Misfiring

[hecticrb25]

Okay a little bit of background.

Driveline is a RB25DET stock internals, dual stage boost controller, HKS Pod, 3" Exhaust, PowerFC, Bosch 040 and 10 PSI.

We just finished installing a gready plenum on his car to get rid of that nasty pipe work, also installed a Q45 throttle body at the same time.

Car was running perfectly before hand, now when it starts up, first rev is fine and for about 3 seconds it runs fine then all of a sudden it starts misfiring. Only problem is that the misfiring sounds random and not like its consistantly coming from one (or more) cylinders.

Little bit of white smoke is coming out the exhaust but thats nothing unusual, probably just condensation from a cold start.

I pulled the manifold off, checked the head (its straight) checked the plenum (its straight) bolted it back up. Also when i disconnect the AAC connections that i had to lengthen to connect under the plenum it makes no difference to the engines behaviour.

Also the longer i leave it running the worse the misfiring becomes... Is there anything i can check on the hand controller to narrow down the problem?

Could anyone suggest something i should try to fix this, i dont think its coils, plugs etc coz it was working fine before hand, must be something to do with the plenum/throttle body upgrade.

Your input is appreciated

Edited July 26, 2007 by hecticrb25

[sweetr33]

did u change the power fc setting to suit q45 throttle body?? car wont produce white smoke from exhaust from condensation, it'll be a mist or steeam....

[hecticrb25]

PowerFC only needs to be changed if you use a Q45 AFM. We do have a Q45 afm to bolt up to it but i want to get this issue sorted before doing more upgrades. I bolted the TPS from the stock throttle body on the Q45 (it came off a S1 and they are the same). Yeah its mist.... i think

Edited July 26, 2007 by hecticrb25

[sweetr33]

ah my bad, misread the post, thought you'd put a q45 afm on, ok, have car idling, disconnect coil pack on cyl 1 via plug, see if engine rpm drop, connect n go through to varify which cylinder has the miss, if its consistent through them all then its not a coil/ignition mis....

[hecticrb25]

Tried that, made no difference.

Just noticed there is a small water leak coming from under the plenum somewhere

Checked the old plenum and its not straight.... however the head is straight?!

You think the head will have to come off and be machined?

[sweetr33]

how are u checking head for straightness?? so no difference to idle rpm when u disconnect the coils?????????? wat was the verdict?

[hecticrb25]

Well when i disconnected the coils it did sound like it was missing more (obviously as i just disconnected a cylinder) however it still missed randomly.

I used a straight edge and placed it on a few different angles on the head.

Probably water getting into the cylinder from a leak yeah?

Edited July 26, 2007 by hecticrb25

[sweetr33]

ok u need to do it to all the cylinder one by one, to varify which sylinder is being affected, could be that u have an air leak at the gasket n its making a particular cylinder or two run lean, squirting water down onto top side or plenum flange where it meets head while engine is running is another way to check for air leaks, engine will miss more if water is being sucked it to engine....

[hecticrb25]

But if water is dripping from underneath somewhere isnt that a sure fire indication of a leak?

BTW used a brand new gasket....

Edited July 26, 2007 by hecticrb25

[sweetr33]

yeah but a water leak isnt going to cause a misfire, unless engine is extremely hot....

[hecticrb25]

Even if water is getting into the chamber?

This would be evident in the sump oil wouldnt it?

[hecticrb25]

Just drained all the water and ran it for a minute, same issue, must be an air leak

[sweetr33]

yeah but there no reason for water to be flowing from somewhere into your intake chamber, not really possible with the greddy plenum unless theres a casting fault.... yeah check engine oil on dipstick i guess, not likely though, check for vacuum leak also, simple things can be overlooked, line for boost gauge/fuel reg/bov etc

[sweetr33]

anyway im off man but try squirting water using a squirter bottle onto the top of the flange plate where the greddy plenum nmeets your head when car is running, make sure u put water back in the engine too dont want it getting hot on u.... you'll know if you hit the area with the air leak as engine revs will play up... good luck

[hecticrb25]

Thanks for the help bud

[hecticrb25]

Lets say the water/air leak is coming from the plenum\head connection and not the boost guage\brake booster\fuel pressure regulator\pcv valve\pollution gear lines.

What would the solution be? Seeing as the faces look flat..... new gasket is all i can think of

Edited July 26, 2007 by hecticrb25

[hecticrb25]

Hey guys.

Found the water leak, water inlet pipe to the plenum from the radiator had a minor crack that was causing that issue.

Now just to find the air leak and all should be fine

BTW the throttle cable mount from the standard plenum isnt the correct one for the greddy plenum, what has everyone else used instead?

Cheers!

[1400r]

this a real greddy plenum

were talking about?

[hecticrb25]

yeah original plenum. not the plenum itself, the pipe connecting had a crack.