wrong? (Leads are definitely in the right order now -I've checked them about twenty times against both the Granny manual and the Bible)
You might have blown a manifold gasket.
Morel likely that you have blown a manifold hose off - depending on the car there will be vaccuum hoses working the brake servo, crankcase breather systems, ignition advance etc - one of these could be blown off by a sudden "pressure" instead of vaccuum.
also a possibility that you have bent a valve stem or badly burnt a valve or seat by having ignition at the wrong time in the cycle - although that would normally take a bit longer, usually.
Depends on the length of inlet tract back to the airflow meters as well - you might have blown one out of kilter.
You could try pulling the plug leads off one at atime while the engine is running - if they all have the same effect (ie making the engine run rougher) then you have a vaccuum / airflow problem I would suggest. If there is no difference on just one cylinder then you need to start examining plugs, doing compression checkes etc on that cylinder.
Morel likely that you have blown a manifold hose off - depending on the car there will be vaccuum hoses working the brake servo, crankcase breather systems, ignition advance etc - one of these could be blown off by a sudden "pressure" instead of vaccuum.
also a possibility that you have bent a valve stem or badly burnt a valve or seat by having ignition at the wrong time in the cycle - although that would normally take a bit longer, usually.
Depends on the length of inlet tract back to the airflow meters as well - you might have blown one out of kilter.
You could try pulling the plug leads off one at atime while the engine is running - if they all have the same effect (ie making the engine run rougher) then you have a vaccuum / airflow problem I would suggest. If there is no difference on just one cylinder then you need to start examining plugs, doing compression checkes etc on that cylinder.
Thanks for the info. I have tried removing the plug leads one at a time - same effect throughout. Checked vaccum hoses - all intact. Tried compression test. All the same (but a bit low at 150 psi with Engine cold? - I dare not run it for long). Hopefully this rules out a bent valve. Is there any check I can do on the air flow meters? I did a diagnostic check on the ECU error codes, it showed all was OK. Even re-set it out of desperation - no difference.
you could take them off and have a ok and see if there's any visible damage.
Also an ohm-meter across two of the terminals (don't ask me which ones) should show a progressive increase in resistance as you open and close the mter valve.
You could also plug a vaccuum meter into the manifold - it should sit at around 20" hg at idle.
>> Edited by tvrgit on Sunday 19th September 15:25
Also an ohm-meter across two of the terminals (don't ask me which ones) should show a progressive increase in resistance as you open and close the mter valve.
You could also plug a vaccuum meter into the manifold - it should sit at around 20" hg at idle.
>> Edited by tvrgit on Sunday 19th September 15:25
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