Weird engine power Issue - Alfa Romeo Forum
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Weird engine power Issue

Hello, I have recently bought a 1.6ts 2005 147 and on low revs (tickover to 2225rpm) it sounds more like a diesel than my citreon van does but once the revs are raised and it gets to 2225rpm the engine note completly changes and it sounds like a petrol engine again. I've tried it quite a few times and it's always at that engine speed it changes even when dropping the revs back down once it goes past 2225rpm it sounds like a diesel again. It really is an instant change like someone's just thrown a switch. I've had a fault code reader on it and it shows a O2 sensor problem would that have this sort off effect on the power and cause such a rough tickover or could it some thing more sinister? also The chap I bought it off told me (a few days after I bought it when I phoned him about something) that it's limited to 70 and I tried and it took ages to get there but wouldn't go past 70. Is it possible this limiter can effect the low range power so much?
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Option one and the most likely....
Variator, variator oh and almost forgot.... Variator!
It's that far gone that it's only charging with enough oil pressure above 2100 rpm.
Might as well get the wallet open and get the cambelt and tensioners done as these need to come off to get to get to the variator in the first place mate! The variator is £119 minimum alone just for the part itself.

Option two. Burnt valve not sealing but as the cylinder pressure builds it seals better..
Head off job and timing belt, tensioners too!
A simple compression test will confirm option two and you can rule out piston ring if you pour a little amount of oil in the spark plug hole and crank it with the compression tester in. If the compression increases in a low cylinder then drops again, it's the ring. If it stays low, it's the valves.
Sorry to be the bearer of bad news but he saw you coming!
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Originally Posted by Grahameo View Post
Option one and the most likely....
Variator, variator oh and almost forgot.... Variator!
It's that far gone that it's only charging with enough oil pressure above 2100 rpm.
Might as well get the wallet open and get the cambelt and tensioners done as these need to come off to get to get to the variator in the first place mate! The variator is £119 minimum alone just for the part itself.

Option two. Burnt valve not sealing but as the cylinder pressure builds it seals better..
Head off job and timing belt, tensioners too!
A simple compression test will confirm option two and you can rule out piston ring if you pour a little amount of oil in the spark plug hole and crank it with the compression tester in. If the compression increases in a low cylinder then drops again, it's the ring. If it stays low, it's the valves.
Sorry to be the bearer of bad news but he saw you coming!
Thanks and sorry for the slow reply I've been so busy it's not real. I had a feeling 9but was hoping not) it would be the variator. the compresion test is fine and all within 5PSI off each other. I will change it but it can wait til after christmas now, Would that also cause the speed limit reduction? I know I cant do more than 70 in the UK but it would be nice to get there the same week I start.
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If your O2 sensor is playing up, then it may be going into limp home mode/ reduced power or even very lean settings of some capacity. This would explain why you are experiencing low performance. Also remember though that the variator is mechanical form albeit more primitive versionof VTEC but based on oil pressure and a solenoid switch to determine its operation. When it stops working as it should, you can also experience up to 20-40 bhp drop in power output and torque. Combine both together and it's got only 120bhp from out the factory gates brand new, there's your explanation mate.
Other down sides are considerably more oil burning, which could probably have coated and clogged the o2 sensor probe!
Remember, there is always, always an initial cause to mechanical and electrical problem on cars, they don't want to run badly. Ignore the original cause, suffer the aftermath further along the car's systems and more often than not, they are bigger more expensive items along the way and time line....
For example : split CV boot left alone, leads to hub/bearing and CV joint issues, leave them alone, then we wonder why a diff explodes or a wheel passes us on the motorway and we wonder where the pretty sparks come from.

In short... The longer we leave faults, the more they multiply and expensive and drastic they become!
Hope this helps mate.
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Thanks

Thanks I've decided to give the old girl a go and ordered a load off parts so a new Varaitor, timing belt kit are on there way and while I'm in there a new water pump is going in and going to change just about every gasket/oil seal I can find and might even change all the cam followers while I'm at it as one of them is slightly tappety and some nice new suspension for the front as the near side has a very worn bush so hopefully that will get it running a lot better ready for when the wife passes her driving test in a few months.
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You might find a fresh sump of oil and a new filter will help .. old oil gets thin and then the variator starts to play up.
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Finally found enough daylight hours to get something done so she's had timing belt, water pump, tensioners, and a new set of hydraulic kifters I decided to try the variator repair kit which has made quite a big diference in the engine sound but it's still low on power. It's showing an o2 sensor fault so I'll get that done but could one dodgy o2 sensor affect the power that much? I dont know if these have a "limp home" mode its stuck in?
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