Very heavy stuttering above 2200 RPM

[Raffadakis]

Dear all,

Saturday, blue skies, why not go for a ride (Volvo 480, 1.7 ES)?
Well... I was accelerating in 2nd gear, up to about 5000 RPM then there was a wierd noise, as if the boost dropped for a second. I switched gear to 3rd and doom began. No matter what gear I had in, above 2200 RPM there was a huge stuttering, as if the RPM limiter would switch in and out every second. I thought the car would fall apart.... the gear knob was shaking!
First thought: Clutch gone... but no, clutch seems to work perfect, easy gearshifting no smell, nothing.
One wierd thing I noticed: When the stuttering begins (2200 RPM) the fuel consumption indicator in the infocenter goes up to 20-25 liters instantly, no matter how much I'm on the gas.
Second guess was, one of the sensors (or even the ECU) must have gone. Is there an RPM sensor for the ECU? If so, where could I find that in the engine compartment? Other suggestion would be the sensor measuring the engine position, as this regulates the ignition.

Does anyone of you have an idea, what it could be?

Many thanks for your help in advance.

Greetz
Raff

[bkf_uk]

Lots of stuutering at higher revs would suggest to me that you have an ignition fault, check leads plugs ect,ect.
Also when was the fuel filter last done? a clogged fuel filter would also have a simmilar effect due to fuel starvation!

[bkf_uk]

Check the pipes going to the turbo controller (the red/yellow/black ones, especially the red one, which if I remember rightly is the one that goes to the wastegate).

2,200 may be too low for boost cut so I may be barking up the wrong tree completely, but checking a couple of pipes shouldn't waste too much of your time!

Ah this could be good! Check the main air inlet piping from the MAF on wards for leaks, if there is a major air leak the car just wont run! in effect the MAF isnt reading correctly! (mine was realy bad when i lost a pipe from the intercooler, it just wouldnt run past 2000 rpm!)

Quckly before the pc dies!!!

[Raffadakis]

Thanks a lot for your hints. Well just for clarification: I wouldnt even call it stuttering but rather "stop-start-stop-start".... so seems to tear the car apart! and it only happens when I got a gear in. Without gear in or clutch down, it's perfectly fine. I was thinking about the MAF, but am not sure, if this wouldn't affect the no-gear in running as well.

HT leads are fine (almost new) and no visible damage so far (will have a better look next weekend). I'll see if I can find my wiring diagram to check which sensor it might be.

The wrong fuel usage display might be related to some faulty input to the ECU I suppose.... so I'm still thinking it might be some sensor involved in the ignition or RPM measuring system.

EDIT: The fuel filter might indeed be something I might check. With the history that car has, nothing is certain....

[Robou]

We're talking ES and I don't know much about names and things but at the moment I have a strong believe that turbo and MAF hardly can contribute to the misbehaviour. If it isn't the fuel filter, try a different coil. When the engine is under load the compression rises and the plugs need a higher voltage to produce a spark. The insulation within the coil may be defective and this gets worse every time a spark finds its way at this spot, a sort of conducting carbonised brigde is building up.

[Raffadakis]

Thank you Robou for your hints. I thought compression was fix and independent from engine load? Isn't that related to cylinder and piston size and movement? It only happens when gear in.... which means to me, that under load, a sensor provides wrong signals to the ECU and/or Fenix ignition control/coil. I'm actually quite convinced, that it has to be the RPM sensor. Did not find any other sensor on the diagrams which might affect the ignition in that way. Knock sensor probably, but honestly do not know how this one works at all
Lambda sond?! But I guess a Lambda sond failure would probably not cause such heavy stuttering.

What is the fuel consumption on the infocenter based on? Any particular sensor? As this rises sky high, once the stuttering begins.

Why does that happen just before I was about to buy new winter tires and give it a oil change....

[Robou]

Blame Murphy.
The moment you put the motor under load you open the throttle, the cylinders fill and this has to be compressed. The quantity of mixture sucked in is decisive for the pressure at spark. What you refer to as being constant is the compression ratio.
I was searching for a logical explanation for your trouble, what you seem to be doing is summing up anything that may be wrong. You started by telling it occured the first time at high revs and high load, then you claim it is above 2200 rpm and now it happens at touching the clutch. This sounds very much like a deteriorating coil as I pointed out.
But unfortunatly not all problems are solved by logic and from a distance. So good luck.

[Robou]

Forgot to say something intelligent about the fuel consumption figure. It is computed by the time the injectors are triggered within a specific covered distance, being about 30 meters. Computing starts at a certain speed and maximises at about 23 Km/l.
Presuming what you read is what happens, it would indicate that the injectors are fully opened. For what reason I don't know, but then a spark dancing in your coil instead of at the plugs could easily cause some strange behaviour in the electronics.
There's an easy way to find out whether the coil is the culprit: Disconnect a HT lead from a plug, insert a well-insulated screwdriver and hold the metal about 2 cm from the block while the engine is running. There should be a spark. If not, the spark is taking the easier way: Through the coil, or maybe somewhere in the distributor. You will hear it.

[Raffadakis]

Thanks againg for your hints. My comments weren't meant as an offence of any kind.
I didn't happen at high revs, but "something" happend when the engine had high revs and after gear change I had the stuttering always above 2200, no matter what gear, except, as said, when there is no gear in. So it seems as if something broke instantly at a point and caused the stuttering above 2200. And after that "something" that happend, every time the stuttering begins (no matter how wide the throttle is open), fuel consumptions rises up to 25l. This is must have been caused by that "something" as before the reading in the infocenter was fine.

I'll check the engine compartment this weekend and will check, whether I visually can see any damage. If not, than off the the electronic/ignition system.