[MONTOUR]

O k guys i need help just finished rebuilding engine and it runs but theres a problem in first gear it runs to 5000rpm and it feels like fuel cut i put a boost guage on it and max boost in third is 8psi car pulls hard to 5000 then sputters i go in to second and pulls hard again and does it again i can't floor it cause it just hesitates what is up !

 

[JOC]

hey, somebody from germany !
maybe you must look after your fuelfilter ! changed sometimes ?
have you a manometer for the fuelpressure ?
i hope you find the problem !
best wishes !
markus

 

[A_Möller]

First and second gear has the same boost limit, so if you shall compare the behaviour in first gear, comapre to 3:rd, 4:th or 5:th.

/A

 

[MONTOUR]

well i was on the autobahn today and as usual i tried to see what would happen first,second,third,fourth,fifth they all sputtered at about 5000rpm also the exhaust smells rich and there is a crack in the main intake hose that connects to the throttle body,i put a little spit on it and reved it up and guess what it made bubbles. Can this be the problem? I was thinking since the exhaust was rich either the coolant temp sensor was bad or the o2 sensor i had the same problem with my 200sx nissan it turned out to be a coolant sensor.another thing i read in the service manual about limp mode for motronic engine controls does this year have it 92?

 

[jimybob]

you must first fix any loose or split hoses the e.c.u will over compensate for the lean mixture caused by an air leak.

 

[A_Möller]

Yes, of course you should fix the leaking hose as soon as possible. But to be honest I don't think that is the major problem. The MAP sensor is mounted close to the throttle and everything happening before that sensor will not affect the mixture. At full throttle you have a over pressure in the intake hoses and you will loose turbo pressure if it leaks. And at lower boost it injects less fuel. Nothing strange with that. How much is 8 psi?

The Alfa has a Weber Marelli P8 control system, not a Bosch Motronic, and as far as I know it doesn't have this "limp mode".

/A

 

[Clive]

Don't know sh*t about turbos, but 8psi is 0.5 bar. Good luck! wink

 

[pyros]

The easiest way to sort this out would be to get a lancia/alfa tester plugged into the car diags port. Will show any problems immediately.

I've had split hoses before, and you can usually tell when you havew got one as anything other than very light throttle will cause the car to judder as even though you are still getting boost, the aps (absolute pressure sensor) is reading atmospheric pressure and not adding extra fuel, and the car runs very very lean.

Steve

 

[pyros]

Oh, and 8psi is just over 0.5 bar (1 bar = 14.3 psi i think)
Which is the level base boost should be set to. In 3rd 4th and 5th the overboost valve allows the full 1- 1.1 bar

 

[A_Möller]

Steve,

Are you really sure about the pressure measured?

If the leak is small compared to the flow, the pressure will be sufficiently higher than the atmospheric pressure. And as the Manifold Absolute Pressure sensor (Absolute Pressure Sensor) reads the actual pressure in the intake manifold, not the turbo downstream pressure, the ECU will always read the correct pressure and give a correct mixture.

I found the boost of 8 psi to be close to 0.55 bar and that in turn is close to 0.6 bar that is the base boost (correct?) which is strange. Could it be a coincidence? Or does it refuse to boost more when the turbo efficency is that low? And how does it know?

/A

 

[pyros]

Hi A,

my previous posting takes into account my personal experiences with split hoses. I've had a split small bore hose coming off of the manifold, a detatched hose from the APS and a cracked intercooler end piece.
In the first two instances the engine ran 'OK' with little or no throttle, but once you moved up the rev range and started applying more throttle the engine would stutter and not pull.
With the cracked intercooler, the engine ran fine but just did not produce any boost.

If you have ever tried to blow into a boost gauge, you will find that atmospheric pressure is actually pretty high, so if you try to apply another 50% pressure (1.5bar abs) even if you have a very small split, most of the pressure will escape out through the split.

If you have a split in a large bore hose, (ie the intercooler pipe) all of the pressure from the turbo will escape out through it, no boost with the APS registering no boost.

However if it is a small bore hose coming off of the manifold, the manifold pressure will not be as high as it should be, but will be above 1 bar abs, but the pressure in the small bore hose at the end after the split, (near the APS sensor) will be far closer to 1Bar than the manifold.

Therefore the engine is getting boost, but the APS is not registering it. Hence the ecu doesn't add enough extra fuel and the engine runs very lean.

This is pretty much my take on the situation, but I'm no expert, if anyone can put me right on any of the points i've made please speak up.

The problem with the guys original problem is that there are so many things that could cause this, you could swap every sensor in the engine and still not cure the problem, it is far easier and faster to take a car with a problem such as this to a fiat/lancia/alfa garage and get the car diagnosed correctly before any major damage is done.

Cheers

Steve

 

[A_Möller]

Your'e right, Steve.

/A

 

[jimybob]

never underestimate the problems even a small split in any hose can cause.1bar=atmospheric pressure,that we all breathe.

 

[Spike Q4]

Concerning Montour's original problem, i have an easy to check advice because i had quite the same problem on the same engine.

If you still couldn't fix the problem, try to check the two underpressure tubes that go to the the small underpressure-box (pierburg) that is fixed on the black front sheet metal. Standing in front of the car you will find it easily on your right hand just above the cooler. Sometimes one the tubes gets loose and it results in the problems you described.

Let us know if you fixed the problem and how!!!

Let's race, Spike Q4

PS: I am interseted in any technical documentation for the 2.0 turbo engine. Who can help?