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Discussion Starter #1
Dear forum members I hope someone more knowledgeable than myself can help me out.
So I've been tackling a loss of power problem for a while now indie shops and dealer don't know why.
I'll state my symptoms and the tests I've done already...

On first/cold start the car is very hesitant with rough idle and misfiring/feeling of stalling when gas pedal is pressed. Turning the car off then starting it up again resolves this issue

While driving I get a few mins of good power and excellent acceleration then power drops. Again turning the car off and on will give back the lost power

Fuel injectors have been changed since then I get the few mins of good power with the old injectors the car was always sluggish

Fuel pump pressure was checked and compared to another v6 156 they both have the same numbers 50psi about 3.44 bar

Maf sensor shows no codes and car doesn't show errors.

My theory is the ecu is retarding timing for some reason. What sensors could cause this?
 

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Discussion Starter #3
They are gta ev6 injectors with a better spray pattern so that must have something to do with it...
I'm thinking knock sensor too I went through the recent repairs and the knock off sensor was changed with a Chinese part recently it might be failing or reading incorrect
 

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Why not record data logs without fault and then with fault? Should be easy enough to compare.

AFAIK, the sensor could be unbolted from the block and wrapped in cotton wool/airlite packaging and because the ECU reads it as present, it wouldn't be able to retard ignition.

If it is not tight to the block, it will rattle and the ECU will continually detect 'knock' until an error of description 'knock limit exceeded' is logged. You don't have a P032* or P033* code logged but as Jetronic77 suggests, do some tests on it to see if it appears to be overly sensitive.
 

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I have read that knock sensors can potentially be triggered by random metal to metal contacts, such as an exhaust rattling against the chassis, etc etc...

Knock sensors are in effect only microphones tuned to pick up 'noise' within a specific range of frequencies. Anything which happens to be within that range could trigger the sensor, no matter if it is actually caused by a 'knock' or not.

Regards,
John.
 

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Discussion Starter #8
Why not record data logs without fault and then with fault? Should be easy enough to compare.

AFAIK, the sensor could be unbolted from the block and wrapped in cotton wool/airlite packaging and because the ECU reads it as present, it wouldn't be able to retard ignition.

If it is not tight to the block, it will rattle and the ECU will continually detect 'knock' until an error of description 'knock limit exceeded' is logged. You don't have a P032* or P033* code logged but as Jetronic77 suggests, do some tests on it to see if it appears to be overly sensitive.
I was getting those errors but after changing the injectors the never came back. Today while driving the car went into full limp mode where I could not fully accelerate, pressing the accelerator completely felt like 30%, shut it off and started it up again it was back to normal. To my understanding and experience this is a clear sign of a crankshaft sensor about to fail, could this be related to the issue mentioned earlier?
Regards, Fady
 

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Yes, I think a failing crank sensor might do that, but most people seem to find that they fail completely and stop the engine; then recover after cooling for a while.


Have you tried running with the maf sensor disconnected? - I don’t think knock induced ignition retardation would cause miss-fires, it looks more like fuelling. Running lean could cause miss-fires and knocking. You have checked the fuel pressure (was the fault showing when you did?) and changed injectors so – maf next. (Maybe a leaf etc getting sucked onto the maf and then dropping off again when you key-off.)

Edit: You won’t necessarily get a code, afaik the ecu has no way of knowing that the maf sensor is misreading.
 

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Discussion Starter #10
Yes, I think a failing crank sensor might do that, but most people seem to find that they fail completely and stop the engine; then recover after cooling for a while.


Have you tried running with the maf sensor disconnected? - I don’t think knock induced ignition retardation would cause miss-fires, it looks more like fuelling. Running lean could cause miss-fires and knocking. You have checked the fuel pressure (was the fault showing when you did?) and changed injectors so – maf next. (Maybe a leaf etc getting sucked onto the maf and then dropping off again when you key-off.)

Edit: You won’t necessarily get a code, afaik the ecu has no way of knowing that the maf sensor is misreading.
With the MAF disconnected the car runs like crap, misfiring badly below 3k rpm and barely picking up above that.
I did a throttle reset now didn't help neither did cleaning the MAF and changing the air filter.
Fuel pressure was stable through the rev range from idle till 7k rpm at 3.44 bar or 50psi.

Im sure it's something electrical not mechanical as I do get a few moments of full power. Could my ecu be fried?
I need a way to log my ecu data so I can post it is that possible?
 

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I was getting those errors but after changing the injectors the never came back. Today while driving the car went into full limp mode where I could not fully accelerate, pressing the accelerator completely felt like 30%, shut it off and started it up again it was back to normal. To my understanding and experience this is a clear sign of a crankshaft sensor about to fail, could this be related to the issue mentioned earlier?
Regards, Fady
Failing crankshaft sensors means the engine quits totally. The engine ecu will think you stalled it. Typically they won't restart until the crankshaft sensor cooled down some aswell. But they do go bad, just don't think this is the issue you are having
 

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With the MAF disconnected the car runs like crap, misfiring badly below 3k rpm and barely picking up above that.
I did a throttle reset now didn't help neither did cleaning the MAF and changing the air filter.
Fuel pressure was stable through the rev range from idle till 7k rpm at 3.44 bar or 50psi.

Im sure it's something electrical not mechanical as I do get a few moments of full power. Could my ecu be fried?
I need a way to log my ecu data so I can post it is that possible?
Multiecuscan can help you
 

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Discussion Starter #14
Multiecuscan can help you
No errors, MAF sensor reading and accelerator pedal show consistent readings when ploted against each other. I'm not experienced enough to understand the spark retard and ignition advance numbers though do I need to have them looked at?
 

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advance should go up with rpm, so use a graph plotting rpm and advance.

There might also be a misfire counter or a knock counter
 

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Is this your pressure regulator, or similar? Fuel pressure regulator ALFA ROMEO 156 Saloon (932) 2.5 V6 24V 190 HP » low prices


If so the small steel pipe would (I assume) connect to the inlet manifold. Manifold pressure then acts on the diaphragm to maintain the rail pressure at a constant amount above manifold pressure. So the rail pressure should not be constant as you rev the engine, but follow the manifold pressure.
Note that on no-load the pressure may not change greatly with revs, but should rise momentarily as you blip the throttle.
 

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Discussion Starter #18
Is this your pressure regulator, or similar? Fuel pressure regulator ALFA ROMEO 156 Saloon (932) 2.5 V6 24V 190 HP » low prices


If so the small steel pipe would (I assume) connect to the inlet manifold. Manifold pressure then acts on the diaphragm to maintain the rail pressure at a constant amount above manifold pressure. So the rail pressure should not be constant as you rev the engine, but follow the manifold pressure.
Note that on no-load the pressure may not change greatly with revs, but should rise momentarily as you blip the throttle.
I had a 2 way gauge connected between the fuel line coming from the pump and through another hose that feeds the engine the pressure remained at 50 psi with momentary blips to 52psi. The link u sent doesn't have a picture but I assume it's the bulged round steel at the end of the fuel rail from the timing chain side, if that's it then yes I have it. Also shutting off the engine the pressure didn't drop so the check valve in the pump is functioning correctly
 

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Ah! It had a picture for me. Here is another link: SAAB ALFA FIAT GM OPEL RENAULT PEUGEOT 3.0bar FUEL PRESSURE REGULATOR 0280160560 | eBay


If your regulator has a rubber hose connecting the steel pipe to the inlet manifold then you should see more than 2psi variation as you open the throttle, but the engine must be on load to see it more than momentarily. Another check would be to (carefully) pull that hose off the regulator: do you get petrol from the regulator, indicating a split diaphragm?
 

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Discussion Starter #20
I'm not sure where it's located but the vacuum hose related to petrol is blue and it goes to the canister removing it didn't give any spit back, I honestly have never seen a fuel pressure regulator in my engine bay I think it's in the fuel pump assembly?
 
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