THE common (Engine check light / misfire) problem

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Polo from Hell
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Posts: 3
Joined: Mon Jun 05, 2017 11:30 am
Drives: 1.2 BMD engine, late 2005
Location: London

THE common (Engine check light / misfire) problem

Post by Polo from Hell »

So, I have a late 2005 (facelift) Polo with a 1.2 BMD engine with 120k miles on the clock.

It seemed to run well, unless you drive for 20 mins or more, at which point the dreaded dash light comes on and the engine goes into limp mode.

Local mechanic connected his laptop and said its misfiring in cylinder 2. He did a compression test and said the engine needed a rebuild. With the high mileage I wasn't surprised, so had the engine rebuilt (new piston rings, new valves, new belts and tensioner, the lot. Valve seats were also checked.

The dash light still comes on, limp mode still engages.
Mechanic connects his laptop and says there is still a misfire on cylinder 2. A migration procedure is carried out, plugs, injectors, coils are all swapped, but the misfire remains stationary in cylinder 2.

Advised to take it to VW main dealer, for a full "investigation" costing £145. Result is a very long list of "problems" but nothing new about the engine, other than to say there is a misfire on cylinder 2 which will require further investigation by migration procedure, for a further £288. However, the fault list kindly informed me that the wiper blades also needed replacing - funny, as I had put new blades on only 2 days before I took the car in. The list of non-engine fixes came to over £5K. I said no thanks!

I purchased a VAG-COM scanner and discovered a little more detail - O2 sensor failed, Camshaft sensor implausible signal, cylinder 2 misfire, 01044 - Control Module Incorrectly Coded - static - no indication on display. Drive battery voltage sporadic, signal too low.

So, having spent over £1K with professionals, I discovered more by spending £160 and using a Foxwell 510 Pro Scanner myself.

I replaced the camshaft sensor, but no change. I have a new lambda sensor on order.

I don't know whether the battery could be an issue? Despite the error message, it doesn't look very old and holds its charge well. The engine always starts first turn of the key.

The wiring loom could also be at fault. I had hoped to find a new loom, but struggling. Can anyone suggest where to buy a loom from? If the problem remains after the new lambda is installed, I'll investigate the wiring loom (but would rather replace it).

Then, if all else fails, off comes the ECU to have it professionally check out.

As for the valves (I know someone will mention these and compression, even after an engine rebuild), I have done further compression tests. When the engine is a little warm, compression is good across all 3 cylinders. Once the engine has gone into limp mode, compression in cylinder 2 falls. However, if I then put a drop of oil in the bore, the compression returns - thus demonstrating that the fall in compression was not valve related. The theory is, it's the misfire that is drying out cylinder 2, which in turn lowers the compression.

So, I just need to solve the misfire. Only things it could be now, are lambda sensor, a wiring fault, or ECU.
coopern
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Joined: Tue Oct 06, 2015 10:11 am
Drives: Polo 1.4 BUD 9N3 petrol manual
Location: West Midlands

Re: THE common (Engine check light / misfire) problem

Post by coopern »

I wonder whether after 20 minutes something is getting too hot to work properly, like a bad wiring connection or the ecu or a sensor for example. Try running the engine with the bonnet open and see if the problem still occurs.
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