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[swordfish]

Hello,,
i have a strange misfire on the 3.2 . it only starts to do it if you give it some boot ,, [ above 3500rpm ] then it starts to misfire ?? . if you stop and switch off the engine and then restart it again  its clear again and runs on all 6 cylinders .until you go above 3500rmp and then it starts to misfire again ,,. if you drive around all day below 3000 rpm it stays on 6 cylinders no problem .  i have fitted the usual suspects . 6 new gm spark plugs and 2 brand new coil  packs  but it still performs the as above .
any help would be appreciated
Thankyou

[Doctor Gollum]

Wiring loom fault or failing fuel pump. In no particular order.

[swordfish]

ok thanks,, still not found were that little oval one wire plug goes to

[Doctor Gollum]

Look harder.

[Kevin Wood]

If it's shutting down cylinders there will be codes stored.

I would read them using the pedal trick and take it from there.

My thoughts are a weak coil pack / plug that's causing a cylinder to miss under load, and then it gets disabled to save the cat.

[cam.in.head]

Has the fuel filter been changed anytime

[terry paget]

Sounds like inadequate fuel supply. Probably kinked fuel pipe, could be blocked filter or tired pump. Easily checked, it should deliver a pint a minute, disconnect the fuel feed line at the engine end and pump fuel into a bottle.

I have bought used Omegas which failed in this way following botched fuel filter changes.

[JamesV6CDX]

Need the codes before doing anything

[Ant - Petrol Blue Thirty Two]

could be filter.......had exactly the same on a vectra = fuel filter blocked/blocking and won't let enough fuel flow when asked for at higher rpm's
 

[Doctor Gollum]

Need the codes before doing anything

True, and you know exactly what the next question will be 

030x codes only paint a partial picture though... They confirm what is happening but not why. With new plugs and coils, there's only wiring and fuel left.

New loom was ultimately what fixed mine.

[zirk]

If its Electrical it should throw a Fault Code and probably stay miss firing untill a Code Reset or Ing. on / off.

If Fuel, may not throw any Codes.

[Kevin Wood]

The fact that once it starts misfiring it only stops when you restart it means the ECU is shutting down a pot, which means there'll be an 030x code, and possibly more if it's injector or ignition wiring or a knock sensor.

[swordfish]

If its Electrical it should throw a Fault Code and probably stay miss firing untill a Code Reset or Ing. on / off.

If Fuel, may not throw any Codes.
that's exactly what it does if you turn the ing off then back on it clears