Help me diagnose this splutter...
 

156 2002, 2.0 JTS petrol. I (the car)had a splutter/cough a year or so ago
and it eventually went away on its own. Its come back now and I would like
to at least figure out what is causing it, if not fix it. The problem:

Its independent of gear (done it in 3rd, 4th 5th). I don't tend to rev over
about 4000 most of the time as its a nice torquey engine. Problem occurs
under load, usually at around 2000 revs. It is repeatable - the 270 degree
slip road onto the M8 at the top of Livingston is about a 50mph corner, 5th
gear. As I come out of it I speed up to er... 70 (ho humm!) and it will
splutter most times there. It also does it in 3rd coming out of the silly
little roundabouts they stick along in-town dual carriageway 40mph
stretches. Its a cough/splutter, lack of power, followed by 'beep beep'
motor control failure - go to dealer. As I feel the splutter starting, if I
back off on the accellerator and just speed up more gradually all is well.
If I drop a cog and increase the revs, all is fine.

I have ruled out dirty fuel as its been through several fill ups.
I have rules out engine temperature as it doesn't make any difference.
I have ruled out spark plugs and electrics because the revs are low, so the
demand is not so much - wouldn't this cause problems at higher revs when
there are more sparks per minute?
I have rules out air flow for the same reason - the engine isn't getting
through as much air as when the revs are higher.

This (in my mind) leaves the knocc sensor, or something else.

Any ideas / suggestions?

GT

Help me diagnose this splutter...
 

On 20/01/2011 12:13, GT wrote:
> 156 2002, 2.0 JTS petrol. I (the car)had a splutter/cough a year or so ago
> and it eventually went away on its own. Its come back now and I would like
> to at least figure out what is causing it, if not fix it. The problem:
>
> Its independent of gear (done it in 3rd, 4th 5th). I don't tend to rev over
> about 4000 most of the time as its a nice torquey engine. Problem occurs
> under load, usually at around 2000 revs. It is repeatable - the 270 degree
> slip road onto the M8 at the top of Livingston is about a 50mph corner, 5th
> gear. As I come out of it I speed up to er... 70 (ho humm!) and it will
> splutter most times there. It also does it in 3rd coming out of the silly
> little roundabouts they stick along in-town dual carriageway 40mph
> stretches. Its a cough/splutter, lack of power, followed by 'beep beep'
> motor control failure - go to dealer. As I feel the splutter starting, if I
> back off on the accellerator and just speed up more gradually all is well.
> If I drop a cog and increase the revs, all is fine.
>
> I have ruled out dirty fuel as its been through several fill ups.
> I have rules out engine temperature as it doesn't make any difference.
> I have ruled out spark plugs and electrics because the revs are low, so the
> demand is not so much - wouldn't this cause problems at higher revs when
> there are more sparks per minute?

*maybe*
> I have rules out air flow for the same reason - the engine isn't getting
> through as much air as when the revs are higher.
>
> This (in my mind) leaves the knocc sensor, or something else.
>
> Any ideas / suggestions?
>

Is it drive by wire? If so, I'd bet on the throttle pot.
Failing that I'd be giving the AFM a stern look.

--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3
Tyger, Tyger Burning Bright (Remove rust to reply)
116 Giulietta 3.0l Sprint 1.7 GTV TS GT 3.2 V6
Triumph Sprint ST 1050: It's blue, see.
#www.cuore-sportivo.co.uk

Help me diagnose this splutter...
 

"Catman" > wrote in message
...
> On 20/01/2011 12:13, GT wrote:
>> 156 2002, 2.0 JTS petrol. I (the car)had a splutter/cough a year or so
>> ago
>> and it eventually went away on its own. Its come back now and I would
>> like
>> to at least figure out what is causing it, if not fix it. The problem:
>>
>> Its independent of gear (done it in 3rd, 4th 5th). I don't tend to rev
>> over
>> about 4000 most of the time as its a nice torquey engine. Problem occurs
>> under load, usually at around 2000 revs. It is repeatable - the 270
>> degree
>> slip road onto the M8 at the top of Livingston is about a 50mph corner,
>> 5th
>> gear. As I come out of it I speed up to er... 70 (ho humm!) and it will
>> splutter most times there. It also does it in 3rd coming out of the silly
>> little roundabouts they stick along in-town dual carriageway 40mph
>> stretches. Its a cough/splutter, lack of power, followed by 'beep beep'
>> motor control failure - go to dealer. As I feel the splutter starting, if
>> I
>> back off on the accellerator and just speed up more gradually all is
>> well.
>> If I drop a cog and increase the revs, all is fine.
>>
>> I have ruled out dirty fuel as its been through several fill ups.
>> I have rules out engine temperature as it doesn't make any difference.
>> I have ruled out spark plugs and electrics because the revs are low, so
>> the
>> demand is not so much - wouldn't this cause problems at higher revs when
>> there are more sparks per minute?
>
> *maybe*
>> I have rules out air flow for the same reason - the engine isn't getting
>> through as much air as when the revs are higher.
>>
>> This (in my mind) leaves the knocc sensor, or something else.
>>
>> Any ideas / suggestions?
>>
>
> Is it drive by wire? If so, I'd bet on the throttle pot.
> Failing that I'd be giving the AFM a stern look.

Yup, I believe there is a small computer between my right foot and the
engine, instead of a cable!

I looked at the MAF (?) sensor in the air intake when I was replacing the
thermostat the other week. I had never seen a MAF before and was thoroughly
un-impressed!. I covered the top of the air intake with a cloth to avoid any
nasties getting in there, and it all looked clean as a whistle when I put
the hose back on. All has been fine for a few weeks since the thermostat
replacement, so I don't think its anything that I've introduced, but
obviously I can't say for sure!

Help me diagnose this splutter...
 

On 20/01/2011 12:57, GT wrote:
<snip symptoms>
>>>
>>
>> Is it drive by wire? If so, I'd bet on the throttle pot.
>> Failing that I'd be giving the AFM a stern look.
>
> Yup, I believe there is a small computer between my right foot and the
> engine, instead of a cable!

Mine has a cable, alright. It's just that it carries a signal (well a
resistance really, but not sure if you can really carry a resistance) to
the ECU.

> I looked at the MAF (?) sensor in the air intake when I was replacing the
> thermostat the other week. I had never seen a MAF before and was thoroughly
> un-impressed!. I covered the top of the air intake with a cloth to avoid any
> nasties getting in there, and it all looked clean as a whistle when I put
> the hose back on. All has been fine for a few weeks since the thermostat
> replacement, so I don't think its anything that I've introduced, but
> obviously I can't say for sure!

Well the MAF on the TS was a known issue. Even if they looked OK, when
the wire got dirty, it was game over.

OTOH if it *was* the MAF, you'd maybe get issues more. I'm definiteley
leaning to the variable resistor on the throttle pedal being worn.


--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3
Tyger, Tyger Burning Bright (Remove rust to reply)
116 Giulietta 3.0l Sprint 1.7 GTV TS GT 3.2 V6
Triumph Sprint ST 1050: It's blue, see.
#www.cuore-sportivo.co.uk

Help me diagnose this splutter...
 

On Thu, 20 Jan 2011 15:42:45 +0000, Catman
> wrote:

>On 20/01/2011 12:57, GT wrote:
><snip symptoms>
>>>>
>>>
>>> Is it drive by wire? If so, I'd bet on the throttle pot.
>>> Failing that I'd be giving the AFM a stern look.
>>
>> Yup, I believe there is a small computer between my right foot and the
>> engine, instead of a cable!
>
>Mine has a cable, alright. It's just that it carries a signal (well a
>resistance really, but not sure if you can really carry a resistance) to
>the ECU.
>
>> I looked at the MAF (?) sensor in the air intake when I was replacing the
>> thermostat the other week. I had never seen a MAF before and was thoroughly
>> un-impressed!. I covered the top of the air intake with a cloth to avoid any
>> nasties getting in there, and it all looked clean as a whistle when I put
>> the hose back on. All has been fine for a few weeks since the thermostat
>> replacement, so I don't think its anything that I've introduced, but
>> obviously I can't say for sure!
>
>Well the MAF on the TS was a known issue. Even if they looked OK, when
>the wire got dirty, it was game over.
>
>OTOH if it *was* the MAF, you'd maybe get issues more. I'm definiteley
>leaning to the variable resistor on the throttle pedal being worn.

The MAF on my diesel Alfa failed and gave EXACTLY the same symptoms as
the OP describes. FWIW.

--
Z
Scotland
Alfa Romeo 156 2.4JTD Veloce Leather (sold)
'Oil' be seeing you..
(Email must have the word 'Alfa' in the
subject line to get through auto-filtering)

Help me diagnose this splutter...
 

On Thu, 20 Jan 2011 12:57:58 -0000, "GT" > wrote:

> I had never seen a MAF before and was thoroughly
>un-impressed!.

Google for it. It's just a hot wire that's cooled by the passing mass
of air. There'll be a control box but I'd expect all you would see is
a tube and a bit of wire. It's been discussed here before.

--
Z
Scotland
Alfa Romeo 156 2.4JTD Veloce Leather (sold)
'Oil' be seeing you..
(Email must have the word 'Alfa' in the
subject line to get through auto-filtering)

Help me diagnose this splutter...
 

"Zathras" > wrote in message
...
> On Thu, 20 Jan 2011 12:57:58 -0000, "GT" > wrote:
>
>> I had never seen a MAF before and was thoroughly
>>un-impressed!.
>
> Google for it. It's just a hot wire that's cooled by the passing mass
> of air. There'll be a control box but I'd expect all you would see is
> a tube and a bit of wire. It's been discussed here before.

Yes - I've seen lots of talk about them here, I was just complete
unimpressed with the actual part - just as you describe - a little bit of
wire poking through the side of the air intake!

Help me diagnose this splutter...
 

"GT" > wrote in message
eb.com...
> "Catman" > wrote in message
> ...
>> On 20/01/2011 12:13, GT wrote:
>>> 156 2002, 2.0 JTS petrol. I (the car)had a splutter/cough a year or so
>>> ago
>>> and it eventually went away on its own. Its come back now and I would
>>> like
>>> to at least figure out what is causing it, if not fix it. The problem:
>>>
>>> Its independent of gear (done it in 3rd, 4th 5th). I don't tend to rev
>>> over
>>> about 4000 most of the time as its a nice torquey engine. Problem occurs
>>> under load, usually at around 2000 revs. It is repeatable - the 270
>>> degree
>>> slip road onto the M8 at the top of Livingston is about a 50mph corner,
>>> 5th
>>> gear. As I come out of it I speed up to er... 70 (ho humm!) and it will
>>> splutter most times there. It also does it in 3rd coming out of the
>>> silly
>>> little roundabouts they stick along in-town dual carriageway 40mph
>>> stretches. Its a cough/splutter, lack of power, followed by 'beep beep'
>>> motor control failure - go to dealer. As I feel the splutter starting,
>>> if I
>>> back off on the accellerator and just speed up more gradually all is
>>> well.
>>> If I drop a cog and increase the revs, all is fine.
>>>
>>> I have ruled out dirty fuel as its been through several fill ups.
>>> I have rules out engine temperature as it doesn't make any difference.
>>> I have ruled out spark plugs and electrics because the revs are low, so
>>> the
>>> demand is not so much - wouldn't this cause problems at higher revs when
>>> there are more sparks per minute?
>>
>> *maybe*
>>> I have rules out air flow for the same reason - the engine isn't getting
>>> through as much air as when the revs are higher.
>>>
>>> This (in my mind) leaves the knocc sensor, or something else.
>>>
>>> Any ideas / suggestions?
>>>
>>
>> Is it drive by wire? If so, I'd bet on the throttle pot.
>> Failing that I'd be giving the AFM a stern look.
>
> Yup, I believe there is a small computer between my right foot and the
> engine, instead of a cable!
>
> I looked at the MAF (?) sensor in the air intake when I was replacing the
> thermostat the other week. I had never seen a MAF before and was
> thoroughly un-impressed!. I covered the top of the air intake with a cloth
> to avoid any nasties getting in there, and it all looked clean as a
> whistle when I put the hose back on. All has been fine for a few weeks
> since the thermostat replacement, so I don't think its anything that I've
> introduced, but obviously I can't say for sure!

Reading around a little and there a few suggestions online that its safe to
unplug the MAF and try the car without it. That doesn't seem right to me -
sensors are there for a reason, surely? If the 'brain' can't sense how much
air is flowing, then how can it manage fuel/air mixes properly?

Help me diagnose this splutter...
 

"GT" > wrote >
> Reading around a little and there a few suggestions online that its safe
> to unplug the MAF and try the car without it. That doesn't seem right to
> me - sensors are there for a reason, surely? If the 'brain' can't sense
> how much air is flowing, then how can it manage fuel/air mixes properly?
>

No doubt someone will be along shortly to offer the technical explanation,
but I've seen it said many times : "disconnect the MAF and see what effect
this has". Apparently this does no harm (obviously you eventually need to
re-connect the old / replacement MAF).

Dave S... :>))

Help me diagnose this splutter...
 

"Catman" > wrote in message
...
>
> Well the MAF on the TS was a known issue. Even if they looked OK, when the
> wire got dirty, it was game over.
>

I can confirm this - now on my 3rd MAF (car is 12 years old, 84k miles).

Apparently the MAF's are / were manufactured by Bosch - serve us right for
putting Johnny Hun components in an Alfa !

A possibly apocryphal tale : I heard a while back that Merc had a big
problems with Bosch MAF's in their tonka toys (I don't know Merc model
numbers) - owners were bringing their Chelsea (or would it be Munich)
tractors back to the dealers in droves with MAF issues.

Dave S.... :>))

156 TS 2.0 SP3 '98 (on 3rd MAF)