6N2 misfire.... end of life help!

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Paul R W
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Joined: Wed Jun 12, 2019 7:21 pm
Drives: 6N2 1.4 petrol 5 door
Location: Kent

6N2 misfire.... end of life help!

Post by Paul R W » Wed Jun 12, 2019 7:49 pm

Hello all, my first post here... thanks in advance for any help!

6N2, 1.4 petrol, 5 door... has served me well but may be heading for the scrap yard if I can't sort this one out.

Rather than embark on an essay I'll list relevant info relating to the problem I've been chasing for the best part
of 9 months now, during which time it's got progressively worse.

Misfire on cylinder 3 when ticking over.
Engine warning light on 80% of the time.
Injector stops working after tickover of more than a few minutes
but comes back into action after restarting the engine.

Leads, plugs and coil have all been replaced.
Compression good.
Injector replaced.
ECU cloned and replaced.

I'm not great with electrics but I've done my best to check the injector loom
and there's nothing that seems obviously out of place, plus the problem doesn't
seem intermittent enough to suggest a dodgy connection... but I'm open to
suggestions!

Also, it t might be coincidental but when I replaced the spark plugs the one on cylinder
3 failed after about 3 months.

Thanks again for your time... I look forward to any suggestions prior to launching
it off Beachy Head!

Paul

937carrera
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Posts: 308
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: 6N2 misfire.... end of life help!

Post by 937carrera » Thu Jun 13, 2019 6:40 pm

Welcome :)

So easy question first, and then some more:

Yyou say the engine management light is on 80% of the time. Have you read what codes are being stored.

What were the compression readings, have you had a leak test done.

Any coolant consumption

How do you know the injector stops working.......... have you seen it stop injecting fuel, or are you assuming that because of the misfire.

Paul R W
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Posts: 5
Joined: Wed Jun 12, 2019 7:21 pm
Drives: 6N2 1.4 petrol 5 door
Location: Kent

Re: 6N2 misfire.... end of life help!

Post by Paul R W » Thu Jun 13, 2019 8:25 pm

Thanks for chipping in 937carrera


Code reader said misfire on cylinder 03.

Haven't got the readings to hand this evening.... no leak test done.

No coolant being used.

Injector diagnosed by using a long screwdriver as a stethoscope and holding it against
each injector in turn (and holding the handle against my ear) while the engine was ticking over.
No 3 injector goes silent (ie no 'clicking' noise) after a couple of minutes tick over.

Question....does the ECU switch off the injector if it registers a persistent misfire?

Cheers

Paul

937carrera
Silver Member
Posts: 308
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: 6N2 misfire.... end of life help!

Post by 937carrera » Thu Jun 13, 2019 8:38 pm

Can you remember which P code errors were shown ?

I don't know about switching the injector off, but I doubt it.

No coolant use rules out a HG leak.

Have you tried running the engine on 3 with the electrical connection off, then reconnecting it and listening to the injector as you do that ?

I was thinking some mechanical problem but with the diagnostics you have done so far I'm thinking something else now.

I assume you have swapped injectors around and the problem stays on number 3 ?

Paul R W
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Posts: 5
Joined: Wed Jun 12, 2019 7:21 pm
Drives: 6N2 1.4 petrol 5 door
Location: Kent

Re: 6N2 misfire.... end of life help!

Post by Paul R W » Thu Jun 13, 2019 9:07 pm

Can't remember the P codes unfortunately but the ex VW mechanic who ran his computer
on the car was equally flummoxed after a few days of fiddling!

Haven't tried running it on 3 and reconnecting it, but after ticking over for a long while
at traffic lights I then usually pull away on 3 cylinders, if I switch the engine off and restart,
it fires on all 4 no problem. I now keep my revs up slightly at lights and it keeps firing on all
cylinders during tick over.

I would say that the problems seems worse in warm weather.

Yes, the pesky problem persists on no.3 if I swap the injectors :evil: :evil: :evil: :evil:

937carrera
Silver Member
Posts: 308
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: 6N2 misfire.... end of life help!

Post by 937carrera » Thu Jun 13, 2019 9:19 pm

Hmm, I think we're going to struggle without knowing the OBD codes.

I'm thinking it is a loom problem, but haven't got my head around why the problem isn't there when you run the engine above tickover.

Have you done continuity tests on the loom from the ECU connections to each injector - 8 tests in total

937carrera
Silver Member
Posts: 308
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: 6N2 misfire.... end of life help!

Post by 937carrera » Thu Jun 13, 2019 9:26 pm

this may help
Attachments
injectors.jpg

Paul R W
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Re: 6N2 misfire.... end of life help!

Post by Paul R W » Fri Jun 14, 2019 7:58 am

That's really helpful, many thanks carrera!

Like I said, electrics are not my strong point... up until now I've stuck a probe
into the injector connector and then the other end into the wire that goes
into the ECU and got good continuity on each one... anything else I should be doing?

Cheers again!

937carrera
Silver Member
Posts: 308
Joined: Sat May 17, 2014 8:19 am
Drives: 2000 Polo GTi
Location: North Yorkshire

Re: 6N2 misfire.... end of life help!

Post by 937carrera » Fri Jun 14, 2019 8:22 am

Well, there are two approaches:

Continuity - resistance for each connection (fuse to injector, injector to ECU) should be no more than 1.5 ohms.

The other way is to actually measure the voltage being delivered to the injector. The approved procedure talks about using an LED test lamp and measuring with the engine cranking so will probably need an assistant. Using a meter I would expect to see something like 11v as there will be voltage drop due to the starter operating.

An alternate way is to have the engine running, then pull each connector off in turn and measuring the voltage, engine running. Terminals 1 to a good earth.

From the above checks you can deduce that the duty cycle pulse for the injectors is provided by the switching of the earth route within the ECU.

Once those checks are done, I would also inspect the two block connectors between the fuse and the injectors. Measure first, inspect, re-measure & run. If you fix it you want to know why !

There's a few diagnostic tips for you to do now, I assume the error codes will return shortly so could you please get those read and posted. If you don't have access to a reader then you can get a generic one for £10-£15 off ebay or if you have a laptop you can buy a lead and download VCDS-Lite

Paul R W
New
Posts: 5
Joined: Wed Jun 12, 2019 7:21 pm
Drives: 6N2 1.4 petrol 5 door
Location: Kent

Re: 6N2 misfire.... end of life help!

Post by Paul R W » Fri Jun 14, 2019 4:17 pm

That's all really really helpful many thanks!

I'll prod further with the wiring and report back after the weekend.....

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