156 V6 Missfire

My 2000 2.5 V6 156 (56000 miles) has a missfire. It is worse when cold and 'pops' through the intake on acceleration and will not rev past 5000 rpm hot or cold. The engine management light is not on and there are no errors logged. We have changed the plugs and tried a replacement coil pack (one cylinder at a time). We have cleaned the MAF which seemed to make a slight improvement. When we disconnect the injectors, one at a time, the engine note changes in the same way for each cylinder. It is worse under load but interestingly the missfire disapears completely for a few seconds if when moving the engine is allowed to 'over run' for a bit i.e. lift throttle at 70 mph allow deceleration to 10 mph then accelerate again car is perfect for 100 yards or so.
Mystified.

iainashbrook wrote:
> My 2000 2.5 V6 156 (56000 miles) has a missfire. It is worse when cold
> and 'pops' through the intake on acceleration and will not rev past
> 5000 rpm hot or cold. The engine management light is not on and there
> are no errors logged. We have changed the plugs and tried a replacement
> coil pack (one cylinder at a time). We have cleaned the MAF which seemed
> to make a slight improvement. When we disconnect the injectors, one at a
> time, the engine note changes in the same way for each cylinder. It is
> worse under load but interestingly the missfire disapears completely
> for a few seconds if when moving the engine is allowed to 'over run'
> for a bit i.e. lift throttle at 70 mph allow deceleration to 10 mph
> then accelerate again car is perfect for 100 yards or so.
> Mystified.

Sounds like it's running lean to me. Air inlet leak or screwed lambda
sensor would be my next ports of call. I could be completely wrong though.


--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3
Tyger, Tyger Burning Bright (Remove rust to reply)
Alfa 116 Giulietta 3.0l (Really) Sprint 1.7 75 TS 156 TS S2
Triumph Speed Triple: Black with extra black bits
www.cuore-sportivo.co.uk

"iainashbrook" > wrote in message
...
>
> My 2000 2.5 V6 156 (56000 miles) has a missfire. It is worse when cold
> and 'pops' through the intake on acceleration and will not rev past
> 5000 rpm hot or cold. The engine management light is not on and there
> are no errors logged. We have changed the plugs and tried a replacement
> coil pack (one cylinder at a time). We have cleaned the MAF which seemed
> to make a slight improvement. When we disconnect the injectors, one at a
> time, the engine note changes in the same way for each cylinder. It is
> worse under load but interestingly the missfire disapears completely
> for a few seconds if when moving the engine is allowed to 'over run'
> for a bit i.e. lift throttle at 70 mph allow deceleration to 10 mph
> then accelerate again car is perfect for 100 yards or so.
> Mystified.

I have the same year and engine, and when mine wouldn't rev past 5000 rpm, I
replaced the MAF. All is fine now. I do not recall anything odd up to 5000
rpm though.

Rgds

Stuart

Originally Posted by catman

iainashbrook wrote:
My 2000 2.5 V6 156 (56000 miles) has a missfire. It is worse when cold
and 'pops' through the intake on acceleration and will not rev past
5000 rpm hot or cold. The engine management light is not on and there
are no errors logged. We have changed the plugs and tried a replacement
coil pack (one cylinder at a time). We have cleaned the MAF which seemed
to make a slight improvement. When we disconnect the injectors, one at a
time, the engine note changes in the same way for each cylinder. It is
worse under load but interestingly the missfire disapears completely
for a few seconds if when moving the engine is allowed to 'over run'
for a bit i.e. lift throttle at 70 mph allow deceleration to 10 mph
then accelerate again car is perfect for 100 yards or so.
Mystified.

Sounds like it's running lean to me. Air inlet leak or screwed lambda
sensor would be my next ports of call. I could be completely wrong though.


--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3
Tyger, Tyger Burning Bright (Remove rust to reply)
Alfa 116 Giulietta 3.0l (Really) Sprint 1.7 75 TS 156 TS S2
Triumph Speed Triple: Black with extra black bits
www.cuore-sportivo.co.uk

Thanks for the reply.
Yes we were thinking that it could be lambda or MAF. We re-sealed the inlet manifolds very well when we re-fitted them post plug swap. There were signs of poor sealing when they were removed. Would a faulty lambda not set off the engine warning light?

iainashbrook wrote:

>
>
> Thanks for the reply.
> Yes we were thinking that it could be lambda or MAF. We re-sealed the
> inlet manifolds very well when we re-fitted them post plug swap. There
> were signs of poor sealing when they were removed. Would a faulty
> lambda not set off the engine warning light?


WD40 on all the joints may help to show up a leak. If the engine revs
rise when you spray, there's your leak. Faulty lambda might show up on
the diagnostic, but I spose it depends on the mode of failure......


--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21 COSOC#3
Tyger, Tyger Burning Bright (Remove rust to reply)
Alfa 116 Giulietta 3.0l (Really) Sprint 1.7 75 TS 156 TS S2
Triumph Speed Triple: Black with extra black bits
www.cuore-sportivo.co.uk

could be a few things i had similar problem, mine was the maf sensor, it
also reoccured when the spark plugs needed changing, and when i had the
clutch changed the guys at the garage plugged the maf sensor plug in upside
down but that did bring the engine management light on. finally i could be a
coil pack going down.
roger
selespeed (not as good as my V6)
Ex 156 Sportwagon 1.6 (yes i know should of learnt that leason first time
around)
Ex 156 2.5 V6
Ex 156 1.6
Ex 145 jr
"James Ewen" > wrote in message
k...
> "iainashbrook" > wrote in message
> ...
>>
>> My 2000 2.5 V6 156 (56000 miles) has a missfire. It is worse when cold
>> and 'pops' through the intake on acceleration and will not rev past
>> 5000 rpm hot or cold. The engine management light is not on and there
>> are no errors logged. We have changed the plugs and tried a replacement
>> coil pack (one cylinder at a time). We have cleaned the MAF which seemed
>> to make a slight improvement. When we disconnect the injectors, one at a
>> time, the engine note changes in the same way for each cylinder. It is
>> worse under load but interestingly the missfire disapears completely
>> for a few seconds if when moving the engine is allowed to 'over run'
>> for a bit i.e. lift throttle at 70 mph allow deceleration to 10 mph
>> then accelerate again car is perfect for 100 yards or so.
>> Mystified.
>
> I have the same year and engine, and when mine wouldn't rev past 5000 rpm,
> I replaced the MAF. All is fine now. I do not recall anything odd up to
> 5000 rpm though.
>
> Rgds
>
> Stuart
>