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WOLFG60

Lupo TDI Misfire

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Hi guys .

I,m new to club lupo as I have just purchased a 2001 TDI (AMF)

I bought the car as a project and was aware that the car was misfiring and smoking  and showing the following faults:

16485 - Mass Air Flow Sensor (G70)  Implausible signal

 18072 - control circuit for pd injectors - electrical malfunction - intermittent

16887 - cylinder 3 - misfire detected-intermittent

17964- charge pressure control - intermittent.

I have since changed the injector loom with a new vag item, replaced the fuel filter . checked the resistance of the injectors and can confirm oil level is at normal level .

The car still smokes ( Diesel smell) but does improve when warm but still misfires intermittently. 

While running I have taken the following readings : Injection quantity deviation CYL 1   -0.40 mg/str CYL 2  -2.71 mg/str  CYL 3  2.99 mg/str

Also while the engine warms up Cyl 3 reading fluctuates down to 1.4 mg/str and then back to 2.99 mg/str.

I was considering replacing the injector seals and carrying a diesel purge as my next step.

Any Ideas would be helpful?

 

Pete

 

 

 

 

Edited by WOLFG60
spelling error

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Can't see replacing the seals or doing a diesel purge having any effect on the quantity of fuel injected ishown n the measuring blocks. For some reason the ECU is not injecting the right amount of fuel at the right time so you get misfiring and unburnt fuel diesel smell.

Either the ECU has a fault and is doing this anyway or information from the engines sensors is causing the ECU to react in this way.

Assuming you have cleared the codes, what returns when you re-check ?

If the mas airflow sensor still shows faulty that would be my first option, mass airflow sets the basic quantity of fuel to inject

 

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Injector 3 isnt happy, could need a clean (diesel purge or whatever) or it might need some mechanical intervention. Do a compression check. It could be worn cam lobe(s) or bearings.

I would try and get the number of codes down though before fixating on the misfire too much. Get the MAF and the charge pressure out of the equation.

Edited by Sausage
added somink

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After clearing the codes only the cylinder 3 misfire occasionally returns . I take it the readings from the VCDS are what the ECU commands.

Also the readings for switch time deviation are (CYL 1  -1)  ( CYL 2  -12)   ( CYL 3  1)  

Does this show possibly a fault on #2 ? 

Will do a compression check to eliminate any mechanical issues

Thanks for the replies

 

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looks more like you have a dodgy injector, no idea what the readings are but 1 and 2 are - and 3 is a + number so maybe that is a clue

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DIesel purge can save a potentially coked injector.

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Ok guys some progress.

Replaced MAF sensor cleared message and no re-occurrence

I replaced all the injector seals and still the same misfire with loads of smoke.

Replaced number 3 injector with a known good one from an AJM engine I had with the same part number.

Still misfires but no smoke!!

Need to do a compression test next . 

messages at the moment  16687 cylinder 3 misfire detected and 17674 pd unit injector implausible signal intermittent.

Am I still having an electrical issue here too?

Any Help appreciated

 

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You maybe having electrical issues, how far you can go depends on your test kit, implausable signal says the injector is not opening when the ECU tells it to or is taking too long to respond.

So idealy you need to look at the drive signal to the injector from the ECU, that needs an ocilliscope or similar.

With that you can see the timing and if it's a clean signal. A poor connection between the ecu and the injector could easliy cause this. If you have a multi meter your only approach is to unplug the ECU and find the wires for the 3 injectors and test the resistence with both ends unplugged.

Also check that the ECU ground and the injectror ground path have the same resistecen to the neagtive terminal of the battery, just in case it's a ground path issue.

The other possibilites are that the injector driver in the ECU is damaged.

Camlobe wear or incorrect adjustment of no 3 injection pump, check cam with dial gauge

Fuel supply issues check / replace filters and lift pump

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Why didnt you do the compression test 1st before (or even while) changing injectors? You have to align the PD injectors up reasonably accurate too when refitting.

What did the cam lobe tips and the injector lobes look like especially on cyl 3?

Otherwise it will be electrics...

Edited by Sausage

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Only have a petrol car tester. Need to borrow one or buy one. Cam lobes look very good with no wear. Alignment of injectors within 0.8mm as per spec.

Anyone local with a diesel compression tester?

In the meantime I could check the ecu connections and wiring resistance. 

Edited by WOLFG60
Additional info

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Spot on Sausage with your recommendation.

Cylinder 3 down on compression.

1 and 2 on 500 psi 3 on 100 psi.

Head coming off next.

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Got the head off . Valves look ok . Both piston rings broken. Luckily no damage evident around cylinder. Got a big list of bits to get. Any ideas where the best place is to get seals and gaskets? 

image.jpeg

image.jpg

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Ouch! That's (partly) what did for my (first) Polo SDI.

As an aside, is the book 'death of a salesman'? :-)

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Sometimes your local engineering shop who builds engines etc will be the cheapest place for bits like rings / pistons even gaskets sets too, but your mileage will vary.

I'd be interested to know why those rings broke, have a good look at the piston too, ring lands etc. Detonation comes to mind, so could be a duff injector or easy start being used.

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Well spotted Loop!! 

Lands look ok . I have replaced the injector with a known good one. Have ordered all the bits I need I can think of. Loads of stripping down and cleaning today. Will let you know my progress.

 

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Ok guys . All back together. Turned the engine over before starting and cylinder 3 now at 475-500 psi other 2 around the same figures. Cleared all fault codes and started engine. Misfire on #3 still evident. May try the original injector in that position or swap them around any other suggestions?

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The code came back or an actual misfire? If you have compression now then you are back at injectors, seals and wiring I would think.

You've had some fun with this one :blink: 

 

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Same code and misfire. Injection quantity deviation no different when I started. #2 and # 3 way out. Harness new and injector 3 swapped with a known good one. And yes I'm having fun.

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I would assume that if vcds is registering injector firing and deviation then that would mean the harness is working properly and the injector is electrically working. Assumptions though can misleading so at this point I would double check that as Carerra-GT posted above with a mutimeter.

You said the cam lobes were good, that means the injector lobes too? I'd have a look at the rockers as well. Do you know this injector works or assume it is? Is it same part number?

The fuel gets to the injectors in a gallery in the head, that might be something to think about if nothing else seems to be it. i.e is 3 getting fuel? Or is it going into the oil?

What did the bore look like on cyl 3 with the broken rings?

 

Edited by Sausage

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All good now guys. Swapped injector 2 and 3 and proved fault with injector 3. Replaced and now working sweet. Next on list big clean and front brakes to do. 

Thanks guys

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Still have it. I had 3 injectors from an AJM bora engine I rebuilt. The fourth one got obliterated when a valve dropped and made a mess. Still had the bits from the old engine and came in handy. Struggling to find a yellow indicator grill at the moment. May have to buy new and paint after.

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