20vt running on 3 cylinders constantly :(

[Orkius 10]

I seriously need some help on this, i'm at a complete loss..

 

i'm hoping one of you guys running 20vt's may have some experience with this.

 

I have a auq motor using qpeng management. it has been running fine for nearly a year now but has developed a constant misfire on cylinder 4. so at the moment it's running on just 3.

it holds idle and doesn't smoke but clearly is running on 3 cylinders. don't appear to be losing oil or coolant either.

 

so far I have swapped the coil packs over and replaced the plugs. they all work fine in the other 3 positions and the problem has not moved. I have had the spark plug out and grounded and its getting a spark. I have also swapped round the injectors with the same results and can here and feel it working.

 

I have also replaced the coil pack loom, as there were plenty of cracked exposed wires. this has not had any effect. the coolant temp sensor is fairly new also.

 

I know my downpipe is cracked, but im ruling this out along with vac/boost leaks as I would think this would affect the general running, not just concentrated on 1 cylinder.

 

the weird thing is that it was playing up before with the same problem. it then cleared its self and ran normal for a few days and then started again. this leads me to think it's an electrical fault but I have run out of ideas

 

im getting to the point where I think there is something up with the ecu, but have no idea what? anyone come across one of these failing?

 

any ideas or advice greatly appreciated

[Harrier 1]

I would get a compression check done next .

[GrahamU 6]

Have you checked the injectors and their wiring?

 

The qpeng ECUs have a diagnostics on the CAN bus output I believe, have you checked that?

[Dox 23]

Is the plug for cyl 4 getting wet with fuel?

[Orkius 10]

Thanks for the replies. Compression test is going to be the next thing.was hoping it wouldn't come to that.

 

Unfortunately I havent invested in the diagnostic reader and have yet to buy the plug for it.

The injectors is definitely getting 12v and signal, tested with meter and you can feel and hear it working.

Plug comes out but is not covered in fuel, rather a light coating of oil.

Think I might have to see what the compression test shows but I'm not expecting good news.

[southerner88 10]

Had a similar issue with my mk4 golf (20vt) the inner rocker cover gasket had cracked and split, causing oil to leak into the spark plug housing. replaced the gasket and cleaned up the housing and havnt had a problem for the 2 months since doing it.

[Orkius 10]

Thanks southerner88 .Will double check that. Don't recall seeing any oil down the hole before But worth checking

[carrots 1]

i am no expert but i am sure ive read somewhere it could be the ignition module

[Orkius 10]

thanks carrots, i have read this too while researching the problem. however, and i stand to be corrected, i'm sure mine doesn't have this as it's an AUQ engine code. i believe the ignition modules were used on the earlier AGU code engines.

[Kevin Bacon 5]

Plug comes out but is not covered in fuel, rather a light coating of oil

 

That is never a good sign.

 

Had the same symptom on my first VR6 Turbo engine on cyl 6. The bore was scratched allowing oil into the combustion chamber and fouling the plug.

[Orkius 10]

Cheers Kevin bacon. That sounds pretty terminal. I guess you can't just polish that kinda thing out?

Hoping it may be something a bit simpler like head gasket...

[Kevin Bacon 5]

20VTs aren't known for lunching HGs (unless they run into mega det). I hope it isn't a bore / ring issue.

 

Good excuse to upgrade to a BAM if it is though :D

[Orkius 10]

So. Compression test done. Done about 3 reads per cylinder. Reads are:

Cyl 1 . 165

Cyl 2 . 163

Cyl 3 . 156

Cyl 4 . 160

 

stayed constant. Reads look ok from my research. Bit low on Cyl 3 but within tolerance I believe. Plus the problem appeared to be on no. 4.

That's one thing ruled out so I guess this must be electrical of some sort. :scratch:

[GrahamU 6]

Plug comes out but is not covered in fuel, rather a light coating of oil.

 

 

I'm still thinking its fuel, either blocked injector or bad electrical feed to injector

[Kevin Bacon 5]

Compressions are OK then, so that's good. My old 9N3 Polo GTI never had even a hint of oil on it's plugs, hence why I was a little concerned by that post.

 

Trouble is though, if you've moved the coil and injector from cylinder 4 to a different one and the problem didn't follow it, it's either a bad injector / coil driver in the ECU, or a mechanical fault I that cylinder.

[Dox 23]

Have you seen a spark at the plug on cyl 4? It could be no spark and the ecu cuts the fuel to that injector?

 

I use a jump lead to make checking for a spark easier

 

 

The other end of the jump lead is earthed on the block

[Orkius 10]

Trouble is though, if you've moved the coil and injector from cylinder 4 to a different one and the problem didn't follow it, it's either a bad injector / coil driver in the ECU, or a mechanical fault I that cylinder.

 

Kevin I'm leaning toward either injector signal from ecu or wiring. But what do you mean by something mechanical in the cylinder?

 

Dox neat trick with the jump lead. Will use that in future. I did try that I gaffer taped mine to the valve cover. Did see a spark. Poss a little weak but maybe not the best earth and daylight had something to do with that. But deffo a spark.

I have swapped the injector out too so can assume that is working mechanically. So next to rewire back to the ecu plug and see if that does it.

[Orkius 10]

Found the problem here. Turns out to be a broken wire/joint at the ecu pin for the injector signal. Motor now runs fine. However just got the whole thing back in and can't select reverse! Any ideas?? All forward gears go in...