Technical Misfire and weird electrical faults suddenly developed- please help

[Matt Hallw]

Hi, please can you help me?
I recently bought a Punto (2000 X reg) 1.2 16v elx from an old couple, which although a bit rough around the edges, is a low mileage example and looks mechanically solid.
It was running great in the 3 months I’ve owned the car, but suddenly started with a misfire 2 days ago. This misfire got bad really quickly. The misfire happens throughout the Rev range regardless of hot or cold engine temp. Engine also hunting on Tickover.
Added to this misfire, I am getting lots of weird electrical issues. These include:
Speedo needle jumping around.
Rev counter jumping around
Temp gauge jumping around
Warning lights lighting up
Power steering failing.
All issues resolve after switching off and on again, but soon return once I start driving again, especially the misfire.
Car taken to local garage. Unable to get a fault code from ecu. Will not connect to any of the machines or software the garage has, but will allow connection to other modules such as PAS.
Can anyone suggest what I should do next as mechanic is baffled other than suggesting an ecu fault.
Should I get a mobile ecu specialist to check ecu and perform a repair or replacement?
Anything else I should check first?
Given the weird electrical issues, I don’t believe this is anything to do with the coil pack, leads or plugs, but will change these as a matter of course once I have got to the bottom of the current problem. If I am wrong about this, please tell me.
The battery is fully charged, so not convinced that is an issue. Had the battery on an optomate charger which indicates good battery condition and holding charge.
I have read a couple of posts on dodgy earth cables. Could a bad earth cable cause the faults I’m am experiencing along with the misfire?
Any suggestions gratefully received.

 

[jackwhoo]

Yes all of that is pointing to faulty main -ve cable.
Put a new -ve cable from battery -ve post to engine/ gearbox AND from engine/ gearbox to vehicle body. Make sure the mounting points are clean.

Please let us know how you get on.

 

[Matt Hallw]

Thank you for your reply.
I will try this tomorrow and will update.
Maybe a stupid question, but could an earthing cable have been disturbed when my new exhaust was fitted a week ago or are the main earthing cables in the engine bay only?

 

[Matt Hallw]

Earth cables checked. No obvious issues, connections all look ok.
Checked fuse box, no obvious symptoms of damp. All sprayed with contact cleaner.
Disconnected battery to try and reset ecu. No difference made.
Not sure if I should go buy a set of plugs next? Will pull them out later and inspect.
Misfire behaving much more like a plug or lead today. So not sure what to do. Still unable to get a reading from ecu.

 

[judderbar]

power steering works independantly of the engine ECU. Likely to be a wiring problem. A failed alternator diode will produce a noisy voltage which might cause problems with electronics. Power steering is very sensitive to an alternator not charging properly. I suppose the mechanic must have checked the battery voltage with the engine running? It should be very near to 14 volts with some revs even if you have a few switches on. Does the radio work ok?

 

[Matt Hallw]

Battery checked and OK. I’ll do a check myself with the multimeter tomorrow.
Radio doesn’t work properly, hasn’t done since I got the car. Seems to have a permanent live feed and right door tweeter making nasty crackling noises. I replaced both door speakers as they had perished, the radio was ok for a while then issue with nasty crackling again. I assumed a blown tweeter. Could this be a sign of something else?
Plugs pulled out. All look like fairly recent replacements. All NGK R plugs. Gaps slightly large, so regapped to 0.9mm. Number 4 was only hand tight.
The leads look recent, but look like cheap unbranded stuff. Came to put No3 lead back on and it came apart!
Took No3 lead off completely. Although only running on 3 cylinders, it is now a consistent misfire. No hunting and no weird electrical issues with the gauges!
Took it for a run on 3 cylinders. No more kangarooing - Again, seems to be running consistently on 3 cylinders and electrical gremlins vanished.
So, maybe lead 3 was arcing out?
I will try and get a new set of leads tomorrow and see if that sorts it out.
I will update once done.
Maybe a simple fix after all? Can a bad lead really cause the gauges to all go crazy?

 

[chris3234]

Battery checked and OK. I’ll do a check myself with the multimeter tomorrow.
Radio doesn’t work properly, hasn’t done since I got the car. Seems to have a permanent live feed and right door tweeter making nasty crackling noises. I replaced both door speakers as they had perished, the radio was ok for a while then issue with nasty crackling again. I assumed a blown tweeter. Could this be a sign of something else?
Plugs pulled out. All look like fairly recent replacements. All NGK R plugs. Gaps slightly large, so regapped to 0.9mm. Number 4 was only hand tight.
The leads look recent, but look like cheap unbranded stuff. Came to put No3 lead back on and it came apart!
Took No3 lead off completely. Although only running on 3 cylinders, it is now a consistent misfire. No hunting and no weird electrical issues with the gauges!
Took it for a run on 3 cylinders. No more kangarooing - Again, seems to be running consistently on 3 cylinders and electrical gremlins vanished.
So, maybe lead 3 was arcing out?
I will try and get a new set of leads tomorrow and see if that sorts it out.
I will update once done.
Maybe a simple fix after all? Can a bad lead really cause the gauges to all go crazy?

Definitely high voltage electric arcs can cause massive RF/EM interfenace that cause causes a lot of strange electrical issues
Not to mention if the voltage is jumping into other circuit's

 

[Matt Hallw]

Are Halfords leads worth bothering with or wait and order a set of Bosh leads with coils from Europarts?

 

[judderbar]

It might help you to know these engines are using the spark plugs with the wasted spark method. So there are only two control wires going to the coil to operate 4 plugs. Two plugs fire at the same time. but only one plug is firing at the correct fuel and air compression moment.


Your car has a single coil block but it has two earth connections for spark control and one 12V connection. So if you can find a way to electrically swap the earth control wires the engine will still run perfectly normally if there are no problems. The only difference will be fault codes will be reported for the wrong cylinders.


So if you have one cylinder not working you can reverse the earth connections on the coils to make sure it is a coil fault rather than an engine fault. If it is a coil fault the faulty cylinder will move to another cylinder and the previous one will work fine. if it is a lead or plug it will not change the result.


This test is much easier on the 8v car because the coil packs are separate and there are two plugs which can be reversed. Your car has only one plug with one 12V wire and two earth control wires. Once you turn the ignition on the coil plug has a permanent 12V in one of the wires. The other wires are then the earth wires.

 

[Matt Hallw]

New leads fitted. Now no spark on cylinder 3.
Tried swapping plugs and leads, still no spark.
Can a coil pack go down on one cylinder?
Tried to order a coil pack with the leads, but out of stock. Stuck without transport which is causing me huge problems. Any ideas what to try next.
When I was investigating the other day, cylinder 3 was sparking. What is going on?

 

[varesecrazy]

Earth cables tend to fail internally.. so looking clean on the outdide masks crumbly green copper

Long time since I had a 4way coil fail

But think it may have dumped a cylinder

Can you swap cables around.. to check its not a bad HT cable ?