Golf MK4 Misfire

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Golf MK4 Misfire

Postby Tmparry01 » Tue Mar 19, 2013 8:20 pm

Hi there,

I have a Golf mk4 1.8T with a 'high boost' misfire.

Above 10psi the car will produse a high frequency misfire, throwing out back smoke / unburned fuel from the exhasut.

All 4 plugs are sooty from the misfire.

I've interchanged the following parts with no improvement:- MAF, Lambda, Fuel pump/filter/injectors/fpr, dvwastegate solenoid (n75), checked for boost leaks, changed ECU, and more.

I think it may be weak spark.....any ideas? Any where to get it tested in Yorkshire (UK)?
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Re: Golf MK4 Misfire

Postby arjen » Tue Mar 19, 2013 8:58 pm

Do you have any fault codes?
And have you replaced the spark plugs?
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Re: Golf MK4 Misfire

Postby AuthorMike » Tue Mar 19, 2013 9:05 pm

The 1.8 20VT engine is one of favorites...I've owned, fixed and modified 5 of these in various forms...

10psi is perhaps right for standard turbo and standard mapping, if its a K03S turbo. I think the K03 turbo boosts lower around 7psi...

Also if I recall back to my SEAT days, you get various types of N75 valves, each affecting the boost level.

The standard bosch recirc valves are known to be a weak spot on these engines too, often replaced by a Forge 007P or similar.

MAFs are known to be problems as are the ignition coils, but it seems you have interchanged most of these parts.

What error codes do you see? What is the history of the car? Do you have VAG-COM to possibly read the live data measuring blocks?
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Re: Golf MK4 Misfire

Postby AuthorMike » Wed Mar 20, 2013 8:57 am

HI - Just reading this again this morning, did the interchanged parts come from another 1.8 20VT MK4 Golf?

I ask as the 1.8T appears in various models, with varying power outputs (from 150bhp to 225bhp [standard figures]), varying components, and even layout.
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Re: Golf MK4 Misfire

Postby mteste03 » Wed Mar 20, 2013 12:01 pm

Hi,

Could you give the engine code as there are about 5 differnt engine codes on the mk4 1.8T.

Think the early AGU had an ign amp that was prone to cause problems. Also on most engine codes ign coils and coil wiring harness caused problems.

Becareful changing lots of parts as I have seen many times a new fault caused from disturbing a componet; then you have two faults together which can make the whole process much harder.

Your most cost effective way maybe to find a good garage or mobile tech who has VAG- COM / Autologic and a picoscope, ask them to do a basic check of ign system and move on from there.

Matt

ps these ign coils are easily damaged so take care swapping them. DO NOT BEND OR TWIST to remove them.
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Re: Golf MK4 Misfire

Postby Tmparry01 » Fri Mar 22, 2013 2:10 pm

Hi sorry for the late reply.
Car is the early AGU variant. K04 turbo upgrade was running 270bhp for about 10k miles until misfire. Yep I changes ignition amp and plugs the first things I tried. Vagcom scan doesn't bring up any fault codes. I think I need to find someone to test the ignition system.... Preferably under load as that's the only time it misfires? Any recommendations in West yorkshire area?
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Re: Golf MK4 Misfire

Postby AuthorMike » Fri Mar 22, 2013 2:45 pm

Ahh K04 upgrade. Good choice, but not without its trickyness. Do you know who mapped the car?

If you use the measuring blocks in VAGCOM could you do a road test, in 4th gear from low revs to high... although for that you may need a private runway, so a rolling road would be better.

http://www.ross-tech.com/vag-com/m_blocks/010-019.html
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Re: Golf MK4 Misfire

Postby Robski » Fri Mar 22, 2013 3:24 pm

Vagcom scan doesn't bring up any fault codes


Had a top quality remap has it ?

Preferably under load as that's the only time it misfires?


Someone with a rolling road would be ideal, however the system can be forced under load :wink:
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