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Old 04-09-2017   #1
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Pulsating boost pressure on twinair engine

Hi everyone, has anyone experienced an uneven power delivery from the twinair engine, it's only under full load, I can hear and feel the turbo spooling up to full boost then backing off and coming in again, it does it quite quickly, it still goes ok, but it makes for an unpleasant acceleration. Thanks guys
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Old 04-09-2017   #2
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Re: Pulsating boost pressure on twinair engine

Quote Originally Posted by Pashers View Post
Hi everyone, has anyone experienced an uneven power delivery from the twinair engine, it's only under full load, I can hear and feel the turbo spooling up to full boost then backing off and coming in again, it does it quite quickly, it still goes ok, but it makes for an unpleasant acceleration. Thanks guys


I wonder if it's an ignition problem, dodgy coil packs are not unknown
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Old 04-09-2017   #3
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Quote Originally Posted by Mercky View Post
I wonder if it's an ignition problem, dodgy coil packs are not unknown
Hi there, it did cross my mind, although I would have thought it would present other issues, its fine in eco mode and when cruising on the motorway for example, but the issue only becomes aparent when you demand full power when accelerating hard 🤔
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Old 05-09-2017   #4
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Re: Pulsating boost pressure on twinair engine

Are you sure that's not just how they are? Fiat/ Marelli have a slightly amusing name for the issue, but it escapes me. Some have reported better results on 98 octane, but I don't see a difference.

Happens at around 4-5k rpm.
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Old 05-09-2017   #5
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Re: Pulsating boost pressure on twinair engine

Quote Originally Posted by Pashers View Post
its fine in eco mode and when cruising on the motorway for example, but the issue only becomes apparent when you demand full power when accelerating hard
Yes mine did the same thing, only apparent on hard acceleration - not in ECO mode - around the 3500 - 4000 RPM.

One coil pack replaced and all ok... luckily i had a spare on hand - easy 10min fix
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Last edited by p6baseunit; 05-09-2017 at 01:27.
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Old 05-09-2017   #6
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Re: Pulsating boost pressure on twinair engine

Quote Originally Posted by UFI View Post
Fiat/ Marelli have a slightly amusing name for the issue, but it escapes me.
You mean "sobbing". Forum member The Twins described it as follows: Instead of vroooom you get v-v-v-vr-oo-oom hence the term 'sobbing'.

See: https://www.fiatforum.com/500/359475...ml#post4033744
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Old 08-09-2017   #7
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Quote Originally Posted by UFI View Post
Are you sure that's not just how they are? Fiat/ Marelli have a slightly amusing name for the issue, but it escapes me. Some have reported better results on 98 octane, but I don't see a difference.

Happens at around 4-5k rpm.
I have no idea, I wouldn't have thought do no, it's quite an obvious fluctuation, enough to make the passengers rock back and forth, a bit nauseating actually. You can hear the turbo pressure coming and going
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Old 08-09-2017   #8
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Quote Originally Posted by AGH1965 View Post
You mean "sobbing". Forum member The Twins described it as follows: Instead of vroooom you get v-v-v-vr-oo-oom hence the term 'sobbing'.

See: https://www.fiatforum.com/500/359475...ml#post4033744
So is it a problem or a quirk??

Cheers for the reply
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Old 08-09-2017   #9
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Re: Pulsating boost pressure on twinair engine

Pashers, I don't know if your car really has this "sobbing" problem. That problem occurred when a Magneti Marelli tuning box was used on a TA. However, forum member UFI stated that his TA suffered from this problem without such a tuning box.

See: https://www.fiatforum.com/500/359475...ml#post4039751
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Old 09-09-2017   #10
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Quote Originally Posted by AGH1965 View Post
Pashers, I don't know if your car really has this "sobbing" problem. That problem occurred when a Magneti Marelli tuning box was used on a TA. However, forum member UFI stated that his TA suffered from this problem without such a tuning box.

See: https://www.fiatforum.com/500/359475...ml#post4039751
Thanks for the reply. The car goes back to fiat main dealer on Monday so I guess we will see, it certainly doesn't feel right to me! I'll update you if i do get any answers! And once again, many thanks 👍🏻
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Old 09-09-2017   #11
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Re: Pulsating boost pressure on twinair engine

Hi , I know it may not be the same engine as the old gt but I had a similar problem , under hard acceleration the turbo would boost up and then slow down , under normal driving it was ok , I found that a small vac pipe had come off from the turbo end , re attached it ad it's been fine since
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Old 10-09-2017   #12
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Re: Pulsating boost pressure on twinair engine

Just a thought could it be the waste gate on the turbo, if its only happening under max boost that would figure?
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Old 11-09-2017   #13
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Quote Originally Posted by marcusgillies View Post
Just a thought could it be the waste gate on the turbo, if its only happening under max boost that would figure?
That's exactly what I think it is, fiat called today and said they couldn't replicate the issue (no idea why) and said there's no fault codes (I could have told them that)
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Old 12-09-2017   #14
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Re: Pulsating boost pressure on twinair engine

I give our twinair 105 a fair poking sometimes and I've never noticed any throbbing. It certainly goes well once you get it between about 3000 and 5000 revs!
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Last edited by Andy43; 12-09-2017 at 20:54.
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Old 13-09-2017   #15
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Re: Pulsating boost pressure on twinair engine

Fiat called today and can't fault the car, they can feel the pulsating but can't find a cause, wastegate and actuator on turbo are in good condition so that's my theory out the window lol
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