Problem With The Gtr

[shepo]

Ive owned it now for two weeks and im already coping grief.

it has an inlet manifold leak, which is causing it to run lean, but here is the catch...

I think that it is over fueling, as it has backfired a few times under load (not even full throttle) and it died on the way to work this morning. it wouldnt fire up again, so i left it for about 5 minutes and it fired up again. But i virtually have to drive it like there is and egg between my foot and the throttle because when you try to accelerate it just pops and farts and carries on.

it has an apexi power fc computer, would it be this trying to compensate for the lean conditions?

any advice would be fantastic!

thanks in advance guys.

[bnr#@]

if you have a leak I would say that its running rich and not lean as not all the air is getting to the cylinders...

Fix the leak first of all then put it on a dyno to check tune/af ratios

[shepo]

but the manifold leak is is sucking air in, therefore running lean.

[Yawn]

I would say that if there is a leak, the pressure or boost from the turbo is released at the point of the leak. It may also be sucking air in, but the majority of the pressure build up would be lost at the point of the leak, causing the engine to receive less air than it normally would.

This results in the ECU thinking the engine has more air than it does, resulting in the over-fuelling.

[shepo]

so would simply changing the manifold gasket fix the problem (in theory)?

and is it a big job, i have heard that there is nearly a days labour involved!?

[Yawn]

Yes it should, if that is your only problem. Yeah its a pretty big job to get the manifold out in a GTR, thats why most people only change their plenums or spray it or whatever when the engine is out.

[shepo]

great, i can see fun times are ahead.

the previous owner already changed the gasket not that long ago.

the car is also running without a cat, and tends to backfire a bit, could it be possible that when this has happened the backpressure has forced the manifold gasket apart?

a long shot i know, but when it backfired under load last night, i could have sworn i saw a bright orange flash from under the bonnet. the car hasent been the same since...

just a theory...

[WRRR]

Inlet leaks will often give you an up and down idle as well. (ie on idle no boost NA so sucks air, on boost +ve pressure bleeds air performance down)

Grab a can of Aerostart and with car idling starting at the turbs spray each of the joints in the pipework moving towards your inlets. If the engine revs rise on spraying you have your leak (or one of them).

As for fixing the inlet leak, pulling off intake etc is a pita due to all the little pipes and shit under the plenum that you can't get to (unless you have little hand/arms and a few special tools) so almost always an engine out job.

If you are going that far have a think about checking/replacing your turbs and ..... and .... and .... bingo $10k later she's all good.

[omega36]

Hey man that sucks, i have the same problem, leak in the inlet manifold on my gtr as well, getting sorted out on monday @ Sabbadin Automotive... will let you know how that goes.

[Godzilla32]

Its a tricky job working around the plenum, throttle bodies, inlet manifold with the engine in the car but by no means impossible. I have done it all about 4-5 times now and its pretty easy when you know what your doing and have the right tools. Pity im not im Melbourne anymore! I could do it for you guys at a good price

Basically you have 6 throttle body gaskets that can leak and one long inlet manifold gasket that can leak on that side of the engine. Give the aerostart a go as it will narrow down your area in which the problem is then you can save time and money.

[shepo]

thanks for the tips, we have narrowed it down to the actual manifold gasket around number 4 cylinder.

however i will be replaceing all of the gaskets at the same time, i just dont want to take any risks.

[Godzilla32]

You'll find the majority of them will break when you pull it apart anyway If they have already been done and there is still a problem, more than likely its due to bad preparation before fitting the new gaskets last time. The surface MUST be spotless or else you will find that it will still leak. If you need anymore help doing the work, PM me and i can answer any other questions you might have

Deren

[shepo]

sounds like that is the case, tahnks for all you help mate.