Daughters 1.4 polo, 2005 dropped onto 3 cylinders - it's luckily not the rubbish 3 cylinder engine!

Anyway, popped off the cover, unplugging injectors to kill engines and no.1 is the dropped cylinder so swapped the coil on plugs around, fault remains on no.1

Swapped the plugs around, still no.1

Had a listen to the injectors, no.1 is muffled compared to the rest so yanked off the injector rail and injectors and no.1 is poor, result

Removed the rail, filled with injector cleaner, let it dwell for a bit then pressurised the rail and used 12v to open the injector, eventfully got them all the same so put back on the engine.

As it was still all apart removed all the coil packs and did a compression test.

No.1 125psi
No.2 210psi
No.3 210psi
No.4 220psi

Added a drop of oil into no.1, it now matches the rest at around 210psi

Bearing in mind the cylinder has been missing so the rings may need shaking up the engine could be okay so put everything together, it now no-longer Sparks or injects when cranking over.

Fuel pump runs, fly by wire throttle opens and I have 12v on each injector and the coil packs also have power when I probe the leads.
By cranking with the coils and injectors unplugged will I have blown the ECU?

I cannot find any relays in this car, the fact that the pump runs for 7 seconds and the throttle pops open implies the ECU has power, I am not seeing it switch earths.

Fuel rail holds pressure, squirting petrol directly in and not as much as a cough so both fuel and sparks are dead.

Is there a common point to look for, I cannot find any relays, all fuses look okay, I am struggling to see how the crank sensor could be screwed as I have not been near it, without any wiring diagrams I cannot prope the ECU to see if I can pick out injectors or sensors.

Help !!!

Anyone want a 55 plate polo

there used to be a common fault where the big fuses next to the battery could develop a hairline crack and cause problems like this.
the earlier polos has a fusebox in the the glove box below the steering, cant remember off hand where the relays were.

Un-plugging cam or crank sensors won't damage anything, in fact it is very difficult to damage modern car ECU's.
But it sounds like a crank or cam sensor signal issue or more likely related wiring harness issue. If the car has tacho the needle will usually kick when the engine is turned on the starter. Cam and crank sensors can be 3 wire (hall effect) or 2 wire (inductive). A non-start due to a crank sensor usually won't flag a fault code unless there is a short but a scanner with live data will usually give you an RPM reading.

The 3 pins on a 3 wires sensor are: refrerence (power), signal and ground, the quickest test is unplug the sensor and with the ignition on check the power and grounds. These unplugged tests are done with the key on. The refrence power to hall effect sensors on most recent european cars is usually 5v, if you don't see 5v on one of the contact on the socket then you have something wrong with the reference circuit. Also check the ground circuit is earthing properly this best done using a test light rather than a meter. The signal wire can be either a pull-up or pull-down design all pull-down design will show 5v on the plug when disconnected.

This Youtube video might help

Scannerdanner video

I cranked it with injectors and coil on plugs all disconnected when doing the compression test.

Thanks for the tips, I will look for 5v to the sensors tomorrow, crank is impossible to see, it is extended on the injector harness, the cam sensor sits earlier on. Harness was not pulled hard, my thought is still that it does not see the engine turning, will also watch the tachometer.

Wires to cam and crank sensors, +5v +5v Earth

RPM needle rises when cranking, takes a couple of seconds to lift

Fuel pump runs

Still not firing an earth to the coil on plug or injectors

MOT runs to Nov 17, seems a pity to scrap it, quite a tidy car.

from a computer point of view, turn it off and on again. - ie disconnect the battery overnight.
also charge the battery

Have had a problem in the past with damp in an ecu, (on the 6n the main ecu is at the base of the windscreen) dryed it out with a fan heater on a cool blow for a couple of hours

edit: also look at clubpolo

[Edited on 19/2/17 by gremlin1234]

Thank you

Car is on charge now, ECU has been unplugged for an hour, did not help.

Dash shows MIL light, picture of a spanner and ESM stays lit where every that lives as a CANBUS car could be related to that.

My old OBD scanner cannot get anything out the ECU so have ordered an ELM one to see if I can read any codes and allow me to watch it during cranking. All earths look good.

Check those dog bone shaped fuses in the battery compartment. They're very thin steel and get very fine cracks in them. If you've not too familiar with VW's they can be hard to spot as they don't look like regular car fuses.

Be good to see Live data from the ECU, it can help save a lot a faffing about

The ones stacked across the battery, they all look okay

I see power on the injectors and coils, the ECU fire them with earth, it's a pest. Car is worth maybe £900 running, £300 not anyone want a dead polo...

Nobody local got a set of Noid lights so that you can see the firing of the injectors in 'real time' ?

Update on this.

Purchased an ELM and read OBD codes, injectors all unplugged which is not a surprise as they were, upon deleting the codes it starts immediately.

Pulled plugs, wedged throttle open and repeated compression test and no.1 is down, drip of oil restores it so rings have had it I guess engine is cold BTW.

Restored plugs, and will not start, checked OBD codes, ignition problem on all 4 coils and throttle body alert, cleared codes and it starts immediately.

So not starting is the ECU shutting down completely, very strange looks like a VW cash in the bank £70 to reset sir! I have never seen this with any other car I have owned, battery disconnected for 24 hours, etc did not sort it out, you have to access the ECU.

Anyone want a nice little polo for £500' 55 plate, quite tidy, drives well now as the miss has disappeared for now.

Regards Mark
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Originally posted by mark chandler
Update on this.

Purchased an ELM and read OBD codes, injectors all unplugged which is not a surprise as they were, upon deleting the codes it starts immediately.

Pulled plugs, wedged throttle open and repeated compression test and no.1 is down, drip of oil restores it so rings have had it I guess engine is cold BTW.

Restored plugs, and will not start, checked OBD codes, ignition problem on all 4 coils and throttle body alert, cleared codes and it starts immediately.

So not starting is the ECU shutting down completely, very strange looks like a VW cash in the bank £70 to reset sir! I have never seen this with any other car I have owned, battery disconnected for 24 hours, etc did not sort it out, you have to access the ECU.

Anyone want a nice little polo for £500' 55 plate, quite tidy, drives well now as the miss has disappeared for now.

Regards Mark
.

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