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Misfire during cold start

maximajim

By maximajim,
in Engines & Forced Induction

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RTED Contributor

RTED

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I have jiggled the wires when warm and it's doesn't not misfire.  IT's series II rb25 so no seperated ignitor.  It's strange it starts to work when the engine just reaches operating temp.

Could be numerous things:

try these.

1st check/replace spark plugs

2nd whilst engine is cold,spray some crc around the intake manifold around the suspect cylinder to check for vacuum leaks. If engine increases rpm you have a gasket leak.

3rd compression test .

Hope this helps.

maximajim Community Regular

maximajim

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I've replaced the spark plug, swapped coils, sprayed #6 runner with carb cleaner. Still the same. I'm thinking sticking injector, has anyone had the same issue?. I can hear the injector clicking.

When started the engine will run fine for approx. 3 seconds and then # 6 will drop. #6 will come back as soon as the engine becomes warm. Like as if when it goes to closed loop the problem corrects itself.

maximajim Community Regular

maximajim

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possibly, I had a leak until I retorqued the head. It doesn't use anymore coolant and oil is no longer appearing in the coolant. However when i did have the coolant leak it did not have this problem.

When #6 comes back the vacuum reads 15mmhg and when at operating temp will read ~20mmhg. I think that should rule out the hg and compressin of #6

predator Grand Master

predator

Posted
Posted

I probably wouldn't worry about it too much unless it's quite major.. all of the RB powered cars I have been in have had a slight hickup at idle every now and then.

Especially if its cylinder 6 at idle, probably has a little less air getting to cylinder 6 from the back of the plenum under low pressure , creating a slight jump.

It may also be to do with the spark plug gap being too short for perfectly smooth idle, but fine for everyday driving and putting the boot in.

maximajim Community Regular

maximajim

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it's not just a little miss, the cylinder is totally dead when cold. If i pull the #6 coil plug after warm up, it sounds the same as when the engine is cold. When its starting to work I can hear a little "bump bump bump" sound as the cylinder comes to life.

Swapped stock ecu with pfc with no help

Nothing but problems with this engine ;)

EVL032 Rising Star

EVL032

Posted
Posted

ey i feel ur pain i have a simular problem mine when cold will occasionally do the same

thaught i fixed it with a new coil pack but shorley enough i happening again but once warm snaps out of it and is fine i have also had an engine rebuilt about 5 months ago only happenin now

  • 2 weeks later...
maximajim Community Regular

maximajim

Posted
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It's driving me nuts...

I changed the fuel injector...no help.

Compression tested.. 140psi, within limits of the other cylinders

pulled coil when running and connected a spark plug.. plug fires

That leaves the Intake gaskets.. has anyone had a misfire caused by it??

  • 14 years later...

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