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Discussion Starter #1
Been having some problems with my cruise control where it will switch itself off. If it is set at 70 mph it will stay on all day, but anything above that and it will switch itself off. The higher it's set the quicker it will turn itself off.
The car then needs to be switched off before the cruise control will be able to work again.

I've scoured the forum and seen the usual brake and clutch switch. But I don't think it's that in my case. I've noticed that the faster you go the more the speedo starts to fluctuate. Say at 80mph (on a private road of course) the speed will jump above and below by about 3mph or so.

Plugged in MES and even at 30mph the N/S front wheel speed jumps quite a bit while the other 3 are smooth. Changed the sensor and gave a blow out in the little hole with a air compressor. Tried it again and it's still the same!

So I'm thinking there may be dirt or rust somewhere giving it a bad reading, but I'm not sure if the wheel speed sensor picks up from the bearing or the cv joint?? Any other ideas what it could be?

Blue line is the N/S front sensor
 

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I'm 90% sure that if any Cruise Control system detects a difference in speed from any given wheel then it de-activates. the Stilo used to knock itself off if one wheel changed speed/if ASR was trying to keep it in check. the 159 seems very similar.

a couple of checks you can do yourself, for free, are:-
1) if you can see the exciter ring on the drive shaft is it a toothed ring or a smooth magnetic 'ring'... check for obvious signs of damage to either chips/breaks/cracks/missing pieces/etc. (edit:- just looked again at the graph and i doubt this will be an exciter ring fault due to the 'slow' fluctuation of speed)

2) swap the front speed sensors and see if the fluctuation fault follows it to the other side. if it does then it is most likely a sensor fault. (edit:- almost certain this is a sensor starting to break down so i'd advise to swap sensors to confirm)

i would have expected to see a 'signal implausable' fault or similar in the engine ECU but this may not throw a MIL even if it has the fault.
 

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Discussion Starter #3
I've put a brand new sensor on that one wheel, and it is still the same.
The graph shows reading at approximately 30mph. Will have to have a look at the exciter ring for any damage!
 

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Ok, so had another look today and it seems as though the sensor picks a signal up from what looks like a magnetic ring on the wheel bearing. (I may be wrong) but this was all covered in grease from the wheel bearing. Cleaned it up but still no difference!

Couldn't see any obvious damage to it. Or does the sensor pick a signal up from the cv joint??

Graph is at approximately 65mph
 

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Ok, so had another look today and it seems as though the sensor picks a signal up from what looks like a magnetic ring on the wheel bearing. (I may be wrong) but this was all covered in grease from the wheel bearing. Cleaned it up but still no difference!

Couldn't see any obvious damage to it. Or does the sensor pick a signal up from the cv joint??

Graph is at approximately 65mph
i dont know where it picks up from, whichever is directly below the sensor beit CV or WB. mag stripes are usually WB and toothed wheels are usually on the CV... 'usually'

i want to say its mechanical, as you've changed the sensor and the chance of a new one being dicky is incredibly slim, but for me there just isnt enough to say its a mechanical fault. i would expect the pulse to be speed related and it doesnt seem to be.

im as stumped as you are :depressed:
 

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Discussion Starter #6
The only thing I can think is maybe some movement it the wheel bearing? Looks like it's seen better days as the grease is coming out of it now. So maybe the slightest movement laterally not just rotational is narrowing the gap slightly? Only sort of explanation I can think of! May try to replace that bearing and go from there!
 

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Same as on mine...speedo jumps and cc cuts out at 60mph. I have f.l bad bearing. Will change next week to ser if it works.
 

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Discussion Starter #8
Think I may order one on Monday too. let me know if it solves it if you get around to it before me
 

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It's strange...swapped that one a year ago and it might been at the same time the cc crashed. Now the bearing is gone again and i really hope it is the problem!..not many good things about that bearing.
 

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I'm told that on the 156 airbag system, Alfa left hand side actually is the right hand side, a mix up over left hand/right hand drive I suppose. Couldn't be the same here could it? Easiest way to tell might be to plot the speeds while driving in tight circles, and check that the outside wheel speeds are being recorded as faster than the inside ones. That, or jack a wheel up and spin it.
 

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Discussion Starter #11
That may be a possibility, I could understand if it said near side front or offside but I would have thought left is left no matter what side drive it is. Never less worth a look at!
 

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Ok, hooked up MultiECU and logged. See attached picture

Seems like all 4 sensors and voltage are totaly mad. No fault code in system. Could a bad battery cause this?

Same behaviour, if i increase speed with cc, it´s ok up to 60mph. But at 60 it cuts out.

Curvo at top is battery and is about 14,5v until it randomly drops.
 

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Discussion Starter #13
I wouldn't have said yours looks like a sensor problem as it is so random, one minute there's 2 playing up then it's the other 2 playing up. Which line is the battery voltage?

Try cleaning the plugs at the sensors, also the plug at the abs.
May be some water ingress, may be worth while changing the battery and getting the alternator checked too
 

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I wouldn't have said yours looks like a sensor problem as it is so random, one minute there's 2 playing up then it's the other 2 playing up. Which line is the battery voltage?

Try cleaning the plugs at the sensors, also the plug at the abs.
May be some water ingress, may be worth while changing the battery and getting the alternator checked too
Instrument panel connections:

The instrument panel E50 is connected from pins 3 and 4 of connector A with the Body Computer M1 and via the latter to the entire CAN: the signal reaches the electronic speedometer (from the ABS control unit M50) via the CAN: the same signal is replicated by pin 16 of M50 at pin 7 of connector A of the Body Computer M1.

The electronic rev counter receives the engine rpm signal received from the engine management control unit M10 via the CAN.

ABS module conn.:

FUNCTIONAL DESCRIPTION
The ABS electronic control unit receives a power supply (at pins 12 and 25) directly from the battery from the line protected by fuses F5 and F4 of the engine compartment junction unit B1.

The ignition-controlled power supply (INT) arrives at pin 23 from the line protected by fuse F42 of the junction unit under the dashboard B2.

The control unit is earthed at pins 11 and 24.

The four sensors K70, K71, K75, K76 send wheel speed signals respectively to pins 19-20, 7-8, 21-22, 9-10 of control unit M50.

The brake pedal switch I30 sends an enablement signal to pin 17 of the control unit M50: all intervention of the ABS is excluded unless the brake pedal is pressed (signal from N.A. contact); switch I30 receives an ignition-controlled power supply (INT) from fuse F37 of junction unit B2.

The "discreet" speedometer signal sent by the Body Computer M1 leaves from pin 16 of M50; the same signal is replicated via the CAN.

Via the CAN line, ABS control unit M50 is connected - from pins 1 and 2 - to the engine management control unit M10, the Body Computer M1 and the instrument panel E50, to manage the ABS warning light and, if the problems concern the EBD function, the low brake fluid level/handbrake applied warning light.

The autodiagnostic data can be read by connecting to connector C of the Body Computer M1 - pin 1: it receives signals from pin 6 of control unit M50 via the special diagnostic line.


Hope this can help you :)
 

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Sensors i think is ok. Even changed one a year ago and that one behaves like the rest.

I will try to clean some connectors/ground and even change battery. Tried to charge it all weekend, still not full.

The dips are present when im standing still as well.
 

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Actually the problem started when front wheel bearings were changed to a non oem. Pretty much sure that it is the fault. Not uncommun if you do a search.
 
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