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tom01997

1.0 AUC misfire & immobiliser issues

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Happy new year all. Apologies for the long post!

I wonder if anybody here is knowledgeable on the AUC engine as fitted to my 2003 Lupo, as I am at a total loss as to what is wrong with mine. A month or so ago it started misfiring.

 

I replaced with a brand new ignition coil, HT leads and spark plugs to eliminate potential spark problems. The misfire remained.

With the engine running, unplugging injector 1 does not change the idle. Nor does unplugging the HT lead. So the issue is on cylinder 1.

I swapped the injector on cylinder 1 over to cylinder 4. The problem stayed on cylinder 1, so the injector is not at fault.

I ran a compression test, and all 4 cylinders sat at 125/126PSI, so it has compression.

Today I fitted a replacement injector wiring loom. The misfire remained on cylinder 1.

I then fitted a replacement fuel rail & injectors. No change.

So, I removed the battery to inspect the wiring which runs to the ECU. I connected the battery to the terminals using a pair of jump leads. By wiggling the wiring loom, I hoped to isolate any wiring issue.

 

But when I fired it up, it cut out after a second, as it would if I had an immobiliser issue. Even after putting the battery back in, it still wouldn't run.

So now, instead of having a misfiring Lupo, I have a non-running Lupo. :rant:

 

Having spent a small fortune on air suspension this (last) year, i'm pretty gutted I can't get it running again.

Any ideas as to what might be wrong with it would be greatly appreciated. Thanks.

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I hate to say it, but it sounds like a loom fault. Try swapping over the power plugs to the injectors. May take a bit of jiggling... injector plug 1 on injector 2, injector plug 2 on injector 1. Will run with injectors firing at the wrong time, but rough as there's not enough air flow to properly mix the fuel air (do it on a warm/hot engine). If the fault moves to cyl 2, you'll know it's probably the loom. Alternatively, swap the pins in the ECU plug...

not running at all is something else. You need diagnostics now.....

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So I managed to get it running again a few days ago, it was an ECU fuse blown.... Oddly on startup it ran fine for 30 seconds, and then the misfire came back.

I ran a similar test to the one you are describing, by removing the rail and putting bottles over the injectors. All four fire the same amount of fuel so I don't think this is a fuelling issue after all, unless the ECU is struggling to get the timing right.

A friend suggested a worn camshaft intake lobe could be causing the problem, so I spent yesterday having the belts and cover off to inspect it. All looked good to me with little in the way of wear.

Think it might be head off time, despite the reasonable compression i still suspect something is amiss.

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Good compression. Don't remove head.

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Thanks mk2, I figured I was barking up the wrong tree.

I have had the OBD plugged in which gave me;

P0301 Cyl 1 Misfire (unsurprising)

P0443 Evap Canister Purge Valve. Is this referring to the charcoal canister under the driver side headlight, and are the valves a common failure? 

P0403 EGR Valve.

I'm struggling to see how either of the latter would be causing a cylinder specific misfire though.

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The readings seem a bit on the low side, but if all the readings are similar (within about 10%) it is probably ok as there will be some variation in reading using different testers etc, but when I did comp test on a 1.0 they were 150 - 160 psi, again that could be down to the testers reading different or the method of doing the comp test, I did 10 seconds cranking with open throttle with all spark plugs removed.

You might want to redo the comp test and then also do a leak down test as well where cylinder is pressurised and then see how long it holds it.

It will just save you some hassle knowing the compression is ok before proceeding.

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Check timing!

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Yes Rich is right check timing and belt tension, it might have jumped a tooth.

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