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Discussion Starter · #1 ·
Hi everyone!
I have a question about the fuelpressure in the 155 Q4.
The workshopmanual says that it should be 2,5bar when the fuelpump is activated by turning the ignitionkey to the MAR-position (without starting the engine). I got that exact reading when I checked the pressure but when I started the engine the fuelpressure decreased to 2,0bar. A friend of mine has asked a local Lancia-mechanic and he had said that the pressure should be the same even when the engine has started. Does anyone of you know how it should be? Could there be some problem with the fuelpump? (I´ve recently changed the fuelfilter.) Or could it be a faulty injctor? When I changed the sparkplugs two weeks ago I noticed that the sparkplug in cylinder nr.3 was slitly darker then the rest and the pistonhead was covered with carbonoil-"dirt".

Best regards / Mårten
 

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Hi ,
You wrong something ,
I have service manual too (Q4).
Fuel pressure is 2.5 bar and ofcourse you must check it when engine is run ! dont mar position .
And additional info ,this is most importand standart fuel pressure ..-when you close back fuel line you must read on gauge 4 bar ,or near 4 bar .
If you read 3 bar or little your fuel pump dead and very dangerous when you run under full boost (like leanmixture)
 

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I read again ,
you see 2 bar when engine run ,
ok you must rise up fuel pressure .
can you make it ?
Q4 have a adjustable pressure regulator ,it placed near butterfly ,look it ,and rise up 2.5bar .
 
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Discussion Starter · #4 ·
Thanks for your reply MaxiBoost!
I´ve tested driving the car with 2,5bar (fuelpressure with engine running) and it performed much better but if I adjust the pressure the way the workshopmanual says it should be adjusted then the pressure is 2,0bar when the engine is running. That is the strange thing, why is there a difference? Something must be wrong.

/Mårten
 
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Discussion Starter · #6 ·
Hi Moppe,

Actually I'm occupied with a similar problem on same engine (see my recent topic on Q4 engine running on three cylinders).
Well, I also had a look to the Q4 manual. They say it should have 2,5bar in MAR position WITHOUT starting the engine. In MAR position the fuel pump begins to work but none of the injectors opens. At this moment there's a higher resistance in the fuel circuit. When the engine runs, fuel is evacuated by the injectors, there's a higher flow in the circuit (at the same pump performance) and pressure decreases. That seems normal to me.
Maybe your problem is another!? But what about your engine? Does it run normally?

(P.S.: Regarding the replacement of an injector, have a look on MaxiBoost's post on the topic mentioned before. He has done it once. Seems to be one hell of work!!!!)
 
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Discussion Starter · #7 ·
Hi Spike Q4,

I´m thinking the same way as you do about the fuelpressure and why it decreases when the engine is running. But I get confused when I hear mechanics saying that it should be the same. Who is right?

My engine runs normally, the only thing is that it sometimes hesitates during overboost and that it consumes more fuel then I think it should. What that depends on I don´t know but I will get a compressiontest to see that there isn´t anything wrong with the cylinders, pistonrings or headgasket.

Regarding changing injectors, I´ve been thinking about that. Isn´t there a chance to remove the intake without removing the cylinderhead? If there was a chance the unthighten the steelband with a screw (I don´t know the english word for that part) that secures the intake to the cylinderhead. I know that there isn´t much space around the intake but if it worked, what a relief!

/Mårten
 
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Discussion Starter · #8 ·
Hi Moppe,

Did you check your spark plug and ignition cable on cylinder no.3 really well? Sometimes spark plugs and ignition cables are defected even if they're giving a spark. However, after the compression test you will know more! I hope it's not a compression loss. Maybe it's the injector that starts to get dirty (like mine that seems to be completely blocked meanwhile).

So long
 
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Discussion Starter · #9 ·
If there was a chance the unthighten the steelband with a screw (I don´t know the english word for that part) that secures the intake to the cylinderhead.
jubilee clips....im sure that the manifold does came off without taking the head off(ive done it on an intergrale)
 

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Hi everyone!
Selfish question: how can I get that Workshop Manual or Service Manual you are talking about? I think I´ve seen it once... is it a big folder full of information that doesn´t come together with the tiny little red book that originally comes with the car?

If that´s the case... I´d love to have it!! :)

Thanks & regards.
 
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Discussion Starter · #11 ·
Hi Moppe and Maxiboost,

the fuel pressure regulator regulates the fuel pressure (honest! :D )relative to the pressure in the inlet manifold. That way the pressure difference in the injectors is constant, making it easier for the computer to calculate fuel delivery from injection pulse length.
If you've fitted a rising rate regulator it gets a bit more complicated, of course.
 
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