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Discussion Starter #1 (Edited)
Solved: Rattle/diesel noise 1750 TBi

Any ideas what this could be?


It's only at cold start and only the first time I push the throttle pedal. Idles just fine after starting. At the second time I rev the rattle noise is always gone. Sometimes it gives me an engine warning light saying the outlet camshaft sensor has not been detected (even after replacement with brand new sensor). This warning light only comes on when I drive away and this noise appears (almost shutting down the engine).

Your input is much appreciated!
 

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It could be one of the camshaft variators is a bit worn, which means the camshaft is a little out of position, and that is what the error code relates to.
 

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With "camshaft variators" you mean the solenoid valves on top of the engine?
I meant the variators themselves, there is one on each camshaft on the 1750 engine unlike the old TS/JTS which just had them on the inlet cam. However you could also have a dodgy solenoid not allowing oil pressure to the camshaft variator when requested, that would similarly cause a rattle and possible cam position sensor error. But I've not come across a solenoid problem on a 1750 engine yet.
 

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Discussion Starter #6 (Edited)
I removed those solenoids and cleaned them. The outlet solenoid had one filter screen broken. I removed the broken screen, disassembled solenoid, cleaned, reassembled and reinstalled, no difference in performance or sound. So the variators are the next items to check. Difficult to replace/check?

Thanks for all the info so far. Great help!

Edit: Ok I've seen them in the official online parts catalog. Not gonna be happy if these are indeed worn.... quite expensive.... But is this most common? And what can be worn about these variators?
 

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Discussion Starter #7 (Edited)
Below I made a kind of checklist to exclude some things and make the problem more clear.

- I checked the solenoid valves with loose wires and the battery. Both worked fine, no problem there.

- It feels like an oil pressure issue. Because pushing the throttle always lets this noise disappear. Like I have to help to push the oil pressure to normal operating pressure. It's like he can't handle the load or rpm's for just a few seconds at initial startup.

- Only when I drive away with low RPM (bit too low) and at first throttle push after cold engine start, the engine warning light shows up. Engine is not running smooth during this noise, jerky acceleration and sometimes engine shutdown. To prevent this I push the throttle sharply for a sec before I engage gear and drive away.

- It's never present during driving and not after a short stop. Only when the engine has cooled completely and only at first throttle push after start. No problems at idling before or after this noise appears.

- If one of the cam variators was worn and timing would be off, this problem would appear no matter what condition the engine has, right? Engine runs just fine and no lack of power.

- I used Petronas Synthium 3000 for oil change.

Maybe it's no problem at all and all the 1750 TBi engine's do this. But I have no reference nearby.
 

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Discussion Starter #8
Bump this thread again, nobody who can push me in a direction where to look?
Car completely shut down during drive away (did not rev before) today. No check engine light.
So can also be fuel, ignition or perhaps air intake problem?
It's remarkable it only happens at cold start and pushing the throttle first time only.

Any help is much appreciated. Also very thankfull for the answers/suggestions already given.

Any other tbi owners recognizing this problem?
 

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Mine has done this for the last 2.5 years and I took it to be a characteristic of the car to be honest, your mileage is similar to mine incidentally.

I haven't seen a check engine light or any other warnings come up though at the same time, had the codes read on a regular basis and nothing has ever shown up. It does only "rattle" momentarily on the first start after leaving it overnight but certainly doesn't sound like a worn TS variator. If I was guessing though I would imagine it absolutely is oil pressure/flow related, logic says it can't be anything else.

I'm up at Alfa Workshop next week for a service and will ask them, I've had the belts changed as well and it was present before and after.
 

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Discussion Starter #10
It looks like you have the same issue as I have. I bought mine with 95.000km and was making that sound too from the beginning. But know it starts to irritate. It should not be standard to rev the engine to let it perform well, even when cold, right?
Oil pressure sounds most plausible indeed because sound and performance is only brief. Maybe next oil change I will flush it first with oil cleaning agents. Don't know how sensitive this engine block is for clogging.

Very curious what they will say in the Alfa workshop. Please, let me (us) know!
 

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Discussion Starter #12
So I dove into the maintenance history of my car. It appears at one point the oil change interval was 1,5 years! Could this be the cause of the noise?

Any news from the Alfa workshop that might explain all this, Wal5?
 

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Detonation, perhaps, until the ECU has calibrated itself to initial conditions? It might be interesting to try a higher RON fuel. Just a wild guess. Oil pressure issues are always worse when hot.
 

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So I dove into the maintenance history of my car. It appears at one point the oil change interval was 1,5 years! Could this be the cause of the noise?

Any news from the Alfa workshop that might explain all this, Wal5?
Sorry missed this and I haven't got an answer I'm afraid, still there after another oil change but I honestly think we are worrying about nothing. Haven't seen any comments from TBi owners saying their car doesn't do it so it may be a "characteristic" of the engine.

I've run mine on super unleaded for years and it certainly isn't detonation, additionally it has always been run on the right oil with changes at a minimum of 12 months.

Still go with the original theory it is related to oil pressure/flow and the Variator/Variator solenoid, can't really be anything else.
 

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I think possibly one variator is slowly draining down when standing. It's quiet at idle because it's against its end stop, and may have a locking pin to hold it. When revved the VVT begins to operate and the cam rattles back and forth until the air has been flushed out by the oil.
 

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Discussion Starter #17
Thanks for your input. But this rattle I'm talking about is distinctive from the rattle of the high pressure fuel pump. And is only heard at first hit of the throttle after cold startup.
 

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Discussion Starter #18
I think possibly one variator is slowly draining down when standing. It's quiet at idle because it's against its end stop, and may have a locking pin to hold it. When revved the VVT begins to operate and the cam rattles back and forth until the air has been flushed out by the oil.
Think you might be right, but how does it happen? And how can it be prevented/solved?
 

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Thanks for your input. But this rattle I'm talking about is distinctive from the rattle of the high pressure fuel pump. And is only heard at first hit of the throttle after cold startup.
You are right, but I hear the fuel pump more noisy at the first engine start. I mean the piping and pump are lack of fuel in this time, but few seconds later after the system filled up with fuel the noise is decreased. Present but not to noisy. I hear it with stethoscope at the starting moments. This problem is present to my some friends 1750 cars from its new age.

Maybe there is a one way valve in the line before pump?

Or I'm totally misunderstood the topic and my English is even worse than I guess :-D...
 

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Think you might be right, but how does it happen? And how can it be prevented/solved?
That I'm afraid I don't know. Listening with an automotive stethoscope would probably identify the noisy variator (or rule them out) but there must be many potential leakage points in the system. Checking the solenoid should be easy enough: swap them. Beyond that: dismantle and inspect - or change the variator and hope the problem goes away - or live with it? I hope someone else has a better answer for you...
 
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