Loom, coilpacks and plugs changed... Still misfiring. What next? (1.8t)

[RickkyP]

The misfiring on my 1.8T seems to be turning into a bit of a saga.

I've changed the Plugs and Coilpacks. While that helped for a bit it the check engine light returned. The loom looked in a pretty sorry state so I took the forums advice and changed the coilpack look. (Properly, re-pinning the ECU etc. I've also replaced all the EGR pipes so its not this.

In terms of physical symptoms, the car is a bit jerky at low throttle when cold, and when accelerating, especially in 2nd gear it feels like the boost is fluctuating so the car accelerates hard, then not so hard, hard and then not so hard.
Interestingly it doesn't seem to do it when cold. Is this because the ECU limits the boost until the engine heats up?

I've tried unplugging the MAF, it doesn't drive much differently, but the revs do drop when I pull out the plug for it.

I've had a good tighten of all the hose clamps, there are no obvious leaks anywhere. I really want to avoid taking it to a garage if I can help it unless anyone knows of a specialist near Hull?

The error codes are:
17705 Pressure Drop between Turbo and Throttle Valve
17763 Cylinder 1 Ignition Open Circuit
17769 Cylinder 3 Ignition Open Circuit
17772 Cylinder 4 Ignition Open Circuit
17766 Cylinder 2 Ignition Open Circuit

 

[RS3 ROCKS]

Sounds like it could be a feeling issue.Check if your pipe is properly connected to your fuel pressure regulator. and if it's operating correctly.

out of interest do you have a pin removal tool for the coil pack plugs?

 

[RS3 ROCKS]

Fueling issue

 

[RickkyP]

I'll look into that, the pipe does look a bit manky.
Would that cause the surging on and off on boost?

Yeah I made a custom tool to do the pins with, I tried with a paperclip which worked for the big plug, but the ECU has much smaller pins. Theres a guide on youtube that I followed, basically you strip the sprung steel out of an old wiper blade, fold it in half and then spend the next however long painstakingly filing it down to fit the plug. Bit of trial and error but once you get it to the right size it works great.

 

[immac]

I hesitate to suggest this as I have had a similar problem today, symptoms very similar, and I am not even sure I fully understand what is happening. Anyway, for what it is worth, there is a solenoid between turbo and ecu: mine has failed today during the remapping and is giving very similar results. Physically, it is at back of engine bay, next to bulkhead, and just a few inches right of centre. If anyone knows this item please give a better explanation if I am near the mark. Or tell me I am wrong, I wont be offended.

Ian

 

[RS3 ROCKS]

Theres so many possibilities. But it's better to start with the simple things and work your way up. It can cause boost issues at low rev's if not connected as this is when it would open. On full throttle it would be closed.

 

[RS3 ROCKS]

Immac i'm sure someone will know the answer. Unfortunately thats not me

 

[RickkyP]

I hesitate to suggest this as I have had a similar problem today, symptoms very similar, and I am not even sure I fully understand what is happening. Anyway, for what it is worth, there is a solenoid between turbo and ecu: mine has failed today during the remapping and is giving very similar results. Physically, it is at back of engine bay, next to bulkhead, and just a few inches right of centre. If anyone knows this item please give a better explanation if I am near the mark. Or tell me I am wrong, I wont be offended.

Ian

Think thats the N75 valve.

I checked the resistance on it which was 30 ohms, I believe thats in normal tolerance?

 

[<tuffty/>]

Ignore the 17705 code for now... The clue is in the open circuit codes...

Have you cleared the codes to see what returns?

Is the coil pack loom earth on the rocker cover bolted down?

What year and engine code? Makes a difference in diagnosis

<tuffty/>

 

[RickkyP]

Ignore the 17705 code for now... The clue is in the open circuit codes...

Have you cleared the codes to see what returns?

Is the coil pack loom earth on the rocker cover bolted down?

What year and engine code? Makes a difference in diagnosis

<tuffty/>

Thanks for the reply.

Its a 2001 AUM 1.8T

The Earthwire is securely attached. I triple checked everything when I ran the new loom wiring through.
If I disconnect the battery for a while to clear the codes the light goes off. It then stays off for the first drive, sometimes the second, but after that returns. Each time it returns its the same, misfire on all 4 cylinders.

 

[<tuffty/>]

Same codes or different ones?

<tuffty/>

 

[RickkyP]

Exact same codes every time.

Also additional information, not sure if its relevant, I was using the car for some short journeys to work while I was down in G Yarmouth, about 2 miles, and I noticed then the surging was pretty bad in 2nd. I've since driven back up to Hull 4 hours drive, and the surging is not as bad, it maybe surges once in 2nd gear then settles down, whereas it would do it for the full rev range before.

 

[<tuffty/>]

The issue you have is wiring related...

The open circuit fault codes happened after replacing the loom? you ran this back to the ECU rather than splice it?

Outputs from the ECU are negative switched... for all 4 ignition faults like this it looks like the 12v feed to the coils is the problem so I would start there

<tuffty/>

 

[RickkyP]

The issue you have is wiring related...

The open circuit fault codes happened after replacing the loom? you ran this back to the ECU rather than splice it?

Outputs from the ECU are negative switched... for all 4 ignition faults like this it looks like the 12v feed to the coils is the problem so I would start there

<tuffty/>

Yeah when I replaced the loom I traced it all the way back to the plug under the airbox and the ECU plug under the windscreen. I re pinned all of the plugs correctly rather than splicing in.
The error codes are the exact same ones that I had before swapping the loom.
The 12v feed has to be part of the wiring I replaced as the loom replaces everything that goes to the coilpacks. I'm pretty certain I got all the pins correctly when I did it. (They all come labelled on the OEM loom replacement) and I followed the Audi service bulletin guide while doing it.
I'll check again, but I'm certain I got it right.

Could the fact that I used the cheap coilpacks from over the counter at a motor parts place rather than Bosch make a difference?

 

[<tuffty/>]

Anything is possible... still got your old coil packs?... try one... see if you only get fault codes for the 'new' ones...

But... the 12v supply is a common feed so I still think its related to that...

<tuffty/>

 

[RickkyP]

Unfortunately I binned them.
I had one changed by the Garage (because it went while I was away from home and I didn't want to abandon the car), I then pre-emptively changed the rest after a 2nd one went.
So 3x are cheap ones I bought, and 1x was fitted by the garage.

Interestingly, before I changed the loom originally I only had the error codes showing on the cylinders I changed the coilpacks for, the garage one was fine, but to test it I swapped it from Cylinder 2 to Cylinder 1 at which point they all started showing errors instead of just 3 of them!

I'll have a look at the 12v feed in a few days when I get back from work, just threw this post out there so I had something I could get stuck into once I'm back at home and have tools etc.
Once warmed up for a min, apart from the surging the car has no noticeable issues at all, no misfiring that I can tell.

 

[RickkyP]

I got back from work this morning and have had another look at the car.

I replaced 1 of the Coilpacks with a known good one, left the battery disconnected to reset the error light and went for a drive.
As usual, on the drive the car felt good, and no error light.

Popped into the shop to get some milk, came back out started car, error light on again, and now I have MORE codes!

17705 - Pressure Drop

17763 Cylinder 1 Open Circuit

17769 Cylinder 3 Open Circuit

17772 Cylinder 4 Open Circuit

17766 Cylinder 2 Open Circuit


1810 Voltage Too Low

1695 Brake Switch (F) Implausible Signal

16486 MAF Signal to low

16946 System Voltage to Low


The low voltage errors are caused by me disconnecting the battery think, and and the MAF sensor, I disconnected a while back to see if it made a difference to performance. I've had the battery disconnected since, so surely it should have reset?
I'm seeing if anyone I know has a code clearer so I can clear them properly instead of just disconnecting the battery.

Now as for the open circuit, I have no idea what is causing this, the car runs fine and I've checked all my new loom wiring again and I can't find anything wrong. The earth lead is connected and I sanded the contact area so its making good contact. The replacement coil has made no difference. No idea what the next course of action is.

Edit: I've checked the resistance between the earth cable from the loom on top of the rocker cover and the battery and its 0.7ohms, which seems a pretty good connection to me.

 

[Squirt]

I've had a similar problem before with an A4 with exact same fault codes, I think you will find the issue is with the breather system, the PCV valve beneath the inlet manifold. Basically a boost leak into the crank case. Also causes misfire fault codes but doesn't seem to physically misfire.

The voltage codes may have been introduced when you opened up the wiring loom?? Not saying your electrical skills aren't any good but it's possible!

 

[RickkyP]

OK, Problem solved!! (I believe)

I'll put this up in case anyone encounters the same issue.
I've just driven to Sheffield to pick up a genuine Vag-Com cable, as all I could do with my crappy one was check error codes, but not actually reset them, so I've been disconnecting the battery to clear the codes. Well it turns out that disconnecting the battery may turn the light off, it doesn't clear the codes!

So all my careful swapping of coil packs was to of no avail as it still held onto the previous codes.

I took my laptop with me and as soon as I got the cable cleared all the codes on the car and drove back, despite some lets call it spirited driving no light turned on. Now I'm home I plugged it all in again, not errors, but I have 2x errors pending 'Cylinder 1 and Cylinder 4 open circuit', well Cylinder 1 and 4 have the cheap coils I got from motorworld in. Cylinders 2 and 3 have the new higher quality one and the used one I bought off ebay just for troubleshooting.

So it seems that poor quality coilpacks is causing the ECU to throw an error code.
I just need to get 2x good quality coilpacks and I reckon that it will fix it. So cheers to everyone who helped out.

Squirt - I've replaced all of the breather system. Already

 

[Squirt]

Oh I see! It's the boost pressure drop fault code that's got me! Although it may be a software issue throwing that code along with the misfire codes.

Or an historic code