Engine F@#ked!

[DriftR_33]

under full boost my engine breaks up, like backfires and sounds like

the engine is missing.

can any one tell me whats wrong!

[mid life crisis]

plugs or and coils is my bet

[slimjim]

plugs or and coils is my bet

<{POST_SNAPBACK}>

Beat me to it

[DriftR_33]

yeah i thaught so.. plugs are 2000k old, but was running rich for w month or so..

and i thaught coil packs were ment to las the life of the motor?

ill check it out.

[Cubes]

Coils... all bets are on coils... :S

[DriftR_33]

cool im pulling it all off today to find the problem, it so happens my mate has and rb25 laying around with coilpacks.

[ish]

interesting i just had the same prob .... changed the plug's and gapped them to .9 .... at first the problem was fixed but seems to change with different wieghts in the car ie 2 people as apposed to 1 etc.

Will be waiting on your finds DriftR_33

[Cubes]

Its better than having the issue i'm having now..

Valve float.. Over 4000rpm with 12-13psi it will begin to miss, run on 5 cylinders. Brought down to an idle it will continue to miss until the lifters bleed back down.

Valve springs

[chops]

Surely not Joel?

Isn't your head all nicely redone recently?

I'd be pissed if I was having valve spring issues so soon after a job like that, sounds too much like incorrect parts selection for the intended application.

[Miller the hoon]

Fuel cut is it an auto

wat boost do you run

james

[4door_Sleeper]

Its better than having the issue i'm having now..

Valve float.. Over 4000rpm with 12-13psi it will begin to miss, run on 5 cylinders. Brought down to an idle it will continue to miss until the lifters bleed back down.

Valve springs

<{POST_SNAPBACK}>

Or you can machine the valve and make it lighter (no thinner than the thickness at the collet (sp??)

4000 is a bit low to have valve float unless someone was trying to do something tricky with the springs. More often than not I have seen double valve springs bind up at this point on modified heads. What springs did you install?

[Cubes]

I am running the stock RB25DE N/A valve springs.. I was hoping they would be good until 17psi, I had always planned on dropping new ones in to suit cams later on.

Sky30 ran his with no issues until 17psi with his N/A head untouched. He did however run a lower pressure pump than I.

Bl4ck32 is running 16psi with no issues BUT he has had his shimmed as Chris Milton Engineering did his head at the same time as mine, mine was apparently ok Bl4ck32's required shimming. Once again he too is using the lower pressure rb20det oil pump.

I'm using the rb25det pump that see's almost 8kg/cm3 (i think the unit is) at 4000rpm+. vs ~5-6kg/cm3 of the rb20det pump.

Maybe the higher pressure pump is slightly contributing to the pump up. I'm also running slightly thicker oil being the mobil 1 5w50.

I didn't experience as severe pump up with the motul 5w40, just power flattening out.

Thinner oil is not an option as its just a patch up. I wouldn't want to be holding third or fourth gear out without the valve transfering its heat to the seat well enough. :S

Either way.. I'm dropping a set of gtr springs in and will ensure seat tension is correct myself... As they say... If you want something done right.. do it your self.

[DriftR_33]

as soon as i accelarate, foot down it will beak up and miss...

light accelaration is ok...

about spark plugs, im pretty sure mine is 1mm or 1.1

[just the way they came]

now im running 13.5 psi do i change the gap to .8 or so?

[4door_Sleeper]

At 400rpm the oil pressure shouldnt matter as the lifters should be full prior to this and I dont think you can over pressurise them (within reason in a motor)

I agree that you should check the clearances and shim acordingly, but I would have hoped Chris Millton dit this correctly (he has a good reputation)

Have you had it on a dyno, just wondering if one (or two) lifters have sh!t themselves.

[4door_Sleeper]

as soon as i accelarate, foot down it will beak up and miss...

light accelaration is ok... 

about spark plugs, im pretty sure mine is 1mm or 1.1

[just the way they came]

now im running 13.5 psi do i change the gap to .8 or so?

<{POST_SNAPBACK}>

Gap them at 0.8.

1.1 is a bit big for 13.5psi, and its an easy enough job to see if it fixes the problem. Whilst you have the plugs out, have a look at the colour and finish (their is a chart somewhere on the forums, or I can send you a copy of mine ) to diagnose any problems.

Inconsistency accross the range will help you diagnose a fault.

[DriftR_33]

thanks for that.. i just wanted to make sure

back to the shed!

[Cubes]

Definitely .8mm is required...

Now back on topic... lol

The car has been on a dyno.... To myself I think it sounds like 1 cylinder that drops, I suspect cylinder 5 as I had an issue after the head was reco'd/worked...

The cylinders exh. valve seats were sitting higher than the rest, I spoke to Tim which said it is of concern and may cause detonation, it should really be fixed if you want to run 20psi+. Which was the origional intention.

I sent the head back to miltons, they fixed it with a bit of griping. Possibly they didn't bother checking seat pressure or just machined the valve seat and slapped it back in. The valve seat was definitely machined, not replaced.

I am going to defintely pull the head off and see whats going on. Replace all lifters, rb26 valve springs and setup everything properly.

I might prior throw it on the dyno again, get it to pump up then quickly pull fuel from that cyl and see what cyl is causing the problems. I should have done this last dyno session but ran out of time.

[DriftR_33]

the plugs i just took out our a rusty brown color and there 2 months old. the ones that were in prior to them and a light black...

what does this mean?

[Cubes]

Take a pic

My plugs have always been a light grey colour.

http://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

[4door_Sleeper]

I am not sure of the specs for the 2 types of valve spring, so this advice may not be relevant, but ....

Avoid the trap of putting in too heavy a spring. Heavy springs take more energy to operate, and have the added disadvantage of applying excessive pressure on the valves and seats (granted this is an equilibrium as the valves have to seat and the springs must force the valves shut at a rate close to the ramp drop of the cam.- too light and the valves may bounce or close too slowly)

The other component to consider when closing a valve (rather than high spring rates) is the reciprocating mass. This is an old trick where the shaft of the valve within the sleeve is machined down to the thickness of the Collet notch, (along the length that remains within the valve sleeve) as this section has no effect on the valves travel. By reducing the mass a lighter spring is required.

4000 rpm isn’t that fast, and you didn’t mention having a ridiculously aggressive cam, so my guess is that you have a sagging/broken/week spring, faulty lifter(s) or a bad valve that has prematurely tuliped,.

In any event it looks like its a cylinder head off job.

Good luck, and let us know what you find..