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Discussion Starter · #1 ·
Morning guys

It's cold in the mornigs again and my engine is back to where it starts allright but after a minute or two i have to stop for red light and it begins running 500-600 revs very unevenly and then stops.
Anybody have a suggestion. A sonsor maby ?
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merry christnmas :D
 

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I presume you have not modified your air intake in any way, so icing in the air intake is not a problem?
Does the problem go away as the engine gets warmer? If not, it sounds like the engine is running a little weak so you could check the air intake route for any leaks (from the thtottle body to the engine). There are many other things it could be but its worth a check.
It may sound obvious but also check that your oil level is topped up. I alweays have a rough tickover and general running when my oil level is near minimum and the 155 (like a lot of alfas it would seem) likes to eat oil quickly!
Finally, if the problem does go away, maybe its so cold in the morning that the oil is too thick and causing a problem until it warms up? What rating is your oil? Does it need changing (i.e. its full of dirt)?
Best to check the simple stuff before getting worried wink
 

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Hammer
If the above quick checks don`t find anything it may be that the air intake temperature sensor is faulty. This would explain a lean mixture when the air is cold.
The sensor is just upwind of the throttle. I don`t know how you would test it (JB, any ideas?) but I guess you could just disconnect it and see if the problem is worse. If the problem is the same then the culprit may be found!

Hurray - a positive email!
:D
 

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Discussion Starter · #4 ·
Thanks Cris

For your answers today.
See here's another possible sensor malfunction.
You have today enlightend me which is the air temp sensor.
But i dont think it could be the one since the fault seems to disappear after a couple of minutes running. The air temp would be the same then.
I'm running with standard air intake with KN filter and Selenia 20K.

By the way, if you attach a multimeter to the temp sensor you should be able to see some changes in Ohms if you puts the sensor in your coffecup fx. :) . If not it must be faulty.

Is there a coolant temp sensor somewhere and does the ECU get informatin from it ?

Cheers.
 
G

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Hi Guys,

The air temperature sensor shouldn't cause the engine to stop - the lambda probe should feed back the weak mixture and cause the ECU to richen the mix.

The air temp sensor should cause the system to select a different map for the ECU, but it shouldn't be far different.

I would possibly look at the engine temperature sensor located on the thermostat housing - this tells the ECU the engine temperature (There is a seperate sensor that drives the dash gauge). If this is not operating correctly then the ECU will be running far too rich, and the engine will idle really badly and stall..

Other alternative is the good old Lambda itself, although I have never come across a failed lambda causing the engine to stall...

Best advice is to get the ECU diagnosed on a dealer computer... This should give a definative answer on what is going on as the diagnostics should be able to show what is happening to the mixture, and the relevant sensor readings..

Hope this helps

J
 

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Hi James,
I agree in principle to your comment on the air temp sensor being corrected by the lambda feedback. However, I have found that at sub-normal tickover speeds, the feedback is not fast/accurate enough to compensate for a originally poor mixture and the engine can still stall.
This is especially prevelant if the revs drop suddenly from high to low when you slow to a stop, its not a problem if you are changing gear as the change forces the revs back up again. If you dip the clutch and take your foot of the accelerator, an originally weak mix can let the revs drop to a point where the engine struggles to recover and the lambda feedback swings to over-fuel. If there is an air leak it fails and the engine dies.
Sounds like I`m making it up but I`ve experieced this in minute detail when dealing with my Autogas conversion. Its amazing what you can learn when you have to!

Blah, blah, blah. I can`t stop spouting today.

Hammer,
Give your car a quick check for air leaks, then take the car for a quick diognosis like James suggests. Its easier in the long run if you don`t know where to look yourself.
 

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Discussion Starter · #9 ·
Thank you

For the advice.
if i chose to have the diagnostic run, wouldn't you suggest to run it on a very cold engine ?

And what does the water temp sensor do and where about is it located ?
 
G

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When you take the unit for diagnostics, the system should be able to see what the problem is no matter what the temperature is - I would try and start with the engine cold, nut it is not always required.

The diagnostic should show if there is a failed sensor in the ECU log.

If this is not the case, then the usual procedure is to check the parameters of all of the sensors.

There should also be the ability to check the mixture ratio in one of the screens (can't remember the name of the screen).

An easy way to see if there is a fault with the air Temperature sensor is to disconnect it. This will bring on the ECU light on the dash, but will also force the ECU to use a default value in place of the reading from the sensor - this should cause the engine to run a little poorly, but it should not stall.

I have found that you can disconnect a number of sensors and the car will still run without stalling...

You can disconnect the lambda, air temp and air flow sensors (all at the same time) and the thing will still run (badly)!!

I still think that the air temp sensor should not cause the issues your having - it doesn't do enough to the overall set-up of the ignition system to cause such problems - infact on my rally car (with a highly tuned 170bhp 1.4 16v vauxhall engine) there is no air temperature sensor and it runs fine all weathers...

hope this lot helps

James
 
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