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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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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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  • 4 months later...

Finally managed to find some time to work on the loop having submitted my dissertation!

Had the ECU tested, and I am told there is nothing wrong with it.

We checked timing, but I foolishly confused the locating pin for the serpentine belt pulley as the timing mark. So incorrectly "fixed" the timing and bent four exhaust valves. Not my finest moment.

Head came off and was sent for a rework (does allow me to guarantee it's not a head problem I suppose...).

Inspected bores, all in good nick with no lipping or scoring.

While head was off, noticed that the precat was clogged so that got "unblocked" in the hope that the problem was cat related all along.

Throttle body, intake manifold and egr piping were cleaned out thoroughly while waiting for the head to come back.

Head refitted with new bolts and gasket, everything back exactly as it should be, torqued to spec etc. New seals on inlet manifold and camshaft seal renewed. Fresh cam belt fitted while we're at it, with crank/cam timing bang on correct.

Threw some new coolant in the tank.

Fired up and let it run for oil to get where it needed to be. Quickly realised the miss on cylinder 1 was still there.

It runs happily for 5 secs after start but then it starts missing, just as before. Its almost as though the ECU is making an active decision to create a misfire on that cylinder.

Checked injectors again and all fire as they should. 

Now I'm back to cracked inlet - sprayed carb cleaner around the manifold again but doesn't seem to be cracked, removed to reinspect and can't find anything amiss.

Any other thoughts would be a massive help, before I just decide to break it and put the money into my Scimitar instead cause I am at a total loss 😅

Cheers

Tom

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If you have eliminated electrical and injectors, then that leaves mechanical like bent conrod, cracked liner, piston, head, valves not opening enough etc. It seems as soon as any heat gets in it it misfires. Maybe run it for a few minutes if it seems safe to do so and then do a compression test when it still has some heat in it.

Is the misfire at idle or only when some revs come on? Any rattle from cams or elsewhere?

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Thanks Sausage, I'll do a compression check cold and warm tomorrow. I did allow it to warm up after refitting the head so i have no problem doing that.

Though it behaves the same when starting from warm - idles fine for first few seconds and then the misfire comes in.

Checked the bottom end whilst the head was off, bores and pistons are all good and turns over freely with no signs of anything amiss. The piston on 1 reaches TDC so doubt a conrod is bent.

The guy that reworked the head checked it all over for damage so I'm confident it's not that now. All valves were opening happily prior to installing the head too.

The misfire is persistent at idle and with revs, no unusual noises from the cam that I can hear. 

Cheers

Tom

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Try swapping 1 and 3 ign and inj wires... see if fault moves. It's twin spark as far as I know, so ign should be unaffected. Inj will just pool fuel a bit behind the inlet valves, but run. It's a curious fault.

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  • 2 years later...
On 1/28/2022 at 4:17 AM, Tobi21jensen said:

Hello 

Tom01997

Did you find out what the problem was? 

I have the exact same problem as you had, only on the 1.4 mpi aud instead. And misfire on both cyl. 1 and 3

Have changed ignition parts, injector and fuel filter and made a compressiontest that looked good after 1 intake valve was changed

Clean crankcase breather. Also check if the replaced wires arent bad qualitty, I have replaced 3 sets, and the 3rd was fine after some diy upgrade with sealant on distributor connection part. Recently noticed OEM cables have the upgrade from factory, circled in picture. Also check if the lenght of rubber sleeve, pointed in bottom of picture, isnt too short, it can also cause misfires. These are oem look how long the sleeves are, like maximum possible lenght.

8A6A7338-9E4C-4CF9-9E22-675CA66974C7.jpeg

Edited by ObjectiveAway
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