2.5 V6 unknown problem - Alfa Romeo Forum
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(Post Link) post #1 of 15 Old 30-07-13 Thread Starter
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Help 2.5 V6 unknown problem

Hi guys,

I've been having a problem with my 2.5 v6 engine on a 166 about a year now... I went to diagnostics a couple of times and they didn't manage to find out anything. The problem occurs when the engine is running cold. It struggles to get to revs, pulls when driven, and most interesting in bangs quite loud though the air filter (i have the sport one). The diagnostics show 5 out of 6 coil packs, ignition fail, and 4 lambdas not working even though I have only 2 and both work fine (we checked the graphs)... Oh, and the car has LPG installed, and runs much better on LPG than on petrol... This problem occurs only on petrol since the car has to warm up to switch to LPG. The problem is gone as soon as the engine gets warmed up.

Please help... I'm realy desperate
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what engine temp does diagnostics show when cold?

describe what you've seen on the lambda graphs? they should alternate between rich and lean TWICE per second

try unplugging the fuel injectors in turn, see if there's one where the engine keeps running the same...
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(Post Link) post #3 of 15 Old 31-07-13 Thread Starter
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Do you mean the air temperature or water? Lambda sensors work fine from 0V to 0,08V (i think). I'll check the injectors as soon as possible, but as I said it only bangs a few times when it's cold, and even more when the air outside is moist. I'll make a video of the BANG! when the car gets back...
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It sounds like it's running weak. It needs to be richer when it's cold.. and moist air usually complicates things because it's harder to set alight.

Have a look at the plugs to see if they're white or look like they've run too hot (dry, white crusty residue).

It'd be interesting to see how much petrol comes out of the fuel pipe when you turn the ignition on. I have no idea how much you should get but "less than normal" would suggest a weak fuel pump (maybe internal tubes split?).

Running well on gas excludes ignition or sensor problems.


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The injectors may need cleaning especially if the spend most of there time off collecting dirt and oil from the induction system as it has LPG. When they are running the spray pattern maybe poor..
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(Post Link) post #6 of 15 Old 06-08-13 Thread Starter
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Thank you for the answers, I forgot to mention some things... The amount of petrol in the exhaust is bigger than it should be. Sometimes there is black smoke blowing out and you can smell the petrol a lot. So the mixture is richer in my opinion than it should be. I can also feel power loss around 4k, but as I said, the lambda sensors and MAF are ok. Stange

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Are you sure the MAF is okay? Does it work differently if you unplug it?


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(Post Link) post #8 of 15 Old 06-08-13 Thread Starter
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I'll try to unplug it but diagnostics didnt show anything about the MAF... yust lambdas, coil packs and ignition failure.
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(Post Link) post #9 of 15 Old 02-09-13 Thread Starter
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Just an update, my alfa spitted out a spark yesterday and the screw on the head is totally worn out so I cant screw a good spark back in... The coil pack was totaly broken and burnt... When we reconnected the battery it wouldnt start and the key code light lid up. I will probably sell the car for parts because the repair cost of the head and everything else is more than 1000€ which is just too much... Most likely I'm leaving the alfa world anybody has any suggestions?
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Alfa GT..


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(Post Link) post #11 of 15 Old 04-09-13 Thread Starter
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So yeah, I guess we'll try to fix the engine... I wont leave the Alfa world that easy If there is no way to fix the screw in the head I will buy a new one, but this means I'll have to get the tools for setting up the cam belt. Anyone knows where could I buy one of these gadgets for a reasonable amount of money? Oh and the compression on the front bank is 14, 11, 8... so probably I'll change the rings also...

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Simeon there should be an engineering place that can tap a new thread and install the correct insert into your head. Not so costly and works very well. See here: http://www.amazon.co.uk/gp/aw/d/B009UFMZGS search for the correct thread size. The link is for 14mm.

Last edited by Ian Lusso; 08-09-13 at 15:12.
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A Helicoil or Time-Sert will repair the broken thread...
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(Post Link) post #14 of 15 Old 09-09-13 Thread Starter
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Thanks guys... I found a guy who will probably fix it for 70€... i already got a spare coil pack and sparks will update this week when i get the car back
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(Post Link) post #15 of 15 Old 14-09-13 Thread Starter
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I got the car back they successfully fixed the thread for 70€ which is quite cheap... I installed everything else and works fine now... More or less... Still think there is lack of power around 3.5k revs and the idle is bad, but when i unplugged the MAF i didnt feel or hear any improvements. What should I focus on when unplugging the MAF?

Thanks, Simeon
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