03 Xsara Picasso misfire/flat spot, surging

[citronut]

this is a 1.6 8V TU petrol,

on idle not every time if the throttle is blipped and on the revls settling back down the engine surges slightly,

on plugging my DIS-LEXIA up it two fault codes came back

P0300 = random misfire
P0304 = misfire on cylinder No.4

whilst running live data it showed the coils pack readings

1 & 4 1.84ms
2 & 3 2,5ms

although 2 & 4 varied as reves were added

somtimes matching 1 & 4 and other times going up to 2.84

any ideas

i took the spark plugs out and they all look the same colour, not sooty ( or sweepy )

[citronut]

ps.

forgot to add

injector time came up as

0.000ms
injector cut off
NO!

this was with the engine running

[Bick]

might be way off but there is an idle control valve on throttle body, it acts as an anti stall. If they seize up (and they do often) when the revs drop the engine tries to stall this valve should come in and stop it. If its not working the engine surges and hunts and sometimes stalls.

[Mandrake]

With the limited information you've given it sounds like an ignition misfire as the differences in charge time between the two coils is excessive, and it's suspicious that one is jumping around while the other is steady. The figure jumping around suggests an intermitent lack of spark or that the spark is jumping to earth somewhere other than the spark plug electrode.

If the spark plugs look ok I'd be suspicious of the spark plug leads. Is the engine one where you could swap the leads for cylinders 1 and 4 with those for cylinders 2 and 3 and see if the charge times and/or misfire codes swap around as well ? (Or if you have a suitable set of leads you can borrow off a known good engine try that...)

It could be a coil but I would rule out the leads first.

PS is there a lack of power when driving ?

[Northern_Mike]

If this is anything at all like the 1.8 motor, then it's a coil. My 1.8 Xantia did the exact same thing. So badly it used to cut out in traffic . Was on the way to pick up new coils for it when it juddered so badly the timing belt broke.

It broke in the outside lane, approaching the Hangar Lane gyratory from the West at about 8:50am.

[citronut]

With the limited information you've given it sounds like an ignition misfire as the differences in charge time between the two coils is excessive, and it's suspicious that one is jumping around while the other is steady. The figure jumping around suggests an intermitent lack of spark or that the spark is jumping to earth somewhere other than the spark plug electrode.

If the spark plugs look ok I'd be suspicious of the spark plug leads. Is the engine one where you could swap the leads for cylinders 1 and 4 with those for cylinders 2 and 3 and see if the charge times and/or misfire codes swap around as well ? (Or if you have a suitable set of leads you can borrow off a known good engine try that...)

It could be a coil but I would rule out the leads first.

PS is there a lack of power when driving ?

thanks Simon but it dont have HT leads but a coil pack directly onto the plugs,

If this is anything at all like the 1.8 motor, then it's a coil. My 1.8 Xantia did the exact same thing. So badly it used to cut out in traffic . Was on the way to pick up new coils for it when it juddered so badly the timing belt broke.

It broke in the outside lane, approaching the Hangar Lane gyratory from the West at about 8:50am.

ok thanks Mike

on this car the surging at ifle is very mild and it just has a flat spot as you start to bring in the gas

[Bick]

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